How does a star go supernova and turn into a neutron star or a black hole?

Neutron stars and black holes are among the most exotic objects in the universe. A lump of neutron star matter the size of a sugar cube would weigh as much as all humanity, and the stars have magnetic fields a trillion times Earth's. Since we can't reproduce such conditions in laboratories, we have to observe neutron stars with telescopes to figure out their properties. Recently the Rossi Explorer, a new X-ray satellite, discovered a remarkable new phenomenon of neutron stars that strip matter from their companion stars: their brightness varies almost periodically more than a thousand times per second. I will describe how this phenomenon gives us a sensitive new tool to probe the properties of neutron stars, and how it may even help us search for black holes.

Intro to Black Holes

A black hole is a region of space in which the matter is so compact that nothing can escape from it, not even light; the "surface" of a black hole, inside of which nothing can escape, is called an event horizon. The matter that forms a black hole is crushed out of existence. Just as the Cheshire Cat disappeared and left only its smile behind, a black hole represents matter that leaves only its gravity behind.

Black holes are usually formed when an extremely massive star dies in a supernova. However, some people think small black holes were formed during the Big Bang, and that the resulting "mini black holes" may be in great abundance in our galaxy.

In principle, black holes can have any mass; black holes formed by stellar death have at least twice the mass of our Sun. Unlike ordinary things (e.g., rocks), which have a size roughly proportional to the cube root of their mass, black holes have radii proportional to their mass. The event horizon of a nonrotating black hole the mass of our Sun has a radius about 3~km. Thus, large black holes aren't very dense! A black hole a billion times as massive as our Sun, such as is thought to exist in the center of some galaxies, has an average density just twenty times the density of air.

Black holes, like any gravitating objects, exert a tidal force. If you approach a black hole feet first, the gravitational force at your feet is greater than the force at your head. The tidal force at the event horizon is smaller for larger black holes: you would get torn to shreds far outside a black hole the mass of our sun, but at the event horizon of a billion solar mass black hole the tidal force would only be a millionth of an ounce!

Strange Facts About Black Holes

  • Light bends so much near black holes that if you were near one and looking away from the hole, you would see multiple images of every star in the universe, and could actually see the back of your own head!
  • Inside a black hole the roles of time and radius reverse: just as now you can't avoid going into the future, inside a black hole you can't avoid going in to the central singularity.
  • If you stood a safe distance from a black hole and saw a friend fall in, he would appear to slow down and almost stop just outside the event horizon. His image would dim very rapidly. Unfortunately for him, from his point of view he would cross the event horizon just fine, and would meet his doom at the singularity.
  • Black holes are the simplest objects in the universe. You can describe one completely by just its mass, spin rate, and electric charge. In contrast, to completely describe a dust mote you're have to specify the position and state of all of its atoms, taking at least $10^{16}$ numbers!
  • As Hawking discovered, black holes can evaporate, but only very slowly. Even one the mass of a mountain will last for ten billion years, and one the mass of the Sun will only evaporate after $10^{67}$ years.

After the completion of thermonuclear reactions in the core of the sun , the outward force due to theses reactions exceed the inward gravitational pull of the core n the star results in expansion and based on the stars weight acc to chandrashekaran limit it make result in forming a dwarf star or neutron star or black hole through super nova explosion


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