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#1    Waspie_Dwarf

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Posted 13 April 2006 - 10:48 PM

Eta Carinae: A Spectacular Show From A Convulsing Massive Star

The Gemini Observatory press release is reproduced below:

Wednesday, 12 April 2006
Although the Homunculus Nebula around the massive star Eta Carinae has been the subject of intense study for many years, it has always been reluctant to divulge its innermost secrets. However, an important chapter in the recent evolution of this unique star was revealed when Nathan Smith (University of Colorado) used the high-resolution infrared spectrograph PHOENIX on the Gemini South telescope to observe the bipolar nebula surrounding Eta Carinae.

Multi-slit spectroscopy (see Figure 1) allowed Smith to reconstruct both the geometry and the velocity structure of the expanding gas in the nebula based on the behavior of the molecular line of hydrogen H2 at 2.1218 microns and the atomic line of ionized iron [Fe II] at 1.6435 microns (Figure 2).

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Figure 1. One of the five PHOENIX spectrograph long-slit aperture positions superposed on a 2-micron HST/NICMOS image of Eta Carinae.

Analysis of the PHOENIX spectrum shows a very well-defined shell structure expanding ballistically at about 500 kilometers per second (Figure 2). A “thick,” warm inner dust shell traced by [Fe II] emission is surrounded by a cooler and denser outer shell that is traced by strong H2 emission. Even though the outer H2 skin is remarkably thin and uniform it contains about 11 solar masses of gas and dust ejected over a period of less than five years. The Gemini spectra show that the density in the outer shell may reach 107 particles per cm3.

The spatio-kinematic structure of H2 emission at the pinched waist of the nebula helps explain the unusual and complex structures seen in other high-resolution images.  The current shape of the Homunculus nebula is of two well-defined polar lobes outlined by an outer massive shell of gas and dust (Figure 3). Smith states that these Gemini/PHOENIX data indicate that most of the mass lost during the Great Eruption of the mid-nineteenth century was limited to the high latitudes of the star, with almost all of the mechanical energy escaping between 45 degrees and the pole.
"The mass distribution in the nebula indicates that its shape is a direct result of an aspherical explosion from the star itself, instead of being pinched at the waist by the surrounding circumstellar material," said Smith.

For more details read “The Structure of the Homunculus: I. Shape and Latitutude Dependence from H2 and [Fe II] velocity Maps of Eta Carinae,”  by Nathan Smith, The Astrophysical Journal , in press or at astro-ph/0602464 .

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Figure 2. Long-slit composite spectrum from Gemini/PHOENIX showing [Fe II] in blue and molecular hydrogen H2 in red, simultaneously. The bright blue feature in the center, which appears stretched horizontally here, is a younger and smaller bipolar nebula called the Little Homunculus.  It was ejected about 50 years after the major eruption that created the larger nebula.


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Figure 3. Model shape (thin line) plotted over the H2 (2.1218-micron) emission from the Homunculus, showing the thin bipolar lobes. The bright streak running diagonally across the image is residual continuum emission from the bright central star (saturated). Spatial scales are converted to astronomical units assuming an age of 160 years and a distance of 2,350 parsecs.

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Eta Carinae

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1995 view by of the supermassive star Eta Carinae surrounded by a billowing par of gas and dust clouds obtained with WFPC2/HST

The giant variable star Eta Carinae is one of the most remarkable stars in the southern sky. It lies just under 8,000 light-years away and, at about 100 times the mass of our Sun, is one of the most massive stars known. Eta Carinae is about five million times brighter than the Sun and is the brightest object outside of the solar system in the mid-infrared at 10-20 microns. It radiates most of its luminosity in the infrared part of the spectrum.

First catalogued by the English astronomer Edmond Halley in 1677, Eta Carinae's brightness has evolved dramatically throughout recent history. The most spectacular events took place during the nineteenth century, when it outshone all bright stars except Sirius. It underwent a great eruption in the mid-19th century and ejected many solar masses of gas and dust. We now observe this mass loss as a spectacular bipolar nebula called The Homunculus. Eta Carinae will probably end its life as a spectacular supernova in the next several thousand years.



Source: Gemini Observatory Press Release

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#2    Waspie_Dwarf

Waspie_Dwarf

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Posted 05 May 2006 - 06:40 PM

Companion Explains "Chameleon" Supernova

The Gemini Observatory press relese is reproduced below:

Using the Gemini South telescope in Chile, Australian astronomers have found a predicted "companion" star left behind when its partner exploded as a very unusual supernova. The presence of the companion explains why the supernova, which started off looking like one kind of exploding star, seemed to change its identity after a few weeks.

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Credit: Gemini South GMOS Images, full Galaxy: Stuart Ryder & Travis Rector, inset Stuart Ryder

The Galaxy NGC 7424 as imaged with the Gemini South Mulit-object Spectrograph.  Inset shows field of SN2001ig as indicated by arrow.


The Gemini observations were originally intended to be reconnaissance for later imaging with the Hubble Space Telescope. “But the Gemini data were so good we got our answer straight away,” said lead investigator, Dr. Stuart Ryder of the Anglo-Australian Observatory (AAO).

Renowned Australian supernova hunter Bob Evans first spotted supernova 2001ig in December 2001. It lies in the outskirts of a spiral galaxy NGC 7424, which is about 37 million light-years away in the southern constellation of Grus (the Crane).

The supernova was monitored over the next month by optical telescopes in Chile. Supernovae are classified according to the features in their optical spectra. SN2001ig initially showed the telltale signs of hydrogen, which had it tagged as a Type II supernova, but the hydrogen later disappeared, which put it into the Type I category.

But how could a supernova change its type? Only a handful of such supernovae, classified as "Type IIb" to indicate their curious change of identity, have ever been seen. Only one (called SN 1993J) was closer than SN 2001ig.

Astronomers studying SN1993J had suggested an explanation: the supernova’s progenitor had a companion star that stripped material off the star before it exploded. This would leave only a little hydrogen on the progenitor—so little that it could disappear from the supernova spectrum within a few weeks.

A decade later observations with the orbiting Hubble Space Telescope and one of the Keck telescopes in Hawai’i confirmed that SN 1993J did indeed have a companion. Ryder and colleagues wondered if SN2001ig might have had a companion as well.

Radio Light Curve Shows Lumps & Bumps

Radio observations also hinted at a companion.

Soon after SN2001ig was discovered, Ryder and his colleagues began monitoring it with a radio telescope, the CSIRO (Commonwealth Scientific and Industrial Research Organisation) Australia Telescope Compact Array in eastern Australia. The radio emission did not fall off smoothly over time but instead showed regular bumps and dips. This suggested that the material in space around the star that exploded—which must have been shed late in its life—was unusually lumpy.

Although the lumps might have represented matter periodically shed from the convulsing star, their spacing was such that another explanation seemed more likely: that they were generated by a companion in an eccentric orbit. As it orbited, the companion would have swept material shed by the progenitor into a spiral (pinwheel) pattern, with denser lumps at the point in the orbit—periastron—where the two stars approached most closely.

Such spirals have been imaged around hot, massive stars called Wolf-Rayet stars by Dr Peter Tuthill of the University of Sydney, using the Keck telescopes. The bumps in the radio light-curve of SN2001ig were spaced in a way consistent with the curvature of one of the spirals Tuthill has imaged.

“Stellar evolution theory suggests that a Wolf-Rayet star with a massive companion could produce this unusual kind of supernova,” said Ryder.

If the supernova progenitor had a companion, it might be visible when the supernova debris had cleared. So the astronomers put in a request to observe with the GMOS (Gemini Multi-Object Spectrograph) camera on the 8-meter Gemini South telescope.

When the time came to observe, the "seeing conditions" (stability of the atmosphere) were excellent. Just an hour and a half was needed to image the supernova field—and reveal a yellow-green point-like object at the location of the supernova explosion.

“We believe this is the companion,” said Ryder. “It’s too red to be a patch of ionized hydrogen, and too blue to be part of the supernova remnant itself.”

The companion has a mass of between 10 and 18 times that of the Sun. The astronomers hope to use GMOS again in coming months to get a spectrum of the companion, to refine this estimate.

Binary companions could explain much of the diversity seen in supernovae, Ryder suggests. “We’ve been able to show the chameleon-like behaviour of SN2001ig has a surprisingly simple explanation,” he said.

This is only the second time a companion star to a Type IIb supernova has been imaged, and the first time the imaging has been done from the ground.

A paper on the observations, “A post-mortem investigation of the Type IIb supernova 2001ig", co-authored by Ryder, University of Tasmania graduate student Clair Murrowood and former AAO astronomer Dr Raylee Stathakis, was published online in Monthly Notices of the Royal Astronomical Society on May 2. It is also available HERE.


