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XMM-Newton X-ray Space Telescope


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#1    Waspie_Dwarf

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Posted 19 April 2006 - 12:55 PM

XMM-Newton reveals a tumbling neutron star

user posted image
This XMM-Newton X-ray image shows the portion of the sky around the pulsar named
'RX J0720.4-3125', which is the central bright object appearing in red.

This spinning star has been observed by XMM-Newton over a few years, and has shown
an unexpected variation in the observed thermal emission. According to astronomers,
this effect is not due to a real variation in temperature, but instead to a changing viewing
geometry. The pulsar is most probably a slowly tumbling star, which exposes different
areas of the surface over time.

Credits: ESA/MPE


19 April 2006
Using data from ESA's XMM-Newton X-ray observatory, an international group of astrophysicists discovered that one spinning neutron star doesn’t appear to be the stable rotator scientists would expect. These X-ray observations promise to give new insights into the thermal evolution and finally the interior structure of neutron stars.

Spinning neutron stars, also known as pulsars, are generally known to be highly stable rotators. Thanks to their periodic signals, emitted either in the radio or in the X-ray wavelength, they can serve as very accurate astronomical ‘clocks’.
The scientists found that over the past four and a half years the temperature of one enigmatic object, named RX J0720.4-3125, kept rising. However, very recent observations have shown that this trend reversed and the temperature is now decreasing.

According to the scientists this effect is not due to a real variation in temperature, but instead to a changing viewing geometry. RX J0720.4-3125 is most probably ‘precessing’, that is it is slowly tumbling and therefore, over time, it exposes to the observers different areas of the surface.

Neutron stars are one of the endpoints of stellar evolution. With a mass comparable to that of our Sun confined into a sphere of 20-40 km diameter, their density is even somewhat higher than that of an atomic nucleus - a billion tonnes per cubic centimetre. Soon after their birth in a supernova explosion their temperature is of the order of 1 000 000 ºC and the bulk of their thermal emission falls in the X-ray band of the electromagnetic spectrum. Young isolated neutron stars are slowly cooling down and it takes a million years before they become too cold to be observable in X-rays.  

Neutron stars are known to possess very strong magnetic fields, typically several trillion times stronger than that of the Earth. The magnetic field can be so strong that it influences the heat transport from the stellar interior through the crust leading to hot spots around the magnetic poles on the star surface.

It is the emission from these hotter polar caps which dominates the X-ray spectrum. There are only a few isolated neutron stars known from which we can directly observe the thermal emission from the surface of the star. One of them is RX J0720.4-3125, rotating with a period of about eight and a half seconds. “Given the long cooling time scale it was therefore highly unexpected to see its X-ray spectrum changing over a couple of years,” said Frank Haberl from the Max-Planck-Institute for Extraterrestrial Physics in Garching (Germany), who led the research group.

“It is very unlikely that the global temperature of the neutron star changes that quickly. We are rather seeing different areas of the stellar surface at different times. This is also observed during the rotation period of the neutron star when the hot spots are moving in and out of our line of sight, and so their contribution to the total emission changes,” Haberl continued.

A similar effect on a much longer time scale can be observed when the neutron star precesses (similarly to a spinning top). In that case the rotation axis itself moves around a cone leading to a slow change of the viewing geometry over the years. Free precession can be caused by a slight deformation of the star from a perfect sphere, which may have its origin in the very strong magnetic field.

During the first XMM-Newton observation of RX J0720.4-3125 in May 2000, the observed temperature was at minimum and the cooler, larger spot was predominantly visible. On the other hand, four years later (May 2004) the precession brought into view mostly the second, hotter and smaller spot, that made the observed temperature increase. This likely explains the observed variation in temperature and emitting areas, and their anti-correlation.
In their work Haberl and colleagues developed a model for RX J0720.4-3125 which can explain many of the peculiar characteristics which have been a challenge to explain so far. In this model the long-term change in temperature is produced by the different fractions of the two hot polar caps which enter into view as the star precesses with a period of about seven to eight years.

In order for such a model to work, the two emitting polar regions need to have different temperatures and sizes, as it has been recently proposed in the case of another member of the same class of isolated neutron stars.

According to the team, RX J0720.4-3125 is probably the best case to study precession of a neutron star via its X-ray emission directly visible from the stellar surface. Precession may be a powerful tool to probe the neutron star interior and learn about the state of matter under conditions which we can not produce in the laboratory.

Additional XMM-Newton observations are planned to further monitor this intriguing object. “We are continuing the theoretical modelling from which we hope to learn more about the thermal evolution, the magnetic field geometry of this particular star and the interior structure of neutron stars in general,” Haberl concluded.


Note:

These results will appear in an article in the scientific journal Astronomy & Astrophysics (astro-ph/0603724). The article, “Evidence for precession of the isolated neutron star RX J0720.4-3125”, is by Frank Haberl (Max-Planck-Institut fur extraterrestrische Physik, Garching, Germany), Roberto Turolla (University of Padua, Italy), Cor P. De Vries (SRON, Utrecht, The Netherlands), Silvia Zane (Mullard Space Science Laboratory, University College London, UK), Jacco Vink (University Utrecht, The Netherlands), Mariano Méndez (SRON, Utrecht, The Netherlands) and Frank Verbunt (University Utrecht, The Netherlands).


Source: ESA - News

"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

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Posted 27 April 2006 - 09:49 PM

XMM-Newton digs into the secrets of fossil galaxy clusters

user posted image
XMM-Newton observations of the fossil galaxy cluster RX J1416.5+2315, show a cloud of hot gas emitting X-rays (in blue). The cloud, reaching temperatures of about 50 million degrees, extend over 3.5 million light years and surround a giant elliptical galaxy believed to have grown to its present size by cannibalising its neighbours.

