Solved: the mysteries of the black hole:
By Steve Connor
Published: 03 November 2005
http://news.independent.co.uk/world/scienc...ticle324378.ece
The concept of black holes, supermassive voids that suck in all matter and light, has caught the public imagination for decades. Now, for the first time, scientists are on the verge of looking into the heart of darkness.
They are probably the strangest things in the known universe. Black holes are so massive and their gravitational pull is so strong that nothing can escape - not even light itself - which is strange indeed for something made of nothing.
A hole in space seems to make no sense at all, yet scientists are convinced that these prisons of light are for real, even though they have never really been seen and the only evidence for their existence is circumstantial.
But astronomers have now got close to staring a black hole in the face. With the help of an array of 10 radio telescopes in America, they have pictured the void at the centre of our own Milky Way galaxy 26 million light years away, where a supermassive black hole sits invisibly like the transparent eye of a hurricane.
This particular black hole is estimated to have a mass equivalent to four million Suns and yet the latest measurements, published in the journal Nature, suggest it occupies a volume with a radius less than the distance between the Earth and the Sun.
This is less than half the size previously estimated, indicating that astronomers are close to defining the crucial outer boundary of one of the most elusive phenomena in cosmology - one that has mystified scientists for decades. "We're getting tantalisingly close to being able to see an unmistakable signature that would provide the first concrete proof of a supermassive black hole at a galaxy's centre," said Zhi-Qiang Shen, of Shanghai Astronomical Observatory in China, one of the leaders of the study.
No light escapes from black holes, which is why they are so invisible. They can however be detected by the radiowaves emitted from their periphery as they gobble up any surrounding matter that falls within range.
The first sign of a black hole within our own galaxy came in February 1974, when two American astronomers, Bruce Balick and Robert Brown, detected a powerful source of radiowaves emanating from the constellation of Sagittarius. Balick and Brown calculated that, whatever the cause of the radiation, the source was coming from the dead centre of the galaxy. They suspected a black hole at the heart of the Milky Way and the race began for astronomers to capture the first image of this radio source, which they called Sagittarius A* (pronounced "A-star").
"Black holes are perhaps the most exotic objects to impinge on the cosmic consciousness," explains astronomer Christopher Reynolds of the University of Maryland, writing in Nature. "They are formed when matter such as that from a dying massive star collapses in calamitously under its own gravity, forming a region of space in which the gravitational field is so strong that it swallows all matter and radiation that come near it."
One way of looking at black holes is how they distort space and time. Imagine the space-time continuum as a rubber sheet. An object the size of the Sun would act like a heavy ball placed on a trampoline, causing a minor indentation. Heavier objects, such as cannonballs, would create further indentations in the space-time continuum but something as heavy and dense as a black hole would cause such a steep dent that it would be like a bottomless pit from which nothing could escape once it fell in.
>This view of black holes comes with the benefit of Einstein's theories of relativity. But the concept actually predated his pioneering work. In fact, black holes, like many cosmological phenomena, were predicted long before scientists began to construct the sort of instruments that could detect them.
Indeed, an English clergyman and scholar called John Michell predicted in 1784 that some stars might be so big, and hence so heavy or massive, that they would create a gravitational field strong enough to prevent light from escaping. If something was 500 times bigger than the Sun, the Rev Michell wrote, "all light emitted from such a body would be made to return towards it, by its own proper gravity".
Such predictions were based on what was known at the time from Isaac Newton's work on gravity. It was not until after Albert Einstein formulated his general theory of relativity that further work could be done on the theory of black holes - although no one actually called them by that name until 1967.
Using Einstein's theory, Karl Schwarzschild, a German physicist, discovered that relativity equations led to the predicted existence of an object so dense that other objects would fall into it and never come out again.
Schwarzschild talked about a "magic sphere" around such an object where gravity was so powerful that nothing within that sphere could escape. Furthermore, all matter within the sphere would be crushed to a point of infinite density occupying virtually no space. This point is known as the "singularity" and every black hole is believed to have a singularity at its centre.
J Robert Oppenheimer, the father of the American atom bomb, calculated that a black holes was the ultimate end-product of a star's lifecycle, the point when it collapsed in on itself and the resulting ultra-dense material gave rise to a singularity.
