Universe Today

Want a black hole wallpaper for your computer desktop background? Here's a nice collection. Just click on an image to see the larger version. Then right-click on the image and choose "Set as Desktop Background".

Black Hole Grabs Starry Snack

Here's an artist's illustration of a black hole drawing material away from a stellar companion. Since black holes are invisible, we can only see them when they're actively feeding, in this case, pulling material away from a star several times the mass of our Sun.

Top-down illustration of a black hole

This is a top-down artist's illustration of a black hole. You can see the black event horizon, where light can't escape. Surrounding this is a swirling disk of hot gas and dust with powerful magnetic fields.

Black Holes Go 'Mano a Mano'

This is a photograph of two galaxies colliding together. And at their centers, astronomers think their supermassive black holes are merging together into an even larger black hole.

Black Hole Fires at Neighboring Galaxy

This is an image of a hot jet blasting out of a supermassive black hole. It's reaching across hundreds of light years into space. The region around a supermassive black hole becomes like the center of a star, creating intense radiation.

Monstrous Black Hole Blast in the Core of a Galaxy Cluster

Here's an image of an enormous black hole at the heart of a galaxy cluster. A black hole like this could weigh a billion times the mass of our Sun, built up over mergers with other galaxies.

We've written many stories about black holes for Universe Today. Here's an article about a shrinking doughnut around a black hole, and here's an article about how the first black holes might have formed.

If you'd like more info on black holes, check out NASA's World Book on Black Holes, and here's more information from NASA from their educational pages.

We've also recorded an episode of Astronomy Cast all about black holes. Listen here, Episode 18: Black Holes Big and Small.

Filed under: Astronomy | Comments Off

Here are some cool black hole images.

Smallest Known Black Hole

This is an artist's illustration of the smallest known black hole, recently discovered by astronomers. Of course, astronomers don't actually know how small a black hole really is, so this is all about the size of the black hole's event horizon.

Black Hole

Here's a picture of a black hole pulling material away from a nearby stellar companion. Sometimes this is the only way you can detect a black hole, since it's invisible unless it's feeding on material.

Fast-Flying Black Hole

This is an artist's illustration of a low-mass black hole spewing out jets from its poles. These microquasars form when a black hole sucks material off a stellar companion.

Galactic Black Hole with Optical Jet

This is an artist's image of a huge optical jets blasting out of a galaxy that contains a supermassive black hole at its center. We don't see the black hole itself, but the superheated torus of gas and dust surrounding the black hole. This material heats up to mimic the cores of stars, releasing a tremendous amount of energy.

Spinning Black Holes

Here's an image of what a supermassive black hole might look like. You can see the dark sphere – the event horizon – in the middle, surrounded by a swirling disk of gas and dust. The rapid rotation of the black hole creates powerful magnetic fields which whip up the the material and form powerful jets that can travel for hundreds of light-years.

We've written many stories about black holes for Universe Today. Here's an article about a black hole breaking the distance record, and here's an article about how an intermediate mass black hole could be destroying stars.

If you'd like more info on black holes, check out NASA's World Book on Black Holes, and here's more information from NASA from their educational pages.

We've also recorded an episode of Astronomy Cast all about black holes. Listen here, Episode 18: Black Holes Big and Small.

Filed under: Astronomy | Comments Off

According to Einstein's general theory of relativity, a black hole in space 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. They are referred to as black because they do not reflect anything that hits them. They absorb all light. Analysis has shown that a black hole does posses a temperature and Hawking radiation.

Although it is invisible, a black hole in space can be observed through its interaction with other matter. One can be inferred by tracking the movement of a group of stars that orbit a region in space which looks empty. Also, one can see gas falling into a relatively small black hole, from a companion star. This gas spirals inward, heating up to very high temperatures and emitting large amounts of radiation that can be detected from Earth bound and Earth-orbiting telescopes. Such observations have resulted in the scientific consensus that black holes exist in our universe.

The existence of a black hole in space was first postulated in 1783. 1915 saw the release of Einstein's theory of general relativity, but it was not until a few years later that Karl Schwarzchild found a solution that the existence of a black hole was possible. His solution is called the Schwarzchild radius. It is used to define the radius of the event horizon of a non rotating black hole.

Some scientists, and many sci-fi fanatics, believe that if you could find a way to connect black holes you could travel across space quickly and efficiently. Others believe that creating a black hole in an enclosed area would allow you to create a spacecraft engine that would never fail and launch our race into interstellar travel.