Credits: Khosroshahi, Maughan, Ponman, Jones, ESA, ING


27 April 2006
Taking advantage of the high sensitivity of ESA's XMM-Newton and the sharp vision of NASA's Chandra X-Ray space observatories, astronomers have studied the behaviour of massive fossil galaxy clusters, trying to find out how they find the time to form…

Many galaxies reside in galaxy groups, where they experience close encounters with their neighbours and interact gravitationally with the dark matter - mass which permeates the whole intergalactic space but is not directly visible because it doesn’t emit radiation.
These interactions cause large galaxies to spiral slowly towards the centre of the group, where they can merge to form a single giant central galaxy, which progressively swallows all its neighbours.

If this process runs to completion, and no new galaxies fall into the group, then the result is an object dubbed a 'fossil group', in which almost all the stars are collected into a single giant galaxy, which sits at the centre of a group-sized dark matter halo. The presence of this halo can be inferred from the presence of extensive hot gas, which fills the gravitational potential wells of many groups and emits X-rays.  

A group of international astronomers studied in detail the physical features of the most massive and hot known fossil group, with the main aim to solve a puzzle and understand the formation of massive fossils. In fact, according to simple theoretical models, they simply could not have formed in the time available to them!

The fossil group investigated, called 'RX J1416.4+2315', is dominated by a single elliptical galaxy located one and a half thousand million light years away from us, and it is 500 thousand million times more luminous than the Sun.

The XMM-Newton and Chandra X-ray observations, combined with optical and infrared analyses, revealed that group sits within a hot gas halo extending over three million light years and heated to a temperature of 50 million degrees, mainly due to shock heating as a result of gravitational collapse.

Such a high temperature, about as twice as the previously estimated values, is usually characteristic of galaxy clusters. Another interesting feature of the whole cluster system is its large mass, reaching over 300 trillion solar masses. Only about two percent of it in the form of stars in galaxies, and 15 percent in the form of hot gas emitting X-rays. The major contributor to the mass of the system is the invisible dark matter, which gravitationally binds the other components.

user posted image
The XMM-Newton spacecraft is the biggest science satellite ever built in Europe. Its telescope mirrors are the most powerful developed so far and, with its sensitive detectors, it sees much more than any previous X-ray satellite.

According to calculations, a fossil cluster as massive as RX J1416.4+2315 would have not had the time to form during the whole age of the universe. The key process in the formation of such fossil groups is the process known as 'dynamical friction', whereby a large galaxy loses its orbital energy to the surrounding dark matter. This process is less effective when galaxies are moving more quickly, which they do in massive 'clusters' of galaxies.

This, in principle, sets an upper limit to the size and mass of fossil groups. The exact limits are, however, still unknown since the geometry and mass distribution of groups may differ from that assumed in simple theoretical models.

“Simple models to describe the dynamical friction assume that the merging galaxies move along circular orbits around the centre of the cluster mass“, says Habib Khosroshahi from the University of Birmingham (UK), first author of the results. “Instead, if we assume that galaxies fall towards the centre of the developing cluster in an asymmetric way, such as along a filament, the dynamic friction and so the cluster formation process may occur in a shorter time scale,” he continues. Such a hypothesis is supported by the highly elongated X-ray emission we observed in RX J1416.4+2315, to sustain the idea of a collapse along a dominant filament.”

The optical brightness of the central dominant galaxy in this fossil is similar to that of brightest galaxies in large clusters (called 'BCGs'). According to the astronomers, this implies that such galaxies could have originated in fossil groups around which the cluster builds up later. This offers an alternative mechanism for the formation of BCGs compared to the existing scenarios in which BCGs form within clusters during or after the cluster collapse.

“The study of massive fossil groups such as RX J1416.4+2315 is important to test our understanding of the formation of structure in the universe,” adds Khosroshahi. “Cosmological simulations are underway which attempt to reproduce the properties we observe, in order to understand how these extreme systems develop,” he concludes.


Note:

The XMM-Newton observations of the fossil galaxy cluster RX J1416.4+2315 were performed in July 2003. Chandra’s observations of the same object where made in September 2001.

The findings will appear in the Monthly Notices of the Royal Astronomical Society (astro-ph/0603606). The article, titled “A fossil galaxy cluster; an X-ray and optical study of RX J1416.4+2315”, is by Habib G. Khosroshahi, Trevor J. Ponman and Laurence R. Jones (School of Physics and Astronomy, The University of Birmingham, UK), Ben J. Maughan († Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA).

Source: ESA - News

"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

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Posted 03 May 2006 - 12:47 PM

XMM-Newton 'spare-time' provides impressive sky survey

user posted image
In its on-going slew survey of the sky, XMM-Newton is able to map with high efficiency very large sky features. Among these, is the 20 000 year-old Vela supernova remnant (right) - occupying a sky area 150 times larger than the full moon. This object is compared here with an image previously taken by the former ROSAT mission (left).

Credits: ESA/ROSAT


3 May 2006
For the past four years, while ESA’s XMM-Newton X-ray observatory has been slewing between different targets ready for the next observation, it has kept its cameras open and used this spare time to quietly look at the heavens. The result is a 'free-of-charge' mission spin-off – a survey that has now covered an impressive 25 percent of the sky.

The rapid slewing of the satellite across the sky means that a star or a galaxy passes in the field of view of the telescope for ten seconds only. However, the great collecting area of the XMM-Newton mirrors, coupled with the efficiency of its image sensors, is allowing thousands of sources to be detected.
Furthermore, XMM-Newton can pinpoint the position of X-rays coming from the sky with a resolution far superior to that available for most previous all-sky surveys. This is sufficient to allow the source of these X-rays to be found in many cases.

