1.2 The History of Black Holes
Because light travels at finite speed, when we look at distant objects we see them as they were, not as they are.
- This means that only a portion of the universe is observable, limited by the speed of light (300,000,000 m/s) and the age of the universe (13,800,000,000 years).
- As they travel towards us, light rays get stretched, causing them to red-shift.
After the Big Bang, there was a ‘dark epoch’ lasting somewhere between 200,000,000 and 500,000,000 years.
- After this, clouds of hydrogen began to collapse, forming the first stars.
- These stars then coalesced, forming the first galaxies.
- The formation of galaxies is deeply interlinked with the formation of the supermassive black holes at their centers.
The escape velocity is the velocity needed to escape the gravitational well of a given object.
- It can be calculated as v=(2Gm/r)^½.
- A black hole is formed when an object grows massive enough that the escape velocity exceeds the speed of light.
Einstein’s Theory of General Relativity claims that gravity is the result of massive objects creating curvatures in spacetime itself.
- A black hole is a unique solution to the equations of general relativity, corresponding to the spacetime curvature generated by a point mass.
- The first evidence supporting this theory was found in 1919 when starlight was observed to curve around the Sun during a solar eclipse.