There are good articles about black holes here and here. WE have a great article here on Universe Today about the proposed "black hole drive". Astronomy Cast offers a good episode about stars forming in and around a black hole.

Filed under: Astronomy | Comments Off

Artist's concept of a black hole from top down. Image credit: NASA

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

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.

Filed under: Astronomy | Comments Off

Artist's illustration of a supermassive black hole. Image credit: NASA

Here on Earth, the gravity you feel on your feet comes from the mass of the planet. If the Earth had more mass, you would feel less gravity. But if the Earth was shrunk down smaller, say to the size of the Moon, you would experience more gravity on its surface because the mass is more concentrated. It would take more energy to jump up. And if the Earth was shrunk down to the size of a marble, it would be impossible to jump up. In fact, the pull of gravity would be so intense that not even light could escape. In essence, that is a black hole.

Black holes are created in nature when a star with about 10 times the mass of our Sun runs out of energy. Without the light energy pushing it apart, gravity is able to crush it together. The pull of gravity is so strong that electrons are crushed together with protons to make neutrons, and then these neutrons are crushed even further. At some point, the star is crushed down to that point when light can no longer escape its pull. Astronomers aren't sure how small they become, but it's possible that a star once many times the mass of our own Sun is crushed down smaller than an atom. That's when it becomes a black hole.

There is another kind of black hole as well: supermassive black holes. These lurk at the heart of galaxies and can contain millions, and even billions of times the mass of the Sun. These monster black holes formed with their galaxies billions of years ago and continue to pile on material. The discovery of these supermassive black holes helped explain mysterious objects called quasars. Astronomers now know that quasars are the cores of galaxies where the supermassive black hole is actively feeding on material. This material piles up around the black hole, like water waiting to go down the drain, and becomes like the core of a star shining with more energy than the rest of the galaxy.

We've written many articles about black holes for Universe Today. Here's an article about how black hole drives could power future spaceships, and here's an article about the search for medium-sized black holes.

If you'd like more info on black holes, check out the Hubble animation about black holes, and here's NASA's World Book on black holes.

We have also done many episodes of Astronomy Cast about black holes. Start here, Episode 18: Black Holes Big and Small.

Filed under: Astronomy | Comments Off

Image credit: NASA

It turns out black holes are not black at all; they give off "Hawking radiation" that causes them to lose energy (and therefore mass) over time. For large black holes, the amount of radiation produced is miniscule, but very small black holes rapidly turn their mass into a huge amount of energy.
Read more…

Filed under: Black Holes | 40 Comments »

Peering Deeper Into the Core of M87: At top left, a VLA image of the galaxy shows the radio-emitting jets at a scale of about 200,000 light-years. Subsequent zooms progress closer into the galaxy's core, where the supermassive black hole resides. In the artist's conception (background). the black hole illustrated at the center is about twice the size of our Solar System, a tiny fraction of the size of the galaxy, but holding some six billion times the mass of the Sun. Credit: Bill Saxton, NRAO/AUI/NSF

Black holes with two distinct ranges of mass have been observed – 'stellar mass' ones, with masses of a few sols (up to ~20), and supermassive black holes (SMBHs), with masses between a few hundred thousand sols and well over a billion sols. Of course, black holes emit no light, so their existence is inferred rather than directly observed; one method is that used to infer the existence of most exoplanets – the motion of nearby objects in the gravitational field of the black hole (it's the star's motion which gives away the presence of most exoplanets).

The nearest SMBH is at the center of our Milky Way galaxy, SgrA*, named after the point source in the brightest radio source in the constellation Sagittarius. Various teams of astronomers have been tracking the positions of stars close to SgrA* for some time now, and their paths trace orbits around the SMBH (they have to observe in the infrared, because the dust between us and SgrA* absorbs 31 magnitudes of optical light!). Here is a really cool summary of the data, as an animation. By applying Kepler's laws to the data, plus a dash of Newton and a pinch of Einstein, the mass of the SMBH can be estimated (it should come out the same, no matter which set of stars' data is use; it does) … about 4 million sols.

All galaxies which have bulges seem to have SMBHs – that includes all normal, and giant, ellipticals, spheroidals, and spirals; dwarf galaxies and irregulars without bulges do not seem to have SMBHs. In fact, galaxies' bulges and their SMBHs seem to know about each other: there is a strong correlation between the SMBH mass and the bulge velocity dispersion.

