Black Hole Research Paper
Could a Black Hole Destroy Earth?
Black holes do not wander around the universe, randomly swallowing worlds. They follow the laws of gravity just like other objects in space. The orbit of a black hole would have to be very close to the solar system to affect Earth, which is not likely.
If a black hole with the same mass as the sun were to replace the sun, Earth would not fall in. The black hole with the same mass as the sun would keep the same gravity as the sun. The planets would still orbit the black hole as they orbit the sun now.
Will the Sun Ever Turn Into a Black Hole?
The sun does not have enough mass to collapse into a black hole. In billions of years, when the sun is at the end of its life, it will become a red giant star. …show more content…
Then, when it has used the last of its fuel, it will throw off its outer layers and turn into a glowing ring of gas called a planetary nebula. Finally, all that will be left of the sun is a cooling white dwarf star.
Could Earth ever get sucked into a black hole?
No, because the Sun is much too small to ever become a black hole. Even if it did, we are too far from the Sun for the gravitational pull to drag us in.
Kerr black holes rotate, unlike static Schwarzschild black holes. Roy Kerr, a mathematician from New Zealand who studied rotating stars in the 1960s, hypothesized that since stars rotate, black holes probably rotate also. Kerr black holes can have ring-shaped singularities. Spinning black holes also have what's called a static limit. The static limit has a radius larger than the event horizon, and is sometimes called the edge, or outer boundary, of the black hole.
Once you cross the static limit of a rotating black hole, you are subject to its effects, which in this case means that it is impossible to stay still—everything inevitably gets dragged along in the direction of rotation of the black hole. Since the static limit is outside the event horizon, however, crossing this boundary is not final. It is possible to enter and leave the zone between the static limit and the event horizon at will, and an object or light ray only gets trapped forever once it crosses the event horizon.
Reissner-Nordstrøm nonrotating black holes are similar to static ones, but they are charged and have two event horizons. This type of black hole is thought to have an electric charge (called Q in physics equations), but it would likely attract the opposite charge as well, balancing it out. The outer event horizon is called the static limit, similar to the outer edge of a rotating black hole.
Extra Features
Two other features can characterize a black hole - the accretion disk and jets.
An accretion disk is matter that is drawn to the black hole. In rotating black holes and/or ones with a magnetic field, the matter forms a disk due to the mechanical forces present. In a Schwarzschild black hole, the matter would be drawn in equally from all directions, and thus would form an omni-directional accretion cloud rather than disk.
The matter in accretion disks is gradually pulled into the black hole. As it gets closer, its speed increases, and it also gains energy. Accretion disks can be heated due to internal friction to temperatures as high as 3 billion K, and emit energetic radiation such as gamma rays. This radiation can be used to "weigh" the black hole. By using the doppler effect, astronomers can determine how fast the material is revolving around the black hole, and thus can infer its mass.
Jets form in Kerr black holes that have an accretion disk. The matter is funneled into a disk-shaped torus by the hole's spin and magnetic fields, but in the very narrow regions over the black hole's poles, matter can be energized to extremely high temperatures and speeds, escaping the black hole in the form of high-speed …show more content…
jets.
They were actually the brainchild of John Mitchell.
AP
I always attributed the discovery of black holes to Einstein.
While Einstein did revive the theory in 1916, John Mitchell actually thought of it first, back in 1783. The idea didn't go anywhere, though, because he didn't know what to do with it.
Mitchell started to develop the theory of black holes when he accepted Newton’s theory that light consists of small material particles, called photons. He wondered how the movement of these light particles is impacted by the gravitational pull of the star they are escaping, and what would happen to these particles if the gravitational pull was so strong that light could not escape.
Mitchell is also the founder of modern seismology, when he suggested earthquakes spread out as waves through the earth.
They are incredibly dense.
Donkey Hotey / Flickr
Black holes have to hold a massive amount of mass in an incredibly small space to have the required gravity to pull light in. For example, to make a black hole with the mass of Earth, the entire planet would need to be squeezed down to a space 9 millimeters across.
A black hole with 4 million times the mass of our sun can fit into the space between Mercury and the Sun. Black holes in the center of galaxies could have a mass of 10 to 30 billion times the mass of our sun.
Having such a large mass in a tiny area means the black hole is incredibly dense, and the forces inside the black hole are incredibly strong.
They are noisy.
Flickr/royalrivers
As everything around the black hole is pulled into its gaping maw, all of this stuff speeds up. The event horizon supercharges the speed of particles close to the speed of light.
Scharf said that when stuff falls through the center of the event horizon there is a gurgling sound. This sound is the energy of motion being converted into sound waves. He described the noise as the sound you hear when water is released from a bath.
In 2003 astronomers using NASA's Chandra X-ray observatory, detected sound waves coming from a supermassive black hole 250 million light years away.
Nothing escapes their pull.
Flickr/tobiasmunich
When anything (be it planets, suns, galaxies or particles of light) passes close to a black hole, they will be pulled in by its gravity. If something else acting on the object, like say a rocket, is stronger than the black hole's gravity, it can escape the pull.
Until, of course, it reaches the event horizon: The point where escape from a black hole is impossible. In order to escape the event horizon, objects must move faster than the speed of light, which is impossible.
This is the "black" part of the black hole, because if light can't escape, then we can't see inside and the area looks empty.
Researchers think that even small black holes would tear you apart before you fall through the event horizon. Gravity is stronger the closer you get to a planet, star, or black hole. If you were falling feet first, gravity at your feet would be so much stronger than at your head. This force would pull you apart.
They slow down time.
Composite Image of Galaxy Cluster MS 0735
NASA, ESA, CXC, STScI, and B. McNamara (University of Waterloo)
Light bends around the event horizon and eventually gets pulled into nothingness as it falls through.
Scharf describes what we would see if a clock were to be sucked into a black in an interview with The Economist. He says the ticking of the clock (if it were to survive the forces of the black hole) would appear to slow down as it approached the event horizon and eventually would seem to freeze altogether.
This freeze in time is due to gravitational time dilation, explained by Einstein's theory of relativity. The gravity of a black hole is so strong, it can slow down time. From the clock's perspective it is still functioning normally. The clock would fade from view as the light from it is stretched further apart. The light would become increasingly red as the wavelength becomes longer and falls out of the visible light spectrum, vanishing from sight.
They are the ultimate energy factories.
Spit, not swallow. en.wikipedia.org Black holes vacuum up the mass surrounding them, and in the black hole this mass gets squished together so hard that space between the individual components of the atoms is compressed, and it is broken down into subatomic particles that can stream away.
These particles are released in jets, as seen in this picture taken with NASA's Chandra X-ray Observatory. These particles propel out of the black hole due to intense magnetic field lines that can cross the event horizon.
Breaking up the particles creates energy, in an efficient manner. Converting mass into energy in this way is 50 times more efficient than nuclear fusion.
