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Topic: Black hole


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In the News (Mon 20 Nov 17)

  
  Black Holes
The event horizon is the point outside the fl hole where the gravitational attraction becomes so strong that the escape velocity (the velocity at which an object would have to go to escape the gravitational field) equals the speed of light.
Black holes almost certainly exist, and one of their basic properties is that they trap light.
In fact, the theoretical prediction of fl holes is due to the General Theory of Relativity, which is built on the principle that the speed of light in a vacuum is constant.
csep10.phys.utk.edu /astr162/lect/blackhole/blackhole.html   (1902 words)

  
  Black hole - Wikipedia, the free encyclopedia
Intermediate-mass fl holes have been proposed as a possible power source for ultra-luminous X ray sources, and in 2004 detection was claimed of an intermediate-mass fl hole orbiting the Sagittarius A* supermassive fl hole candidate at the core of the Milky Way galaxy.
Black holes require the general relativistic concept of a curved spacetime: their most striking properties rely on a distortion of the geometry of the space surrounding them.
The "surface" of a fl hole is the so-called event horizon, an imaginary surface surrounding the mass of the fl hole.
en.wikipedia.org /wiki/Black_hole   (5465 words)

  
 Learn more about Black hole in the online encyclopedia.   (Site not responding. Last check: )
Black holes are believed to form from the gravitational collapse of astronomical objects containing two or more solar masses.
Black holes are also the leading candidates for energetic astronomical objects such as quasars and gamma ray bursts.
Though the mechanism of formation is still not clear, there is increasing evidence that the growth of the fl hole is intimately related to the growth of the spheroidal component (elliptical galaxy, or bulge of a spiral galaxy) in which it lives.
www.onlineencyclopedia.org /b/bl/black_hole.html   (1285 words)

  
 Supermassive black hole - Wikipedia, the free encyclopedia
The process of transporting this angular momentum outwards appears to be the constraining factor in fl hole growth, and leads to the formation of accretion disks.
Such supermassive fl holes in the center of many galaxies are thought to be the "engine" of active objects such as Seyfert galaxies and quasars.
This manifests as a correlation between the mass of the spheroid (the bulge of spiral galaxies, and the whole galaxy for ellipticals) and the mass of the supermassive fl hole.
en.wikipedia.org /wiki/Supermassive_black_hole   (944 words)

  
 Black Holes - Crystalinks
Supermassive fl holes containing millions to billions of solar masses could also form wherever a large number of stars are packed in a relatively small region of space, or by large amounts of mass falling into a "seed" fl hole, or by repeated fusion of smaller fl holes.
The current picture is that all galaxies may have a supermassive fl hole in their center, and that this fl hole swallows gas and dust in the middle of the galaxies generating huge amounts of radiation - until all the nearby mass has been swallowed and the process shuts off.
Though the details are still not clear, it seems that the growth of the fl hole is intimately related to the growth of the spheroidal component - an elliptical galaxy, or the bulge of a spiral galaxy - in which it lives.
www.crystalinks.com /black_holes.html   (3279 words)

  
 Sea and Sky's Cosmic Wonders: Black Holes
This is because fl holes challenge the very foundation of the physical laws we tend to hold dear hear on Earth.
Black holes are so massive that their escape velocity is faster than the speed of light.
Black holes are so massive, that they distort space-time into a deep, bottomless well from which nothing can escape.
www.seasky.org /cosmic/sky7a10.html   (1229 words)

  
 black hole. The Columbia Encyclopedia, Sixth Edition. 2001-05
Called a primordial, or mini, fl hole, it would have been created during the “big bang,” in which the universe was created (see cosmology).
Beginning with a giant star collapsing on itself or the collision of two neutron stars, waves of radiation and subatomic particles are propelled outward from the nascent fl hole and collide with one another, releasing the gamma radiation.
However, a fl hole can be detected by the effect of its gravitational field on nearby objects (e.g., if it is orbited by a visible star), during the collapse while it was forming, or by the X rays and radio frequency signals emitted by rapidly swirling matter being pulled into the fl hole.
www.bartleby.com /65/bl/blackhol.html   (883 words)

