write the article about black hole
Answers
How does a black hole form?
We think that a black hole can form when a very massive star collapses at the end of its lifetime. Stars become like our sun because of energy from nuclear reactions going on deep inside the star. They convert hydrogen to helium, and that gives off energy, which becomes light. Once that hydrogen is used up, they can start using helium in their nuclear "furnaces." But eventually any star will run out of "fuel." Stars like our sun will collapse and become a "white dwarf." But very massive stars — ten times heavier than our sun — have such strong gravity that when they collapse they can't stop. Everything in the star collapses to a tiny point that still has the mass and gravity of the star but no longer shines. In fact the gravity is so strong that even light can't escape. That is why we call it a black hole. If you could visit a black hole (don't get too close!), you would probably see a black "ball" a few miles across.
Does a black hole "suck" down everything in its vicinity?
The gravity of a black hole is the same as the gravity of a star with the same mass. For instance, if the sun suddenly became a black hole (couldn't happen, but just for instance), Earth would continue to orbit the black sun as usual. The danger is that if you get too close to the black hole, like only a few miles away, the gravity would be extremely strong and it would be hard to escape.
Have astronomers found any black holes?
Yes, we think so. Of course a black hole itself would be hard to see! But we can see when hot gases are "sucked" into the black hole. The collisions and explosions that occur when that happens generate huge bursts of light, including X-rays. We know of several stars that appear to have invisible but very massive companion stars. They look as if the invisible companion is pulling gas from the regular star. The only thing we know of that could do that is a black hole. We also see incredible explosions in the centers of some galaxies. The only thing we know of that can make such spectacular explosions is a very big black hole — a black hole with the mass of millions of stars! Such a huge black hole can pull in whole stars!
How do black holes have energy if they form from dead or burned-out stars?
Black holes form from large stars that collapse when they run out of fuel for their nuclear reactions. There are many forms of energy — heat, light, energy of motion, and the energy of gravity. Black holes have LOTS of gravitational energy!
Are there any black holes in our galaxy, and if so, are there any plans to explore them?
Fortunately for us there are no black holes near our solar system. Unfortunately this means that we can't send a space probe to explore one. We believe that there are several black holes in our galaxy. Some are about the size of stars. We can tell that a black hole is there by how it affects a companion star. Of course we can't see the black hole — it's black! But we can see that a star is going around in orbit around something else that we can't see, and we can see gases that the black hole has "sucked off" from the other star. We also think that most if not all galaxies have a big black hole at each center. Our own Milky Way probably has a big black hole at its center, but it's hard to tell for sure because there are so many stars in the way when we look toward the center. (The center is in the constellation Sagittarius, which you can see during the summer, towards the south). I'm not sure what would happen to someone who went into a black hole, but I don't think it would be pleasant!
Could a beam of light orbit a black hole?
That's an interesting idea. I think that it could, but only if it happened to come in at just the right angle so it would be in a perfectly circular orbit. That seems unlikely, so it would be more likely that it would either pass by the black hole in a curved path or go into the black hole.
What is meant by the term associated with black holes called the "event horizon"?
What you are describing we usually call the "event horizon." Imagine a black hole, and a beam of light passing by. The gravity of the black hole is tugging on the light (and matter) nearby, but the beam of light has energy so it keeps trying to go on by. The gravity bends the light beam, but if the light isn't too close it can still pass by the black hole. If it gets too close, the gravity of the black hole bends the light into the hole and it can't escape. This would be true no matter what direction the light is coming from around the hole. So there would be a sphere around the black hole where, if light went in, it couldn't come out. That sphere is the "event horizon." I guess it's called that because it's the limit at which you could see an event occur, and a horizon is the limit of which you can see (usually we mean the sky).
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