Black Holes

What are black holes? Have you ever had to vacuum your bedroom? When you do, watch closely because you will see the dirt and crumbs start to move towards the vacuum cleaner.  A black hole is similar to a vacuum cleaner, cleaning up debris left behind in outer space. However, it is not suction power that makes things fall into a black hole.  Suction would not be strong enough.  Instead, a black hole uses the power of gravity to pull things towards it. How do black holes form?  When a large star runs out of fuel it can no longer support its heavy weight. The pressure from the star's massive layers of hydrogen press down forcing the star to get smaller and smaller and smaller.  Eventually the star will get even smaller than an atom. Imagine that for a moment, an entire star squashed up into less space than a tiny atom. How can something get smaller but retain the same amount of mass, or stuff? It is really quite simple. If you take a sponge the size of a soda can, you can easily squish it in your hands until it is completely covered. But here is the interesting part. If you make something smaller by squishing it, its gravity becomes much stronger. Imagine then, if you squish a star into the size of an atom how powerful its gravity would become. A black hole's gravity becomes so powerful that anything, including light that gets too close, gets pulled in. That's right, not even light can escape the grasp of a black hole. Anatomy of a Black HoleBlack holes are made up of 3 main parts. The very outer layer of a black hole is called the Outer Event Horizon. Within the Outer Event Horizon you would still be able to escape from a black hole's gravity because the gravity is not as strong here. The middle layer of a black hole is called the Inner Event Horizon. If you didn't escape the black hole's gravity before you entered the Inner Event Horizon, then you have missed your chance to escape. The gravity in this layer is much stronger and does not let go of objects it captures. At this point you would begin to fall towards the center of the black hole. The center of a black hole is called the Singularity. This is simply a big word that means squashed up star. The Singularity is where the black hole's gravity is the strongest. How can you fall into a black hole? Think of the Earth. When you are in outer space you can float around. If you get too close to the Earth you will be pulled in by its gravity. On the Earth, you could leave again in a rocket ship. However, if you fall into a black hole, there would be no way to get out because the gravity is so powerful.

Black Holes: The Hungriest Objects in Space! 

Have you ever heard of a black hole? You might well have done. But we are not talking about a hole in the ground, we are talking about the ones that astronomers believe exist in our gigantic Universe. Despite their name, scientists believe that there is a lot more to these objects. So what exactly is a black hole?

If you were to ask an astronomer this question, they are most likely to say that a black hole must be one of the most strangest objects ever. They are almost like an incredibly strong vacuum cleaner without the noise - not only would the crumbs from under your bed be unable to escape, but anything that happens to travel past would have a hard job trying to wriggle free from its clutches, too. Do you know what causes a black hole to gobble up everything in sight? Have a go at guessing what the answer might be before you carry on reading. Perhaps you can get into a group with your friends and think of some answers - drawing pictures of a black hole might be able to help you to figure it out! If you have not already figured it out, the answer to the question is gravity - the force that does not only keep the planets in orbit around the Sun, but keeps our feet on the ground. You might think that the earth would have to have some pretty strong gravity to allow us to walk and run on its surface, but a black hole is even stronger - even light has a pretty tough time of pulling away and that is the fastest thing that we know of, racing at a speed of 186,000 miles per second. For that reason, black holes are probably the darkest things that you will ever find!       Image: NASA   Just where this strong gravity comes from is certainly not in the name. You might be amazed to learn that these objects are not empty; they are filled with lots and lots of material that is crammed into a very small space - just imagine stuffing your house (and everything that is in it) into a thimble! Because there is so much material in one place, this is what causes the strong gravity. Now, isn’t that cool? So how are these objects made? Do they appear out of nowhere or have they always been there? Scientists have been wondering this, too, and they think that there are two types that can be formed; a stellar-mass black hole and a supermassive black hole. Can you guess which one is bigger? That’s right! The supermassive black hole. Because one type is larger than the other, astronomers think that they also must be made in different ways. A stellar-mass black hole is pretty easy to remember; just imagine a black round object that is around 3 to 15 times bigger than our Sun. You might be surprised to know that this type of black hole is made when a gigantic star reaches a grand old age, causing it to explode in a very bright burst of light - so luminous that it can outshine a galaxy! Astronomers call this explosion a supernova and they happen when an old star has finished burning all of its fuel. There is often material left over from a supernova and scientists call this a stellar remnant which they think then collapses in on itself transforming into a very compact object. And there we have it - a stellar-mass black hole is made!             The second type of black hole, the supermassive black hole, is the same as 100 million Suns all squashed into one place. However, unlike its smaller cousin, astronomers are not entirely sure of how they are made - one thing they are positive of though is that there is one right in the middle of our galaxy, the Milky Way, and there could be more in the centre of other galaxies, too - our Universe really is quite an interesting place! It’s pretty fair to say black holes are hungry all of the time and they are always wondering where their next galactic meal is coming from. Quite recently in December 2011, astronomers have noticed that our Galaxy’s black hole has set its sights on a nearby cloud of dust and gas. The scientists who have been watching this cloud for the past seven years with huge telescopes in Chile, South America, have noticed that not only is this cloud moving in the direction of the black hole, but it has also doubled in speed reaching more than 8 million kilometres per hour - now that is pretty fast! Astronomers think that this supermassive black hole will get its meal in a couple of years' time. But what happens when it does? Well, seeing as our strange friend has no manners, it is very likely to belch out very powerful beams of high energy X-ray radiation when it has finished eating - just like the X-rays you might have had at the dentist, but much more powerful!