  
 Curious About Astronomy? Black Holes and Quasars
The fl hole at the center of this galaxy is thought to be around 60 million times the mass of our Sun; material around it gets shot off in the form of huge jets which travel at nearly the speed of light and are easily visible in this Chandra x-ray image.
Black holes sound like they're straight out of a science fiction story: objects so dense that nothing in the universe can escape from their gravitational pull.
Though the concept of a fl hole was first proposed in 1783, it was Albert Einstein's 1915 theory of general relativity which put the idea on a firm theoretical footing.
curious.astro.cornell.edu /blackholes.php   (1701 words)

  
 BBC - Science & Nature - Space - Black Holes
Black holes were once thought to be the monsters of the Universe, devouring everything around them in a frenzied cosmic feast.
Black holes are regions of space where gravity is so strong that not even light can escape, making them impossible to see.
If the fl hole is really large and has lots of debris in its disc, then it can reveal itself as one of the brightest objects in the Universe - a quasar.
www.bbc.co.uk /science/space/deepspace/blackholes   (423 words)

  
 CNN.com - Black hole seen ripping star apart - Feb. 18, 2004
As it approached a supermassive fl hole that packs as much mass as 100 million suns, the star was stretched by tidal forces similar to those that raise the oceans on Earth.
Black holes are known to be sloppy eaters.
It is a relatively quiet fl hole compared to many, reflecting in part the maturity of the galaxy and, theorists say, a lack of nearby material on which to dine.
www.cnn.com /2004/TECH/space/02/18/shc.blackhole.star/index.html   (1206 words)

  
 Frequently Asked Questions About Black Holes
In the quasar case, a supermassive fl hole (a billion solar masses or so) lies at the center of a galaxy, and gas near the fl hole forms an accretion disk around the hole; again X-rays, and other forms of light, are the result.
So, even if all of the objects in the universe were to end up in fl holes, after a long, long time, the holes would gradually lose their matter, and the matter would disperse througout the universe (as a thin gas of particles).
But, for a pair near a fl hole, one of the particles may fall into the hole, leaving the other without a partner; the particle left behind can't be quickly annihilated by its now missing partner (which is what happens normally).
www.phys.vt.edu /~jhs/faq/blackholes.html   (3432 words)

  
 Supermassive Black Holes
The most plausible candidate is a rotating, supermassive fl hole of order a billion solar masses at their center.
It is now believed that many galaxies have supermassive fl holes at their centers, and that whether such galaxies are active galaxies is a question of whether mass is being fed into these fl holes.
The simplest ideas for the origin of such supermassive fl holes are that they are conglomerations of many star-size fl holes that were formed during the history of a galaxy, or perhaps that galaxies formed around large fl holes that then grew by accreting matter.
csep10.phys.utk.edu /astr162/lect/active/smblack.html   (995 words)

  
 CNN.com - Runaway black hole headed our way - Nov. 22, 2002
Such "cannonball" fl holes were predicted in theory, but "GRO J1655-40 is the first one that has been found in the real universe," Mirabel said.
Scientists were able to follow the runaway fl hole by tracking its companion star, an elderly red giant from which GRO J1655-40 constantly siphons matter.
Black holes are regions of space so warped and dense that even light cannot escape their grasp.
archives.cnn.com /2002/TECH/space/11/22/runaway.blackhole/index.html   (431 words)

  
 Chandra :: Resources :: Q&A: Black Holes
Black holes are thought to result from the collapse of certain very massive stars at the ends of their evolution.
Q: When a star and a fl hole encounter one another, some of the matter in the star may enter the fl hole while a lot of the star's matter may be spun off out into space.
Detection of stellar mass fl holes in distant elliptical's is currently very difficult...Nevertheless, your Chandra team has revealed X-ray evidence for some fl holes in binaries, particularly in globular clusters, of certain elliptical's like NGC 4697.
chandra.harvard.edu /resources/faq/black_hole/bhole-main.html   (2308 words)

  
 Black Holes
Black holes are the densest, most massive singular objects in the universe.
This is the very center of the fl hole, and is where the mass of the original star (and all acquired matter) lies.
In a Kerr fl hole (a fl hole that assumes the star's core was spinning and had a magnetic field when it collapsed), the singularity is theorized to be ring-shaped.
filer.case.edu /~sjr16/stars_blackhole.html   (1193 words)

