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    Black Hole Detection Methods
    By Usman Anwer | September 14th 2008 09:07 AM | Print | E-mail | Track Comments
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    Black holes have been a research concentration for a number of years now. Advanced telescopes like Chandra X-ray Observatory and the Swift Gamma Ray Burst Telescope make it easier to observe the effects of black holes on their local neighborhood. Black holes have intrigued me for a number of years now as the physics involved can help us understand behavior of singularities and behavior of matter in extreme situations. Also, study of black holes may expose the source of the large amount of energy given out by quasars. The particular point that I find interesting is the detection of these exotic objects. So far, extensive models on the workings of black holes are only based on the effect they have on the surroundings. To understand further models and embellish those already researched upon, advanced detection techniques are required. One method is to look for X-ray binaries. These are pairs of a visible star and a neutron star / black hole. The unseen object pulls in material from the visible star. As the material approaches the black hole, it is flattened into a disk and is swirled into it. The friction between flowing gas heats it to very high temperatures, producing strong X-rays. These X-rays can be detected by the Chandra X-ray Observatory. The results from X-ray imaging can be complemented by measurement of the orbital velocities of the companions; a high orbital velocity will indicate a dense object, such as a black hole. Some of the matter being sucked in is ejected in form of high-speed jets, creating more x-rays and radio waves. Currently, several telescopes are used to determine the nature of black holes through X-ray imaging – and this approach has led to many interesting findings. One of them is the black hole in the globular cluster NGC 4472, about 50 million light years away in the Virgo Cluster. This was an aberration as so far no black holes had been observed in a globular cluster. ESA’s XMM-Newton telescope’s exceptional sensitivity to variable sources and Chandra’s fine angular resolution, helped established that it was in fact a black hole and that it was in the globular cluster. That is not all. Detail from X-rays detected by XMM-Newton showed that this source had brightness uncharacteristic of black holes – it was beyond the Eddington Limit. This gave birth to a new class of black holes called Ultraluminous X-ray Objects (ULXs). The high brightness suggests that these black holes have an intermediate mass – also a new class in the black hole catalog. This discovery is also of paramount importance as it provides a link between stellar black holes and super massive black holes. Improvement in X-ray technology will certainly help detect more black holes and understand their evolution better. Further, gamma ray telescopes will help test theories on black holes and study the behavior of matter near them. The Gamma Ray Large Area Space Telescope (GLAST) is one of these. Gamma Rays are high frequency electromagnetic waves that are generated by black holes and neutron stars. Studying them will help us tackle hitherto unresolved problems. One of them is that of Hawking Radiation. In 1970s, Professor Stephen Hawking from the University of Cambridge asserted that combining gravity with quantum mechanics would mean that black holes are unstable and give out energy in form of radiation. This idea has bizarre implications like micro black holes and existence of some of these in the present day universe. According to the theory, most miniature black holes should evaporate quickly, but those of mass of about 1012 kilograms can exist for 14 billion years. If they do, GLAST will detect gamma rays from them and help synthesize gravity with quantum mechanics . Another aspect which GLAST will work on is super-massive black holes. These black holes lie in galactic nuclei and release powerful jets of matter that can reach very close to the speed of light. Collectively, the energy the release in gamma rays from these can be greater than that released by our entire galaxy over all wavelengths. Current models reason that the hole’s rotational energy is converted into this kinetic energy. GLAST can help us see how, and therefore help us understand active galactic nuclei (AGNs). The birth of black holes and the collision of two black holes is another interesting concentration. Present ideas link these with gamma ray bursts. GLAST can resolve if this connection is legitimate. Gravitational Lensing is another technique. According to Einstein’s theory of general relativity, mass warps spacetime, thus affecting the motion of light i.e a massive body can bend light. Multiple images of objects are produced when a lens crosses the observer and the object. The technique has been successful in finding type II Quasars – a form of super-massive black holes. The observations were made by Advanced CCD Imaging Spectrometer (ACIS) and clearly showed the lensing phenomenon. While myriads of sources and libraries of data are available, more research is required to decipher the full nature of black holes. This is necessary for advancement of modern theories like quantum gravity and also for understanding of matter and energy in extreme conditions – and it all lies on the observations we make, so detection technology and techniques should be on a priority list. References 1.Black Hole Boldly Goes Where No Black Hole Has Gone Before, Tom Maccarone, University of Southampton, United Kingdom and Norbert Schartel, ESA XMM-Newton Project Scientist (http://chandra.harvard.edu/press/07_releases/press_010307.html) 2.Stellar Black holes, Chandra X-ray Field Guide (http://chandra.harvard.edu/xray_sources/blackholes_stellar.html ) 3.Window on the Extreme Universe, William B. Atwood, Peter F. Michelson, and Steven Ritz, Scientific American, December 2007. 4.Type 2 Quasar: Gravitational Lens Helps Chandra Find Rare Type of Black Hole (http://chandra.harvard.edu/photo/2000/type2/index.html) 5.Exploring Black Holes with Chandra (Flash Application) (http://chandra.harvard.edu/resources/flash/ex_bh.html)