By comparing XMM-Newton survey’s data with those obtained over a decade ago by the international ROSAT mission, which also performed an all-sky survey, scientists can now check the long-term stability, or the evolution, of about two thousand objects in the sky.  

An initial look shows that some sources have changed their brightness level by an incredible amount. The most extreme of these are variable stars and more surprisingly galaxies, whose unusual volatility may be due to large quantities of matter being consumed by an otherwise dormant central black hole.

The slew survey is particularly sensitive to active galactic nuclei (AGN) - galaxies with an unusually bright nucleus – which can be traced out to a distance of ten thousand million light years.

While most stars and galaxies look like points in the sky, about 15 percent of the sources catalogued by XMM-Newton have an extended X-ray emission. Most of these are clusters of galaxies - gigantic conglomerations of galaxies which trap hot gas that emit X-rays over scales of a million light years.

Eighty-one of these clusters are already famous from earlier work but many other clusters, previously unknown, appear in this new XMM-Newton sky catalogue.

Scientists hope that the newly detected sources of this kind also include very distant clusters which are highly luminous in X-rays, as these objects are invaluable for investigating the evolution of the Universe. Follow-up observations by large optical telescopes are now needed to determine the distances of the individual galaxies in the newly discovered clusters.

An initial look shows that some sources have changed their brightness level by an incredible amount. The most extreme of these are variable stars and more surprisingly galaxies, whose unusual volatility may be due to large quantities of matter being consumed by an otherwise dormant central black hole.

The slew survey is particularly sensitive to active galactic nuclei (AGN) - galaxies with an unusually bright nucleus – which can be traced out to a distance of ten thousand million light years.

While most stars and galaxies look like points in the sky, about 15 percent of the sources catalogued by XMM-Newton have an extended X-ray emission. Most of these are clusters of galaxies - gigantic conglomerations of galaxies which trap hot gas that emit X-rays over scales of a million light years.

user posted image
Eighty-one galaxy clusters – objects that make extended X-ray emissions - are know from former sky surveys (see image). Previously unknown sources of these kind are now being catalogued thanks to XMM-Newton's slew sky survey.
Studying these objects, especially when highly luminous, is very important to investigate the evolution of the Universe.

Credits: ESA and the XMM-Newton EPIC consortium


Eighty-one of these clusters are already famous from earlier work but many other clusters, previously unknown, appear in this new XMM-Newton sky catalogue.
Scientists hope that the newly detected sources of this kind also include very distant clusters which are highly luminous in X-rays, as these objects are invaluable for investigating the evolution of the Universe. Follow-up observations by large optical telescopes are now needed to determine the distances of the individual galaxies in the newly discovered clusters.

Using traditional pointed observations, it takes huge amounts of telescope-time to image very large sky features, such as old supernova remnants, in their entirety. The slewing mechanism provides a very efficient method of mapping these objects, and several have been imaged including the 20 000 year-old Vela supernova remnant, which occupies a sky area 150 times larger than the full moon.

Extraordinarily bright, low-mass X-ray binary systems of stars (called 'LMXB') – either powered by matter pulled from a normal star, or exploding onto the surface of a neutron star, or being consumed by a black hole - are observed with sufficient sensitivity to record their detailed light spectrum. Passes across these huge X-ray sources can help astronomers to understand the long-term physics of the interaction between the two stars of the binary system.

Many areas of astronomy are expected to be influenced by the XMM-Newton sky survey. Today, 3 May 2006, the XMM-Newton scientist have released a part of the catalogue resulting from the initial processing of the highest quality data obtained so far.

Such data correspond to a sky coverage of about 15 percent, and include more than 2700 very bright sources and a further 2000 sources of lower significance. Currently, about 55 percent of the catalogue entries have been identified with known stars, galaxies, quasars and clusters of galaxies.

A faster turn-around of slew-data processing is now planned to catch interesting transient (or temporary) targets in the act, before they have a chance to fade. This will give access to rare, energetic events, which only a sensitive wide-angle survey such as XMM-Newton’s can achieve.

It is planned to continually update the catalogue as XMM-Newton charts its way through the stars. This will cover at least 80 percent of the sky, leaving a tremendous legacy for the future.

Source: ESA - News

"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

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Posted 10 May 2006 - 09:23 PM

XMM-Newton reveals the origin of elements in galaxy clusters

user posted image
These X-ray images of the clusters of galaxies ‘Sersic 159-03’(right) and ‘2A 0335+096’ (left) were taken by the European Photon Imaging Camera (EPIC) on-board ESA’s XMM-Newton, in November 2002 and August 2003 respectively. Thanks to these observations, astronomers could determine the abundances of nine chemical elements in the clusters ‘plasma’ – a gas containing charged particles such as ions and electrons. These elements include oxygen, iron, neon, magnesium, silicon, argon, calcium, nickel, and - detected for the first time ever in a galaxy cluster - chromium. The distribution of silicon (produced by ‘type Ia’ and ‘core collapse’ supernova types) relative to iron (mainly produced by ‘type Ia’ supernovae) in these two clusters is very different, showing that they had a different evolution.

Credits: ESA and the XMM-Newton EPIC consortium


10 May 2006
Deep observations of two X-ray bright clusters of galaxies with ESA’s XMM-Newton satellite allowed a group of international astronomers to measure their chemical composition with an unprecedented accuracy. Knowing the chemical composition of galaxy clusters is of crucial importance to understanding the origin of chemical elements in the Universe.

