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What Is a Black Hole? National Aeronautics and Space Administration Can black holes be used to travel through spacetime? Where are black holes located? It’s a science fiction cliché to use black holes to travel through space. Dive into one, the story goes, Black holes are everywhere! As far as astronomers can tell, there are prob- and you can pop out somewhere else in the Universe, having traveled thousands of light years in the blink of an eye. ably 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 — a But that’s fiction. In reality, this probably won’t work. Black holes twist space and time, in a sense punching a hole in the fabric of the pretty fair distance, about 16 quadrillion kilometers! That’s certainly too far Universe. There is a theory that if this happens, a black hole can form a tunnel in space called a wormhole (because it’s like a tunnel away to affect us. The giant black hole in the center of the Galaxy is even formed by a worm as it eats its way through an apple). If you enter a wormhole, you’ll pop out someplace else far away, not needing to farther away: at a distance of 26,000 light years, we’re in no danger of travel through the actual intervening distance. being sucked into the vortex. The neutron star companion While wormholes appear to be possible mathematically, they would be violently unstable, or need to be made of theoretical For a black hole to be dangerous, it would have to be very close, probably of a black hole spirals in and is destroyed as it merges with the forms of matter which may not occur in nature. The bottom line is that wormholes probably don’t exist. When we invent less than a light year away. Not only are there no black holes that close, black hole - NASA/CXC/M.Weiss interstellar travel, we’ll have to go the long way around. there aren’t any known that will ever get that close. So don’t fret too much over getting spaghettified anytime soon. What can we learn from black holes? Fermi There Black holes represent the ultimate endpoints jets flare and erupt, astronomers can learn about the are probably of matter. They twist and rip space and time, dynamic processes that can shape the growth of the The Fermi Gamma Ray Space millions of stellar-mass pushing our imagination to its limits. But they host galaxies. Telescope is a NASA observatory built to study black holes in our own Milky also teach us a lot about the way the Universe What happens at the very edge of a black hole, the most energetic and extreme environments in the Way Galaxy, but only one works. where light cannot escape, where space and time universe, such as black holes. Fermi was launched into supermassive black hole, right As matter falls into a black hole, it heats up swap places, where even Einstein’s General Relativ- Earth orbit in June, 2008 and is surveying the sky with the in the center, tipping the cosmic and emits X-rays. By studying how black holes ity is stretched to the breaking point? Black holes are most sensitive gamma ray telescope ever built. Fermi is able to scales at 4 million times the mass emit X-rays using observatories like Chandra, a natural laboratory where we can investigate such observe jets of gamma rays emitted of the Sun. But don’t worry — scientists can learn about how black holes eat questions. from supermassive black holes in the at nearly 26,000 light years matter, how cores of distant galaxies. away, it’s too far away for Einstein predicted that when a black hole forms, it us to fall into it. much they can create ripples in the fabric of space, like the can eat, and waves made when you throw a rock in a pond. No What is a black hole? how fast they one has ever detected these gravitational waves, can eat it — but scientists are building experiments right now all of which to look for them. If they are detected, these waves Most people think of a black hole For the Earth, that velocity is about 11 are critical to can teach us much about how gravity works. Some as a voracious whirlpool in space, sucking kilometers per second (7 miles/second). But understand- scientists even think gravitational SSU NASA E/PO/A. Simonnet down everything around it. But that’s not really an object’s escape velocity depends on its gravity: ing the phys- waves were made in the Big Bang. true! A black hole is a place where gravity has got- more gravity means a higher escape velocity, because ics of black If we can detect these waves, it will ten so strong that the escape velocity is faster than the gravity will “hold onto” things more strongly. The Sun holes. Some Glossary be like looking back all the way to the closer you are to it, the stronger the force light. But what does that mean, exactly? has far more gravity than the Earth, so black holes are Time Zero, the start of everything Accretion Disk: A disk of matter that forms Event Horizon: The distance from the center of a black hole where the escape velocity of its gravity will be. Gravity is what keeps us on the Earth, its escape velocity is much higher — more shooting out there is. when a large amount of material falls powerful jets of into a black hole. The disk is outside the is equal to the speed of light. Mass: The quantity of matter that makes up an but it can be overcome. If you toss a than 600 km/s (380 miles/s). That’s 3000 object. charged particles Falling into a black hole would be the event horizon of the black hole. Fric- Gamma-ray Burst: A titanic explosion of high- rock up in the air, it will only go up a times faster than a jet plane! The collapse of the core in a massive last thing you’d ever do, but for scien- tion and other forces heat the disk, which energy light, thought to be due to the Supernova: An exploded, or exploding, star. and gamma rays. then emits light. formation of a black hole. little way before the Earth’s gravity slows If you take an object and squeeze it down in star triggers a gamma ray burst - tists, black holes are just the beginning Wormhole: A theoretical shortcut through space NASA/Dana Berry. Fermi is discovering The velocity needed for an caused when a black hole punches through the it and pulls it back down. If you throw it size, or take an object and pile mass onto it, its of our exploration of space, time, and Escape Velocity: Gravity: The attractive force of an object which many of these monster object to become essentially free of the depends on its mass, and your distance fabric of spacetime. While possible mathemati- a little harder, it goes faster and higher gravity (and escape velocity) will go up. At some black holes, which reside in the cores of distant everything in between. gravitational effect of another object. from it. The more massive an object, or cally, in reality they probably do not exist. before coming back down. If you could point, if you keep doing that, you’ll have an object galaxies. By studying how the gamma rays in the throw the rock hard enough, it would with so much gravity that the escape velocity is Credits: References: have enough velocity that the Earth’s faster than light. Since that’s the ultimate speed “Black Holes: From Here to Infinity” was developed as part of the NASA Fermi Education and Public Fermi Main Page: http://www.nasa.gov/fermi gravity could not slow it down enough Outreach (E/PO) Program at Sonoma State University, CA under the direction of Professor Lynn SSU E/PO: http://epo.sonoma.edu limit of the Universe, anything too close would Cominsky. to stop it. The rock would have enough get trapped forever. No light can escape, and Artist’s concept of “spaghettification” near a Written by Dr. Philip Plait. Layout and design by Aurore Simonnet. Additional help by Dr. Kevin McLin, www.nasa.gov velocity to escape the Earth. The strong magnetic field generated by the it’s like a bottomless pit: a black hole. and Fermi Scientists Dr. Steve Ritz and Dr. David Thompson. black hole SSU NASA E/PO/A. Simonnet material in an accretion disk channels material onto the poles of the black hole - NASA/Dana Berry. at at least th one k bl in ac h k t h o s l r e A e is s t m r b o o n o rn e ve How do black holes form? ry How do black holes affect things near them? d a y! The most common way for a black hole to form is probably in a supernova, an exploding star. When a star with about 25 times the mass If black holes are black, Are we in danger of being gobbled up by a black hole? Actually, no. of the Sun ends its life, it explodes. The outer part of the star screams outward at high speed, but the inner part of the star, its core, collapses down.
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