Source: Gemini Observatory Press Relese

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#3    Waspie_Dwarf

Waspie_Dwarf

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Posted 10 May 2006 - 10:21 PM

Spitzer Spies the Remnants of a Shy Star

Written by Linda Vu, Spitzer Science Center
May 10, 2006, 2006


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NASA/JPL-Caltech/P. Morris (NASA Herschel Science Center)

The (Almost) Invisible Aftermath of a Massive Star's Death
For the universe's biggest stars, even death is a show. Massive stars typically end their lives in explosive cataclysms, or supernovae, flinging abundant amounts of hot gas and radiation into outer space. Remnants of these dramatic deaths can linger for thousands of years and be easily detected by professional astronomers.

However, not all stars like attention. Thirty thousand light-years away in the Cepheus constellation, astronomers think they've found a massive star whose death barely made a peep. Remnants of this shy star's supernova would have gone completely unnoticed if the super-sensitive eyes of NASA's Spitzer Space Telescope hadn't accidentally stumbled upon it.

The three-panels illustrate just how shy this star is. Unlike most supernova remnants, which are detectable at a variety of wavelengths ranging from radio to X-rays, this source only shows up in mid-infrared images taken by Spitzer's Multiband Imaging Photometer, or MIPS (right). The remnant can be seen as a red-orange blob at the center of the picture.

Although the visible-light (left) and near-infrared (middle) images capture the exact same region of space, the source is completely invisible in both pictures. Astronomers suspect that the remnant's elusiveness is due to its location, away from our Milky Way galaxy's dusty main disk, which contains most of the galaxy's stars. A supernova is most noticeable when the material expelled during the star's furious death throes violently collides with surrounding dust. Since the shy star sits away from the galaxy's dusty and crowded disk, the hot gas and radiation it flung into space had little surrounding material to crash into. Thus, it is largely invisible at most wavelengths. However, MIPS' sensitive mid-infrared eyes did not need dust to see the remnant. The instrument was able to directly detect the oxygen-rich gas from the supernova's explosive death throes.

The visible-light (left) image is a three-color composite with data from the Digital Sky Survey. In this image, B band (0.44 microns) is represented as blue, R band (0.55 microns) is green, and I band (0.9 microns) is red.

The near-infrared (middle) image is a two color composite with data from Spitzer's Infrared Array Camera, or IRAC. In this image, Milky Way stars are captured 4.5 microns are represented in blue, and dust at 8.0 microns is green. The far-infrared image (left) combines the IRAC data of the middle panel with MIPS data at 24 microns. This wavelength shows the supernova remnant and is represented in red.



Big stars usually aren't shy about anything, not even death. At the end of their lives, they throw explosive tantrums, called supernovae, flinging abundant amounts of hot gas and radiation into space. Remnants of this cosmic fury can last for several thousand years and be easily detected by most telescopes used by professional astronomers.

But, not all stars like attention. Thirty thousand light-years away in the Cepheus constellation, astronomers think they've found a massive star whose death barely made a "peep." Remnants of this shy star's supernova would have gone completely unnoticed if the infrared eyes of NASA's Spitzer Space Telescope hadn't accidentally stumbled upon it.

"This source is really trying to avoid detection," said Dr. Patrick Morris of NASA's Herschel Science Center at the California Institute of Technology in Pasadena, Calif. He is the lead author of a paper on the discovery, which was published in the April 2006 Astrophysical Journal Letters.

So, what makes this lone star so unusual? Morris suspects that it sits away from the mobs of stars that occupy the main disk of our Milky Way galaxy. Our galaxy's disk is a crowded and dusty place, whereas the regions above and below are comparatively dust-free. It is this dust that allows exploding stars to be readily detected. Expelled material violently collides with surrounding dust, giving off bright light of various wavelengths. The putative supernova remnant discovered by Spitzer did not have enough dust around it to amplify its final death throes.

In fact, when Morris and his team first found this object, the thought that it could be a supernova remnant did not immediately cross their minds. The object was completely invisible to previous all-sky surveys taken by radio and X-ray telescopes. It did not even show up in visible-light images. Team members thought that the object was most likely a planetary nebula, or a star whose outer layers are gently puffed off in its last stages of life.

"There are various flavors of planetary nebulas; however, these objects normally have a bright star in the middle, a lot of dust, and a big range of chemistry. Our object shows none of this," said Morris.

For two years the team sifted through astronomical archives, literature, and additional Spitzer data in hopes of determining what the source could be. After months of comparing Spitzer's observations of the source to many examples from other object classes, Morris' team carefully ruled out the possibility that the source could be anything other than a supernova remnant.

The team was further inclined to believe this theory when they found traces of oxygen in the region with Spitzer's infrared spectrograph. Many known supernova remnants are surrounded by oxygen gas released from the cores of their aging stars.

Morris is currently planning to conduct deep radio observations of the object to confirm that it is indeed a supernova remnant. If his suspicions are correct, it will be the first supernova remnant ever to be discovered solely by its infrared properties. At 25 times the mass of our sun, the object will be among the three smallest and youngest remnants in the Milky Way.

Source: NASA/CalTech - Spitzer- Happenings

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#4    Waspie_Dwarf

Waspie_Dwarf

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Posted 11 May 2006 - 10:39 PM

Twin Explosions In Gigantic Dusty Potato Crisp

The European Southern Observatory (ESO) press release pr-17-06 is reproduced below:

11 May 2006
For immediate release

Twin Explosions In Gigantic Dusty Potato Crisp


ESO's Very Large Telescope, equipped with the multi-mode FORS instrument, took an image of NGC 3190, a galaxy so distorted that astronomers gave it two names. And as if to prove them right, in 2002 it fired off, almost simultaneously, two stellar explosions, a very rare event.

This beautiful edge-on spiral galaxy with tightly wound arms and a warped shape that makes it resemble a gigantic potato crisp lies in the constellation Leo ('the Lion') [1] and is approximately 70 million light years away. It is the dominant member of a small group of galaxies known as Hickson 44, named after the Canadian astronomer, Paul Hickson. In addition to NGC 3190 [2], Hickson 44 consists of one elliptical and two spiral galaxies. These are, however, slightly out of the field of view and therefore not visible here.


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The beautiful edge-on spiral galaxy NGC 3190 with tightly wound arms and a warped shape that makes it resemble a gigantic potato crisp, as seen by ESO's Very Large Telescope. Supernova SN 2002bo is found in between the 'V' of the dust lanes in the south-western part of NGC 3190. SN 2002cv is obscured by a large amount of dust and is therefore not visible. Its position is however indicated on the above image. This colour composite is based on images obtained on 26 March 2003 with FORS1 on UT2 (Kueyen) in four filters (B, V, R and I) for a total exposure time of 14 minutes. The observations were done in the framework of a programme aiming at studying the physics of Type Ia supernovae. The field of view is 6.15 x 5 arcminutes. North is up and East is to the left. The data extraction from the archive, data reduction and final colour processing of the image was done by Henri Boffin (ESO).

In 1982, Hickson published a catalogue of over 400 galaxies found in compact, physically-related groups of typically 4 to 5 galaxies per group (see the image of Robert's Quartet in ESO PR Photo 34/05 as another example). Such compact groups allow astronomers to study how galaxies dynamically affect each other, and help them test current ideas on how galaxies form. One idea is that compact groups of galaxies, such as Hickson 44, merge to form a giant elliptical galaxy, such as NGC 1316 (see ESO PR 17/00).

Indeed, signs of tidal interactions are visible in the twisted dust lane of NGC 3190. This distortion initially misled astronomers into assigning a separate name for the southwestern side, NGC 3189, although NGC 3190 is the favoured designation.

NGC 3190 has an 'Active Galactic Nucleus', and as such, the bright, compact nucleus is thought to host a supermassive black hole.

In March 2002, a new supernova (SN 2002bo) was found in between the 'V' of the dust lanes in the southeastern part of NGC 3190. It was discovered independently by the Brazilian and Japanese amateur astronomers, Paulo Cacella and Yoji Hirose. SN 2002bo was caught almost two weeks before reaching its maximum brightness, allowing astronomers to study its evolution. It has been the subject of intense monitoring by a world-wide network of telescopes. The conclusion was that SN 2002bo is a rather unusual Type Ia supernova [3]. The image presented here was taken in March 2003, i.e. about a year after the maximum of the supernova which is 50 times fainter on the image than a year before.

While observing SN 2002bo in May 2002, a group of Italian astronomers discovered another supernova, SN 2002cv, on the other side of NGC 3190. Two supernovae of this type appearing nearly simultaneously in the same galaxy is a rare event, as normally astronomers expect only one such event per century in a galaxy. SN 2002cv was best visible at infrared wavelengths as it was superimposed on the dust lane of NGC 3190, and therefore hidden by a large quantity of dust. In fact, this supernova holds the record for the most obscured Type Ia event.