Clusters, or conglomerates, of galaxies are the largest objects in the Universe. By looking at them through optical telescopes it is possible to see hundreds or even thousands of galaxies occupying a volume a few million light years across. However, such telescopes only reveal the tip of the iceberg. In fact most of the atoms in galaxy clusters are in the form of hot gas emitting X-ray radiation, with the mass of the hot gas five times larger than the mass in the cluster’s galaxies themselves.
Most of the chemical elements produced in the stars of galaxy clusters - expelled into the surrounding space by supernova explosions and by stellar winds - become part of the hot X-ray emitting gas. Astronomers divide supernovae into two basic types: ‘core collapse’ and ‘Type Ia’ supernovae. The ‘core collapse’ supernovae originate when a star at the end of its life collapses into a neutron star or a black hole. These supernovae produce lots of oxygen, neon and magnesium. The Type Ia supernovae explode when a white dwarf star consuming matter from a companion star becomes too massive and completely disintegrates. This type produces lots of iron and nickel.  

Respectively in November 2002 and August 2003, and for one and a half day each time, XMM-Newton’s made deep observations of the two galaxy clusters called ‘Sersic 159-03’ and ‘2A 0335+096’. Thanks to these data the astronomers could determine the abundances of nine chemical elements in the clusters ‘plasma’ – a gas containing charged particles such as ions and electrons.

These elements include oxygen, iron, neon, magnesium, silicon, argon, calcium, nickel, and - detected for the first time ever in a galaxy cluster - chromium. "Comparing the abundances of the detected elements to the yields of supernovae calculated theoretically, we found that about 30 percent of the supernovae in these clusters were exploding white dwarfs (‘Type Ia’) and the rest were collapsing stars at the end of their lives (‘core collapse’)," said Norbert Werner, from the SRON Netherlands Institute for Space Research (Utrecht, Netherlands) and one of the lead authors of these results.


"This number is in between the value found for our own Galaxy (where Type Ia supernovae represent about 13 percent of the supernovae ‘population’) and the current frequency of supernovae events as determined by the Lick Observatory Supernova Search project (according to which about 42 percent of all observed supernovae are Type Ia)," he continued.

The astronomers also found that all supernova models predict much less calcium than what is observed in clusters and that the observed nickel abundance cannot be reproduced by these models. These discrepancies indicate that that the details of supernova enrichment is not yet clearly understood. Since clusters of galaxies are believed to be fair samples of the Universe, their X-ray spectroscopy can help to improve the supernova models.

The spatial distribution of elements across a cluster also holds information about the history of clusters themselves. The distribution of elements in 2A 0335+096 indicates an ongoing merger. The distribution of oxygen and iron across Sersic 159-03 indicates that while most of the enrichment by the core collapse supernovae happened long time ago, Type Ia supernovae still continue to enrich the hot gas by heavy elements especially in the core of the cluster.


Note

This work is presented in two papers in the Astronomy & Astrophysics journal. The first one, published in April 2006 and titled ‘XMM-Newton spectroscopy of the cluster of galaxies 2A 035+096’ (A&A Volume 449, Page 475), is by N.Werner , J.S.Kaastra and J.A.M.Bleeker (SRON, Utrecht, The Netherlands), J.de Plaa and J.Vink (SRON and Utrecht University, Utrecht, The Netherlands), T.Tamura (JAXA, Kanagawa, Japan), J.R.Peterson (Stanford University, CA, USA), F.Verbunt (Utrecht University, The Netherlands).

The second article, to appear in 2006 and titled ‘Chemical evolution in Sersic 159-03 observed by XMM-Newton’ (A&A 2006 and astro-ph/0602582), is by J.de Plaa, J.Vink and J.A.M.Bleeker (SRON and Utrecht University, Utrecht, The Netherlands), N.Werner, J.S.Kaastra and M.Mendez (SRON, Utrecht, The Netherlands), A.M.Bykov (A.F. Ioffe Institute for Physics and Technology, St.Petersburg, Russia), M.Bonamente (University of Alabama, Hunstville, AL, USA), J.R. Peterson (Stanford University, CA, USA).

This research is in particular the result of the cooperation between the SRON Utrecht and the Utrecht University in the Netherlands.

Source: ESA - News

"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

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Posted 12 June 2006 - 02:35 PM

XMM-Newton spots the greatest of great balls of fire

user posted image
This X-ray image shows a comet-like blob of gas about 5 million light-years long hurling through a distant galaxy cluster at nearly 1 000 kilometres per second. The 'comet' is confined to the orange regions in this image. The head is the lower right, with reddish areas. The tail fans outward because there is less pressure to confine it. The colour red refers to regions of lower entropy, a thermodynamical measure of disorder. The orange regions have higher entropy.
This entropy map, different from brightness or temperature, helps scientists separate the cold and dense gas of the 'comet' from the hotter and more rarefied gas of the cluster. The data show with remarkable detail the process of gas being stripped from the comet's core (entropy goes up) and forming a large tail containing lumps of colder and denser gas. The 'comet' itself is a low-entropy gas; the ambient medium is a high entropy gas; the core of the comet has even lower entropy. The researchers estimate that a sun's worth of mass is lost every hour.

Credits: University of Maryland, Baltimore County (UMBC)


12 June 2006
Thanks to data from ESA’s XMM-Newton X-ray satellite, a team of international scientists found a comet-like ball of gas over a thousand million times the mass of the sun hurling through a distant galaxy cluster over 750 kilometres per second.

This colossal 'ball of fire' is by far the largest object of this kind ever identified.
The gas ball is about three million light years across, or about five thousand million times the size of our solar system. It appears from our perspective as a circular X-ray glow with a comet-like tail nearly half the size of the moon.

"The size and velocity of this gas ball is truly fantastic," said Dr Alexis Finoguenov, adjunct assistant professor of physics in the Department of Physics at the University of Maryland, Baltimore County (UMBC), and an associated scientist at the Max Planck Institute for Extra-Terrestrial Physics in Garching, Germany. "This is likely a massive building block being delivered to one of the largest assembly of galaxies we know."  

