1652 words 7 pagesPHYS1160
A black hole is a point in space where there is extreme gravitational pull, so extreme that light itself cannot escape. The strength of gravity is so strong due to the fact that an immense amount of matter has been contained in a small space.
The existence of black holes was first theorized by John Mitchell in 1783. Mitchell accepted Newton’s laws of gravity and suggested that light escaping from the surface of a star would have its speed reduced due to the gravitation pull of the star, and therefore if a star’s gravitation pull was strong enough even light would not be able to escape. Using the approximate speed of light he reasoned that if an object was approximately 500 times the mass of the sun light would not be able …show more content…
First of all what led astronomers to believe that there lies a black hole at the centre of our galaxy? By monitoring and observing numerous stars that lie in the centre of our galaxy astronomers have found that the majority of these stars have orbits consistent with orbiting stars, i.e. they have elliptical shaped orbits. This suggests that the gravity which makes these stars orbit in such a fashion derives from a single object at their centre. By using the data taken from these stars and their orbits astronomers have been able to determine the mass of the object which they appear to be orbiting; astronomers have found that there lies a mass of “4 million solar masses within a region about the size of our solar system.”  This suggests that there is in fact a black hole at the centre of our galaxy.
Further evidence of a black hole in the centre of our galaxy arose from a study of the centre of our galaxy, focused on a known radio source referred to as Sagittarius A. The centre of our galaxy is abundant with tiny dust particles, preventing visible light observations. Astronomers therefore were only able to used x-rays or infared too observe this part of our galaxy. American astronomers Bruce Balick and Robert Brown were one of the firsts to recognise the radio source known as Sagittarius A.  This discovery lead to a closer obsesrvation of Sagittarius A, with findings of extremely high speed gas and stars orbiting around the centre of