SMBHs can acquire mass in several ways, the most spectacular of which is when the hot plasma that pervades a rich cluster of galaxies falls into the gravitational center of the cluster, which is usually a cD galaxy (a kind of giant elliptical). At the heart of such galaxies is an SMBH, often with a mass of many billion sols. The plasma is compressed, heated, and ends up on an accretion disk around the SMBH; from there most disappears through the event horizon, but some is jetted out along the poles at ultra-relativistic speeds, to form giant radio lobes. These are called DRAGNs (double radio active galaxy nuclei).

It is the accretion disks around SMBHs that are responsible for quasars' brilliance and variability; look down the barrel of a jet … and you have a blazar; they are natural particle accelerators which can do in less than one second what the LHC can't, even in a dozen lifetimes.

How SMBHs formed in the first place is essentially unknown today … it is a hot topic!

Lots of Universe Today stories on supermassive black holes; for example, Beyond Any Reasonable Doubt: A Supermassive Black Hole Lives in Centre of Our Galaxy, X-Ray Flare Echo Reveals Supermassive Black Hole Torus, How Do You Weigh a Supermassive Black Hole? Take its Temperature, and What Happens When Supermassive Black Holes Collide?, to mention just a few.

More to explore: Astronomy Cast's episodes Quasars, and Black Holes Big and Small.

Filed under: Astronomy | Comments Off

Peering Deeper Into the Core of M87: At top left, a VLA image of the galaxy shows the radio-emitting jets at a scale of about 200,000 light-years. Subsequent zooms progress closer into the galaxy's core, where the supermassive black hole resides. In the artist's conception (background). the black hole illustrated at the center is about twice the size of our Solar System, a tiny fraction of the size of the galaxy, but holding some six billion times the mass of the Sun. Credit: Bill Saxton, NRAO/AUI/NSF

What an event horizon is – its behavior – is described by applying the equations of Einstein's theory of General Relativity (GR); as of today, the theoretical predictions concerning event horizons can be tested in only very limited ways. Why? Because we don't have any black holes we can study up close and personal (so to speak) … which is perhaps a very good thing!

If the black hole is not rotating, its event horizon has the shape of a sphere; it's like a 2D surface over a 3D ball. Except, not quite; GR is a theory about spacetime, and contains many counter-intuitive aspects. For example, if you fall freely into a black hole (one sufficiently massive that tidal forces don't rip you to pieces and smear you into a plastic-wrap thin layer of goo, a supermassive black hole for example), you won't notice a thing as you pass through the event horizon … and that's because it's not the event horizon to you! In other words, the location of the event horizon of a black hole depends upon who is doing the observing (that word 'relativity' really does some heavy lifting, if you'll excuse the pun), and as you fall (freely) into a black hole, the event horizon is always ahead of you.

You'll often read that the event horizon is where the escape velocity is c, the speed of light; that's a not-too-bad description, but it's better to say that the path of any ray of light, inside the event horizon, can never make it beyond that horizon.

If you watch – from afar! – something fall into a black hole, you'll see that it gets closer and closer, and light from it gets redder and redder (increasingly redshifted), but it never actually reaches the event horizon. And that's the closest we've come to testing the theoretical predictions of event horizons; we see stuff – mass ripped from the normal star in a binary, say – heading down into its massive companion, but we never see any sign of it hitting anything (like a solid surface). In the next decade or so it might be possible to study event horizons much more closely, by imaging SgrA* (the supermassive black hole – SMBH – at the center of our galaxy), or the SMBH in M87, with extremely high resolution.

The Universe Today article Black Hole Event Horizon Measured is about just this kind of black hole-normal star binary, Black Hole Flares as it Gobbles Matter is about observations of matter falling into a SMBH, and Maximizing Survival Time Inside the Event Horizon of a Black Hole describes some of the weird things about event horizons.

There's more on event horizons in the Astronomy Cast Relativity, Relativity and More Relativity episode, and the Black Hole Surfaces one.

Filed under: Astronomy | Comments Off

Stephen Hawking, weightless (courtesy Zero Gravity Corporation)

At least that's the way we understand it today (no black-hole-pining-away has yet been observed), and the theory may be wrong too.

Cosmologist, astrophysicist, and physicist Stephen Hawking showed, in 1974, that black holes should emit electromagnetic radiation with a blackbody spectrum; this process is also called black hole evaporation. In brief, this theoretical process works like this: particle-antiparticle pairs are constantly being produced and rapidly disappear (through annihilation); these pairs are virtual pairs, and their existence (if something virtual can be said to exist!) is a certain consequence of the Uncertainty Principle. Normally, we don't ever see either the particle or antiparticle of these pairs, and only know of their existence through effects like the Casimir effect. However, if one such virtual pair pops into existence near the event horizon of a black hole, one may cross it while the other escapes; and the black hole thus loses mass. A long way away from the event horizon, this looks just like black body radiation.