The image was obtained with a total exposure time of 14 minutes only. Yet, with the amazing power of the Very Large Telescope, it reveals a large zoo of galaxies of varying morphologies. How many can you find?

Notes

[1] The constellation 'Leo' represents the Lion. Many ancient civilisations, e.g. Sumerian, Babylonian, Persian, Syrian, Greek, all identified this constellation as a lion. In Greek Mythology, the first of Hercules' twelve tasks was to slay the Nemean lion and bring back its skin.

[2] 'NGC' stands for 'New General Catalogue' (of nebulae and clusters) that was published in 1888 by J.L.E. Dreyer in the 'Memoirs of the Royal Astronomical Society'.

[3] Type Ia supernovae are believed to result from the explosion of old stars known as 'white dwarfs' - the endpoint of most low mass stars such as our Sun. However, a white dwarf only explodes when its mass reaches a certain critical value (about 1.4 times the mass of our Sun). The general consensus is that this critical mass can only be attained if the white dwarf has a nearby companion star from which it can gain matter. Their generally uniform properties combined with their intrinsic brightness means that Type Ia supernovae can be used to measure relative distances (see ESO PR 21/98). They have been used to infer that the Universe is currently accelerating.

SN 2002bo has been extensively studied by Benetti et al. (2004, MNRAS, 348, 261), while SN 2002cv has been described by Di Paola et al. (2002, A&A, 393, L21).

Technical Information: ESO PR Photo 17/06 is based on data extracted from the ESO Science Archive. It is a colour composite based on images obtained on 26 March 2003 with FORS1 on UT2 (Kueyen) in four filters (B, V, R and I) for a total exposure time of 14 minutes. The observations were done in the framework of a programme aiming at studying the physics of Type Ia supernovae. The field of view is 6.15 x 5 arcminutes. North is up and East is to the left. The data extraction from the archive, data reduction and final colour processing of the image was done by Henri Boffin (ESO).


Source: ESO Press Release pr-17-06

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#5    Waspie_Dwarf

Waspie_Dwarf

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Posted 08 June 2006 - 06:05 PM

Distant ball of dust not dusty enough

The UC Berkley press release is reproduced below:

By Robert Sanders, Media Relations | 06 June 2006

BERKELEY – One of the youngest supernova remnants known, a glowing red ball of dust created by the explosion 1,000 years ago of a supermassive star in a nearby galaxy, the Small Magellanic Cloud, exhibits the same problem as exploding stars in our own galaxy: too little dust.

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The supernova remnant 1E0102.2-7219 (inset) sits next to the emission-line nebula N76 in a bright, star-forming region of the Small Magellanic Cloud, which is located about 200,000 light years from Earth. Image on right shows glowing dust grains in three wavelengths of infrared radiation: 24 microns (red) measured by the Multiband Imaging Photometer (MIPS) aboard NASA's Spitzer Space Telescope; and 8.0 microns (green) and 3.6 micron (blue) measured by Spitzer's Infrared Array Camera (IRAC). The red bubble is the 120 Kelvin dust envelope around E0102 that is being heated by the shock wave created in the explosion of the 20-solar-mass progenitor star some 1,000 years ago. Most of the blue stars are in the SMC, though some are in our own galaxy, the Milky Way.

The closeup of E0102 on the left is a composite of the infrared observations by Spitzer (red), an optical image (0.5 micron oxygen emission line) captured by the Hubble Space Telescope (green), and X-ray measurements by NASA's Chandra X-ray Observatory satellite (blue). The X-ray ring is generated when the reverse shock slams into stellar material that was expelled during the explosion. (Credit: NASA, JPL-Caltech, UC Berkeley)


Recent measurements by University of California, Berkeley, astronomers using infrared cameras aboard NASA's Spitzer Space Telescope show, at most, one-hundredth the amount of dust predicted by current theories of core-collapse supernovae, barely the mass of the planets in the solar system.

The discrepancy presents a challenge to scientists trying to understand the origins of stars in the early universe, because dust produced primarily from exploding stars is believed to seed the formation of new-generation stars. While remnants of supermassive exploding stars in the Milky Way galaxy also show less dust than predicted, astronomers had hoped that supernovae in the less-evolved Small Magellanic Cloud would accord more with their models.

"Most of the previous work was focused only on our galaxy because we didn't have enough resolution to look further away into other galaxies," said astrophysicist Snezana Stanimirovic, a research associate at UC Berkeley. "But with Spitzer, we can obtain really high resolution observations of the Small Magellanic Cloud, which is 200,000 light years away. Because supernovae in the Small Magellanic Cloud experience conditions similar to those we expect for early galaxies, this is a unique test of dust formation in the early universe."

Stanimirovic reports her findings in a presentation and press briefing today (Tuesday, June 6) at a meeting of the American Astronomical Society in Calgary, Alberta, Canada.

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Snezana Stanimirovic

Stanimirovic speculates that the discrepancy between theory and observations could result from something affecting the efficiency with which heavy elements condense into dust, from a much higher rate of dust destruction in energetic supernova shock waves, or because astronomers are missing a very large amount of much colder dust that could be hidden from infrared cameras.

This finding also suggests that alternative sites of dust formation, in particular the powerful winds from massive stars, may be more important contributors to the dust pool in primordial galaxies than are supernovae.

Massive stars - that is, stars that are 10 to 40 times bigger than our sun - are thought to end their lives with a massive collapse of their cores that blows the outer layers of the stars away, spewing out heavy elements like silicon, carbon and iron in expanding spherical clouds. This dust is thought to be the source of material for the formation of a new generation of stars with more heavy elements, so-called "metals," in addition to the much more abundant hydrogen and helium gas.

Stanimirovic and colleagues at UC Berkeley, Harvard University, the California Institute of Technology (Caltech), Boston University, and several international institutes form a collaboration called the Spitzer Survey of the Small Magellanic Cloud (S3MC). The group takes advantage of the Spitzer telescope's unprecedented resolution to study interactions in the galaxy between massive stars, molecular dust clouds and their environment.

According to Alberto Bolatto, a research associate at UC Berkeley and principal investigator of the S3MC project, "the Small Magellanic Cloud is like a laboratory for testing dust formation in galaxies with conditions much closer to those of galaxies in the early universe."

"Most of the radiation produced by supernova remnants is emitted in the infrared part of the spectrum," said Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "With Spitzer, we can finally see what these objects really look like."

Called a dwarf irregular galaxy, the Small Magellanic Cloud and its companion, the Large Magellanic Cloud, orbit the much larger Milky Way. All three are around 13 billion years old. Over eons, the Milky Way has pushed and pulled these satellite galaxies, creating internal turbulence probably responsible for the slower rate of star formation, and thus the slowed evolution that makes the Small Magellanic Cloud look like much younger galaxies seen farther away.

"This galaxy has really had a wild past," Stanimirovic said. Because of this, however, "the dust content and the abundance of heavy elements in the Small Magellanic Cloud are much lower than in our galaxy," she said, "while the interstellar radiation field from stars is more intense than in the Milky Way galaxy. All these elements were present in the early universe."

Thanks to 50 hours of observing with Spitzer's Infrared Array Camera (IRAC) and Multiband Imaging Photometer (MIPS), the S3MC survey team imaged the central portion of the galaxy in 2005. In one piece of that image, Stanimirovic noticed a red spherical bubble that she discovered corresponded exactly with a powerful X-ray source observed previously by NASA's Chandra X-ray Observatory satellite. The ball turned out to be a supernova remnant, 1E0102.2-7219, much studied during the past few years in the optical, X-ray and radio bands, but never before seen in the infrared.

Infrared radiation is emitted by warm objects, and in fact, radiation from the supernova remnant, visible in only one wavelength band, indicated that the 1,000-year-old dust bubble was nearly uniformly 120 Kelvin, corresponding to 244 degrees Fahrenheit below zero. E0102, among the youngest third of all known supernova remnants, probably resulted from the explosion of a star 20 times the size of the sun, and the debris has been expanding at about 1,000 kilometers per sec (2 million miles per hour) ever since.

The infrared data provided an opportunity to see if earlier generations of stars - ones with low abundances of heavy metals - correspond more closely to current theories of dust formation in exploding supermassive stars. Unfortunately, the amount of dust - nearly one-thousandth the mass of the Sun - was at least 100 times less than predicted, similar to the situation with the well-known supernova remnant Cassiopeia A in the Milky Way.

The S3MC team plans future spectroscopic observations with the Spitzer telescope that will provide information about the chemical composition of dust grains formed in supernova explosions.

The work was sponsored by the National Aeronautics and Space Administration and the National Science Foundation.

NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, based in Washington, D.C. Science operations are conducted at the Spitzer Science Center at Caltech, also in Pasadena. JPL is a division of Caltech.