But the real turning point came in 1967, when the American astrophysicist, John Wheeler, actually coined the term "black hole" - and launched a wave of popular fascination with these gravity-defying voids.
In 1971, the first experimental evidence from space for the existence of black holes came with data captured by the American Uhuru satellite. Its instruments detected a source of X-rays coming from a star that appeared to be orbiting an invisible companion that was estimated to be five times the mass of the Sun.
This was the first of several contenders for the "smaller" kind of black hole caused by the collapse of a stellar objects. But in more recent years scientists have been chasing much, much bigger black holes.
These black holes are supermassive affairs, like the one at the centre of our own galaxy which is estimated to weigh in at about 4 million times the mass of the Sun.
But astronomers believe there are even bigger ones, 10 billion times the mass of the Sun, at the heart of every galaxy, said the cosmologist Marcus Chown, author of The Universe Next Door. "No one knows how they form. No one knows why they are at the centre of galaxies. It's even possible they were there first and seeded the formation of galaxies such as the Milky Way."
Such is the mystery surrounding black holes that a small minority of scientists still cannot quite bring themselves to believe in them. "The truth is we don't absolutely know for sure that black holes exist. No one has actually seen a black hole, " explained Mr Chown.
This is why the latest study is so important, because scientists are getting so tantalising close to taking that first image of a black hole in all its mysterious splendour. But what would "nothing" look like? How can we take an image of something that swallows up all matter and radiation?
Professor Reynolds said that we may not be able to see a black hole itself, but we should be able to see the boundary or "event horizon" beyond which all matter is swallowed up. "What is needed is a more discerning test than simply detecting something massive and compact; we need to find the event horizon, the defining property of a black hole," he said.
"As physical phenomena go, event horizons are tricky to observe... High-resolution imaging, however, does provide a compelling way to search for an event horizon. If a black hole is surrounded by an almost spherical distribution of radiation matter ... a sufficiently high-resolution image should reveal a shadow around it.
"This dark circle is caused by radiation from sources behind the black hole that are being swallowed by the event horizon. Surrounding this shadow would be a bright ring - the result of the strong deflection by the black hole's gravitational field of those light rays that do scrape past it."
Fred Lo, director of the US National Radio Astronomy Observatory, which runs the array of telescopes that collected the latest data, said that, with a slightly higher resolution, telescopes should soon be able to see this shadow of a black hole.
"The extremely strong gravitational pull of a black hole has several effects that would produce a distinctive 'shadow' that we think we could see if we can image details about half as small as those in our latest images," Dr Lo said. "Seeing that shadow would be the final proof that a supermassive black hole is at the centre of our galaxy."
Mr Chown said that the best way to get the final elusive proof of the existence of supermassive black holes is to observe the one that is closest to us. "The proof will be to see a bright ring with a dark region inside it - presumably, the bright ring is matter super-heated as it falls into the black hole and the dark region is the black hole," Mr Chown said. "Fred Lo and his people have come the closest yet to getting that proof."
Black holes are so strange that they may defy the laws of physics as we know them, for instance by creating "wormholes" in space. When we are finally able to see black holes with our own eyes, we may have also found gateways to other universes.
J Robert Oppenheimer, the father of the American atom bomb, calculated that a black holes was the ultimate end-product of a star's lifecycle, the point when it collapsed in on itself and the resulting ultra-dense material gave rise to a singularity.
But the real turning point came in 1967, when the American astrophysicist, John Wheeler, actually coined the term "black hole" - and launched a wave of popular fascination with these gravity-defying voids.
In 1971, the first experimental evidence from space for the existence of black holes came with data captured by the American Uhuru satellite. Its instruments detected a source of X-rays coming from a star that appeared to be orbiting an invisible companion that was estimated to be five times the mass of the Sun.
This was the first of several contenders for the "smaller" kind of black hole caused by the collapse of a stellar objects. But in more recent years scientists have been chasing much, much bigger black holes.
These black holes are supermassive affairs, like the one at the centre of our own galaxy which is estimated to weigh in at about 4 million times the mass of the Sun.
But astronomers believe there are even bigger ones, 10 billion times the mass of the Sun, at the heart of every galaxy, said the cosmologist Marcus Chown, author of The Universe Next Door. "No one knows how they form. No one knows why they are at the centre of galaxies. It's even possible they were there first and seeded the formation of galaxies such as the Milky Way."