Black Hole Facts by Jerry Coffey on December 3, 2009
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Artist's concept of a black hole from top down. Image credit: NASA
One of the most awe inspiring phenomenon in space is the black hole. Black hole facts are searched for every day. Amateur astronomers as well as the professionals often ponder questions related to black holes. So, for the fun of it and because we want to help educate you, we here on Universe Today decided to put together a few black holes facts to intrigue your mind and satisfy a little of your curiosity. | | | | |
Fact 1
As black hole facts go, this is basic one. A black hole is a place where the gravity well is so great that a gravitational time dilation has occurred. This causes time to stop. This causes an event horizon into which objects can fall or be pulled, but those objects will never reappear. That is the basic definition according to Einstein’s theory of general relativity.
Fact 2
There is no limit to how small or how large a black hole can be. The size and mass of a black hole are directly related. The more massive a black hole is, the more space it takes up. In fact, the Schwarzschild radius ( the radius of the event horizon of a black hole) and the mass are directly proportional to one another. Therefore, if one black hole weighs ten times as much as another, its radius is ten times as large. For example, a black hole with a mass equal to that of our Sun would have a radius of 3 kilometers, a typical 10-solar-mass black hole would have a radius of 30 kilometers, and so on.
Fact 3
The nearest black hole is 1,600 light years away. That is about 16 quadrillion kilometers for Earth.
Fact 4
One the interesting black hole facts is that they can not suck up all of the matter in the Universe. Each black hole has its own event horizon, much like the gravitational field of a planet. If matter is not in that horizon it will never get sucked into the black hole.
Fact 5
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This one tips the scales on the heavy end as black hole facts go: there is a super massive black hole at the center of the Milky Way galaxy. It weighs in at about 4 million solar masses. Luckily, there is no reason to worry. This giant sucker is over 30,000 light years away.
Fact 6
The last of the black hole facts I have to offer today is that many theorists believe that a black hole can eventually evaporate. How is that? Steven Hawking proposed that black holes were not entirely black. They emit radiation. The energy that produces the radiation comes from the mass of the black hole. As the radiation is emitted, the black hole loses mass. The black hole emits more radiation the smaller it gets. In effect, a black hole evaporates more quickly as it shrinks.
These black hole facts are just a few of the little tidbits and teasers that you can find by doing some research. Here is a list of a few more. Here on Universe Today we have a great article about a practical use for black holes: as spacecraft engines. No one can get to a black hole without space travel. Astronomy Cast offers a good episode about interstellar travel
Read more: http://www.universetoday.com/46687/black-hole-facts/#ixzz2O7sIWUbY
Ten things you don't know about black holes
By Phil Plait | October 30, 2008 8:48 pm
Well, they’re black, and they’re like bottomless holes. What would you call them?
-Me, when a friend asked me why they’re named what they are
Ah, black holes. The ultimate shiver-inducer of the cosmos, out-jawing sharks, out-ooking spiders, out-scaring… um, something scary. But we’re fascinated by ‘em, have no doubt — even if we don’t understand a whole lot about them. |
But then, that’s why I’m here. Allow me to be your tour guide to infinity. Or the inverse of it, I suppose. Since it’s Halloween this seems appropriate… and my book Death from the Skies! just came out, and there’s lots of ways a black hole can destroy the Earth. Mwuhahahaha.
So below I present ten facts about black holes — the third in my series of Ten Things You Don’t Know (the first was on the Milky Way; the second about the Earth). Regular readers will know a few of these since I’ve talked about them before, but I’m hoping you don’t know all of these. And if you do, then feel free to leave a comment preening about your superior intellect. Mind you, this list is nowhere near complete: I could have picked probably 50 things that are weird about black holes. But I like these.
1) It’s not their mass, it’s their size that makes them so strong.
OK, first, a really quick primer on black holes. Bear with me!
The most common way for a black hole to form is in the core of a massive star. The core runs out of fuel, and collapses. This sets off a shockwave, blowing up outer layers of the star, causing a supernova. So the star’s heart collapses while the rest of it explodes outwards (this is the Cliff’s notes version; for more details on the process — which is way cool, so you should read it — check out my description of it).
As the core collapses, its gravity increases. At some point, if the core is massive enough (about 3 times the mass of the Sun), the gravity gets so strong that right at the surface of the collapsing core the escape velocity increases to the speed of light. That means that nothing can escape the gravity of this object, not even light. So it’s black. And since nothing can escape, well, read the quotation at the top of the page.
The region around the black hole itself where the escape velocity equals the speed of light is called the event horizon. Any event that happens inside it is forever invisible.
OK, so now you know what one is, and how they form. Now, I could explain why they have such strong gravity, but you know what? I’d rather let this guy do it. I hear he’s good.
So there you go. Sure, the mass is important, but sometimes it’s the little things that count.
2) They’re not infinitely small.
So OK, they’re small, but how small are they?
I was writing about black holes in my previous job, and we got in a fun discussion over just what we meant by black hole: did we mean the object itself that collapses down to a mathematical point, or the event horizon surrounding it? I said the event horizon, but my boss said it was the object. I decided she had a point (HAHAHAHAHA! A "point"! Man, I kill me), and made sure that when I wrote about the event horizon versus the black hole itself I was making myself clear.
Like I said above, to the collapsing core, its clock keeps ticking, so it sees itself collapsing all the way down to a point, even if the event horizon has some finite size.
What happens to the core? The actual mass that collapsed?
Out here, we’ll never know for sure. We can’t see in, and it sure enough isn’t gonna send any info out. But our math in these situations is pretty good, and we can at least apply them to the collapsing core, even when it’s smaller than the event horizon.
It will continue to collapse, and the gravity increases. Smaller, smaller… and when I was a kid I always read that it collapses all the way down to a geometric dot, an object with no dimensions at all. That really bugged me, as you can imagine… as well it should. Because it’s wrong.
At some point, the collapsing core will be smaller than an atom, smaller than a nucleus, smaller than an electron. It’ll eventually reach a size called the Planck Length, a unit so small that quantum mechanics rules it with an iron fist. A Planck Length is a kind of quantum size limit: if an object gets smaller than this, we literally cannot know much about it with any certainty. The actual physics is complicated, but pretty much when the collapsing core hits this size, even if we could somehow pierce the event horizon, we couldn’t measure its real size. In fact, the term "real size" doesn’t really mean anything at this kind of scale. If the Universe itself prevents you from measuring it, you might as well say the term has no meaning.
And how small is a Planck Length? Teeny tiny: about 10-35 meters. That’s one one-hundred quintillionth the size of a proton.
So if someone says a black hole has zero size, you can be all geeky and technical and say, not really, but meh. Close enough.
3) They’re spheres. And they’re definitely not funnel shaped.
The gravity you feel from an object depends on two things: the object’s mass, and your distance from that object. This means that anyone at a given distance from a massive object — say, a million kilometers — would feel the same force of gravity from it. That distance defines a sphere around an object: anyone on that sphere’s surface would feel the same gravity from the object at the center.
The size of an event horizon of a black hole depends on the gravity, so really the event horizon is a sphere surrounding the black hole. From the outside, if you could figure out how to see the event horizon in the first place, it would look like a pitch black sphere.