Source: UC Berkley Press Release

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#6    Waspie_Dwarf

Waspie_Dwarf

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Posted 09 June 2006 - 01:42 AM

SPACE IS DUSTY, AND ASTRONOMERS FINALLY KNOW WHY

The Gemini Observatory press release is reproduced below:

Thursday, 08 June 2006

McMaster University and Gemini Observatory News Release

FOR RELEASE AFTER 11 AM (EST) ON THURSDAY, JUNE 8, 2006

HAMILTON, ON. June 8, 2006 - Massive star supernovae have been major "dust factories" ever since the first generations of stars formed several hundred million years after the Big Bang, according to an international study published in Science Express today.


The scientific team trained their telescopes on Supernova 2003gd, which exploded in the spiral galaxy NGC 628 located about 30 million light-years from Earth. The light from the 2003gd first reached Earth on March 17, 2003. At its brightest, it could be seen in an amateur astronomer's telescope. While many supernovae are discovered each year, this particular one stood out because it was relatively nearby and could be followed for a long-than-usual time by the specialized infrared detectors of the Spitzer Space Telescope, and by an optical spectrograph on the Gemini North telescope.

"2003gd is, quite literally, the smoking gun," says Doug Welch, professor, physics & astronomy at McMaster University, and one of 17 astronomers involved in the study. "These carbon and silicon dust particles which form from the supernovae blast make possible the many generations of high-mass stars and all the heavy elements they produce. These are elements which make up the bulk of everything around us on Earth, including you and me."

In August 2004, Welch and co-author Geoff Clayton of Louisiana State University, visited the Gemini North telescope in Hawaii to take optical spectra, with the Gemini Multi-object Spectrograph (GMOS), of ancient massive star supernovae in their hunt for the formation of dust.

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Gemini Observatory Image

Gemini Multi-object Spectrograph (GMOS) image of galaxy NGC 628 (M74) taken in August 2001 which contains the star which became SN 2003gd. See Gemini story on the detection of the progenitor star for SN 2003gd with the data from this image published in January 2004. Image obtained with the Gemini North telescope on Mauna Kea Hawai‘i. Image is rotated ~ 135 degrees counter-clockwise from north up.

Full Resolution Images of galaxy shown above

Making space dust requires elements heavier than hydrogen and helium - the only elements in existence after the Big Bang. Once dust is available stars form much more quickly and efficiently. Up until now, the efficiency and rapidity of the creation of dust by massive star supernovae has been unknown.

"We have finally shown that supernovae could have been major contributors to the dust present in the early Universe," said Ben Sugerman, of the Space Telescope Science Institute in Baltimore, MD. "Until now, the available evidence has pointed to the contrary."

Supernovae expand and dissipate into space quickly, so scientists require extremely sensitive telescopes to study them even a few months after the initial explosion. Dust does not begin to form until two years after an explosion, so while astronomers have suspected that most supernovae do produce dust, their ability to confirm this stellar dust production in the past was limited by the available technology.

The study utilized Hubble Space Telescope data as well as new observations from the Spitzer Space Telescope (currently trailing the Earth along its orbit) and the Gemini North telescope of the Gemini Observatory on Mauna Kea, Hawai'i.

"This work demonstrates the enormous value of working in different parts of the spectrum and the critical need for both ground-based and space-based facilities," says Welch.

Funding for the research was provided in part by the Natural Sciences and Engineering Research Council. Canada's participation in the Gemini Observatory is funded by the National Research Council of Canada's Herzberg Institute for Astrophysics. The Gemini Observatory consists of twin 8-meter telescopes in Hawai'i and Chile funded by an international partnership that includes: US, UK, Canada, Australia, Brazil, Argentina and Chile.

McMaster University, a world-renowned, research-intensive university, fosters a culture of innovation, and a commitment to discovery and learning in teaching, research and scholarship. Based in Hamilton, the University, one of only four Canadian universities to be listed on the Top 100 universities in the world, has a student population of more than 23,000, and an alumni population of more than 115,000 in 128 countries.

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Spitzer Space Telescope  Image

Animated GIF showing field around SN 2003gd revealing the change in the supernova relative to the surrounding galaxy (flashing star at center).

Full Resolution Image

See additional story from Spitzer Space Telescope below...

Also see related Gemini result on SN 2002hh in the galaxy NGC 6946 by Barlow et al.

Additional Images::

NGC628_RGB_fig.jpg (2329x2325 80dpi)

A mosaic of images from the Spitzer Space Telescope covering the entire galaxy NGC 628 on July 28, 2004. Normal stars appear blue, hot dust (about 200 deg Celsius) appears green, and cooler dust appears red. NGC 628 is 30 million light years away from Earth. The white box shows the area enlarged in the other images. The green object at the centre of the white box is the supernova 2003gd.

NGC628_rgb.jpg (2250x1154 300dpi)

A pair of false colour images of the spiral galaxy NGC 628 was obtained with the Spitzer Space Telescope (these images were used to make the animated GIF sequence at right). Each was produced by combining images at three different infrared wavelengths. Stars of any sort appear blue, hot dust appears green and cool dust appears red. Supernova 2003gd is near the centre of each frame. The left image was taken on Jul 28, 2004 when its dust had a temperature of about 200 deg Celsius. In the right image, taken on Jan 15, 2005, the dust has cooled below detection limits. The centre of NGC 628 is at the right. A spiral arm containing cool dust can be seen sweeping from upper right through the central part of the image.


Source: Gemini Observatory press release

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#7    Waspie_Dwarf

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Posted 09 June 2006 - 01:51 AM

A Massive Star's Death and the Dusty Universe

Written by Linda Vu, Spitzer Science Center
June 8, 2006


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NASA/JPL-Caltech/B.E.K. Sugerman (STScI)

Supernova Dust Factory in M74
Astronomers using NASA's Spitzer Space Telescope have spotted a "dust factory" thirty million light-years away in the spiral galaxy M74. The factory is located at the scene of a massive star's explosive death, or supernova.

While astronomers have suspected for years that supernovae could be producers of cosmic dust particles, the technology to confirm this suspicion has only recently become available.

The dust factory, also known as supernova SN 2003gd, is shown at the center of the two small insets from Spitzer's Infrared Array Camera (IRAC). A white arrow points to its exact location. The yellow-green dot shown in the July 2004 inset (top) shows that the source's temperature is warmer than the surrounding material. This is because newly formed dust within the supernova is just starting to cool. By January 2005, the dust had cooled and completely faded from IRAC's view. However, it was still detected in January 2005 by another instrument aboard Spitzer called the Multiband Imaging Photometer (MIPS). The MIPS image is not shown here.

The larger image to the right of the insets is the galaxy M74, as seen by Spitzer's Infrared Array Camera. The white box to the left of the galaxy's center identifies the location of the supernova remnant. In all the images, the blue dots represent hot gas and stars. The galaxy's cool dust is shown in red.

The images are false-color, infrared composites, in which 3.6-micron light is blue, 4.5-micron light is green, and 8-micron light is red.



When the universe was only 700 million years old, some of its galaxies were already filled with lots of dust. But where did all of this dust come from? Astronomers using NASA's Spitzer Space Telescope think they may have found the source in type II supernovae, the violent explosions of the universe's most massive stars.

Cosmic dust is an important component of galaxies, stars, planets, and even life. Until recently, astronomers knew of only two places where dust formed: in the outflows of old sun-like stars that are billions of years old, and in space through the slow condensation of molecules. The problem with these two scenarios is that neither explains how the universe got so dusty only a few hundred million years after its birth. Astronomers have theorized that the missing dust might be produced in supernova explosions, but evidence for this has been hard to find.

Using the space-based Spitzer and Hubble Space Telescopes and the ground-based Gemini North Telescope atop Mauna Kea in Hawaii, Dr. Ben Sugerman of the Space Telescope Science Institute in Baltimore, Md. and his colleagues found a significant amount of heated dust in the remains of a massive star called supernova SN 2003gd. The supernova remnant is located approximately 30 million light-years away in the spiral galaxy M74.

Stars like the progenitor of supernova SN 2003gd have relatively short lives of just tens of millions of years. Since Sugerman's work shows supernovae produce copious amounts of dust, he believes the explosions could account for much of the dust in the early universe. His findings will be published in the June 8 issue of Science Express.

"This discovery is interesting because it is finally showing that supernovae are significant contributors to dust formation, when evidence up to now has been inconclusive," said Sugerman.

Because supernovae fade fairly quickly, scientists need very sensitive telescopes to study them even a few months after the initial explosions. Scientists have suspected that most supernovae do produce dust, but their ability to study this dust production in the past has been limited by technology.

"People have suspected for 40 years that supernovae could be producers of dust, but the technology to confirm this has only recently become available," said Sugerman. "The advantage of using Spitzer is that we can actually see the warm dust as it forms."

