According to Wikipedia,
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that marks the point of no return. It is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics. Quantum mechanics predicts that black holes emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass or greater.
Objects whose gravity field is too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, although its interpretation as a region of space from which nothing can escape was not fully appreciated for another four decades. Long considered a mathematical curiosity, it was during the 1960s that theoretical work showed black holes were a generic prediction of general relativity. The discovery of neutron stars sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality.
Black holes of stellar mass are expected to form when massive stars collapse in a supernova at the end of their life cycle. After a black hole has formed it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may be formed.
Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter. Astronomers have identified numerous stellar black hole candidates in binary systems, by studying their interaction with their companion stars. There is growing consensus that supermassive black holes exist in the centers of most galaxies. In particular, there is strong evidence of a black hole of more than 4 million solar masses at the center of our Milky Way.
Here are reports about some of the scientific research projects studying black holes.
Black holes are surrounded by many mysteries, but now researchers from the Niels Bohr Institute, among others, have come up with new groundbreaking theories that can explain several of their properties. The research shows that black holes have properties that resemble the dynamics of both solids and liquids.
Astronomers have used the Hobby-Eberly Telescope at The University of Texas at Austin's McDonald Observatory to measure the mass of what may be the most massive black hole yet -- 17 billion Suns -- in galaxy NGC 1277. The unusual black hole makes up 14 percent of its galaxy's mass, rather than the usual 0.1 percent. This galaxy and several more in the same study could change theories of how black holes and galaxies form and evolve.
The point of no return: In astronomy, it's known as a black hole -- a region in space where the pull of gravity is so strong that nothing, not even light, can escape. Black holes that can be billions of times more massive than our sun may reside at the heart of most galaxies. Such supermassive black holes are so powerful that activity at their boundaries can ripple throughout their host galaxies.
The current issue of Science Express, the online advance publication of the journal, features a paper by the Event Horizon telescope team -- a collaboration which includes Perimeter Associate Faculty member Avery Broderick -- that may shed light on the origin of the bright jets given off by some black holes. In a world first, the team has been able to look at a distant black hole and resolve the area where its jets are launched from. This is the first empirical evidence to support the connection between black hole spin and black hole jets that has been long suspected on theoretical grounds.
"This is a very nice confirmation of theoretical predictions," says S. George Djorgovski, professor of astronomy, who will present the results at the conference. "These close pairs are a missing link between the wide binary systems seen previously and the merging black-hole pairs at even smaller separations that we believe must be there."
Massive black holes have been found at the centres of almost all galaxies, where the largest galaxies -- who are also the ones embedded in the largest halos of dark matter -- harbour the most massive black holes. This led to the speculation that there is a direct link between dark matter and black holes, i.e. that exotic physics controls the growth of a black hole. Scientists at the Max Planck Institute of Extraterrestrial Physics, the University Observatory Munich and the University of Texas in Austin have now conducted an extensive study of galaxies to prove that black hole mass is not directly related to the mass of the dark matter halo but rather seems to be determined by the formation of the galaxy bulge. Their findings are published Jan. 20, 2011 in journal Nature.
All massive galaxies host a central supermassive black hole, which may shine brightly as an active galactic nucleus if the black hole is pulling in nearby gas clouds. In the local universe, however, active black holes are rarely seen in small "dwarf" galaxies. The galaxies studied by Trump and his coauthors are about 10 billion light-years away, giving astronomers a view of galaxies as they appeared when the universe was less than a quarter of its current age.
Five large space telescopes were involved in this hundred days compaign that took place in late 2009. The heart of the campaign consisted of repeated visible, X-ray and gamma-ray observations with ESA's XMM-Newton and INTEGRAL satellites, which monitored Markarian 509 for six weeks. This was followed by long observations with NASA's Chandra X-ray satellite, using the Low Energy Transmission Grating, and the NASA/ESA Hubble Space Telescope using the new Cosmic Origins Spectrograph. Prior to these observations short snapshots to monitor the behaviour of the source at all wavelengths were taken with the Swift satellite.
Although their origin remains a mystery and although they are invisible, black holes found at galaxy centers make their presence known through the effects they have on their celestial surroundings. The Milky Way's black hole, a monster with a mass four million times that of the Sun, feeds on some of its neighbors and thrusts others out into the intergalactic void.
In 2003 it became clear from astronomical observations that there is a connection between the X-ray emission from a black hole and its jet outflow. This connection needs to be explained if we want to understand how the black hole engine works. In the first years after this connection was discovered, it seemed that it was the same for all feeding black holes, but soon oddballs were found. These unusual examples still have a clear connection between the energy released in the X-ray emission and that put in the jet ejection. But the proportion differs from that in the "standard" black holes. As the number of oddballs grew, it started to appear that there were two groups of black hole engines working in a slightly different way, as if one were running on petrol and the other on diesel.