Some people think of black holes as being circles, or worse, funnel-shaped. The funnel thing is a misconception from people trying to explain gravity as a bending in space, and they simplify things by collapsing 3D space into 2D; they say the space is like a bed sheet, and objects with mass bend space the same way that a massive object (a bowling ball, say) will warp a bed sheet. But space is not 2D, it’s 3D (even 4D if you include time) and so this explanation can confuse people about the actual shape of a black hole event horizon.
I’ve had kids ask me what happens if you approach a black hole from underneath! They sometimes don’t get that black holes are spheres, and there is no underneath. I blame the funnel story. Sadly, it’s the best analogy I’ve seen, so we’re stuck with it. Use it with care.
4) Black holes spin!
It’s kind of an odd thought, but black holes can spin. Stars rotate, and when the core collapses the rotation speeds way, way up (the usual analogy is that of an ice skater who brings in his arms, increasing his rotation rate). As the core of the star gets smaller it rotates more rapidly. If it doesn’t quite have enough mass to become a black hole, the matter gets squeezed together to form a neutron star, a ball of neutrons a few kilometers across. We have detected hundreds of these objects, and they tend to spin very rapidly, sometimes hundreds of times a second!
The same is true for a black hole. Even as the matter shrinks down smaller than the event horizon and is lost to the outside Universe forever, the matter is still spinning. It’s not entirely clear what this means if you’re trying to calculate what happens to the matter once it’s inside the event horizon. Does centrifugal force keep it from collapsing all the way down to the Planck length? The math is fiendish, but do-able, and implies that matter falling in will hit matter inside the event horizon trying to fall further but unable to due to rotation, This causes a massive pile up and some pretty spectacular fireworks… that we’ll never see, because its on the other side of infinity. Bummer.
5) Near a black hole, things get weird
The spin of the black hole throws a monkey in the wrench of the event horizon. Black holes distort the fabric of space itself, and if they spin that distortion itself gets distorted. Space can get wrapped around a black hole — kind of like the fabric of a sheet getting caught up in a rotating drill bit.
This creates a region of space outside the event horizon called the ergosphere. It’s an oblate spheroid, a flattened ball shape, and if you’re outside the event horizon but inside the ergosphere, you’ll find you can’t sit still. Literally. Space is being dragged past you, and carries you along with it. You can easily move in the direction of the rotation of the black hole, but if you try to hover, you can’t. In fact, inside the ergosphere space is moving faster than light! Matter cannot move that fast, but it turns out, according to Einstein, space itself can. So if you want to hover over a black hole, you’d have to move faster than light in the direction opposite the spin. You can’t do that, so you have to move with the spin, fly away, or fall in. Those are your choices.
I suggest flying away. Fast. Because…
6) Approaching a black hole can kill you in fun ways. And by fun, I mean gruesome, horrifying, and really really ookie.
Sure, if you get too close, plop! You fall in. But even if you keep your distance you’re still in trouble… |
Gravity depends on distance. The farther you are from an object, the weaker its gravity. So if you have a long object near a massive one, the long object will feel a stronger gravitational force on the near end versus a weaker force on the far end! This change in gravity over distance is called the tidal force (which is a bit of a misnomer, it’s not really a force, it’s a differential force, and yes, it’s related to why we have ocean tides on Earth from the Moon).
The thing is, black holes can be small — a BH with a mass of about three times the Sun has an event horizon just a few kilometers across — and that means you can get close to them. And that in turn means that the tidal force you feel from one can get distressingly big. | Praying to this guy won’t help. |
Let’s say you fall feet first into a stellar-mass BH. It turns out that as you approach, the difference in gravity between your head and your feet can get huge. HUGE. The force can be so strong that your feet get yanked away from your head with hundreds of millions of times the force of Earth’s gravity. You’d be stretched into a long, thin strand and then shredded.
Astronomers call this spaghettification. Ewwww.
So getting near a black hole is dangerous even if you don’t fall in. Evidently, there really is a tide in the affairs of men.
7) Black holes aren’t always dark
The thing is, black holes can kill from a long way off. | Disk of DOOOOOM!
Image credit: NASA/CXC |
Matter falling into a black hole would rarely if ever just fall straight in and disappear. If it has a little bit of sideways motion it’ll go around the black hole. As more matter falls in, all this junk can pile up around the hole. Because of the way rotating objects behave, this matter will create a disk of material whirling madly around the hole, and because the gravity of the hole changes so rapidly with distance, matter close in will be orbiting much faster than stuff farther out. This matter literally rubs together, generating heat through friction. This stuff can get really hot, like millions of degrees hot. Matter that hot glows with intense brightness… which means that near the black hole, this matter can be seriously luminous.
Worse, magnetic and other forces can focus two beams of energy that go plowing out of the poles of the disk. The beams start just outside the black hole, but can be seen for millions or even billions of light years distant.
They’re bright.
In fact, black holes that are eating matter in this way can glow so brightly that they become the brightest continuously-emitting objects in the Universe! We call these active black holes.
And as if black holes aren’t dangerous enough, the matter gets so hot right before it makes the final plunge that it can furiously emit X-rays, high-energy forms of light (and the beams can emit even higher energy light than that). So even if you park your spaceship well outside the event horizon of a black hole, if something else falls in and gets shredded, you get rewarded by being fried by the equivalent of a gazillion dental exams.
I may have mentioned this: black holes are dangerous. Best to stay away from them.
8) Black holes aren’t always dangerous. | I’m right there with you, dude. |
Having said that, let me ask you a question: if I were to take the Sun and replace it with a black hole of the exact same mass, what would happen? Would the Earth fall in, be flung away, or just orbit like it always does?
Most people think the Earth would fall in, sucked inexorably down by the black hole’s powerful gravity. But remember, the gravity you feel from an object depends on the mass of the object and your distance from it. I said the black hole has the same mass as the Sun, remember? And the Earth’s distance hasn’t changed. So the gravity we’d feel from here, 150 million kilometers away, would be exactly the same! So the Earth would orbit the solar black hole just as nicely as it orbits the Sun now.
Of course, we’d freeze to death. You can’t have everything.
9) Black holes can get big.
Q: What happens if two stellar-mass black holes collide?
A: You get one bigger black hole.
You can extrapolate from there. Black holes can eat other objects, including other black holes, so they can grow. We think that early on in the Universe, when galaxies were just forming, matter collecting in the center of the nascent galaxy can collapse to form a very massive black hole. As more matter falls in, the hole greedily consumes it, and grows. Eventually you get a supermassive black hole, one with millions or even billions of times the mass of the Sun.
However, remember that as matter falls in it can get hot. It can be so hot that the pressure from light itself can blow off material that’s farther out, a bit like the solar wind but on a much grander scale. The strength of the wind depends on many things, including the mass of the black hole; the heftier the hole, the windier the, uh, wind. This wind prevents more matter from falling in, so it acts like a cutoff valve for the ever-increasingly girthy
hole.
Not only that, but over time the gas and dust around the black hole (well, pretty far out, but still near the center of the galaxy) gets turned into stars. Gas can fall into a black hole more easily than stars (if gas clouds collide head-on their motion relative to the black hole can stop, allowing them to fall in; stars are too small and too far apart for this to happen). So eventually the black hole stops consuming matter because nothing more is falling into it. It stops growing, the galaxy becomes stable, and everyone is happy. | Don’t panic!
