BLACK HOLES

by Bozkurt Selvi, January 2011

A black hole is one of the strangest objects in space. A black hole’s gravity is so strong that even light cannot escape from it, so it appears black. Light is the fastest thing we know of at a speed of 300.000 kilometers per second. If light cannot escape from a black hole then nothing else that we know can.

Parts of a Black Hole
A black hole is made out of two parts:
• Event Horizon: This is the “no way back” sign. If you pass the event horizon it’s impossible to turn back because when you pass it the gravitational pull is so strong that you can’t get back.
• Singularity: Singularity is the weirdest. Because it’s smaller than an atom, but stars go inside it. Nobody knows what happens inside a singularity.

 
How Does a Black Hole Form?
If a star (min 10 times bigger than the Sun) runs out of fuel it dies with a SUPERNOVA. Then it collapses inside. At last it squashes really hard and its atoms just flow away and after that it’s a BLACKHOLE.


What Types of Black Holes Are There?
There are 3 types of black holes.
• Stellar:
This one forms with a star. They are very small (75 km etc.). Because they have collapsed so many times.
If the Earth turned into a black hole (stellar) it would be as big as a fingernail. If a human turned to a black hole it would be smaller than a grain of salt.
• Super Massive:
These are formed in the centre of galaxies. These are millions of times heavier than our Sun. In our galaxy (Milky Way) there is one of them. But no need to worry, it’s really far away.
• Miniature:
Astronomers think that miniature black holes might have formed in the beginning of the universe. But astronomers do not have any evidence of their existence. Miniature black holes have event horizons as small as the width of an atom. These miniature black holes contain as much matter as Mt. Everest .
 
Detecting Black Holes
People can’t see black holes with telescopes etc. so people detect black holes differently.
Black holes are detected as surrounding dust and gas are funneled by the force of gravity into a disc around the black hole. The gas and dust molecules in the disc swirl around the black hole so fast that they heat up and spread X-rays. These X-rays can be detected from Earth.
There are 2 satellites out in Space that detects black holes:

• XMM Newton:
It was launched into Earth orbit in 1999 by NASA and the European Space Agency. It observes the universe in high-energy x-rays. Matter near black holes puts out x-rays as it swirls around just before the black hole swallows it up. By observing these x-rays, XMM can help scientists understand the black hole.
• LISA:
Stands for Laser Interferometer Space Antenna. NASA’s going to launch LISA in 2015. LISA’s three spacecraft will form a triangle. This spacecraft triangle will orbit the Sun just like Earth does. LISA’s three spacecraft will be “connected” by laser beams to make a giant virtual antenna.
LISA is going to look for gravitational waves. These ripples are formed when a massive object such as a black hole moves in space-time. No one has detected a gravitational wave before but scientists think that they really exist. But gravitational waves are very weak. LISA is really sensitive to detect them. This will also help us to learn about other massive objects.
 
Extras
• Astronomers using NASA's Chandra X-ray Observatory have found the youngest black hole known to exist in our cosmic neighborhood. The 30 year old black hole provides an opportunity to watch a black hole develop from infancy.(Nov/14/2010)
• Black holes have the longest lifetime. They die by evaporating (because of Hawking Radiation).
• Nothing that a black hole swallows disappears forever. When it dies it blows out the atoms of the swallowed things.
• One type of black hole is a QUASAR. It is really far away. The nearest one is 2 billion light years away. They are new born galaxies and they are really powerful.

If two PULSARs smashes together, one black hole forms with a gamma ray explosion.