Such is the mystery surrounding black holes that a small minority of scientists still cannot quite bring themselves to believe in them. "The truth is we don't absolutely know for sure that black holes exist. No one has actually seen a black hole, " explained Mr Chown.
This is why the latest study is so important, because scientists are getting so tantalising close to taking that first image of a black hole in all its mysterious splendour. But what would "nothing" look like? How can we take an image of something that swallows up all matter and radiation?
Professor Reynolds said that we may not be able to see a black hole itself, but we should be able to see the boundary or "event horizon" beyond which all matter is swallowed up. "What is needed is a more discerning test than simply detecting something massive and compact; we need to find the event horizon, the defining property of a black hole," he said.
"As physical phenomena go, event horizons are tricky to observe... High-resolution imaging, however, does provide a compelling way to search for an event horizon. If a black hole is surrounded by an almost spherical distribution of radiation matter ... a sufficiently high-resolution image should reveal a shadow around it.
"This dark circle is caused by radiation from sources behind the black hole that are being swallowed by the event horizon. Surrounding this shadow would be a bright ring - the result of the strong deflection by the black hole's gravitational field of those light rays that do scrape past it."
Fred Lo, director of the US National Radio Astronomy Observatory, which runs the array of telescopes that collected the latest data, said that, with a slightly higher resolution, telescopes should soon be able to see this shadow of a black hole.
"The extremely strong gravitational pull of a black hole has several effects that would produce a distinctive 'shadow' that we think we could see if we can image details about half as small as those in our latest images," Dr Lo said. "Seeing that shadow would be the final proof that a supermassive black hole is at the centre of our galaxy."
Mr Chown said that the best way to get the final elusive proof of the existence of supermassive black holes is to observe the one that is closest to us. "The proof will be to see a bright ring with a dark region inside it - presumably, the bright ring is matter super-heated as it falls into the black hole and the dark region is the black hole," Mr Chown said. "Fred Lo and his people have come the closest yet to getting that proof."
Black holes are so strange that they may defy the laws of physics as we know them, for instance by creating "wormholes" in space. When we are finally able to see black holes with our own eyes, we may have also found gateways to other universes.
====================
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http://www.fourmilab.ch/gravitation/orbits/ Orbits in Strongly Curved Spacetime Sorry--it appears your browser doesn't understand Java applets. Introduction The display above shows, from three different physical perspectives, the orbit of a low-mass test particle, the small red circle, around a non-rotating black hole (represented by a grey...
http://www.damtp.cam.ac.uk/user/gr/public/bh_intro.html Introduction to Black Holes What is a black hole? A black hole is a region of spacetime from which nothing can escape, even light. To see why this happens, imagine throwing a tennis ball into the air. The harder you throw the tennis ball, the faster it is travelling when it leaves your hand and...
http://www.astro.ku.dk/~cramer/RelViz/text...ib4/exhib4.html Kerr's rotating Black Holes. Let's generalise some of the formulas used in the static Schwarzschild case, to the case of rotating Black Holes. The Kerr metric is written in Boyer-Lindquist coordinates: where the coordinate functions are given (with G=c=1): the specific angular momentum is...
http://www.astro.princeton.edu/~library/preprints/pop563.abs MASSIVE BLACK HOLES AND LIGHT ELEMENT NUCLEOSYNTHESIS IN A BARYONIC UNIVERSE Nickolay Y. Gnedin, Jeremiah P. Ostriker Princeton University Observatory, Princeton, NJ 08540 Martin J. Rees Institute of Astronomy, Cambridge CB3 OHA...
http://casa.colorado.edu/~ajsh/schwp.html More about the Schwarzschild Geometry #160 Back to Dive into the Black Hole #160 Forward to White Holes and Wormholes #160 Andrew Hamilton's Homepage #160 Other Relativity and Black Hole links index | movies | approach | orbit | singularity | dive | Schwarzschild | wormhole | collapse...
http://theory.uwinnipeg.ca/mod_tech/node61.html Next: Questions Up: Gravity Previous: Gravity as Curved Space: #160#160 Black Holes Einstein's special theory of relativity states, however, that nothing can travel faster than the speed of light, which is: c = 3 x 108m/s If a star, for exle, collapses beyond some critical radius...
