Keeling,+Allison

//**Astronomy⭐️🌙**// I would like to research astronomy, specifically learning about black holes. //Please list your sources in MLA format//
 * Proposal**
 * Sources**

A black hole is one of the most extreme objects imaginable. The gravitational field close to a black hole is so intense that nothing can escape--not even light (1). A black hole cannot be observed directly, as it gives out no light, but material falling towards a black hole spirals around it like water going down a plug-hole, forming an accretion disc. Material approaching a black hole is gravitationally accelerated to very high speed, then rapidly decelerates as it crashes into the disc. The energy supplied by in-falling matter heats the disc to several million kelvin so that it emits X-rays (2). Accretion also causes some of the orbiting material to be squirted out along its rotation axis in a narrow jet. A compact X-ray source and/or a jet of superheated material indicates the presence of a black hole.
 * Research Outline**

A black hole may form when a star reaches the end of its life and a stellar remnant of mass greater than about 5 x [10.sup.30]kg collapses under its own gravity. (The Sun's mass, [M.sub.sun], is about 2 x [10.sup.30]kg.) Scattered within our own galaxy, astronomers have found many X-ray sources that are probably due to black holes formed by collapsing stars.

The most massive black holes are found at the center of galaxies. Some of these are in radiation output vastly exceeds that of the Galaxy M87 is an elliptical extending from its otherwise 7052 contains evidence of black holes. These black holes have been deduced to have masses several million times that of the Sun, and are likely to have formed at the same time as the galaxies themselves.

Some of the best evidence for supermassive black holes comes from our own Milky Way and galaxies such as M101 (5) in which the stars trace out a spiral pattern and rotate within a thin disc. According to Sir Martin Rees (6), black hole expert and Britain's Astronomer Royal, detailed observations of stars very close to the centre of our galaxy, moving at 3 million kilometres per hour, suggest they are orbiting an object with mass about 3 million [M.sub.sun], concentrated within a region about 10 million km across--that's less than ten times the Sun's diameter. The presence of a compact X-ray source at the centre of the Milky Way (7) is further corroboration.

Astronomers are using powerful computers to explore the bizarre behavior of matter and light close to supermassive black holes. Research is still going on. These simulations take days to compute, but the results are worth the wait, as they have produced images showing how the light from accretion discs (8) is contorted by the intense gravitational field of rotating black holes. In a separate study, simulations have revealed how a spinning black hole can be slowed down by interaction with a surrounding magnetic field (9). Energy can thus be extracted from a black hole itself, not just from the in-falling material. hole can be slowed down by 1 Black hole For an object mass m to escape from the surface of a sphere Mass M and radius R (Figure 1.1) and not fall back, it must Increase its gravitational potentials energy by at least E: E = GMm/R where G is the universal gravitational constant (G = 6.67 x [10.sup.-11] N m.sup.2][kg.sup.-2]). If the object's kinetic energy is equal to E, then it can just escape: 1/2 m [v.sup.2] = GMm/R so its escape velocity is [v.sup.esc] = [square root of 2 GM/R] If [v.sub.sec] is greater than the speed of light f(c =3.0 x [10.sup.8] m [s.sup.-1] then nothing can escape; the massive sphere is a black hole. Put another way, to form a black hole of mass M, the mass Must be concentrated within a radius less than R, where R = 2GM/[c.sup.2] (This derivation uses classical physics to describe the effect of gravity on light, which is not strictly valid. However, it predicts the same black-hole radius as a more Rigorous approach using the equations of relatively).

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 * Rough Draft**