OK, maybe a little. |
In fact, when we look into the Universe today, we see that pretty much every large galaxy has a supermassive black hole in its heart. Even the Milky Way has a black hole at its core with a mass of four millions times that of the Sun. Before you start running around in circles and screaming, remember this: 1) it’s a long way off, 26,000 light years (260 quadrillion kilometers), 2) its mass is still very small compared to the 200 billion solar masses of our galaxy, and therefore 3) it can’t really harm us. Unless it starts actively feeding. Which it isn’t. But it might start sometime, if something falls into it. Though we don’t know of anything that can fall into it soon. But we might miss cold gas.
Hmmm.
Anyway, remember this as well: even though black holes can cause death and destruction on a major scale, they also help galaxies themselves form! So we owe our existence to them.
10) Black holes can be low density.
Of all the weirdnesses about black holes, this one is the weirdest to me.
As you might expect, the event horizon of a black hole gets bigger as the mass gets bigger. That’s because if you add mass, the gravity gets stronger, which means the event horizon will grow.
If you do the math carefully, you find that the event horizon grows linearly with the mass. In other words, if you double the black hole’s mass, the event horizon radius doubles as well.
That’s weird! Why?
The volume of a sphere depends on the cube of the radius (think way back to high school: volume = 4/3 x π x radius3). Double the radius, and the volume goes up by 2 x 2 x 2 = 8 times. Make the radius of a sphere 10 times bigger and the volume goes up by a factor of 10 x 10 x 10 = 1000.
So volume goes up really quickly as you increase the size of a sphere.
Now imagine you have two spheres of clay that are the same size. Lump them together. Is the resulting sphere twice as big?
No! You’ve doubled the mass, but the radius only increases a little bit. Because volume goes as radius cubed, to double the radius of your final clay ball, you’d need to lump together eight of them.
But that’s different than a black hole. Double the mass, double the size of the event horizon. That has an odd implication…
Density is how much mass is packed into a given volume. Keep the size the same and add mass, and the density goes up. Increase the volume, but keep the mass the same, and the density goes down. Got it?
So now let’s look at the average density of matter inside the event horizon of the black hole. If I take two identical black holes and collide them, the event horizon size doubles, and the mass doubles too. But volume has gone up by eight times! So the density actually decreases, and is 1/4 what I started with (twice the mass and eight times the volume gives you 1/4 the density). Keep doing that, and the density decreases.
A regular black hole — that is, one with three times the Sun’s mass — with have an event horizon radius of about 9 km. That means it has a huge density, about two quadrillion grams per cubic cm (2 x 1015). But double the mass, and the density drops by a factor of four. Put in 10 times the mass and the density drops by a factor of 100. A billion solar mass black hole (big, but we see them this big in galaxy centers) would drop that density by a factor of 1 x 1018. That would give it a density of roughly 1/1000 of a gram per cc… and that’s the density of air!
A billion solar mass black hole would have an event horizon 3 billion km in radius — roughly the distance of Neptune to the Sun.
See where I’m going here? If you were to rope off the solar system out past Neptune, enclose it in a giant sphere, and fill it with air, it would be a black hole!
That, to me, is by far the oddest thing about black holes. Sure, they warp space, distort time, play with our sense of what’s real and isn’t… but when they touch on the everyday and screw with that, well, that’s what gets me.
I first thought of this at a black hole conference at Stanford a few years back. I was walking with noted black hole expert Roger Blandford when it hit me. I did a quick mental calculation to make sure I had the numbers right, and related to Roger that a solar system full of air would be a black hole. He thought about it for a moment and said, "Yes, that sounds about right."
And that, me droogs, was one of the coolest moments of my hole life. But thinking about it still makes my brain hurt.
Conclusion:
Well, what can I say? Black holes are weird.
As it so happens, there was a lot more that could be said about them, of course. What about wormholes? What about how they form? what about Hawking radiation? Can black holes totally evaporate?
You can find answers to these and other questions elsewhere on the web (and even on this very blog); I couldn’t cover everything in just ten sections! But I’ll note (shocker) that chapter 5 of my book Death from the Skies! talks in detail about how they form, and what they can do if you get too close to them. Later chapters also talk about the black hole in the core of the Milky Way, and what will happen to black holes a long time from now… literally, 1060, 1070, even a googol years from now.
But even then, that’s not the scariest thing about black holes. I almost didn’t put this in the post, it’s so over the top mind-numbingly horrifying. But I’m a scientist, and we’re skeptics here, so we can take it. So I present to you, the worst thing about black holes of all: |
Interesting facts about black holes * If you fell into a black hole, gravity would stretch you out like spaghetti. Don't worry; your death would come before you reached singularity. * Black holes do not "suck." Suction is caused by pulling something into a vacuum, which the massive black hole definitely is not. Instead, objects fall into them. * Albert Einstein first predicted black holes in 1916 with his general theory of relativity. * The term "black hole" was coined in 1967 by American astronomer John Wheeler. * The first object considered to be a black hole is Cygnus X-1. Rockets carrying Geiger counters discovered eight new x-ray sources. In 1971, scientists detected radio emission coming from Cygnus X-1, and a massive hidden companion was found and identified as a black hole. * Cygnus X-1 was the subject of a 1974 friendly wager between Stephen Hawking and a fellow physicist Kip Thorne, with Hawking betting that the source was not a black hole. In 1990, he conceded defeat. * Miniature black holes may have formed immediately after the Big Bang. Rapidly expanding space may have squeezed some regions into tiny, dense black holes less massive than the sun. * If a star passes too close to a black hole, it can be torn apart. * Astronomers estimate there are anywhere from ten million to a billion stellar black holes, with masses roughly thrice that of the sun, in the Milky Way. * The interesting relationship between string theory and black holes give rise to more types of massive giants than found under conventional classical mechanics.
How big can a black hole get?
There is no limit to how large a black hole can be. However, the largest blackholes we think are in existence are at the centers of many galaxies, and have masses equivalent to about a billion suns (i.e., a billion solar masses). Their radii would be a considerable fraction of the radius of our solar system
How is time changed in a black hole?
Well, in a certain sense it is not changed at all. If you were to enter a black hole, you would find you watch ticking along at the same rate as it always had (assuming both you and the watch survived the passage into the black hole). However, you would quickly fall toward the center where you would be killed by enormous tidal forces (e.g., the force of gravity at you feet, if you fell feet first, would be much larger than at you head, and you would be stretched apart).
Although your watch as seen by you would not change its ticking rate, just as in special relativity (if you know anything about that), someone else would see a different ticking rate on your watch than the usual, and you would see their watch to be ticking at a different than normal rate. For example, if you were to station yourself just outside a black hole, while you would find your own watch ticking at the normal rate, you would see the watch of a friend at great distance from the hole to be ticking at a much faster rate than yours. That friend would see his own watch ticking at a normal rate, but see your watch to be ticking at a much slower rate. Thus if you stayed just outside the black hole for a while, then went back to join your friend, you would find that the friend had aged more than you had during your separation.