The gas ball is in a galaxy cluster called Abell 3266, millions of light years from Earth, thus posing absolutely no danger to our solar system. Abell 3266 contains hundreds of galaxies and great amounts of hot gas that is nearly a hundred million degrees. Both the cluster gas and the giant gas ball are held together by the gravitational attraction of unseen dark matter.

"What interests astronomers is not just the size of the gas ball but the role it plays in the formation and evolution of structure in the universe," said Dr Francesco Miniati, who worked on this data at UMBC while visiting from the Swiss Federal Institute of Technology in Zurich, Switzerland.

Abell cluster 3266 is part of the Horologium-Reticulum super-cluster and is one of the most massive galaxy clusters in the southern sky. It is still actively growing in size, as indicated by the gas ball, and will become one of the largest mass concentrations in the nearby universe.


Using XMM-Newton data, the science team produced an entropy map (entropy is a thermodynamical property that provides a measure of disorder). The map allows for the separation of the cold and dense gas of the comet from the hotter and more rarefied gas of the cluster. This is based on X-ray spectra. The data show with remarkable detail the process of gas being stripped from the comet's core and forming a large tail containing lumps of colder and denser gas. The researchers estimate that a sun's worth of mass is lost every hour.

"In Abell 3266 we are seeing structure formation in action," said Prof. Mark Henriksen (UMBC), co-author of the results. "Dark matter is the gravitational glue holding the gas ball together. But as it races through the galaxy cluster, a tug-of-war ensues where the galaxy cluster eventually wins, stripping off and dispersing gas that perhaps one day will seed star and galaxy growth within the cluster."


Note

The findings, resulting from a research effort led by the University of Maryland, Baltimore County, appear in the 1 June 2006 issue of the Astrophysical Journal (volume 643, page 790).

The European Space Agency’s XMM-Newton X-ray mission was launched in December 1999. With its powerful mirrors, it is helping to solve many mysteries about the most energetic phenomena taking place in the Universe.

Source: ESA - News

"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

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Posted 07 July 2006 - 09:48 PM

Supernova leaves behind mysterious object

user posted image
This image, obtained thanks to ESA's XMM-Newton X-ray telescope on 23 August 2005, shows the aftermath of a 2000-year-old star explosion. In the heart of the central blue dot in this image, smaller than a pinpoint, likely lies a neutron star only about 20 kilometers across. The nature of this object is like nothing detected before.
Scientists from the Istituto Nazionale di Astrofisica (INAF) in Milan have detected unusual X-ray pulsations. Understanding the central source's true nature will lead to new insights about supernovae, neutron stars and their evolution.

Credits: ESA/XMM-Newton/A.De Luca (INAF-IASF )


6 May 2006
Thanks to data from ESA’s XMM-Newton satellite, a team of scientists taking a closer look at an object discovered over 25 years ago have found that it is like none other known in our galaxy.

The object is in the heart of supernova remnant RCW103, the gaseous remains of a star that exploded about 2 000 years ago. Taken at face value, RCW103 and its central source would appear to be a textbook example of what is left behind after a supernova explosion: a bubble of ejected material and a neutron star.
A deep, continuous 24.5-hour observation has revealed something far more complex and intriguing, however. The team, from the Istituto di Astrofisica Spaziale e Fisica Cosmica (IASF) of the Istituto Nazionale di Astrofisica (INAF) in Milan, Italy, has found that the emission from the central source varies with a cycle that repeats itself every 6.7 hours. This is an astonishingly long period, tens of thousands of times longer than expected for a young neutron star. Also, the object's spectral and temporal properties differ from an earlier XMM-Newton observation of this very source in 2001.

"The behaviour we see is especially puzzling in view of its young age, less than 2 000 years," said Andrea De Luca of IASF-INAF, the lead author. "It is reminiscent of a multimillion-year-old source. For years we have had a sense that the object is different, but we never knew how different until now."  

The object is called 1E161348-5055, which the scientists have conveniently nicknamed 1E (where E stands for Einstein Observatory which discovered the source). It is embedded nearly perfectly in the centre of RCW 103, about 10 000 light years away in the constellation Norma. The near-perfect alignment of 1E in the centre of RCW 103 leaves astronomers rather confident that the two were born in the same catastrophic event.

When a star at least eight times more massive than our sun runs out of fuel to burn, it explodes in an event called a supernova. The stellar core implodes, forming a dense nugget called a neutron star or, if there's enough mass, a black hole. A neutron star contains about a sun's worth of mass crammed into a sphere only about 20 kilometres across.

Scientists have searched for years for 1E's periodicity in order to learn more about its properties, such as how fast it is spinning or whether it has a companion.

"Our clear detection of such a long period together with secular variability in X-ray emission makes for a very weird source," said Patrizia Caraveo of INAF, a co-author and leader of the Milano Group. "Such properties in a 2000-year-old compact object leave us with two probable scenarios, essentially a source that is accretion-powered or magnetic-field-powered."

user posted image
In August 2005, ESA's XMM-Newton observed the centre (blue dot in the image) of the supernova remnant RCW103 - the aftermath of a 2000-year-old star explosion.
The light curve on the right of the image unambiguously shows X-ray pulsation with a period of 6.67 hours - an astonishingly long period for the young neutron star expected to lie there.

The puzzling nature of this object (1E161348-5055), reminiscent of a multimillion-year-old source, is like nothing detected before.