http://www.alcyone.com/max/writing/essays/...vaporation.html Black hole evaporation 30Es3 Essays A brief analysis of the mathematical results of Hawking radiation. Black hole evaporation. The Hawking temperature T of a Schwarzschild (nonrotating, uncharged) black hole with mass m is given by the equation (in geometrized units) [reference 1] T = hbar/(8 pi k...
http://www.ahuimanu.k12.hi.us/tqjr99/Stars/black_holes.htm Black Holes Little is known about black holes, because they are too dangerous to study up close. Although we know very little about black holes we do know a few facts. Black holes are made up of densely packed material, sucked in by the immense force of gravity. We know how black holes are formed...
http://nrmedia.com/catalog/blackholes.htm Black Holes Join us for the most dazzling detective story in the history of science. Black Holes features mesmerizing photography, computer animation, and a cast of intrepid cosmic...
http://gopher.udel.edu/mvb/PS146htm/146nobh.html Quarks, Gluons, and the Big Bang PHYS146 Maurice Barnhill Class Notes VI. Black Holes and Quasars Next section Previous section End of section Index of notes Syllabus Announcements Outline of Hawking Chapter 6 Black Holes History of the...
http://wonka.physics.ncsu.edu/~blondin/Blackhole/title.html HOW DO WE SEE BLACK HOLES ? John Blondin Theoretical Astrophysics Department of Physics North Carolina State University...
http://www.weburbia.com/physics/universe.html [Relativity FAQ] - [Copyright] Updated by PEG 27 June 1997 Original by Philip Gibbs, 17 March 1997 Is the big bang a black hole? This question can be made into several more specific questions with different answers. Why did the universe not collapse and form a black hole at the beginning...
http://www.infozine.com/z9905/e-nasa.shtml The Kansas City Health Environment infoZine - Email This Article Astronomers Discover 'Middleweight' Black Holes The field of black holes, formerly dominated by heavyweights packing the gravitational punch of a billion Suns and lightweights just a few times heavier...
http://www.badastronomy.com/mad/1998/bigcrunch.html Is it possible for a giant black hole to crush under it's own gravity...
http://www.newton.dep.anl.gov/newton/askas...ysics/PHY77.HTM Ask A Scientist Physics Archive Index Key: PHY077 Author: Alex Botvinnik Subject: Is there a way to escape from black holes? Text: According to Steven Hawking from A Brief History..., when two black holes merge, they form one black hole greater than or equal to the sum of the...
http://antwrp.gsfc.nasa.gov/htmltest/gifcity/bh_pub_faq.html Frequently Asked Questions (FAQs) on Black Holes to Internet newsgroup: sci.physics Answers posted by Matt McIrvin of Harvard University, last updated 02-FEB-1995. Text in this file is NOT copyrighted by RJN. Contents: 1. What is a black hole, really? 2. What happens to you if you fall in...
http://www.physics.purdue.edu/astr263l/forum/blackholes.html Question: What is a black hole? How is it formed? (Asked by Tom Engle, Tony Hinton, Mark Kelsey, Jim Kelly and Rodney Curran) Stellar Collapse Black holes are some of the weirdest objects one encounters in the study of astronomy and astrophysics. As you may have read above, the stellar life...
http://www.alienq.com/articles/black.htm Black Holes A black hole is actually a point in space where formations of faster than light Primary Energy Particles of different charge potential meet and cause a tornado like effect. The now swirling clouds of energy cause a tremendous condensation and thus slowing of energy formations. The speed...
http://www.phy.mtu.edu/bht/rsgrow.html Approaching the Black Hole The first frame depicts the observer in empty space looking toward the constellation Orion. The three stars in Orion's belt are visible to the right of the center of the screen. Sirius can be seen as the brightest star in the sky below and to left of Orion's belt, and...
http://solar-center.stanford.edu/art/black-hole.html STIS RECORDS A BLACK HOLE'S SIGNATURE May 12, 1997 Photo No.: STScI-PRC97-12 The colorful zigzag on the right is not the work of a flamboyant artist, but the signature of a supermassive black hole in the center of galaxy M84, discovered by Hubble Space Telescope's Space Telescope...