It turns out that the smaller the mass a black hole has, the faster it will lose mass due to Hawking radiation; right at the end, the black hole disappears in an intense burst of gamma radiation (because the black hole's temperature rises as it gets smaller). We won't see any of the black holes in the Milky Way explode any time soon though … not only are they likely still gaining mass (from the cosmic microwave background, at least), but a one sol black hole would take over 10^67 years to evaporate (the universe is only 13 billion years old)!

There are many puzzles concerning black holes and Hawking radiation; for example, black hole evaporation via Hawking radiation seems to mean information is lost forever. The root cause of these puzzles is that quantum mechanics and General Relativity – the two most successful theories in physics, period – are incompatible, and we have no experiments or observations to help us work out how to resolve this incompatibility.

Colorado University's Andrew Hamilton has a good introduction to this topic, as does Usenet Physics FAQ (often recognized by John Baez' association with it).

Some Universe Today stories which include Hawking radiation are Synthetic Black Hole Event Horizon Created in UK Laboratory, How to Escape from a Black Hole, and When Black Holes Explode: Measuring the Emission from the Fifth Dimension.

Black Holes Big and Small, and The Large Hadron Collider and the Search for the Higgs-Boson are two Astronomy Casts relevant to Hawking radiation.

Filed under: Astronomy | Comments Off

Magnetic field around a black hole. Image credit: NASA

As you are likely aware, there are numerous ways in which the Universe could kill us all, destroying the Earth and whatever signs of human life, or life in general, existed on our planet. Gamma Ray Bursts, Coronal Mass Ejections, or just the odd asteroid or comet slamming into the Earth would easily take out most of the life on our planet. But, what about black holes? Do we have to worry about them, too? Could a black hole wipe out all life on Earth, sucking us all into oblivion? It's possible, but not very likely. And by not very likely, it's calculated that the odds of being killed by a black hole are about one in one trillion.

First, a black hole has to get to the Earth. There are two ways of this happening. The first is that we create one ourselves, the second that a black hole wandering the galaxy happens upon our little Solar System, and meanders in towards the Sun. We'll start with the first scenario: creating our own destruction.

How could we make our own black hole? Well, theoretically, when you slam protons together with enough force, there is the potential for the creation of a small, short-lived black hole. Particle colliders like the Large Hadron Collider in Geneva, Switzerland, which is scheduled to start operating again in November 2009, could potentially create miniscule black holes through the collisions of protons. There were many headlines from the mainstream media about the potential of the LHC to create runaway black holes that would find their way to the center of the Earth and devour it from the inside, causing, "total destruction." Sounds scary, doesn't it? Even more, two people were suing to stop the LHC because of the potential hazard they thought it posed.

However, the LHC is in no way going to destroy the Earth. This is because any black holes created by the LHC will almost instantly evaporate, due to what's called Bekenstein-Hawking radiation, which theorizes that black holes do indeed radiate energy, and therefore have a limited lifespan. A black hole with the mass of, say, a few protons, would evaporate in trillionths of a second. And even if it were to stick around, it wouldn't be able to do much damage: it would likely pass through matter as if it didn't exist. If you want to know whether the LHC has destroyed the Earth, go here.

Of course, there are other ways of creating black holes than the LHC, namely cosmic rays that slam into our atmosphere on a regular basis. If these are creating mini-black holes all of the time, none of them seem to be swallowing the Earth whole…yet. Other scientific experiments also aim at studying the properties of black holes right here on Earth, but the danger from these experiments is very, very minimal.

Now that we know black holes created here on Earth aren't likely to kill us all, what about a black hole from the depths of space wandering into our neighborhood? Black holes generally come in two sizes: supermassive and stellar. Supermassive black holes reside in the hearts of galaxies, and one of these is not likely to come barrelling our way. Stellar black holes form from a dying star that, in the end, gives up its fight against gravity and implodes. The smallest black hole that can form from this process is about 12 miles across. The closest black hole to our solar system is Cygnus X-1, which is about 6,000 light years away, much too far to pose a threat by muscling it's way into our vicinity (although there are other ways that it could potentially harm us if it were closer, like blasting us with a jet of X-rays, but that's a whole other story). The creation process for a black hole of this variety – a supernova – could potentially sling the black hole across the galaxy, if the supernova happened in a binary pair and the explosion was asymmetric.

