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What is a Black Hole ?

What is a Black Hole?


As we have discussed before the stability of the star is maintained by the pressure balance between the gravitational inward pull and the radiation pressure. Depending on the mass of the star, its end fate is decided. We have discussed briefly about the white dwarf and the neutron star. But what is the fate of the star when the mass is so high not to be balanced by even the neutron’s degeneracy pressure? BLACK HOLE is the answer. Such high mass stars end their fate by forming a black hole.

black_hole
A black hole accreting matter (www.space.com)



What is a black hole? Let us first understand the escape velocity. Escape velocity is that velocity at which an object is thrown will make it to escape the gravitational pull of the celestial body. A star with high mass when collapses due to gravitational inward pressure, a stage is reached when the escape velocity almost equals to the velocity of light 300,000 km/s, it forms a black hole.  Black hole can grow by accreting matter from nearby regions and can turn into a super massive black hole (SMBH) of about million solar mass or greater. Most of the galaxies in our universe harbor a SMBH at their centre. Our own Milky Way has a SMBH of about million solar mass.



milkyway_galaxy
A SMBH at the centre of our Milky Way galaxy  (www.spacedaily.com)

The size of a stellar mass black hole is about few km. The black hole is detected and characterized by the motion of nearby celestial objects. Recent studies have shown that an intermediate mass black hole (few thousand solar mass) does exist and there are certain claims of even detecting them. Interacting black holes are also understood as the source of gravitational waves which is an ongoing field of research.  Scientists from all over the world are now putting an enormous effort to understand these exciting objects of our universe. We hope new physical insights can be learned from these studies which may modify our understanding of physics.

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Check your Astro Knowledge
Watchout for the next article to know the correct answer....



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The solution to Quiz3 (link for the corresponding question)
Option A- (Billion times stronger than the sun)

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