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Black Holes

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Mary Pham

on 6 June 2016

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Transcript of Black Holes

Are we in danger of being gobbled up by a black hole? Actually, no. We’re pretty safe. The gravity from a black hole is only dangerous when you’re very close to it. Surprisingly, from a large distance, a black hole's gravity is no different than the gravity from a star with the same mass. So stellar-mass black holes don’t go around tearing up stars and eating everything in sight. Stars, gas, planets, and anything else would have to get up close and personal to a black hole to get trapped. The odds of that happening are pretty small.
Black Holes
By: Mary and Michael

Light has no mass, but why can it be trapped?
Newton thought that only objects with mass could produce a gravitational force on each other. Applying Newton's theory of gravity, one would conclude that since light has no mass, so the force of gravity couldn't affect it. Einstein discovered that the situation is a bit more complicated than that. First he discovered that gravity is produced by a curved space-time. Then Einstein theorized that the mass and radius of an object actually curves space-time. In other words, straight lines are no longer straight if exposed to a strong gravitational field; instead, they are curved. This is what it meant by "curved space," and this is why light becomes trapped in a black hole.
What are black holes?
A black hole is a region of space time exhibiting such strong gravitational effects that nothing—including particles and electromagnetic radiation such as light—can escape from inside it. The gravity is so strong because matter has been squeezed into a tiny space. Since no light can get out, people can't see black holes. They are invisible. Scientists use space telescopes with special tools that can help find black holes.
How big are black holes?
The smallest black holes are as small as just one atom. A large black hole is called "stellar." Its mass can be up to 20 times more than the mass of the sun. The largest black holes are called "super massive." These black holes have masses that are more than 1 million suns together. Scientists have found proof that every large galaxy contains a super massive black hole at its center. The super massive black hole at the center of the Milky Way galaxy is called Sagittarius A. It has a mass equal to about 4 million suns and would fit inside a very large ball that could hold a few million Earths.
How are black holes formed?
Black holes are made when very large stars die. When the star runs out of fuel from the nuclear burning in the core, it is no longer able to support itself from collapsing under its own weight. The star first collapses and then the outer layers rebound to form a supernova explosion (which is an exploding star that blasts part of the star into space). What's left at the core is a Neutron Star or a Black Hole depending on the initial mass of the star. To form a black hole, the mass left at the core after the explosion must be more than about 3 times the mass of the Sun.
Structure of black holes
Black 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 there, but the probability is small unless you had something the speed of light. 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 do they affect things near them?
What evidence proves black holes are there?
Astronomers have found convincing evidence from a super massive black hole in the center of our own Milky Way galaxy, the galaxy NGC 4258, the giant elliptical galaxy M87, and several others. Scientists verified the existence of the black holes by studying the speed of the clouds of gas orbiting those regions. Based on the motion of the material whirling about the center, the object is estimated to be about 3 billion times the mass of our Sun and appears to be concentrated into a space smaller than our solar system.
What's inside a black hole?
No one really knows what's at the center of a black hole because if you go in one, you will not survive. The theory is that when you enter a black hole, it rips and pulls you apart making you almost like spaghetti. Therefore we cannot send cameras into a black hole, which means we cannot learn about what happens to things when they go inside a black hole. Black holes are not empty and have a lot of mass material that has been sucked and stuffed into a small space.
Where are black holes located?
Black holes are everywhere! As far as astronomers can tell, there are probably millions of black holes in our Milky Way Galaxy alone. That may sound like a lot, but the nearest one discovered is still 1600 light years away— which is a pretty fair distance, about 16 quadrillion kilometers! That’s certainly too far away to affect us. The giant black hole in the center of the Galaxy is even farther away- at a distance of 30,000 light years, we’re in no danger of being sucked in to the vortex. For a black hole to be dangerous, it would have to be very close, probably less than a light year away. Not only are there no black holes that close, there are not any known that will ever get that close. So don’t worry too much over getting spaghettified.
Stephen Hawking
Stephen Hawking made headlines with this bold statement: “there are no black holes.” He did not actually mean there are no black holes, he meant black holes seem to break two fundamental laws of physics — Einstein’s laws of relativity and quantum mechanics. First a quick physics reminder. Einstein’s theory of general relativity first conceived a black hole as an object with a gravitational pull so powerful that anything— gas, dust, stars, planets, whole galaxies, even light— that crossed the event horizon would fall in and be forever trapped and ultimately crushed, never to escape. But with the quantum mechanics emerging in the mid-20th century, many people believed that this information (the particles and matter sucked into the black hole) had to be kept, somewhere. According to quantum mechanics, a black hole could shred a book into its subatomic particles, but as long as all the pieces still existed, it was possible to reconstruct that book. Hawking’s proposal, “apparent horizon”, which only holds matter for a limited amount of time and holds matter and energy prisoner before eventually releasing them, in a more garbled form.
Who discovered black holes
Albert Einstein first predicted black holes in 1916 with his general theory of relativity. Using Newton’s Laws in the late 1790s, John Michell of England and Pierre-Simon Laplace of France independently suggested the existence of an "invisible star." Michell and Laplace calculated the mass and size– which is now called the "event horizon"– that an object needs in order to have an escape velocity greater than the speed of light. In 1967 John Wheeler, an American theoretical physicist, applied the term "black hole" to these collapsed objects.
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