Black holes do not wander around the universe, randomly swallowing worlds. They follow the laws of gravity just like other objects in space. The orbit of a black hole would have to be very close to the solar system to affect Earth, which is not likely.
If a black hole with the same mass as the sun were to replace the sun, Earth would not fall in. The black hole with the same mass as the sun would keep the same gravity as the sun. The planets would still orbit the black hole as they orbit the sun now.
Will the Sun Ever Turn Into a Black Hole?
The sun does not have enough mass to collapse into a black hole. In billions of years, when the sun is at the end of its life, it will become a red giant star. …show more content…
Then, when it has used the last of its fuel, it will throw off its outer layers and turn into a glowing ring of gas called a planetary nebula. Finally, all that will be left of the sun is a cooling white dwarf star.
Could Earth ever get sucked into a black hole?
No, because the Sun is much too small to ever become a black hole. Even if it did, we are too far from the Sun for the gravitational pull to drag us in.
Kerr black holes rotate, unlike static Schwarzschild black holes. Roy Kerr, a mathematician from New Zealand who studied rotating stars in the 1960s, hypothesized that since stars rotate, black holes probably rotate also. Kerr black holes can have ring-shaped singularities. Spinning black holes also have what's called a static limit. The static limit has a radius larger than the event horizon, and is sometimes called the edge, or outer boundary, of the black hole.
Once you cross the static limit of a rotating black hole, you are subject to its effects, which in this case means that it is impossible to stay still—everything inevitably gets dragged along in the direction of rotation of the black hole. Since the static limit is outside the event horizon, however, crossing this boundary is not final. It is possible to enter and leave the zone between the static limit and the event horizon at will, and an object or light ray only gets trapped forever once it crosses the event horizon.
Reissner-Nordstrøm nonrotating black holes are similar to static ones, but they are charged and have two event horizons. This type of black hole is thought to have an electric charge (called Q in physics equations), but it would likely attract the opposite charge as well, balancing it out. The outer event horizon is called the static limit, similar to the outer edge of a rotating black hole.
Extra Features
Two other features can characterize a black hole - the accretion disk and jets.
An accretion disk is matter that is drawn to the black hole. In rotating black holes and/or ones with a magnetic field, the matter forms a disk due to the mechanical forces present. In a Schwarzschild black hole, the matter would be drawn in equally from all directions, and thus would form an omni-directional accretion cloud rather than disk.
The matter in accretion disks is gradually pulled into the black hole. As it gets closer, its speed increases, and it also gains energy. Accretion disks can be heated due to internal friction to temperatures as high as 3 billion K, and emit energetic radiation such as gamma rays. This radiation can be used to "weigh" the black hole. By using the doppler effect, astronomers can determine how fast the material is revolving around the black hole, and thus can infer its mass.
Jets form in Kerr black holes that have an accretion disk. The matter is funneled into a disk-shaped torus by the hole's spin and magnetic fields, but in the very narrow regions over the black hole's poles, matter can be energized to extremely high temperatures and speeds, escaping the black hole in the form of high-speed …show more content…
jets.
They were actually the brainchild of John Mitchell.
AP
I always attributed the discovery of black holes to Einstein.
While Einstein did revive the theory in 1916, John Mitchell actually thought of it first, back in 1783. The idea didn't go anywhere, though, because he didn't know what to do with it.
Mitchell started to develop the theory of black holes when he accepted Newton’s theory that light consists of small material particles, called photons. He wondered how the movement of these light particles is impacted by the gravitational pull of the star they are escaping, and what would happen to these particles if the gravitational pull was so strong that light could not escape.
Mitchell is also the founder of modern seismology, when he suggested earthquakes spread out as waves through the earth.
They are incredibly dense.
Donkey Hotey / Flickr
Black holes have to hold a massive amount of mass in an incredibly small space to have the required gravity to pull light in. For example, to make a black hole with the mass of Earth, the entire planet would need to be squeezed down to a space 9 millimeters across.
A black hole with 4 million times the mass of our sun can fit into the space between Mercury and the Sun. Black holes in the center of galaxies could have a mass of 10 to 30 billion times the mass of our sun.
Having such a large mass in a tiny area means the black hole is incredibly dense, and the forces inside the black hole are incredibly strong.
They are noisy.
Flickr/royalrivers
As everything around the black hole is pulled into its gaping maw, all of this stuff speeds up. The event horizon supercharges the speed of particles close to the speed of light.
Scharf said that when stuff falls through the center of the event horizon there is a gurgling sound. This sound is the energy of motion being converted into sound waves. He described the noise as the sound you hear when water is released from a bath.
In 2003 astronomers using NASA's Chandra X-ray observatory, detected sound waves coming from a supermassive black hole 250 million light years away.
Nothing escapes their pull.
Flickr/tobiasmunich
When anything (be it planets, suns, galaxies or particles of light) passes close to a black hole, they will be pulled in by its gravity. If something else acting on the object, like say a rocket, is stronger than the black hole's gravity, it can escape the pull.
Until, of course, it reaches the event horizon: The point where escape from a black hole is impossible. In order to escape the event horizon, objects must move faster than the speed of light, which is impossible.
This is the "black" part of the black hole, because if light can't escape, then we can't see inside and the area looks empty.
Researchers think that even small black holes would tear you apart before you fall through the event horizon. Gravity is stronger the closer you get to a planet, star, or black hole. If you were falling feet first, gravity at your feet would be so much stronger than at your head. This force would pull you apart.
They slow down time.
Composite Image of Galaxy Cluster MS 0735
NASA, ESA, CXC, STScI, and B. McNamara (University of Waterloo)
Light bends around the event horizon and eventually gets pulled into nothingness as it falls through.
Scharf describes what we would see if a clock were to be sucked into a black in an interview with The Economist. He says the ticking of the clock (if it were to survive the forces of the black hole) would appear to slow down as it approached the event horizon and eventually would seem to freeze altogether.
This freeze in time is due to gravitational time dilation, explained by Einstein's theory of relativity. The gravity of a black hole is so strong, it can slow down time. From the clock's perspective it is still functioning normally. The clock would fade from view as the light from it is stretched further apart. The light would become increasingly red as the wavelength becomes longer and falls out of the visible light spectrum, vanishing from sight.
They are the ultimate energy factories.
Spit, not swallow. en.wikipedia.org Black holes vacuum up the mass surrounding them, and in the black hole this mass gets squished together so hard that space between the individual components of the atoms is compressed, and it is broken down into subatomic particles that can stream away.
These particles are released in jets, as seen in this picture taken with NASA's Chandra X-ray Observatory. These particles propel out of the black hole due to intense magnetic field lines that can cross the event horizon.
Breaking up the particles creates energy, in an efficient manner. Converting mass into energy in this way is 50 times more efficient than nuclear fusion.