"Dust particles in space are the building blocks of comets, planets, and life, yet our knowledge of where this dust was made is still incomplete. These new observations show that supernovae can make a major contribution to enriching the dust content of the universe," said Dr. Michael Barlow of University College London in the United Kingdom.

This research is part of a collaboration called the Survey for Evolution of Emission from Dust in Supernovae (SEEDS), which is led by Barlow.

Source: NASA/CalTech - Spitzer- Happenings

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#8    Waspie_Dwarf

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Posted 29 June 2006 - 04:47 PM

The Hooked Galaxy

The European Southern Observatory (ESO) press release 22-06 is reproduced below:

28 June 2006
For Immediate Release

The Hooked Galaxy

ESO's VLT Image of Supernova in Interacting Galaxy



Life is not easy, even for galaxies. Some indeed get so close to their neighbours that they get rather distorted. But such encounters between galaxies have another effect: they spawn new generations of stars, some of which explode. ESO's VLT has obtained a unique vista of a pair of entangled galaxies, in which a star exploded.

Because of the importance of exploding stars, and particularly of supernovae of Type Ia [1], for cosmological studies (e.g. relating to claims of an accelerated cosmic expansion and the existence of a new, unknown, constituent of the universe - the so called 'Dark Energy'), they are a preferred target of study for astronomers. Thus, on several occasions, they pointed ESO's Very Large Telescope (VLT) towards a region of the sky that portrays a trio of amazing galaxies.

MCG-01-39-003 (bottom right) is a peculiar spiral galaxy, with a telephone number name, that presents a hook at one side, most probably due to the interaction with its neighbour, the spiral galaxy NGC 5917 (upper right). In fact, further enhancement of the image reveals that matter is pulled off MCG-01-39-003 by NGC 5917. Both these galaxies are located at similar distances, about 87 million light-years away, towards the constellation of Libra (The Balance).

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ESO PR Photo 22/06 is a composite image based on data acquired with the FORS1 multi-mode instrument in April and May 2006 for the European Supernova Collaboration. The observations were made in four different filters (B, V, R, and I) that were combined to make a colour image. The field of view covers 5.6 x 8.3 arcmin. North is up and East is to the left. The observations were done by Ferdinando Patat and the Paranal Science team (ESO), and the final processing was done by Olivia Blanchemain, Henri Boffin and Haennes Heyer (ESO).

NGC 5917 (also known as Arp 254 and MCG-01-39-002) is about 750 times fainter than can be seen by the unaided eye and is about 40,000 light-years across. It was discovered in 1835 by William Herschel, who strangely enough, seems to have missed its hooked companion, only 2.5 times fainter.

As seen at the bottom left of this exceptional VLT image, a still fainter and nameless, but intricately beautiful, barred spiral galaxy looks from a distance the entangled pair, while many 'island universes' perform a cosmic dance in the background.

But this is not the reason why astronomers look at this region. Last year, a star exploded in the vicinity of the hook. The supernova, noted SN 2005cf as it was the 84th found that year, was discovered by astronomers Pugh and Li with the robotic KAIT telescope on 28 May. It appeared to be projected on top of a bridge of matter connecting MCG-01-39-003 with NGC5917. Further analysis with the Whipple Observatory 1.5m Telescope showed this supernova to be of the Ia type and that the material was ejected with velocities up to 15 000 km/s (that is, 54 million kilometres per hour!).

Immediately after the discovery, the European Supernova Collaboration (ESC [2]), led by Wolfgang Hillebrandt (MPA-Garching, Germany) started an extensive observing campaign on this object, using a large number of telescopes around the world.

There have been several indications about the fact that galaxy encounters and/or galaxy activity phenomena may produce enhanced star formation. As a consequence, the number of supernovae in this kind of system is expected to be larger with respect to isolated galaxies. Normally, this scenario should favour mainly the explosion of young, massive stars. Nevertheless, recent studies have shown that such phenomena could increase the number of stars that eventually explode as Type Ia supernovae. This notwithstanding, the discovery of supernovae in tidal tails connecting interacting galaxies remains quite an exceptional event. For this reason, the discovery of SN2005cf close to the 'tidal bridge' between MCG-01-39-002 and MCG-01-39-003 constitutes a very interesting case.

The supernova was followed by the ESC team during its whole evolution, from about ten days before the object reached its peak luminosity until more than a year after the explosion. As the SN becomes fainter and fainter, larger and larger telescopes are needed. One year after the explosion, the object is indeed about 700 times fainter than at maximum.

The supernova was observed with the VLT equipped with FORS1 by ESO astronomer Ferdinando Patat, who is also member of the team led by Massimo Turatto (INAF-Padua, Italy), and at a latter stage by the Paranal Science Team, with the aim of studying the very late phases of the supernova. These late stages are very important to probe the inner parts of the ejected material, in order to better understand the explosion mechanism and the elements produced during the explosion.

The deep FORS1 images reveal a beautiful tidal structure in the form of a hook, with a wealth of details that probably include regions of star formation triggered by the close encounter between the two galaxies.

"Curiously, the supernova appears to be outside of the tidal tail", says Ferdinando Patat. "The progenitor system was probably stripped out of one of the two galaxies and exploded far away from the place where it was born."

Life may not be easy for galaxies, but it isn't much simpler for stars either.

Technical information: ESO PR Photo 22/06 is a composite image based on data acquired with the FORS1 multi-mode instrument in April and May 2006 for the European Supernova Collaboration. The observations were made in four different filters (B, V, R, and I) that were combined to make a colour image. The field of view covers 5.6 x 8.3 arcmin. North is up and East is to the left. The observations were done by Ferdinando Patat and the Paranal Science team (ESO), and the final processing was done by Olivia Blanchemain, Henri Boffin and Haennes Heyer (ESO).


Notes
[1]: Type Ia supernovae are a sub-class of supernovae that were historically classified as not showing the signature of hydrogen in their spectra. They are currently interpreted as the disruption of small, compact stars, called white dwarfs, that acquire matter from a companion star.

[2]: The European Supernova Collaboration includes 10 institutions across Europe (Stockholm, MPA, Barcelona, CNRS, ESO, ICSTM, ING, IoA, Padua, Oxford) and most of the observational and theoretical expertise on supernovae in Europe.


Source: ESO Press Release pr-22-06

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#9    Waspie_Dwarf

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Posted 14 July 2006 - 09:37 PM

Astronomers See Our Origins in 20-Year-Old Star Explosion

In 1987 a massive star exploded in a neighboring galaxy, an event called a supernova. It was the closest supernova to Earth since the invention of the telescope centuries ago. Major observatories and millions of people worldwide turned to watch the death of this star.

Now, nearly 20 years after the star's death, the explosion is revealing signs of life---in the form of dust particles that are the building blocks of rocky planets and all living creatures. And astronomers once again are captivated.

IPB Image
Image above: This image of SN 1987A combines data from NASA's orbiting Chandra X-ray Observatory and the 8-meter Gemini South infrared telescope in Chile, which is funded primarily by the National Science Foundation. The X-ray light detected by Chandra is colored blue here. The infrared light detected by Gemini South is shown as green and red, marking regions of slightly higher and lower-energy infrared, respectively. The core remain of the star that exploded in 1987 is not visible here. The ring is produced by hot gas (largely the X-ray light) and cold dust (largely the infrared light) from the exploded star interacting with the interstellar region. Credit: Gemini/NASA

"Supernova 1987A is changing right before our eyes," said Dr. Eli Dwek, a cosmic dust expert at NASA Goddard Space Flight Center in Greenbelt, Md. For several years Dwek has been following this supernova, named 1987A for the year it was discovered in the Large Magellanic Cloud, a neighboring dwarf galaxy. "What we are seeing now is a milestone in the evolution of a supernova."

Using infrared telescopes, Dwek and his colleagues detected silicate dust created by the star from before it exploded. This dust survived the intense radiation from the explosion. Nearly 20 years onward, the supernova shock wave blasting through the debris that was shed by the star prior to its fiery death is now sweeping up this dust, making the material "visible" to infrared detectors.

Dust---chemical particles and crystals finer than beach sand---is both a frustration and a fascination for astronomers. Dust can obscure observations of distant stars. Yet dust is the stuff from which all solid bodies are formed. This is why dust research, as bland as it sounds, is one of the most important topics in astronomy and astrobiology.

Dust is made in stars and hurled into space by stellar winds and supernovae, and it is found everywhere in the universe. But little is known about its origin and the processes that affect it. How much dust is made in a star? How much survives the star explosion and subsequent journey through interstellar space? And how do wispy dust clouds form planets and ultimately life?