http://www.treasure-net.com/smatters/sm-5grav.htm Science Matters! - Black Holes and Gravity - Questions - Q501 - Is there a theoretical limit to the pull of gravity? [No Answer Yet - Do You have a candidate answer?] Q502 - Is it possible for matter to be so densely packed that a shock wave can travel faster than the speed of...
http://laplace.physics.ubc.ca/~matt/Movies/YM/index.html r_h, the black hole radius), W(r,t) = -1---i.e. the kink falls into the black hole. Weak field evolution, W® vs r: (0.8MB MPEG) Interpolating evolutions (top, weak field bottom, black hole formation) W® vs log(1+r): (1.6MB MPEG) Near-critical evolutions. Here the intermediate...
http://godel.ph.utexas.edu/Members/matt/Movies/YM/index.html r_h, the black hole radius), W(r,t) = -1---i.e. the kink falls into the black hole. Weak field evolution, W® vs r: (0.8MB MPEG) Interpolating evolutions (top, weak field bottom, black hole formation) W® vs log(1+r): (1.6MB MPEG) Near-critical evolutions. Here the intermediate...
http://www.unc.edu/depts/mhplanet/Universe/BHoles.html Black Holes Black holes, those mysterious, invisible gravity whirlpools, have been in the news as one of the most exciting scientific ideas of this century. Many people envision a black hole as some tremendous whirling current traveling through space, devouring any hapless planets or stars in...
http://www.sciencenews.org/sn_arc97/1_18_97/fob2.htm January 18, 1997 Galactic and stellar black holes get real by R. Cowen In my entire scientific life . . . the most shattering experience has been the realization that an exact solution of Einstein's equations of general relativity . . . provides the absolutely exact representation...
http://www.astro.ku.dk/RelViz/ostman/bhe.html Black Holes and Electromagnetism Black Holes and Electromagnetism Boris V. Gudiksen Bjørn Østman Abstract: Contents Black Hole Electrodynamics Accretion Disks Black Hole Magnetosphere Flux Freezing Disc Field Lines Black Hole Electrodynamics Black hole electrodynamics is the theory of...
http://www.cvc.org/astronomy/brown.htm Black Holes by Norman Brown BCC/Summer Science Could Cygnus X-1 be a black hole? Abstract Scientists believe that certain areas of space are like giant, powerful vacuum cleaners that suck in any matter that comes to close. That matter is sucked in, crushed to infinite density, and it disappears...
http://www.crystalinks.com/black_holes.html BLACK HOLESA black hole is a star that has collapsed into a tiny point known as a singularity. It is so dense that it sucks in everything near it, including light. Black holes can be seen via the death throes ofthe matter being sucked in. Although it becomes invisible past a certain point, an...
http://www.herts.ac.uk/astro_ub/a42_ub.html Astronomy Use Back at top of this Browser to return to previous position on your last page. BLACK HOLES A collapsar is a star which has collapsed because nuclear fusion is no longer taking place within its core and, as well as white dwarfs and neutron stars, there is a final type of object which a...
http://www.phy.syr.edu/courses/modules/LIG...warzschild.html Home PREFACE PRIMEVAL SPECIAL GENERAL CONCLUSION Dictionary Newton Equivalence Einstein Schwarzschild Comments? Schwarzschild's Spacetime: Introducing the Black Hole K. Schwarzschild(1873-1916) Just months after Einstein published his work on his Theory of Gravitation, Karl Schwarzschild (1916...
http://www.ebtx.com/ntx/ntx24a.htm Black Hole T-Symmetry Violation W hen black holes were first postulated (seriously-Chandrasikar), there was a gut reaction by the general physics community that could not take them seriously. The underlying reason for this reaction was (and always is) a postulate in opposition...
http://www.physics.ucsb.edu/Research/activities/bh.phtml String theory, M-theory, and black holes There are two questions that presently interest me most: 1) What is string/M-theory? It is now clear...
http://www-xray.ast.cam.ac.uk/oday/bh.html GO BACK Black holes Black holes are thought to exist in the centres of many large elliptical galaxies, for exle M87, one of the largest galaxies in our Milky Way's neighbourhood. The core of M87 has recently been observed by the Hubble Space telescope: Another large galaxy, Centaurus A was...