Credits: ESA/XMM-Newton/A.De Luca (INAF-IASF )


1E could be an isolated magnetar, an exotic subclass of highly magnetized neutron stars. Here, the magnetic field lines act as brakes for the spinning star, liberating energy. About a dozen magnetars are known. But magnetars usually spin several times per minute. If 1E is spinning only once every 6.67 hours, as the period detection indicates, the magnetic field needed to slow the neutron star in just 2000 years would be too big to be plausible.
A standard magnetar magnetic field could do the trick, however, if a debris disk, formed by leftover material of the exploded star, is also helping to slow down the neutron star spin. This scenario has never been observed before and would point to a new type of neutron star evolution.

Alternatively, the long 6.67-hour period could be the orbital period of a binary system. Such a picture requires that a low-mass normal star managed to remain bound to the compact object generated by the supernova explosion 2000 year ago. Observations do allow for a companion of half the mass of our Sun, or even smaller.


But 1E would be an unprecedented example of a low-mass X-ray binary system in its infancy, a million times younger than standard X-ray binary systems with light companions. Young age is not the only peculiarity of 1E. The source's cyclic pattern is far more pronounced than that observed for dozens of low-mass X-ray binary systems calling for some unusual neutron star feeding process.

A double accretion process could explain its behaviour: The compact object captures a fraction of the dwarf star's wind (wind accretion), but it is also able to pull out gas from the outer layers of its companion, which settles in an accretion disc (disc accretion). Such an unusual mechanism could be at work in an early phase of the life of a low-mass X-ray binary, dominated by the effects of the initial, expected, orbital eccentricity.

"RCW 103 is an enigma," said Giovanni Bignami, director of CESR,Toulouse, and co-author. "We simply don't have a conclusive answer to what is causing the long X-ray cycles. When we do figure this out, we're going to learn a lot more about supernovae, neutron stars and their evolution."

Had the star exploded in the northern sky, Cleopatra could have seen it and considered it to be an omen of her unhappy end, Caraveo said. Instead the explosion took place deep in the southern sky, and no one recorded it. Nevertheless, the source is a good omen for X-ray astronomers hoping to learn about stellar evolution.


Note

The findings appear on the 6 July 2006 issue of Science Express. The article, titled "A long-period, violently-variable X-ray source in a young SNR", is by A. De Luca, P.A. Caraveo, S. Mereghetti and A. Tiengo (INAF-IASF Milano, Italy), and G.F. Bignami (CESR, CNRS-UPS, Toulouse, France, and Università degli Studi di Pavia, Italy).

The authors work builds upon observations by Gordon Garmire of Pennsylvania State University and Eric Gotthelf of Columbia University who have studied the source with Einstein, ROSAT, ASCA and Chandra and already found hints of a long period.

Source: ESA - News

Edit: Oops! I put the same image in twice.

Edited by Waspie_Dwarf, 07 July 2006 - 11:27 PM.

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#7    frogfish

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Posted 07 July 2006 - 11:22 PM

Could it be a magnetar?

EDIT: Nevermind..it says in the second article...

Edited by frogfish, 07 July 2006 - 11:25 PM.

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#8    Atheist God

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Posted 12 July 2006 - 12:43 AM

Quote


Could it be a magnetar?

EDIT: Nevermind..it says in the second article...


If a magnetar passed within 6 light years and if it was only 10 to 20 kilometers wide it could rip the atmosphere from our planet. A threat I wouldn't take lightly as one the just recently passed within 20,000 light years actually effected our planet. original.gif

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#9    frogfish

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Posted 12 July 2006 - 01:29 AM

Quote

A threat I wouldn't take lightly as one the just recently passed within 20,000 light years actually effected our planet.

Never heard of this? Do you have a link?

Edited by frogfish, 12 July 2006 - 01:29 AM.

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#10    angrycrustacean

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Posted 12 July 2006 - 04:33 AM

Quote


A threat I wouldn't take lightly as one the just recently passed within 20,000 light years actually effected our planet. original.gif


I can't find anything about that.

I did however find this:

Quote

Known Magnetars

    * SGR 1806-20, located 50,000 light-years from Earth on the far side of our Milky Way galaxy in the constellation of Sagittarius.
    * 1E 1048.1-5937, located 9,000 light-years away in the constellation Carina. The original star, out of which the magnetar formed, had a mass 30 to 40 times that of the Sun.


So, if this alleged magnetar 20,000 light years away affected our planet, is this one 9,000 away also affecting it? Or are you just plain wrong?

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#11    Roj47

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Posted 12 July 2006 - 10:36 AM

Quote


If a magnetar passed within 6 light years and if it was only 10 to 20 kilometers wide it could rip the atmosphere from our planet. A threat I wouldn't take lightly as one the just recently passed within 20,000 light years actually effected our planet. original.gif


Only heard of a Magnetar when this link began, but here are some possibilities I have found -

http://www.space.com/scienceastronomy/brig...ash_050218.html

http://mcdonaldobservatory.org/news/releases/2005/0218.html

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#12    Lilly

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Posted 12 July 2006 - 02:52 PM

Ah yes, the dreaded Gamma Ray Bursts!

Quote

The scientists calculated that gamma-ray radiation from a relatively nearby star explosion, hitting the Earth for only ten seconds, could deplete up to half of the atmosphere's protective ozone layer. Recovery could take at least five years. With the ozone layer damaged, ultraviolet radiation from the Sun could kill much of the life on land and near the surface of oceans and lakes, disrupting the food chain. While gamma-ray bursts in our Milky Way galaxy are indeed rare, NASA scientists estimate that at least one nearby event probably hit the Earth in the past billion years. Life on Earth is thought to have appeared at least 3.5 billion years ago. Dr. Bruce Lieberman, a paleontologist at the University of Kansas, originated the idea that a gamma-ray burst specifically could have caused the great Ordovician extinction. "We don't know exactly when one came, but we're rather sure it did come - and left its mark. What's most surprising is that just a 10-second burst can cause years of devastating ozone damage."