These are the questions that scientists such as Eli Dwek and his colleague Dr. Patrice Bouchet of the Observatoire de Paris want to answer. With 1987A, they have a perfect laboratory to watch the process unfold.

This is new territory for astronomers, said Bouchet, whose research team made infrared observations of SN 1987A with the Gemini South telescope in Chile. Bouchet’s team is witnessing processes never before seen. This is the first time scientists have direct evidence of dust from a large star surviving a supernova; the first time they detect cold dust intermingled in hot, X-ray-emitting gas of millions of degrees; and the first time they are witnessing sputtering, the process in which dust is eroded by collisions with hot gas.

They frankly don't know what to expect, and they have already stumbled upon a few surprises.

Infrared telescopes are crucial for this kind of observation. The dust is over a hundred degrees below the freezing point of water and too cold to emit visible light. Infrared is a less-energetic form of radiation than visible light. So while optical telescopes like Hubble can see gas, infrared instruments, similar to night-vision goggles, are needed to see the cold, dark dust.

Through high-resolution infrared imaging with the 8-meter Gemini South telescope, the science team determined that the dust is in the region of the equatorial ring of gas around SN 1987A. This ring of gas and dust, about a light year across, is expanding only very slowly. This suggests that the ring was shed by the star about 600,000 years before it exploded, and that the dust in the ring was formed in the stellar wind and not in the following supernova explosion.

The blast wave from the star’s explosion has now caught up with the ring. The collision has shocked the gas and raised the gas temperature to 10 million degrees, which heats the dust, causing it to glow at infrared wavelengths.

"This much was expected," said Bouchet. "The collision between the ejecta of Supernova 1987A and the equatorial ring was predicted to occur sometime in the interval of 1995 to 2007, and it is now underway."

With the location of the dust determined, the scientists used the fine eye of NASA's Spitzer Space Telescope to determine the composition of the dust. To their great surprise, the dust was pure silicate particles.

Another key finding is that the team has detected far less dust than expected. A star as massive as the one that blew apart in SN 1987A likely produced more silicate dust in the years before the supernova. The under-abundance of dust detected by Spitzer and Gemini South could mean that supernova blast waves destroy more dust than thought possible. If confirmed, this will have broad implications for determining dust origins throughout the universe.

Yet this is a work in progress. "Overall, we are witnessing the interaction of the supernova blast wave with its surrounding medium, creating an environment that is rapidly evolving at all wavelengths," said Bouchet.

For that reason scientists are planning a series of new infrared, optical, and X-ray observations of SN 1987A with Spitzer, Hubble and Chandra, NASA's three Great Observatories, now that the supernova has once again become very interesting. Who knows what will be revealed once the dust settles?


Christopher Wanjek
Goddard Space Flight Center


Source: NASA - Exploring the Universe - Stars and Galaxies

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#10    Waspie_Dwarf

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Posted 21 July 2006 - 11:34 AM

Stellar Explosion Portends Bigger Blast To Come

The Harvard-Smithsonian Center for Astrophysics press release is reproduced below:

Release No.: 06-20
For Release: EMBARGOED until 1:00 p.m. EDT, Wednesday, July 19, 2006


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Click on image for high resolution version

This artist's conception illustrates a star system like RS Ophiuchi, known as a symbiotic star system. The white dwarf orbits within the extended gaseous envelope of the red giant companion and gathers surrounding material into an accretion disk. When the white dwarf goes nova, it ejects two jets of material in opposite directions.
Credit: Rob Hynes, LSU


Cambridge, MA - On February 12, 2006, skygazers spotted a nova that appeared when a faint star brightened dramatically, becoming visible to the unaided eye. The cause of the brightening was a thermonuclear explosion that blasted off a white dwarf star's outer layers while leaving the core unscathed.

This nova was more exciting to astronomers than any fireworks display," said Jennifer Sokoloski (Harvard-Smithsonian Center for Astrophysics), lead author on a paper appearing tomorrow in the journal Nature.

Yet the eruption was minuscule compared to what will come. Astronomers predict that the star in question may eventually explode violently as a supernova in the distant future, ripping itself apart and scattering its gaseous remains across space. Similar explosions are bright enough to be seen across billions of light-years of space. This nearby system within the Milky Way offers astronomers a unique opportunity to refine their physical understanding of one type of rare star system that can generate such powerful blasts.

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On February 12, the recurrent nova RS Ophiuchi underwent a powerful eruption that caused it to brighten briefly to naked-eye visibility. These radio images show RS Ophiuchi at 21 (top) and 27 (bottom) days after the outburst, as observed with the Very Long Baseline Array at a wavelength of 18 centimeters. The expanding shell shows radii roughly 27 and 30 times the Earth-Sun distance in these images, matching that expected from X-ray observations of the same object, assuming a distance of about 5200 light-years. The "jet" to the east (left), clearly present on day 27, is not seen on day 21. Such jets have been seen in white dwarf systems in the past, but never so clearly and so early. In particular, these images give the most precise measurement yet of how soon a jet appears after an outburst.
Observations showed that the white dwarf source of the outburst is nearly as massive as it can be, weighing about 1.4 times as much as the Sun. In a few hundred thousand years, the white dwarf may accumulate enough mass to explode as a Type Ia supernova. Such supernovae allow astronomers to measure the size and expansion of the universe.
Credit: NRAO/CfA


"Astronomers use such supernovae to measure the expansion of the universe, so it's important for us to understand how the star systems that generate those explosions evolve prior to their demise," said Sokoloski.

The star system under study, RS Ophiuchi, is located about 5,000 light-years from Earth in the direction of the constellation Ophiuchus. RS Ophiuchi consists of a dense, white dwarf star (a stellar core about the size of the Earth but containing more mass than the Sun) and a bloated red giant star. The red giant companion emits a stellar wind that spills material onto the white dwarf. When enough of that material has accumulated, theorists say, a gigantic thermonuclear explosion occurs.

Interestingly, the white dwarf star orbits inside the extended gaseous envelope of its companion. The material ejected from the white dwarf during the nova plows into this surrounding material, creating a shock wave that both heats gas to emit energetic X-rays and accelerates electrons to emit radio waves.

"What we could infer from the X-ray data, we could image with the radio telescopes," explained Michael Rupen (National Radio Astronomy Observatory), who studied RS Ophiuchi using the National Science Foundation's Very Long Baseline Array.

Using satellites and ground-based telescopes, independent teams studied RS Ophiuchi at multiple wavelengths. Their observations showed that the explosion was more complex than scientists generally assumed. Standard computer models presume a spherical explosion with matter ejected in all directions equally. Observations of RS Ophiuchi showed evidence for two opposing jets of matter and a possible ring-like structure.

"The radio images represent the first time we've ever seen the birth of a jet in a white dwarf system," said Rupen. "We literally see the jet 'turn on.'"

Systems such as RS Ophiuchi eventually may produce a vastly more powerful explosion - a supernova - when the white dwarf accumulates enough mass to cause it to collapse and explode violently. Because such supernova explosions (called Type 1a supernovae by astronomers) all are triggered as the white dwarf reaches the same mass, they are thought to be nearly identical in their intrinsic brightness. This makes them extremely valuable as "standard candles" for measuring distances in the universe.

With the Rossi X-ray Timing Explorer, the scientists calculated the mass of the white dwarf to be close to 1.4 times that of the Sun - nearly as massive as a white dwarf can become before collapsing.

"One day, RS Ophiuchi will explode. What happened this February was just a little hiccup-a precursor of greater things to come," said Koji Mukai (NASA Goddard Space Flight Center), co-author on the Nature report.

Authors on the Nature paper were Sokoloski, Gerardo Luna of the Harvard-Smithsonian Center for Astrophysics, Mukai, and Scott Kenyon of the Center.

The Rossi X-ray Timing Explorer is managed by NASA Goddard. The Very Long Baseline Array is an instrument of the National Radio Astronomy Observatory, which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Source: CfA Press Release

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#11    Waspie_Dwarf

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Posted 21 July 2006 - 11:45 AM

"Special Case" Stellar Blast Teaching Astronomers New Lessons About Cosmic Explosions

The National Radio Astronomy Observatory press release is reproduced below:

A powerful thermonuclear explosion on a dense white-dwarf star last February has given astronomers their best look yet at the early stages of such explosions, called novae, and also is giving them tantalizing new clues about the workings of bigger explosions, called supernovae, that are used to measure the Universe.

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Radio images of RS Ophiuchi at 21 (top) and 27 (bottom) days after the outburst, as observed with the VLBA at a wavelength of 18 centimeters. The expanding shell shows radii roughly 27 and 30 times the Earth-Sun distance in these images, matching that expected from X-ray observations of the same object (Sokoloski et al.), assuming a distance of about 5200 light-years. The "jet" to the east (left), clearly present on day 27, is not seen on day 21. Such jets have been seen in white dwarf systems in the past, but never so clearly and so early. In particular, these images give the most precise measurement yet of how soon a jet appears after an outburst.
Images from Rupen, Mioduszewski, & Sokoloski; a similar, independent imaging sequence appears in O'Brien et al.

