* Astronomy

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Primordial black hole dark matter

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BlackHole geometry

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The Most Massive Black Holes in the Universe

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RE: Black Holes

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Singularities

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RE: Black Holes

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Times Change, But Do Supermassive Black Holes Remain the Same?
Have supermassive black holes changed since the dawn of our Universe nearly 14 billion years ago?

This question has stumped astronomers for decades. However, thanks to NASA's infrared eyes in the sky -- the Spitzer Space Telescope -- scientists may be one-step closer to solving this mystery.

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A low-dust quasar called SDSS J0005-0006
Credit NASA/JPL-Caltech

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Research by UK astronomers, published today in Nature (7th December 2006) reveals that the processes at work in black holes of all sizes are the same and that supermassive black holes are simply scaled up versions of small Galactic black holes.
For many years astronomers have been trying to understand the similarities between stellar-mass sized Galactic black hole systems and the supermassive black holes in active galactic nuclei (AGN).In particular, do they vary fundamentally in the same way, but perhaps with any characteristic timescales being scaled up in proportion to the mass of the black hole. If so, the researchers proposed, we could determine how AGN should behave on cosmological timescales by studying the brighter and much faster galactic systems.
Professor Ian McHardy, from the University of Southampton, heads up the research team whose findings are published today (along with colleagues Drs Elmar Koerding and Christian Knigge and Professor Rob Fender, and Dr Phil Uttley, currently working at the University of Amsterdam). Their observations were made using data from NASA’s Rossi X-ray Timing Explorer and XMM Newton’s X-ray Observatory.

"By studying the way in which the X-ray emission from black hole systems varies, we found that the accretion or ‘feeding’ process - where the black hole is pulling in material from its surroundings - is the same in black holes of all sizes and that AGN are just scaled-up Galactic black holes. We also found that the way in which the X-ray emission varies is strongly correlated with the width of optical emission lines from black hole systems. These observations have important implications for our understanding of the different types of AGN, as classified by the width of their emission lines. Thus narrow line Seyfert galaxies, which are often discussed as being unusual, are no different to other AGN; they just have a smaller ratio of mass to accretion rate" - Professor Ian McHardy.

The research shows that the characteristic timescale changes linearly with black hole mass, but inversely with the accretion rate (when measured relative to the maximum possible accretion rate). This result means that the accretion process is the same in black holes of all sizes. By measuring the characteristic timescale and the accretion rate, the team argues this simple relationship can help determine black hole masses where other methods are very difficult, for example in obscured AGN or in the much sought after intermediate mass black holes.

"Accretion of matter into a black hole produces strong X-ray emission from very close to the black hole itself. So, studying the way in which the X-ray emission varies with time, known as the X-ray lightcurves, provides one of the best ways of understanding the behaviour of black holes.
It has been known for over two decades that characteristic timescales can be seen in the X-ray lightcurves of Galactic black hole systems" - Professor Ian McHardy.

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NASA Telescope Sees Black Hole Munch On A Star
A giant black hole has been caught red-handed dipping into a cosmic cookie jar of stars by NASA's Galaxy Evolution Explorer. This is the first time astronomers have seen the whole process of a black hole eating a star, from its first to nearly final bites.

"This type of event is very rare, so we are lucky to study the entire process from beginning to end" - Dr. Suvi Gezari of the California Institute of Technology, Pasadena, Calif. Gezari is lead author of a new paper appearing in the Dec. 10 issue of Astrophysical Journal Letters.

For perhaps thousands of years, the black hole rested quietly deep inside an unnamed elliptical galaxy. But then a star ventured a little too close to the sleeping black hole and was torn to shreds by the force of its gravity. Part of the shredded star swirled around the black hole, then began to plunge into it, triggering a bright ultraviolet flare that the Galaxy Evolution Explorer was able to detect.
Today, the space-based telescope continues to periodically watch this ultraviolet light fade as the black hole finishes the remaining bits of its stellar meal. The observations will ultimately provide a better understanding of how black holes evolve with their host galaxies.

"This will help us greatly in weighing black holes in the universe, and in understanding how they feed and grow in their host galaxies as the universe evolves" - Dr. Christopher Martin of Caltech, a co-author of the paper and the principal investigator for the Galaxy Evolution Explorer.

In the early 1990s, three other resting, or dormant, black holes were suspected of having eaten stars when the joint German-American-British Röntgen X-ray satellite picked up X-ray flares from their host galaxies. Astronomers had to wait until a decade later for NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton X-ray observatory to confirm those findings, showing that the black holes' X-rays had faded dramatically -- a sign that stars were swallowed.
Now, Gezari and her colleagues have, for the first time, watched a similar feeding frenzy unfold, as it happens, through the ultraviolet eyes of the Galaxy Evolution Explorer. They used the telescope's detectors to catch an ultraviolet flare from a distant galaxy, then watched the flare diminish over time, as the galaxy's central black hole consumed the star. Additional data from Chandra, the Canada France Hawaii Telescope in Hawaii and the Keck Telescope, also in Hawaii, helped the team chronicle the event in multiple wavelengths over two years.
Black holes are heaps of concentrated matter whose gravity is so strong that even light cannot escape. Supermassive black holes are believed to reside at the cores of every galaxy, though some are thought to be more active than others. Active black holes drag surrounding material into them, heating it up and causing it to glow. Dormant black holes, like the one in our Milky Way galaxy, hardly make a peep, so they are difficult to study.
That's why astronomers get excited when an unsuspecting star wanders too close to a dormant black hole, an event thought to happen about once every 10,000 years in a typical galaxy. A star will flatten and stretch apart when a nearby black hole's gravity overcomes its own self-gravity. The same phenomenon happens on Earth every day, as the moon's gravity tugs on our world, causing the oceans to rise and fall. Once a star has been disrupted, a portion of its gaseous body will then be pulled into the black hole and heated up to temperatures that emit X-rays and ultraviolet light.

"The star just couldn't hold itself together. Now that we know we can observe these events with ultraviolet light, we've got a new tool for finding more" - Dr. Suvi Gezari

The newfound feeding black hole is thought to be tens of millions times as massive as our sun. Its host galaxy is located 4 billion light-years away in the Bootes constellation.

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Two groups of European researchers are going ga-ga over gamma-ray blasts from different sources, both thought to be black holes acting up.
One gamma-ray source, known as IGR J717497-2821, appears to be a newborn black hole. The other, LS 5039, is an unusual high-energy modulator that researchers call the first-ever "gamma-ray clock."

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