10 seconds...and *zap* the game's all over.


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#13    frogfish

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Posted 13 July 2006 - 02:24 AM

GRBs and SGRs are rare original.gif

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#14    Waspie_Dwarf

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Posted 26 July 2006 - 10:45 AM

Old pulsars still have new tricks to teach us

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An artists impression of the 'luminescent' magnetosphere surrounding a pulsar. The pulsar itself is invisible in this view and sits at the very centre of the image. Above the pulsar's magnetic poles, charged particles are accelerated outwards along the magnetic field lines and produce intense beamed radiation that can be observed by XMM-Newton.

Credits: W.Becker/Max-Planck Institut für extraterrestrische Physik


26 July 2006
The super-sensitivity of ESA's XMM-Newton X-ray observatory has shown that the prevailing theory of how stellar corpses, known as pulsars, generate their X-rays needs revising. In particular, the energy needed to generate the million-degree polar hotspots seen on cooling neutron stars may come predominately from inside the pulsar, not from outside.

Thirty-nine years ago, Cambridge astronomers Jocelyn Bell-Burnell and Anthony Hewish discovered the pulsars. These celestial objects are the strongly magnetised spinning cores of dead stars, each one just 20 kilometres across yet containing approximately 1.4 times the mass of the Sun. Even today, they perplex astronomers across the world.
"The theory of how pulsars emit their radiation is still in its infancy, even after nearly forty years of work," says Werner Becker, Max-Planck Institut für extraterrestrische Physik, Garching, Germany. There are many models but no accepted theory. Now, thanks to new XMM-Newton observations, Becker and colleagues may have found a crucial piece of the puzzle that will help theorists explain why cooling neutron stars have hotspots at their polar regions.  

Neutron stars are formed with temperatures of more than billion (1012 K) degrees during the collapse of massive stars. As soon as they are born they begin to cool down. How they cool must depend on the physical properties of the superdense matter inside them.

Observations with previous X-ray satellites have shown that the X-rays from cooling neutron stars come from three regions of the pulsar. Firstly, the whole surface is so hot that it emits X-rays. Secondly, there are charged particles in the pulsar’s magnetic surroundings that also emit X-rays as they move outwards, along the magnetic field lines. Thirdly, and crucially for this latest investigation, younger pulsars show X-ray hotspots at their poles.

Until now, astronomers believed that hotspots are produced when the charged particles collide with the pulsar's surface at the poles. However, the latest XMM-Newton results have cast doubt on this view.

user posted image
The faint pulsar PSR B1929+10 captured by the unrivalled sensitivity of ESA’s XMM-Newton orbiting X-ray observatory. It is speeding through space in the direction of the arrow at a speed of 177 kilometres per second. At this speed, the pulsar leaves a trail of X-ray emitting electron plasma stretching across space.

Credits: W.Becker/Max-Planck Institut für extraterrestrische Physik


XMM-Newton captured detailed views of the X-ray emission from five pulsars, each of which was up to several million years old. "No other X-ray satellite can do this work. Only XMM-Newton is capable of observing details of their X-ray emission," says Becker. He and his collaborators found no evidence of surface emission, nor of polar hotspots, although they did see emission from the outwardly moving particles.

The lack of surface emission is no surprise. In the several million years since their birth these pulsars have cooled from billions of degrees to much less than 500 000 degrees Celsius, meaning that their surface-wide X-ray emission has faded from view.

However, the lack of the polar hotspots in old pulsars is a big surprise and shows that the heating of the polar surface regions by particle bombardment is not efficient enough to produce a significant thermal X-ray component. "In the case of three-million-year-old pulsar PSR B1929+10 the contribution from any heated polar region is less than seven percent of the total detected X-ray flux," says Becker.

It seems that the conventional view is not the only way to look at the problem. An alternative theory is that the heat trapped in the pulsar since its birth will be guided to the poles by the intense magnetic field within the pulsar. This is because the heat is carried on electrons, which are electrically charged and so will be directed by magnetic fields.

This means that the polar hot spots in younger pulsars are produced predominantly from heat within the pulsar, rather than from the collision of particles from outside the pulsar. They will therefore fade from view in the same way as the surface-wide emission. "This view is still under discussion but is very much supported by the new XMM-Newton observations," says Becker.

Nearly forty years since the discovery of pulsars, it seems that old pulsars still have new tricks to teach astronomers.

Note:

The findings appear in an article titled 'A Multiwavelength study of the Pulsar PSR B1929+10 and its X-ray trail' by Werner Becker et al., published in The Astrophysical Journal on 10 July 2006 (vol. 645, pp 1421). Previous papers in this study are:

'Revealing the X-Ray Emission Processes of Old Rotation-powered Pulsars: XMM-Newton Observations of PSR B0950+08, PSR B0823+26, and PSR J2043+2740', by Becker, et al., 2004 (ApJ, 615, 908),

'A Multiwavelength Study of PSR B0628-28: The First Overluminous Rotation-powered Pulsar?', by Becker, et al., 2005, (ApJ, 633, 367).


Source: ESA - News

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#15    Waspie_Dwarf

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Posted 04 January 2007 - 02:48 AM

Black hole boldly goes where no black hole has gone before

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Black holes are, by definition, invisible. But the region around them can flare up
periodically when the black hole feeds. As gas falls into a black hole, it will heat to high
temperatures and radiate brightly, particularly in X-rays.

Thanks to ESA’s XMM-Newton data, astronomers found one stellar-mass black hole by
chance feeding in a globular star cluster in a galaxy named NGC 4472 (or M49), about
fifty million light-years away in the Virgo Cluster.