  
Using the National Science Foundation's Very Long Baseline Array (VLBA) and other telescopes, "We have seen structure in the blast earlier than in any other stellar explosion," said Tim O'Brien of the University of Manchester's Jodrell Bank Observatory in the U.K.

"We see evidence that the explosion may be ejecting material in jets, contrary to theoretical models that assumed a spherical shell of ejected material," O'Brien added.

The explosion occurred in a star system called RS Ophiuchi, in the constellation Ophiuchus. RS Ophiuchi consists of a dense white dwarf star with a red giant companion whose prolific stellar wind dumps material onto the surface of the white dwarf. When enough of this material has accumulated, theorists say, a gigantic thermonuclear explosion, similar to a hydrogen bomb but much larger, occurs.

Systems such as RS Ophiuchi may eventually produce a vastly more powerful explosion -- a supernova -- when the white dwarf accumulates enough mass to cause it to collapse and explode violently. Because such supernova explosions (called Type 1a supernovae by astronomers) all are triggered as the white dwarf reaches the same mass, they are thought to be identical in their intrinsic brightness. This makes them extremely valuable as "standard candles" for measuring distances in the Universe.

"We think the white dwarf in RS Ophiuchi is about as massive as a white dwarf can get, and so is close to the point when it will become a supernova," said Jennifer Sokoloski, of the Harvard- Smithsonian Center for Astrophysics. "If astronomers use such supernovae to measure the Universe, it's important to fully understand how these systems evolve prior to the explosion," she added.

RS Ophiuchi is a "recurrent" nova that experienced such blasts in 1898, 1933, 1958, 1967, and 1985 prior to this year's event. Sokoloski also pointed out that RS Ophiuchi is "a very special type of system," in which the nova explosions occur inside a gaseous nebula created by the stellar wind coming from the red giant companion to the white dwarf.

"This means that we can track the outward-moving blast wave from the explosion by observing X-rays produced as the blast plows through this nebula," said Sokoloski, who led a team using the Rossi X-Ray Timing Explorer (RXTE) satellite to do so. "One natural way to produce what we observe is with an explosion that was not spherical," she added.

Another surprise came when the radio waves coming from RS Ophiuchi indicated that a strong magnetic field is present in the material ejected by the explosion. "This is the first case we've seen that showed signs of such a magnetic field in a recurrent nova," said Michael Rupen who, with Amy Mioduszewski, both of the National Radio Astronomy Observatory, and Sokoloski, did another study of the system using the VLBA.

Rupen pointed out the importance of observing the object with both X-ray and radio telescopes. "What we could infer from the X-ray data, we could image with the radio telescopes," he said.

All the researchers agree that their studies show that the explosion is more complex than scientists previously thought such blasts to be. "It's a jet-like explosion, probably shaped by the geometry of the binary-star system at the center," said O'Brien. Rupen added that RS Ophiuchi showed the "earliest detection ever of such a jet. In fact, we could actually tell -- within a couple of days -- when the jet turned on."

The new information is valuable for understanding not just nova explosions but other stellar blasts, the scientists believe. "The physics is analogous to the physics of supernova explosions, so what we're learning from this object can be applied to supernovae and possibly to stellar explosions in general," Sokoloski said. In addition, she said, "in the early days of this explosion, we saw changes in the blast wave that it would take hundreds of years to see in a supernova explosion."

The teams led by O'Brien and Sokoloski reported their findings in the July 20 edition of the scientific journal Nature. Rupen and Mioduszewski are submitting their results to the Astrophysical Journal Letters. Working with O'Brien were Mike Bode of Liverpool John Moores University in the U.K., Richard Porcas of the Max Planck Institute for Radioastronomy in Germany, Tom Muxlow of Jodrell Bank Observatory, Stewart Eyres of the University of Central Lancashire in the U.K., Rob Beswick, Simon Garrington and Richard Davis, all of Jodrell Bank, and Nye Evans of Keele University in the U.K. Working with Sokoloski were Gerardo Luna of the Harvard Smithsonian Center for Astrophysics, Koji Mukai of NASA's Goddard Space Flight Center and Scott Kenyon of the Harvard-Smithsonian Center for Astrophysics.

In addition to the VLBA, O'Brien's group used the NSF's Very Large Array (VLA), the Multi-Element Radio-Linked Interferometer Network (MERLIN) in the U.K., and the European VLBI Network (EVN).

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.


Source: NRAO Press Release

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#12    Waspie_Dwarf

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Posted 21 July 2006 - 12:10 PM

Nuclear explosion on a dead star

The Max Planck Society press release is reproduced below:


SP / 2006 (67)
July 19th, 2006
Nuclear explosion on a dead star

Astronomers probe the aftermath of a giant outburst of RS Ophiuchi

A team of astronomers from the UK and Germany have found that a nuclear explosion on the surface of a star 5,000 light years from Earth resulted in a blast wave moving at over 1,700 km per second. Dr. Richard Porcas from the Max Planck Institute for Radio Astronomy in Bonn coordinated the observations with the European VLBI network (EVN). The discovery, reported in the 20th July issue of Nature, was made by bringing together many of the world's radio telescopes into arrays capable of seeing the aftermath of the explosion in incredible detail.

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Fig. 1: Artist's impression of the binary system RS Ophiuchi. Hydrogen-rich gas is transferred from a red giant onto the surface of a white dwarf and has just exploded there.
Image: David A. Hardy & PPARC (www.astroart.org)


During the night of 12th February this year Japanese astronomers reported that a star called RS Ophiuchi had suddenly brightened and become clearly visible in the night sky. Although this was the latest in a series of such outbursts that have been spotted over the last hundred years or so, it was the first since 1985 and therefore an opportunity to bring to bear new, more powerful, telescopes in an effort to understand the causes and consequences of these eruptions.

Dr Tim O'Brien of The University of Manchester's Jodrell Bank Observatory requested urgent observations with the VLBA (the Very Long Baseline Array of radio telescopes extending from Hawaii to the Caribbean). "Our first observations, made only two weeks after the explosion was reported, showed an expanding blast wave already comparable in size to Saturn's orbit around the Sun. However, we needed to use the world's most powerful radio telescopes because, from a distance of 5,000 light years, its apparent size on the sky was only 5 millionths of a degree - the size of a football seen from 2,700 km away."

The blast wave results from a huge nuclear explosion which takes place on the surface of one of a pair of stars, about 5,000 light years from Earth, which are closely circling one another. Gas captured from one star, a red giant, builds up on the surface of its white dwarf companion (a super-dense dead star about the size of the Earth which was once the core of a star like the Sun whose outer layers have been lost into space).

Eventually enough gas collects on the white dwarf for thermonuclear reactions to begin, similar to those which power the Sun but which runaway into a massive explosion. In less than a day, its energy output increases to over 100,000 times that of the Sun, and the gas (about the mass of the Earth) is thrown into space at speeds of several thousand km per second. This ejected matter then slams into the extended atmosphere of the bloated red giant and sets up blast waves that accelerate electrons to almost the speed of light. The electrons release radio waves as they move through a magnetic field that are then picked up by the telescope arrays.

Over the following months, the team continued to track the outburst using the European VLBI Network (EVN) which includes telescopes in South Africa and China, the MERLIN array of radio telescopes in the UK, and the Very Long Baseline Array (VLBA) and Very Large Array (VLA) in the USA, a truly global effort.


Dr Richard Porcas of the Max Planck Institute for Radio Astronomy in Bonn, who was also involved in the 1985 observing campaign of the last outbreak of RS Oph, coordinated the European VLBI Network observations. "A week after our first observations, we combined telescopes across Europe with two in China and another in South Africa and were surprised to find that the blast wave had become distorted. Over the next few months our observations have shown it turning from a ring into a cigar-like shape. It's going to need a lot more work to understand exactly what causes this but either the explosion shoots jets of matter in opposite directions or somehow the atmosphere of the red giant is shaping the ejected material."

user posted image
Fig. 2: First radio image of the blast wave taken with the VLBA telescope in the USA 14 days after the explosion. The colours relate to radio brightness with blue being faintest and red brightest. The binary star system itself would be at the centre but is invisible in this image.
Image: NRAO/AUI/NSF


Once the outburst is over, gas will again build up on the white dwarf until at some point, maybe another 20 years in the future, RS Oph should explode again. An important question which the astronomers hope to answer is whether in each explosion the white dwarf throws off all the matter it has collected from the red giant or whether it is hoarding some material and therefore gradually increasing in mass.