Black Hole Facts by Jerry Coffey on December 3, 2009
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Artist's concept of a black hole from top down. Image credit: NASA
One of the most awe inspiring phenomenon in space is the black hole. Black hole facts are searched for every day. Amateur astronomers as well as the professionals often ponder questions related to black holes. So, for the fun of it and because we want to help educate you, we here on Universe Today decided to put together a few black holes facts to intrigue your mind and satisfy a little of your curiosity. | | | | |
Fact 1
As black hole facts go, this is basic one. A black hole is a place where the gravity well is so great that a gravitational time dilation has occurred. This causes time to stop. This causes an event horizon into which objects can fall or be pulled, but those objects will never reappear. That is the basic definition according to Einstein’s theory of general relativity.
Fact 2
There is no limit to how small or how large a black hole can be. The size and mass of a black hole are directly related. The more massive a black hole is, the more space it takes up. In fact, the Schwarzschild radius ( the radius of the event horizon of a black hole) and the mass are directly proportional to one another. Therefore, if one black hole weighs ten times as much as another, its radius is ten times as large. For example, a black hole with a mass equal to that of our Sun would have a radius of 3 kilometers, a typical 10-solar-mass black hole would have a radius of 30 kilometers, and so on.
Fact 3
The nearest black hole is 1,600 light years away. That is about 16 quadrillion kilometers for Earth.
Fact 4
One the interesting black hole facts is that they can not suck up all of the matter in the Universe. Each black hole has its own event horizon, much like the gravitational field of a planet. If matter is not in that horizon it will never get sucked into the black hole.
Fact 5
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This one tips the scales on the heavy end as black hole facts go: there is a super massive black hole at the center of the Milky Way galaxy. It weighs in at about 4 million solar masses. Luckily, there is no reason to worry. This giant sucker is over 30,000 light years away.
Fact 6
The last of the black hole facts I have to offer today is that many theorists believe that a black hole can eventually evaporate. How is that? Steven Hawking proposed that black holes were not entirely black. They emit radiation. The energy that produces the radiation comes from the mass of the black hole. As the radiation is emitted, the black hole loses mass. The black hole emits more radiation the smaller it gets. In effect, a black hole evaporates more quickly as it shrinks.
These black hole facts are just a few of the little tidbits and teasers that you can find by doing some research. Here is a list of a few more. Here on Universe Today we have a great article about a practical use for black holes: as spacecraft engines. No one can get to a black hole without space travel. Astronomy Cast offers a good episode about interstellar travel
Read more: http://www.universetoday.com/46687/black-hole-facts/#ixzz2O7sIWUbY
Ten things you don't know about black holes
By Phil Plait | October 30, 2008 8:48 pm
Well, they’re black, and they’re like bottomless holes. What would you call them?
-Me, when a friend asked me why they’re named what they are
Ah, black holes. The ultimate shiver-inducer of the cosmos, out-jawing sharks, out-ooking spiders, out-scaring… um, something scary. But we’re fascinated by ‘em, have no doubt — even if we don’t understand a whole lot about them. |
But then, that’s why I’m here. Allow me to be your tour guide to infinity. Or the inverse of it, I suppose. Since it’s Halloween this seems appropriate… and my book Death from the Skies! just came out, and there’s lots of ways a black hole can destroy the Earth. Mwuhahahaha.
So below I present ten facts about black holes — the third in my series of Ten Things You Don’t Know (the first was on the Milky Way; the second about the Earth). Regular readers will know a few of these since I’ve talked about them before, but I’m hoping you don’t know all of these. And if you do, then feel free to leave a comment preening about your superior intellect. Mind you, this list is nowhere near complete: I could have picked probably 50 things that are weird about black holes. But I like these.
1) It’s not their mass, it’s their size that makes them so strong.
OK, first, a really quick primer on black holes. Bear with me!
The most common way for a black hole to form is in the core of a massive star. The core runs out of fuel, and collapses. This sets off a shockwave, blowing up outer layers of the star, causing a supernova. So the star’s heart collapses while the rest of it explodes outwards (this is the Cliff’s notes version; for more details on the process — which is way cool, so you should read it — check out my description of it).
As the core collapses, its gravity increases. At some point, if the core is massive enough (about 3 times the mass of the Sun), the gravity gets so strong that right at the surface of the collapsing core the escape velocity increases to the speed of light. That means that nothing can escape the gravity of this object, not even light. So it’s black. And since nothing can escape, well, read the quotation at the top of the page.
The region around the black hole itself where the escape velocity equals the speed of light is called the event horizon. Any event that happens inside it is forever invisible.
OK, so now you know what one is, and how they form. Now, I could explain why they have such strong gravity, but you know what? I’d rather let this guy do it. I hear he’s good.
So there you go. Sure, the mass is important, but sometimes it’s the little things that count.
2) They’re not infinitely small.
So OK, they’re small, but how small are they?
I was writing about black holes in my previous job, and we got in a fun discussion over just what we meant by black hole: did we mean the object itself that collapses down to a mathematical point, or the event horizon surrounding it? I said the event horizon, but my boss said it was the object. I decided she had a point (HAHAHAHAHA! A "point"! Man, I kill me), and made sure that when I wrote about the event horizon versus the black hole itself I was making myself clear.
Like I said above, to the collapsing core, its clock keeps ticking, so it sees itself collapsing all the way down to a point, even if the event horizon has some finite size.
What happens to the core? The actual mass that collapsed?
Out here, we’ll never know for sure. We can’t see in, and it sure enough isn’t gonna send any info out. But our math in these situations is pretty good, and we can at least apply them to the collapsing core, even when it’s smaller than the event horizon.
It will continue to collapse, and the gravity increases. Smaller, smaller… and when I was a kid I always read that it collapses all the way down to a geometric dot, an object with no dimensions at all. That really bugged me, as you can imagine… as well it should. Because it’s wrong.
At some point, the collapsing core will be smaller than an atom, smaller than a nucleus, smaller than an electron. It’ll eventually reach a size called the Planck Length, a unit so small that quantum mechanics rules it with an iron fist. A Planck Length is a kind of quantum size limit: if an object gets smaller than this, we literally cannot know much about it with any certainty. The actual physics is complicated, but pretty much when the collapsing core hits this size, even if we could somehow pierce the event horizon, we couldn’t measure its real size. In fact, the term "real size" doesn’t really mean anything at this kind of scale. If the Universe itself prevents you from measuring it, you might as well say the term has no meaning.
And how small is a Planck Length? Teeny tiny: about 10-35 meters. That’s one one-hundred quintillionth the size of a proton.
So if someone says a black hole has zero size, you can be all geeky and technical and say, not really, but meh. Close enough.
3) They’re spheres. And they’re definitely not funnel shaped.
The gravity you feel from an object depends on two things: the object’s mass, and your distance from that object. This means that anyone at a given distance from a massive object — say, a million kilometers — would feel the same force of gravity from it. That distance defines a sphere around an object: anyone on that sphere’s surface would feel the same gravity from the object at the center.
The size of an event horizon of a black hole depends on the gravity, so really the event horizon is a sphere surrounding the black hole. From the outside, if you could figure out how to see the event horizon in the first place, it would look like a pitch black sphere.