Credits: ESA, NASA and Felix Mirabel


3 January 2007
Astronomers have found a black hole where few thought they could ever exist, inside a globular star cluster. The finding has broad implications for the dynamics of stars clusters and also for the existence of a still-speculative new class of black holes called 'intermediate-mass' black holes.

The discovery is reported in the current issue of Nature. Tom Maccarone of the University of Southampton in England leads an international team on the finding, made primarily with the European Space Agency's XMM-Newton satellite.

Globular clusters are dense bundles of thousands to millions of old stars, and many scientists have doubted that black holes could survive in such an exclusive environment. Computer simulations show that a newly formed black hole would first sink towards the centre of the cluster but quickly get gravitationally slingshot out entirely when interacting with the cluster's myriad stars.


The new finding provides the first convincing evidence that some black hole might not only survive but grow and flourish in globular clusters. What has astonished astronomers is how quickly the black hole was found.

linked-image
Globular clusters are dense bundles of thousands to millions of old stars, and many
scientists have doubted that black holes could survive in such an exclusive environment.

Computer simulations show that a newly formed black hole would first sink towards the
centre of the cluster but quickly get gravitationally slingshot out entirely when interacting
with the cluster's myriad stars.

New XMM-Newton findings provided the first convincing evidence that some black hole
might not only survive but grow and flourish in globular clusters.

Credits: ESA/Hubble


"We were preparing for a long, systematic search of thousands of globular clusters with the hope of finding just one black hole," said Maccarone. "But bingo, we found one as soon as we started the search. It was only the second globular cluster we looked at."

The search continues to find more, Maccarone said, yet only one black hole was needed to resolve the decades-old discussion about black holes and globular clusters.

Scientists say there are two main classes of black holes. Supermassive black holes containing the mass of millions to billions of suns are found in the core of most galaxies, including our own. A quasar is one kind of supermassive black hole. Stellar-size black holes contain the mass of about ten suns. These are created from the collapsed core of massive stars. Our galaxy likely contains millions of these black holes.

linked-image
Astronomers using XMM-Newton data found that the elliptical galaxy (named NGC 4472
or M49) shown in this image hosts a stellar-mass black hole in the act of feeding. This
black hole is the first ever found in a globular star cluster.

The galaxy is situated about fifty million light-years away in the constellation Virgo,
one of the many members of the Virgo galaxy cluster. This image was taken in
December 1996 at the KPNO 0.9-metre telescope.

Credits: NOAO/AURA/NSF


Black holes are, by definition, invisible. But the region around them can flare up periodically when the black hole feeds. As gas falls into a black hole, it will heat to high temperatures and radiate brightly, particularly in X-rays. Maccarone's team found one such stellar-mass black hole by chance feeding in a globular cluster in a galaxy named NGC 4472, about fifty million light-years away in the Virgo Cluster.

XMM-Newton is extremely sensitive to variable X-ray sources and can efficiently search across large patches of the sky. The team also used NASA's Chandra X-ray Observatory, which has superb angular resolution to pinpoint the X-ray source's location. This allowed them to match up the position of the X-ray source with optical images to prove that the black hole was indeed in a globular cluster.

Globular clusters are some of the oldest structures in the universe, containing stars over 12 thousand million years old. Black holes in a cluster would likely have formed many thousand millions of years ago, which is why astronomers have assumed they would have been kicked out a long time ago.

Details in the X-ray light detected by XMM-Newton leave little doubt that this is a black hole - the object is too bright, and varies by too much to be anything else. In fact, the source is 'extra bright', - an Ultraluminous X-ray object, or ULX. ULXs are brighter than the 'Eddington limit' for stellar mass black holes, the brightness level at which the outward force from X-rays is expected balance the powerful gravitational forces from the black hole. Thus it is often suggested that the ULXs might be intermediate mass black holes – black holes of thousands of solar masses, heavier than the 10-solar-mass stellar black holes, and lighter than the million to thousand million solar mass black holes in quasars. These black holes might then be the missing links between the black holes formed in the death throes of massive stars and the ones in the centres of galaxies.

It is perhaps possible for a stellar-mass black hole to gain enough mass through merging with other stellar-mass black holes or accreting star gas to stay locked in a cluster. About 100 solar masses would do. Once entrenched, the black hole has the opportunity to merge with other black holes or accrete gas from a local neighbourhood rife with star-stuff. In this way, they could grow into IMBHs.

"If a black hole is massive enough, there's a good chance it can survive the pressures of living in a globular cluster, since it will be too heavy to be kicked out," said Arunav Kundu of Michigan State University, a co-author on the Nature report. "That's what is intriguing about this discovery. We may be seeing how a black hole can grow considerably, become more entrenched in the cluster, and then grow some more.

"On the other hand," continued Kundu, "there are a variety of ways to make ULXs without requiring intermediate mass black holes. In particular, if the light goes out in a different direction than the one from which the gas comes in, it doesn't put any force on the gas. Also, if the light can be 'focused' towards us by reflecting off the gas in the same way that light from a flashlight bulb bounces off the little mirror in the flashlight, making the object appear brighter than it really is."

Ongoing work will help to determine whether this object is a stellar-mass black hole showing an unusual manner of sucking in gas, allowing it to be extra bright, or an IMBH. The team, which also includes Steve Zepf from Michigan State University, and Katherine Rhode from Wesleyan University, has data for thousands of other globular clusters, which they are now analyzing in an effort to determine just how common this phenomenon is.


Note

The findings appear on line in the 4 January issue of the journal Nature, in the article titled: "A black hole in a globular cluster", by Thomas J. Maccarone, Arunav Kundu, Stephen E. Zepf and Katherine L. Rhode.


Source: ESA - News

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