If a stellar black hole were to plow through the Solar System, it would be pretty ugly. The object would likely be accompanied by an accretion disk of heated, radioactive matter that would announce the presence of the black hole by frying our atmosphere with gamma and X-rays. Add to that the tidal forces of the black hole disrupting the Sun and other planets, and you have a huge mess on your hands, to say the least. It's possible that a number of planets, and even the Sun, could be flung out of the Solar System, depending on the mass, velocity, and approach of the black hole. Yikes.

Artist's rendering of a black hole. Image Credit: NASA

There lies one last possiblity for black holes to wreak their havoc on the Earth: Primordial Black Holes. These are miniature black holes theorized to have been created in the intense energies of the Big Bang (which the LHC plans to mimic on a MUCH smaller scale). Many of them most likely evaporated billions of years ago, but a black hole that started out with the mass of a mountain (10 billion tons) could potentially still be lurking around the galaxy. A hole of this size would shine at a temperature of billions of degrees from Bekenstein-Hawking radiation, and it's likely we would see it coming due to observatories like NASA's Swift.

From a few yards a way, the black hole's gravity would be barely noticeable, so this kind of black hole wouldn't have an effect on the gravity of the Solar System. At less than an inch, though, the gravity would be intense. It would suck up air as it passed through the atmosphere of the Earth, and start to make a small accretion disk. To such a tiny black hole, the Earth seems close to a vacuum, so it would probably pass right through, leaving a wake of radiation in its path and nothing more.

A black hole of this variety with a mass of the Earth, however, would be roughly the size of a peanut, and would be able to potentially swing the Moon straight into the Earth, depending, of course, on the trajectory and speed of the black hole. Yikes, again. Not only that, if it were to impact the Earth, the devastation would be total: as it entered the atmosphere, it would suck up a lot of gas and form a radioactive accretion disk. As it got closer, people and objects on the surface would be sucked up into it. Once it impacted the surface, it would start swallowing up the Earth, and probably eat its way all the way through. In this scenario, the Earth would end up being nothing more than a wispy disk of debris around the remaining black hole.

Black holes are scary and cool, and none of the scenarios depicted here are even remotely likely to happen, even if they're fun to think about. If you want to learn more about black holes,  Hubblesite has an excellent encyclopedia, as does Stardate.org. You can also check out the rest of our section on black holes in the Guide to Space, or listen to the multiple Astronomy Cast episodes on the subject, like Episodes 18, or the questions show on Black, Black Holes. Much of the information on the likelihood and aftereffects of a black hole collision with the Earth in this article is taken from chapter 5 in Phil Plait's "Death from the Skies!"

Filed under: Astronomy | Comments Off

Question: What is on the other side of a black hole?

Answer: There is no other side.

Science fiction has populated the idea that a black hole serves a portal to another world. If you could pass through, where does a black hole go? Perhaps you'll come to some other dimension, or re-emerge from some other part of the Universe?

No, a black hole only leads to death, for you, your spaceship, and another else that's unlucky enough to fall in.

Imagine you fell into a star like our Sun, there would be no question what would happen to you. The intense heat, gravity and pressure would kill you. If you compress more than 5x the mass of the Sun into a tight little area, you get a black hole. But the gravity, heat and pressure are all still there, just much more intense.

If you actually fell into a black hole, the tidal forces pulling at you are so extreme that the force on your feet is dramatically stronger than the force at your head. You would be stretched out and torn into pieces, and then those pieces would be torn into pieces. You would eventually be pulled into a stream of atoms, winding their way down to the surface of the black hole. For this process, scientists have a technical term: spaghettification.

Let's say you could survive this journey. Where does the black hole lead? No where. All of the mass of the star that came before the black hole is still there, pulling at you with all its gravity. This intense gravity would tear every molecule apart, and all the atoms. Protons and electrons would be crushed together to create neutrons, and then these would be crushed together even further into some kind of exotic form of superdense matter.

It's even possible that the heart of a black hole is single point of infinitely small size, containing the mass of many stars. This black hole is not a portal to anywhere, it's just a final destination.

Here's an article I did about how to maximize your time while falling into a black hole.

Filed under: Black Holes, Questions | 22 Comments »

Our Milky Way's black hole is quiet – too quiet – some astronomers might say. But according to a team of Japanese astronomers, the supermassive black hole at the heart of our galaxy might be just as active as those in other galaxies, it's just taking a little break. Their evidence? The echoes from a massive outburst that occurred 300 years ago.
Read more…

Filed under: Astronomy, Black Holes | 11 Comments »