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What is a Black hole ?
Black holes cannot be seen as they don't reflect any light.
The centre of black hole is called singularity - a point of infinite density i.e the space curvature extends to infinity.
According to scientists, billons of black holes exists of which millions are having the abode Milky way galaxy
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Can‘t see , but how do we know their existence
- But scientists know they exist because they rip apart stars that get too close to them and because they can send tremors through space.
- It was a collision between two black holes more than a billion years ago that triggered what are called ‘gravitational waves’.
- Albert Einstein even wrote a paper in 1939 claiming that stars could not collapse under gravity because matter could not be compressed beyond a certain point.
- The principal exception was the American scientist John Wheeler,emphasized that many stars would eventually collapse, and pointed out the posed for theoretical physics.
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Formation of Black holes
- During most of the life of a normal star, over many billions of years, it will support itself against its own gravity by thermal pressure, caused by nuclear processes which convert hydrogen into helium.
- The explosive force of nuclear fusion inside them creates outward pressure which is constrained by gravity pulling everything inwards.
- Eventually, however, the star will exhaust its nuclear fuel. The star will now contract.
- For more detail , check out Chandrashekhar limit and Tolmann Volkoff Oppenheimer approximation
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Singularity
- if you take pressure out of the calculation,a uniform spherically symmetric star would contract to a single point of infinite density,I.e,Singularity.
- A singularity is what you end up with when a giant star is compressed to an unimaginably small point.
- It refers not only to the end of a star but also to a far more fundamental idea about the starting-point for the formation of the entire universe.
- All our theories of space are formulated on the assumption that space-time is smooth and nearly flat,so they break down at the singularity.In fact, the singularity marks the end of time itself.
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Einstein‘s View
- It was already clear that a uniform spherical star would contract to a point of infinite density, a singularity.
- Einstein’s Theory of General Relativity says that objects distort the space-time around them.
- At this point of infinite density, one can’t predict the future, which in turn implies that something strange could happen whenever a star collapsed.
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Information
- All the black hole will remember is the total mass, the state of rotation and the electric charge.
- A black hole has a boundary, called the event horizon. This is where gravity is just strong enough to drag light back and prevent it escaping.
- Because nothing can travel faster than light, everything else will get dragged back also.
- There is a black hole with a mass of about four million times that of the sun at the centre of our Milky Way galaxy.
- Scientists believe that there are huge black holes at the centre of virtually all galaxies.
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Properties
- With no light escaping from the black hole, there is no way that anyone watching from a distance could actually witness your descent. In space, no one can hear you scream; and in a black hole, no one can see you disappear.
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