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Black Holes-The Space Vacuum Cleaner
We usually describe Black Holes as 'huge, monstrous vacuum cleaners'. But infact, what are they?

Black Holes are a type of space warp. Now, if we imagine space as a stretched rubber sheet, planets, stars, etc. will make a dip in it. This is a warp. The depth of the warp created determines the gravitational force of the heavenly body. In a black hole, the warp is so deep that even light cannot escape. Because of this, is 'black', so it is called black hole. To imagine the power of a black hole, there is a simple example. The Sun is almost 150,000,000 km(exactly 149,600,000 km) away from Earth. However, if the Sun could form a black hole, it could suck in the Earth from that far! There is a certain area around a black hole called the event horizon. If an object enters the event horizon, it gets sucked into the black hole. The disk of a black hole which we see in pictures is called an acceration disk.

In a black hole, gravity differs greatly over a short distance, so objects going into a black hole are 'stretched' into long shapes before being sucked in. This is called spaghettification.

A black hole is also a shortcut to another place or even time in the Universe. If a spacecraft travels fast enough, it can travel to another time in the Universe.

Now, how are black holes made? When an extra-large star(around more than 15 solar masses) dies, it collapses onto itself. That is,When the star is still in the Middle Sequence, the outward radiation pressure and gravity are balanced. However, when it is dying, this is not the case. The gravity overcomes the radiation pressure and the star collapses onto itself. Then, the escape velocity of the star starts increasing. This keeps on happening till the escape velocity increases the speed of light(300,000 km/s). That is when the star becomes 'black', that is, a black hole.

As we know, galaxies produce quite a lot of power from their centre. Most of these galaxies, including our Milky Way are thought to have massive black holes at their centre, powering the whole galaxy. As this shows, black holes can be enormous. Recently, two black holes were discovered having event horizons the size of 5 solar systems!

Now this gives rise to a question, how can we detect black holes if light cannot escpe from them? The answer is very easy. Black holes can be detected if gas from a nearby star is being 'torn' from it and then sucked into the hole as we can detect such activity. When taking in so much of matter, a lot of energy in form of gamma ray jets and X-rays escape. If such gamma ray jets are directed to Earth, then this radiation can be detected. Thus, detecting a black hole is quite easy now.

Now, the interesting part, it is the brightest of the stars that turn in the darkest objects in the Universe(black holes)!

Some stars have close companions. They are called binary stars. Sometimes, the companion star turns into a black hole. Then the other star is torn and swirled around the hole before being sucked in. At this time, huge amounts of X-rays are sent out which studied by probes in space orbiting Earth. For example, a supergiant star in the Cygnus constellation has an invisible companion called Cygnus X-1. This star has probably turned into a black hole.

So, we find that black holes are one of the most interesting objects in space. There is always something more to find out!

By Aditya Rajesh, Class-7-B, The Millennium School, Al-Qusais, Dubai, UAE