Dr Tim O'Brien, who also studied RS Oph's previous outburst in 1985 for his doctoral thesis, concludes "If the white dwarf is increasing in mass then it will eventually be ripped apart in a titanic supernova explosion and the cycle of outbursts will come to an end."


---------------------------------------------------


The European VLBI Network (EVN) is a joint facility of European, Chinese, South African and other radio astronomy institutes funded by their national research councils, conducting unique, high resolution, radio astronomical observations of cosmic radio sources. It is the most sensitive VLBI array in the world, thanks to the collection of extremely large telescopes like the Effelsberg 100 metre telescope that contribute to the network.


MERLIN is the Multi-Element Radio Linked Interferometer Network, an array of seven radio telescopes distributed around Great Britain, with separations of up to 217 km. At a frequency of 5GHz, the resolution of MERLIN is better than 50 milliarcseconds, somewhat greater than that of the Hubble Space Telescope. It is operated by the University of Manchester as a National Facility of the UK Particle Physics and Astronomy Research Council.


The Very Long Baseline Array (VLBA) is a system of ten radio-telescope antennas, each with a dish 25 metres in diameter and weighing 220 tonnes. From Mauna Kea on the Big Island of Hawaii to St. Croix in the U.S. Virgin Islands, the VLBA spans more than 8000 km, providing astronomers with the sharpest vision of any telescope on Earth or in space. Dedicated in 1993, the VLBA has an ability to see fine detail equivalent to being able to stand in New York and read a newspaper in Los Angeles. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
[TOB]

Related links:

[1] VLBI group at the Max Planck Institute for Radio Astronomy

[2] Jodrell Bank Observatory

[3] European VLBI Network

[4] MERLIN

[5] Very Long Baseline Array (VLBA)

Original work:

T. J. O'Brien, M. F. Bode, R. W. Porcas, T. W. B. Muxlow, S. P. S. Eyres, R. J. Beswick, S. T. Garrington, R. J. Davis, A. Evans
An asymmetric shock wave in the 2006 outburst of the recurrent nova RS Ophiuchi, T.
Nature Vol. 442 (July 20, 2006)


Source: Max Planck Society press release

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#13    Waspie_Dwarf

Waspie_Dwarf

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Posted 02 August 2006 - 11:25 PM

Supernova Remnant E0102 in the Small Magellanic Cloud

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Reminiscent of a U.S. July 4 Independence Day celebration, here is a NASA Hubble Space Telescope image of a cosmic explosion that is quite similar to fireworks on Earth. In the nearby galaxy, the Small Magellanic Cloud, a massive star has exploded as a supernova, and begun to dissipate its interior into a spectacular display of colorful filaments.

The supernova remnant (SNR), known as "E0102" for short, is the greenish-blue shell of debris just below the center of the Hubble image. Its name is derived from its cataloged placement (or coordinates) in the celestial sphere. More formally known as 1E0102.2-7219, it is located almost 50 light-years away from the edge of the massive star-forming region, N 76, also known as Henize 1956 in the Small Magellanic Cloud. This delicate structure, glowing a multitude of lavenders and peach hues, resides in the upper right of the image.

Determined to be only about 2,000 years old, E0102 is relatively young on astronomical scales and is just beginning its interactions with the nearby interstellar medium. Young supernova remnants like E0102 allow astronomers to examine material from the cores of massive stars directly. This in turn gives insight on how stars form, their composition, and the chemical enrichment of the surrounding area. As well, young remnants are a great learning tool to better understand the physics of supernova explosions.

E0102 was observed in 2003 with the Hubble Advanced Camera for Surveys. Four filters that isolate light from blue, visible, and infrared wavelengths and hydrogen emission were combined with oxygen emission images of the SNR taken with the Wide Field Planetary Camera 2 in 1995.

The Small Magellanic Cloud is a nearby dwarf galaxy to our own Milky Way. It is visible in the Southern Hemisphere, in the direction of the constellation Tucana, and lies roughly 210,000 light-years distant.

Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

Acknowledgment: J. Green (University of Colorado, Boulder)

Image Type: Astronomical
STScI-PRC2006-35


Source: HubbleSite - Newsdesk

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#14    Waspie_Dwarf

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Posted 24 August 2006 - 06:00 PM

Supernova Remnant E0102 in the Small Magellanic Cloud

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This active region of star formation in the Large Magellanic Cloud (LMC), as photographed by NASA's Hubble Space Telescope, unveils wispy clouds of hydrogen and oxygen that swirl and mix with dust on a canvas of astronomical size. The LMC is a satellite galaxy of the Milky Way.

This particular region within the LMC, referred to as N 180B, contains some of the brightest known star clusters. The hottest blue stars can be brighter than a million of our Suns. Their intense energy output generates not only harsh ultraviolet radiation but also incredibly strong stellar "winds" of high-speed, charged particles that blow into space. The ultraviolet radiation ionizes the interstellar gas and makes it glow, while the winds can disperse the interstellar gas across tens or hundreds of light-years. Both actions are evident in N 180B.

Also visible etched against the glowing hydrogen and oxygen gases are 100 light-year-long dust streamers that run the length of the nebula, intersecting the core of the cluster near the center of the image. Perpendicular to the direction of the dark streamers, bright orange rims of compact dust clouds appear near the bottom right of and top left corners of the image. These dark concentrations are on the order of a few light-years in size. Also visible among the dust clouds are so-called "elephant trunk" stalks of dust. If the pressure from the nearby stellar winds is great enough to compress this material and cause it to gravitationally contract, star formation might be triggered in these small dust clouds. These dust clouds are evidence that this is still a young star-formation region.

This image was taken with Hubble's Wide Field Planetary Camera 2 in 1998 using filters that isolate light emitted by hydrogen and oxygen gas. To create a color composite, the data from the hydrogen filter were colorized red, the oxygen filter were colorized blue, and a combination of the two filters averaged together was colorized green. The amalgamation yields pink and orange hydrogen clouds set amid a field of soft blue oxygen gas. Dense dust clouds block starlight and glowing gas from our view point.

For more information, contact:

You-Hua Chu, University of Illinois, Urbana, Illinois,
(phone) 217-333-5535, (e-mail) chu@astro.uiuc.edu, or

Ray Villard, Space Telescope Science Institute,
Baltimore, Md., (phone) 410-338-4514, (e-mail) villard@stsci.edu, or

Keith Noll, Space Telescope Science Institute,
Baltimore, Md., (phone) 410-338-1828, (e-mail) noll@stsci.edu

Credit:NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

Acknowledgment:Y.-H. Chu (University of Illinois, Urbana - Champaign) and Y. Nazé (Universite de Ličge, Belgium)

Image Type: Astronomical
STScI-PRC2006-41


Source: HubbleSite - Newsdesk

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#15    Waspie_Dwarf

Waspie_Dwarf

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Posted 29 August 2006 - 05:07 PM

Supernova Remnant Cassiopeia A - December 2004

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A new image taken with NASA's Hubble Space Telescope provides a detailed look at the tattered remains of a supernova explosion known as Cassiopeia A (Cas A). It is the youngest known remnant from a supernova explosion in the Milky Way. The new Hubble image shows the complex and intricate structure of the star's shattered fragments.

The image is a composite made from 18 separate images taken in December 2004 using Hubble's Advanced Camera for Surveys (ACS), and it shows the Cas A remnant as a broken ring of bright filamentary and clumpy stellar ejecta. These huge swirls of debris glow with the heat generated by the passage of a shockwave from the supernova blast. The various colors of the gaseous shards indicate differences in chemical composition. Bright green filaments are rich in oxygen, red and purple are sulfur, and blue are composed mostly of hydrogen and nitrogen.

A supernova such as the one that resulted in Cas A is the explosive demise of a massive star that collapses under the weight of its own gravity. The collapsed star then blows its outer layers into space in an explosion that can briefly outshine its entire parent galaxy. Cas A is relatively young, estimated to be only about 340 years old. Hubble has observed it on several occasions to look for changes in the rapidly expanding filaments.

In the latest observing campaign, two sets of images were taken, separated by nine months. Even in that short time, Hubble's razor-sharp images can observe the expansion of the remnant. Comparison of the two image sets shows that a faint stream of debris seen along the upper left side of the remnant is moving with high speed - up to 31 million miles per hour (fast enough to travel from Earth to the Moon in 30 seconds!).

Cas A is located ten thousand light-years away from Earth in the constellation of Cassiopeia. Supernova explosions are the main source of elements more complex than oxygen, which are forged in the extreme conditions produced in these events. The analysis of such a nearby, relatively young and fresh example is extremely helpful in understanding the evolution of the universe.

Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

Acknowledgment: R. Fesen (Dartmouth College) and J. Long (ESA/Hubble)

Image Type: Astronomical
STScI-PRC2006-30


Source: HubbleSite - Newsdesk

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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