Some people think of black holes as being circles, or worse, funnel-shaped. The funnel thing is a misconception from people trying to explain gravity as a bending in space, and they simplify things by collapsing 3D space into 2D; they say the space is like a bed sheet, and objects with mass bend space the same way that a massive object (a bowling ball, say) will warp a bed sheet. But space is not 2D, it’s 3D (even 4D if you include time) and so this explanation can confuse people about the actual shape of a black hole event horizon.
I’ve had kids ask me what happens if you approach a black hole from underneath! They sometimes don’t get that black holes are spheres, and there is no underneath. I blame the funnel story. Sadly, it’s the best analogy I’ve seen, so we’re stuck with it. Use it with care.
4) Black holes spin!
It’s kind of an odd thought, but black holes can spin. Stars rotate, and when the core collapses the rotation speeds way, way up (the usual analogy is that of an ice skater who brings in his arms, increasing his rotation rate). As the core of the star gets smaller it rotates more rapidly. If it doesn’t quite have enough mass to become a black hole, the matter gets squeezed together to form a neutron star, a ball of neutrons a few kilometers across. We have detected hundreds of these objects, and they tend to spin very rapidly, sometimes hundreds of times a second!
The same is true for a black hole. Even as the matter shrinks down smaller than the event horizon and is lost to the outside Universe forever, the matter is still spinning. It’s not entirely clear what this means if you’re trying to calculate what happens to the matter once it’s inside the event horizon. Does centrifugal force keep it from collapsing all the way down to the Planck length? The math is fiendish, but do-able, and implies that matter falling in will hit matter inside the event horizon trying to fall further but unable to due to rotation, This causes a massive pile up and some pretty spectacular fireworks… that we’ll never see, because its on the other side of infinity. Bummer.
5) Near a black hole, things get weird
The spin of the black hole throws a monkey in the wrench of the event horizon. Black holes distort the fabric of space itself, and if they spin that distortion itself gets distorted. Space can get wrapped around a black hole — kind of like the fabric of a sheet getting caught up in a rotating drill bit.
This creates a region of space outside the event horizon called the ergosphere. It’s an oblate spheroid, a flattened ball shape, and if you’re outside the event horizon but inside the ergosphere, you’ll find you can’t sit still. Literally. Space is being dragged past you, and carries you along with it. You can easily move in the direction of the rotation of the black hole, but if you try to hover, you can’t. In fact, inside the ergosphere space is moving faster than light! Matter cannot move that fast, but it turns out, according to Einstein, space itself can. So if you want to hover over a black hole, you’d have to move faster than light in the direction opposite the spin. You can’t do that, so you have to move with the spin, fly away, or fall in. Those are your choices.
I suggest flying away. Fast. Because…
6) Approaching a black hole can kill you in fun ways. And by fun, I mean gruesome, horrifying, and really really ookie.
Sure, if you get too close, plop! You fall in. But even if you keep your distance you’re still in trouble… |
Gravity depends on distance. The farther you are from an object, the weaker its gravity. So if you have a long object near a massive one, the long object will feel a stronger gravitational force on the near end versus a weaker force on the far end! This change in gravity over distance is called the tidal force (which is a bit of a misnomer, it’s not really a force, it’s a differential force, and yes, it’s related to why we have ocean tides on Earth from the Moon).
The thing is, black holes can be small — a BH with a mass of about three times the Sun has an event horizon just a few kilometers across — and that means you can get close to them. And that in turn means that the tidal force you feel from one can get distressingly big. | Praying to this guy won’t help. |
Let’s say you fall feet first into a stellar-mass BH. It turns out that as you approach, the difference in gravity between your head and your feet can get huge. HUGE. The force can be so strong that your feet get yanked away from your head with hundreds of millions of times the force of Earth’s gravity. You’d be stretched into a long, thin strand and then shredded.
Astronomers call this spaghettification. Ewwww.
So getting near a black hole is dangerous even if you don’t fall in. Evidently, there really is a tide in the affairs of men.
7) Black holes aren’t always dark
The thing is, black holes can kill from a long way off. | Disk of DOOOOOM!
Image credit: NASA/CXC |
Matter falling into a black hole would rarely if ever just fall straight in and disappear. If it has a little bit of sideways motion it’ll go around the black hole. As more matter falls in, all this junk can pile up around the hole. Because of the way rotating objects behave, this matter will create a disk of material whirling madly around the hole, and because the gravity of the hole changes so rapidly with distance, matter close in will be orbiting much faster than stuff farther out. This matter literally rubs together, generating heat through friction. This stuff can get really hot, like millions of degrees hot. Matter that hot glows with intense brightness… which means that near the black hole, this matter can be seriously luminous.
Worse, magnetic and other forces can focus two beams of energy that go plowing out of the poles of the disk. The beams start just outside the black hole, but can be seen for millions or even billions of light years distant.
They’re bright.
In fact, black holes that are eating matter in this way can glow so brightly that they become the brightest continuously-emitting objects in the Universe! We call these active black holes.
And as if black holes aren’t dangerous enough, the matter gets so hot right before it makes the final plunge that it can furiously emit X-rays, high-energy forms of light (and the beams can emit even higher energy light than that). So even if you park your spaceship well outside the event horizon of a black hole, if something else falls in and gets shredded, you get rewarded by being fried by the equivalent of a gazillion dental exams.
I may have mentioned this: black holes are dangerous. Best to stay away from them.
8) Black holes aren’t always dangerous. | I’m right there with you, dude. |
Having said that, let me ask you a question: if I were to take the Sun and replace it with a black hole of the exact same mass, what would happen? Would the Earth fall in, be flung away, or just orbit like it always does?
Most people think the Earth would fall in, sucked inexorably down by the black hole’s powerful gravity. But remember, the gravity you feel from an object depends on the mass of the object and your distance from it. I said the black hole has the same mass as the Sun, remember? And the Earth’s distance hasn’t changed. So the gravity we’d feel from here, 150 million kilometers away, would be exactly the same! So the Earth would orbit the solar black hole just as nicely as it orbits the Sun now.
Of course, we’d freeze to death. You can’t have everything.
9) Black holes can get big.
Q: What happens if two stellar-mass black holes collide?
A: You get one bigger black hole.
You can extrapolate from there. Black holes can eat other objects, including other black holes, so they can grow. We think that early on in the Universe, when galaxies were just forming, matter collecting in the center of the nascent galaxy can collapse to form a very massive black hole. As more matter falls in, the hole greedily consumes it, and grows. Eventually you get a supermassive black hole, one with millions or even billions of times the mass of the Sun.
However, remember that as matter falls in it can get hot. It can be so hot that the pressure from light itself can blow off material that’s farther out, a bit like the solar wind but on a much grander scale. The strength of the wind depends on many things, including the mass of the black hole; the heftier the hole, the windier the, uh, wind. This wind prevents more matter from falling in, so it acts like a cutoff valve for the ever-increasingly girthy
hole.
Not only that, but over time the gas and dust around the black hole (well, pretty far out, but still near the center of the galaxy) gets turned into stars. Gas can fall into a black hole more easily than stars (if gas clouds collide head-on their motion relative to the black hole can stop, allowing them to fall in; stars are too small and too far apart for this to happen). So eventually the black hole stops consuming matter because nothing more is falling into it. It stops growing, the galaxy becomes stable, and everyone is happy. | Don’t panic!
