Astro News
- Recent Updates of Astro News
- Active Mercury(07/09)
- Hubble Status Report: Directly Observes a Planet Orbiting Another Star(01/09)
- A Non-trivial Answer to a Trivial Astronomical Question-The Origin Of Absolute Magnitude(07/08)
- Assault by a Black Hole(04/08)
- New Lakes Discovered on Titan(01/08)
- ˇ§Deviant Behaviourˇ¨ in the Solar System(10/07)
- Cosmic Ripples - Cosmic Microwave Background - CMB(07/07)
- Interplanetary Superhighway(04/07)
- Is Pluto a Planet?(01/07)
- Breathing Moonrocks(10/06)
- My Thoughts on the Theory of Relativity, Quantum Mechanics, Superstring Theory and Dark Matter(07/06)
- Space-time Vortex(04/06)
- Radio Astronomy(01/06)
- Neutrino Astronomy(10/05)
- The Active Earth(07/05)
- What is Dark Energy?(04/05)
- The Mysterious Black Holes(01/05)
- Intermediate-Mass Black Holes And Quasisoft X-Ray Sources(10/04)
- Time Travel: From a Scientific Approach(07/04)
- What is Astrobiology?(04/04)
- Black Hole: From Fantasy To Reality (II)(01/04)
- Black Hole: From Fantasy To Reality (I)(10/03)
- From The Oldest Light In The Universe To The Fate Of The Universe(7/03)
- The Cosmic HERO(4/03)
- Quaoar - the Tenth Member of the Solar System?(1/03)
- The First Chinese Telescope in Space(10/02)
- Diamonds and Other Stardust(7/02)
- Supermassive Black Hole in Andromeda Galaxy(4/02)
- Detection of Solar Neutrinos(1/02)
- Simultaneous Multiple Wavwlength Observation(10/01)
- Celestial Distance(7/01)
- Solar-Terrestrial Relations(7/00)
- Fundamental Particles in Astronomy(4/00)
- The Solar Maximum in 2000(1/00)
- Hubble Constant(10/99)
- New Findings on Cosmology(7/99)
- Strange Stars(4/99)
- How Strong Stellar Magnetic Field Can Be?(1/99)

Important notices

Astronomers all along rely on radiation emitted from accretion disk of binary as the only clue for detection of black holes. But the method used to search for isolated black holes in recent years opens up a new way of black hole hunting. Researchers, by analysis of a lot of the starlight in the direction of the core of the Milky Way, found in two cases that the luminosity of the stars increased in a couple of hundreds of days and then backed to the normal level. Analysis showed this might be due to the fact that a black hole passed in front of the star. The gravitation of a black hole can function as a convex lens and focus starlight, resulting in transience increase of apparent brightness of the star. This is the so called "gravitational microlensing" effect. The discovery of isolated black holes agrees with the stellar evolution theory that black hole can be formed naturally when a massive star collapses under its own gravitation. Binary system is not a necessary for its formation.

One of the exciting discoveries brought about by the Hubble Space Telescope is that it confirms what astronomers have all along been guessing about the existence of "Supermassive Black Holes" in the centres of galaxies. In the cores of many so-called "active galaxies", we can observe extremely powerful radio sources with double-lobed structure and jets of high-energy particles. The only theory to explain these powerful energy sources is that, in the cores of those galaxies, there are supermasive black holes devouring matter in a large scale. By using the Hubble Space Telescope, astronomers discover that in the vicinity of the cores of many active galaxies, there exist high-speed swirling gas discs. Their rotation speeds can reach up to a few hundreds of kilometers per second. Based on the swirling speed of gases, astronomers can estimate the mass of the invisible object hiding in the core. Taking the famous M87 elliptical galaxy as example, the dark matter in its core runs up to 2.4 billion solar masses! Other than the active galaxies, supermassive black holes can also be found in the centres of ordinary galaxies. But the mass of the black holes is only at the level of one million solar masses.


M87's Jet: A Cosmic Searchlight: Streaming out from the centre of the galaxy M87 like a cosmic searchlight is one of nature's most amazing phenomena, a jet of electrons and other sub-atomic particles travelling at nearly the speed of light, powered by the central massive object of the galaxy. In this NASA Hubble Space Telescope image, the jet contrasts with the bright glow from the combined light of billions of unseen stars and the point-like globular clusters that make up this galaxy.

Apart from small black holes formed as a result of star evolution and supermassive black holes discovered at the centres of galaxies, astronomers found also middle scale black holes of size ranging from a few thousands to tens of thousands of solar masses in the centres of globular clusters. With the help of new observation techniques, researchers can, using the velocity distribution data of stars in a cluster, directly deduce the mass of black hole at the centre. This method doesn't require the observation of accretion disk. Studies show that mass of clusters or galaxies is always directly proportional to the mass of the central black hole. That is to say, the larger the star clusters or galaxies, the more massive the black hole in the centre. This result implies that there should be a link between clusters and galaxies. We believe that during the course of the evolution of the Universe, stars and clusters might have been formed before the galaxies. Later on, clusters might violently collide and merge with each other to form galaxies. Then the merging of galaxies produced even larger galaxies. When the host clusters or galaxies merged, the black holes at the centers would also fuse into one. During the merging process, the central black holes would grow even larger by sucking in extra matter with the help of the gravitational pull of galaxies. In other words, soon after the Universe comes into being, medium-size black holes at the centre of clusters could be the seed of supermassive black holes at the centers of galaxies today!

In 2002, based on the observation results from the Chandra X-ray Observatory and the Hubble Space Telescope, astronomers employed computer to simulate the merging process of two supermassive black holes at the centre of NGC 6240. Through the optical telescope, NGC 6240 is shaped like a butterfly. It is so odd-looking because it is in fact the result of the collision of two spiral galaxies. X-ray observation shows that at the centre of the galaxy, there are two X-ray sources, which are 3,000 light years from each other. They could be two supermassive black holes about to be merged. It is estimated that the two supermassive black holes will merge into an even bigger black hole over the next few billion years.


The centre of NGC 6240 as observed by the Hubble Space Telescope

The centre of NGC 6240 as observed by the Chandra X-ray Observatory. 
The two dots in the centre are believed to be the sources of X-ray produced by the two black holes.

In 2003, astronomers studied extremely remote sources of X rays by using the Chandra X ray Observatory. For some of those X ray sources, no visible counterparts can be seen in optical range. Astronomers suspect that these X-ray sources could be originated from the supermassive black holes at the centres of some extremely remote galaxies. If that is true, these could be the farthest galaxies ever observed in human history. The farther we look towards the edge of the Universe, the further back in time we are exploring. Judging from the distance of those X-ray source from the Earth, these galaxies may be created 500 millions years after the birth of the Universe (currently the Universe is 13.7 billions years old)!

If that is the case, the number of black holes may be far more than we can think of. The wide spectrum of black holes in term of size and astronomical phenomena associated undoubtedly made them a unique mysterious celestial body of the Universe. Leaving fantasy and returning to reality, we will always find that the Universe is surprisingly far more complicated and mysterious than our imagination. This is the course of science development.

Photo Credit : NASA