  
 Black Holes
Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the Sun.
Since fl holes are small (only a few to a few tens of kilometers in size), and light that would allow us to see them cannot escape, a fl hole floating alone in space would be hard, if not impossible, to see.
However, if a fl hole passes through a cloud of interstellar matter, or is close to another "normal" star, the fl hole can accrete matter into itself.
imagine.gsfc.nasa.gov /docs/science/know_l2/black_holes.html   (1395 words)

  
 NASA - Black Hole
The fundamental descriptions of fl holes are based on equations in the theory of general relativity developed by the German-born physicist Albert Einstein.
The gravitational force is strong near a fl hole because all the fl hole's matter is concentrated at a single point in its center.
The surface of a fl hole is known as the event horizon.
www.nasa.gov /worldbook/blackhole_worldbook.html   (794 words)

  
 Black Holes - Science Background
A fl hole is defined by the escape velocity that would have to be attained to escape from the gravitational pull exerted upon an object.
A fl hole is an object so compact that, within a certain distance of it, even the speed of light is not fast enough to escape.
Because everything in the central region is tightly packed to start with, a fl hole in the center of a galaxy can become more and more massive as stars orbiting the event horizon can ultimately be captured by gravitational attraction and add their mass to the fl hole.
amazing-space.stsci.edu /resources/explorations/blackholes/teacher/sciencebackground.html   (3801 words)

  
 SPACE.com -- Odd Black Hole Defies Explanation
Black holes can't be seen, because any light that enters them is trapped.
A stellar fl hole results from the collapse of a single, massive star and is typically a few times the mass of the Sun.
The X-rays are likely generated by a fl hole consuming matter from a young, massive companion star, according to Kaaret, who led the study.
space.com /scienceastronomy/blackhole_medium_040608.html   (629 words)

  
 BLACK HOLES by Ted Bunn
Loosely speaking, a fl hole is a region of space that has so much mass concentrated in it that there is no way for a nearby object to escape its gravitational pull.
We suspect that most of the fl holes that are actually out there were produced in the deaths of massive stars, and so we expect those fl holes to weigh about as much as a massive star.
If you were falling into a smaller fl hole, say one that weighed as much as the Sun, tidal forces would start to make you quite uncomfortable when you were about 6000 kilometers away from the center, and you would have been torn apart by them long before you crossed the horizon.
cosmology.berkeley.edu /Education/BHfaq.html   (5729 words)

  
 Chandra :: Resources :: Black Holes (Illustrations)
The AGN contains a supermassive fl hole attracting gas from the central regions of a galaxy, while the stellar-mass fl hole, typically with a mass about 5-10 times that of the Sun, is rapidly pulling gas from a normal companion star.
Stellar-mass fl holes can therefore be used as scale-models of AGN, and the mechanism that drives the wind - causing gas in the disk to lose energy and fall onto the fl hole - is expected to be the same for both classes.
This fl hole is surrounded by hot gas shown in red and yellow, which acts as fuel for the fl hole engine.
chandra.harvard.edu /resources/illustrations/blackholes.html   (982 words)

  
 Stars are born near our galaxy’s black hole - Space.com- msnbc.com
The supermassive fl hole is surrounded by a disk of gas (yellow and red).
Black holes are best known for ripping stars apart, but new observations of the supermassive fl hole at the center of the Milky Way show that it’s actually helping stars form.
In this model, food for the fl hole is being stolen to create stars, countering conventional fl hole models that the accretion disc is the engine that feeds the fl hole.
www.msnbc.msn.com /id/9685478   (836 words)

  
 SPACE.com -- New Twists on the Milky Way's Big Black Hole
A spinning fl hole drags space around with it and allows atoms to orbit nearer to the fl hole than is possible for a non-spinning fl hole, as seen in the right-hand artist's rendering of a stellar fl hole.
Astronomers know the fl hole is smaller than the diameter of Earth's orbit; they suspect it is about 10 times smaller but have not been able to measure it with enough precision to know for sure.
A spinning fl hole drags space with it, allowing atoms to orbit closer to the fl hole than if it were not spinning.
www.space.com /scienceastronomy/mystery_monday_031124.html   (1013 words)

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