OK, maybe a little. |
In fact, when we look into the Universe today, we see that pretty much every large galaxy has a supermassive black hole in its heart. Even the Milky Way has a black hole at its core with a mass of four millions times that of the Sun. Before you start running around in circles and screaming, remember this: 1) it’s a long way off, 26,000 light years (260 quadrillion kilometers), 2) its mass is still very small compared to the 200 billion solar masses of our galaxy, and therefore 3) it can’t really harm us. Unless it starts actively feeding. Which it isn’t. But it might start sometime, if something falls into it. Though we don’t know of anything that can fall into it soon. But we might miss cold gas.
Hmmm.
Anyway, remember this as well: even though black holes can cause death and destruction on a major scale, they also help galaxies themselves form! So we owe our existence to them.
10) Black holes can be low density.
Of all the weirdnesses about black holes, this one is the weirdest to me.
As you might expect, the event horizon of a black hole gets bigger as the mass gets bigger. That’s because if you add mass, the gravity gets stronger, which means the event horizon will grow.
If you do the math carefully, you find that the event horizon grows linearly with the mass. In other words, if you double the black hole’s mass, the event horizon radius doubles as well.
That’s weird! Why?
The volume of a sphere depends on the cube of the radius (think way back to high school: volume = 4/3 x π x radius3). Double the radius, and the volume goes up by 2 x 2 x 2 = 8 times. Make the radius of a sphere 10 times bigger and the volume goes up by a factor of 10 x 10 x 10 = 1000.
So volume goes up really quickly as you increase the size of a sphere.
Now imagine you have two spheres of clay that are the same size. Lump them together. Is the resulting sphere twice as big?
No! You’ve doubled the mass, but the radius only increases a little bit. Because volume goes as radius cubed, to double the radius of your final clay ball, you’d need to lump together eight of them.
But that’s different than a black hole. Double the mass, double the size of the event horizon. That has an odd implication…
Density is how much mass is packed into a given volume. Keep the size the same and add mass, and the density goes up. Increase the volume, but keep the mass the same, and the density goes down. Got it?
So now let’s look at the average density of matter inside the event horizon of the black hole. If I take two identical black holes and collide them, the event horizon size doubles, and the mass doubles too. But volume has gone up by eight times! So the density actually decreases, and is 1/4 what I started with (twice the mass and eight times the volume gives you 1/4 the density). Keep doing that, and the density decreases.
A regular black hole — that is, one with three times the Sun’s mass — with have an event horizon radius of about 9 km. That means it has a huge density, about two quadrillion grams per cubic cm (2 x 1015). But double the mass, and the density drops by a factor of four. Put in 10 times the mass and the density drops by a factor of 100. A billion solar mass black hole (big, but we see them this big in galaxy centers) would drop that density by a factor of 1 x 1018. That would give it a density of roughly 1/1000 of a gram per cc… and that’s the density of air!
A billion solar mass black hole would have an event horizon 3 billion km in radius — roughly the distance of Neptune to the Sun.
See where I’m going here? If you were to rope off the solar system out past Neptune, enclose it in a giant sphere, and fill it with air, it would be a black hole!
That, to me, is by far the oddest thing about black holes. Sure, they warp space, distort time, play with our sense of what’s real and isn’t… but when they touch on the everyday and screw with that, well, that’s what gets me.
I first thought of this at a black hole conference at Stanford a few years back. I was walking with noted black hole expert Roger Blandford when it hit me. I did a quick mental calculation to make sure I had the numbers right, and related to Roger that a solar system full of air would be a black hole. He thought about it for a moment and said, "Yes, that sounds about right."
And that, me droogs, was one of the coolest moments of my hole life. But thinking about it still makes my brain hurt.
Conclusion:
Well, what can I say? Black holes are weird.
As it so happens, there was a lot more that could be said about them, of course. What about wormholes? What about how they form? what about Hawking radiation? Can black holes totally evaporate?
You can find answers to these and other questions elsewhere on the web (and even on this very blog); I couldn’t cover everything in just ten sections! But I’ll note (shocker) that chapter 5 of my book Death from the Skies! talks in detail about how they form, and what they can do if you get too close to them. Later chapters also talk about the black hole in the core of the Milky Way, and what will happen to black holes a long time from now… literally, 1060, 1070, even a googol years from now.
But even then, that’s not the scariest thing about black holes. I almost didn’t put this in the post, it’s so over the top mind-numbingly horrifying. But I’m a scientist, and we’re skeptics here, so we can take it. So I present to you, the worst thing about black holes of all: |
Interesting facts about black holes * If you fell into a black hole, gravity would stretch you out like spaghetti. Don't worry; your death would come before you reached singularity. * Black holes do not "suck." Suction is caused by pulling something into a vacuum, which the massive black hole definitely is not. Instead, objects fall into them. * Albert Einstein first predicted black holes in 1916 with his general theory of relativity. * The term "black hole" was coined in 1967 by American astronomer John Wheeler. * The first object considered to be a black hole is Cygnus X-1. Rockets carrying Geiger counters discovered eight new x-ray sources. In 1971, scientists detected radio emission coming from Cygnus X-1, and a massive hidden companion was found and identified as a black hole. * Cygnus X-1 was the subject of a 1974 friendly wager between Stephen Hawking and a fellow physicist Kip Thorne, with Hawking betting that the source was not a black hole. In 1990, he conceded defeat. * Miniature black holes may have formed immediately after the Big Bang. Rapidly expanding space may have squeezed some regions into tiny, dense black holes less massive than the sun. * If a star passes too close to a black hole, it can be torn apart. * Astronomers estimate there are anywhere from ten million to a billion stellar black holes, with masses roughly thrice that of the sun, in the Milky Way. * The interesting relationship between string theory and black holes give rise to more types of massive giants than found under conventional classical mechanics.
How big can a black hole get?
There is no limit to how large a black hole can be. However, the largest blackholes we think are in existence are at the centers of many galaxies, and have masses equivalent to about a billion suns (i.e., a billion solar masses). Their radii would be a considerable fraction of the radius of our solar system
How is time changed in a black hole?
Well, in a certain sense it is not changed at all. If you were to enter a black hole, you would find you watch ticking along at the same rate as it always had (assuming both you and the watch survived the passage into the black hole). However, you would quickly fall toward the center where you would be killed by enormous tidal forces (e.g., the force of gravity at you feet, if you fell feet first, would be much larger than at you head, and you would be stretched apart).
Although your watch as seen by you would not change its ticking rate, just as in special relativity (if you know anything about that), someone else would see a different ticking rate on your watch than the usual, and you would see their watch to be ticking at a different than normal rate. For example, if you were to station yourself just outside a black hole, while you would find your own watch ticking at the normal rate, you would see the watch of a friend at great distance from the hole to be ticking at a much faster rate than yours. That friend would see his own watch ticking at a normal rate, but see your watch to be ticking at a much slower rate. Thus if you stayed just outside the black hole for a while, then went back to join your friend, you would find that the friend had aged more than you had during your separation.