http://www.rdrop.com/users/green/school/glossary.htm acceleration disk A sheet of gas and dust surrounding any massive object growing in size by attracting material. accretion disk A disk shape formed by gas as it spirals into a black hole. atom The basic unit of matter. binary star system A system in which two stars orbit around a common center of...
http://www.ktca.org/newtons/11/blckhole.html Black Holes Teacher's Guides Index BLACK HOLES What is a black hole? Why can't light escape from a black hole? How could a star become a black hole? Does this have anything to do with ordinary, everyday gravity? David embarks on a dangerous and...
http://www.leyada.jlm.k12.il/proj/black/black.htm Black Holes- Birth, Life Death According to the most recent theories, black holes are the consequence of the death of a big star, which is, minimum, 3 times as massive as the sun. The gravitational pull of such an object is so big, that neither light, nor any other kind of electromagnetic...
http://www.aps.org/BAPSAPR98/abs/S910001.html Previous abstract | Graphical version | Text version | Next abstractSession M8 - Probing Black Holes and Neutron Stars with the Rossi Explorer. INVITED session, Monday morning, April 20 Room C213, Columbus Conv. Center [M8.01] QPOs from Black Hole Candidates: Disk Oscillations or Frame Dragging...
http://www.berlinet.de/schmelzer/PG/blackHole.html Black Holes in Post-Relativistic Gravity The collaps into a black hole looks slightly different in PG - and effect of the different notion of completeness in PG and GR, similar to the big bang scenario. To see why, we have to compute the harmonic time coordinate with the appropriate...
http://helios.augustana.edu/physics/club/b...mate-abyss.html On Thursday, October 16, 1997... At twelve noon... In the John Deere Lecture Hall... The Augustana Physics Club presents... Black Holes The Ultimate Abyss The most powerful forces in the universe are black holes. They are objects in space formed over thousands of years that suck up...
http://www.sciencenews.org/sn_arch/10_5_96/fob1.htm October 5, 1996 Firm Evidence of Milky Way Black Hole By Ron Cowen Astronomers have speculated for 25 years that a monster lurks at the center of the Milky Way. Now they appear to have proof. The beast in our cosmic backyard is a black hole -- a dark, dense object as massive as 2.5...
http://www.rdrop.com/users/green/school/form.htm Main Page Black Hole Formation Black Hole Detection Event Horizon Primordial Black Holes Quasars Hawking Radiation The Information Paradox Frame Dragging Likely Black Hole Candidates Our Attempts To Contact Stephen Hawking Glossary References Used About the Authors There are two main...
http://www.ess.sunysb.edu/simswg/siswg/node72.html Next: Added Capabilities with SIM: Up: Three Candidate Imaging Programs Previous: Young Stellar Objects Black Hole Candidates in Virgo Cluster Galaxies: A Unique Opportunity The combination of HST/WFPC2 images and HST/FOS spectra has allowed the successful detection of a M and M...
http://www.newton.dep.anl.gov/newton/askas...tron/AST204.HTM Ask A Scientistcopy Astronomy Archive Black holes and generating gravity Author: heidi m olson How do black holes generate gravity? Why are not they stronger or weaker than they are? Response #: 1 of 1 Author: samuel p bowen All matter attracts other matter. That is gravity. Black...
http://www.aas.org/publications/baas/v29n5...bs/S078014.html Previous abstract Next abstract Session 78 - Seyfert Galaxies. Display session, Friday, January 09 Exhibit Hall, [78.14] Weighting black holes in AGNs with SIM T. Boeker, R. J. Allen (STScI) We present results from simulations of the synthesis imaging mode of the Space Interferometer Mission (SIM...
http://www.natashascafe.com/html/hole.html Recipe for Making Black Holes Take 70 Kilograms of any mass. Compress to less than 10-23 cm or 1 divided by 100,000 billion billion When the radius becomes 10 billion times smaller than an electron you have created a black hole. The Earth with a mass of...
http://www.aps.org/praw/lilienfe/99winner.html 1999 JULIUS EDGAR LILIENFELD PRIZE to Stephen William Hawking University of Cambridge Citation: For boldness and creativity in gravitational physics, best illustrated by the prediction that black holes should emit black body radiation and evaporate, and for the special gift of making...