Astronomy

Could anything consume a small black hole?

Could anything consume a small black hole?


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Whenever I read about black holes, it is normally involving how they devour anything that comes too close… regardless of how big anything is.

But what if it were a really small black hole vs something really large? How about something like a large star or neutron star… could a black hole be small enough to get devoured / consumed by something like that or would it just not be possible?


Black holes don't "devour". They can't "eat" things. But things can "fall into" a black hole. It really is just gravity, but really really intense gravity.

A really small black hole would have a mass of about 3 times the mass of the sun. All neutron stars are smaller than that (or they would turn into black holes). A really large star could be more massive and would be much much larger in volume. A black hole could orbit with such a star, but if it got close enough it would pull gas off the star which would then fall into the black hole, causing it to get larger.

There is no way that a large star can in any way "pull apart" or otherwise "consume" a black hole.

There is a theoretical notion of the quasi-star. These are similar to a Thorne-Żytkow objects. In normal stars, the outer layers are prevented from collaping by energy from nuclear fusion in the core. In a quasi-star, the core collapses into a black hole and the release of energy from matter falling into the black hole prevents the collapse of the star. A steady state can be achieved, as if more matter starts to fall in, more energy is released causing the star to grow, and reducesing the amount of matter falling in. Nevertheless, ultimately all the matter from the star would fall in.

Smaller black holes can't form from stars. We don't know if they exist at all, but if they do, very very small black holes could be too small to interact much with regular matter. A very small black hole could be smaller than a proton, and even if one fell into the Earth, it could pass through the gaps between and inside atoms. Such a black hole would be very hot, due to Hawking radiation.


Black hole: Expert confronts fears ENTIRE UNIVERSE will collapse into supermassive giant

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Black hole: Animation outlines how the 'heartbeat' works

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National Science Foundation program director Dr Pesce addressed fears the entire universe could collapse into a supermassive black hole on a recent Space.com Ask Me Anything (AMA). One space enthusiast asked the expert: "Have we, to date, witnessed a perceivable increase in the mass of a black hole due to matter falling into it? And, if this is the case, and black holes simply get larger and larger as they consume matter, doesn't that mean that eventually the Universe will simply collapse into one supermassive black hole?"

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Dr Pesce was, fortunately, able to reassure the public the Universe's demise by a black hole was 'not possible'.

So probably the whole Universe collapsing into a black hole is not possible

Dr Joe Pesce

He said: "Black holes generally 'feed' slowly [in a relative sense] such that the added mass is a small percentage of the total mass.

"This is true for a stellar-sized black hole [say with 5 times the mass of the Sun] pulling mass from a nearby companion star, or a supermassive black hole [say with 1 billion times the mass of the Sun] consuming a star with two to three solar masses.

"If we had sensitive enough instruments we could measure that change, but I don't believe we are quite there yet."

Black hole: Dr Pesce addressed fears the entire universe could collapse into a supermassive monster (Image: Getty)

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The Universe is now known to be expanding at an ever-expanding rate.

As a result, content is continually getting farther away from everything else.

The astronomer added: "So probably the whole Universe collapsing into a black hole is not possible."

The biggest black holes, such as the one in M87 boasts 6.5 billion solar masses.

Black hole: M87 (pictured) boasts 6.5 billion solar masses (Image: Getty)

However, the galaxy in which that big black hole resides is found has trillions of solar masses in gas, dust, stars, dark matter.

Therefore, although the black hole is unimaginably massive, it is relatively minuscule compared with the rest of its cosmic neighbourhood.

However, astronomers have now detected a black hole so large it even dwarfs M87.

Space scientists have since the 1990s suspected most large galaxies in the Universe are likely to have one.


Could anything consume a small black hole? - Astronomy

How long would it take a primordial black hole to eat the earth if one fell to the center of it? Would it just sit there forever eating an atom at a time? (assuming event horizon the size of an atomic nucleus with 1,000,000,000 tonnes mass.)

A billion tons may seem like a lot, but it's actually miniscule compared to the mass of the Earth, which weighs about 6x10 21 tons! A black hole that weighs a billion tons would have an event horizon that's only about 10 -15 meters. So it would be so small that it would really only eat particles that happened to run into it, which wouldn't happen very often. If you were to plant it in the center of the Earth, it would just sit there forever, never consuming enough matter for anyone to notice.

If instead of setting it in the Earth's core, you were to drop it from the surface of the Earth, it would sink down through the middle, pop out the other side, and slide back and forth through the Earth for all eternity. If you assume that the black hole would only consume atoms that it happens to run into, then I calculate that it would take about 10 28 years for it to consume the entire Earth, far longer than the age of the Universe. This assumes that the black hole wouldn't lose any mass due to Hawking radiation. If you factor that in, it would probably *never* consume the whole Earth.

This page was last updated on June 27, 2015.

About the Author

Christopher Springob

Chris studies the large scale structure of the universe using the peculiar velocities of galaxies. He got his PhD from Cornell in 2005, and is now a Research Assistant Professor at the University of Western Australia.


What to Name a Bunch of Black Holes? You Had Some Ideas.

Recently, astronomers asked aloud which plural term would best suit the most enigmatic entity in the cosmos. The responses were plentiful.

In April, during the fetchingly (or chillingly) titled Black Hole Week, a group of astronomers initiated what amounted to a kind of cosmic Rorschach test.

The astronomers work on planning for the European Space Agency’s Laser Interferometer Space Antenna, or LISA, a gravitational-wave detector that, once in orbit, could harvest the signals of black-hole collisions and any other events or objects that rumple space-time, going all the way back to the Big Bang.

Jocelyn Kelly Holley-Bockelmann, an astronomer Vanderbilt University and chair of the NASA LISA Study Team, which provides the American space agency with information about the mission, described herself as giggling “like a loon” at some of the names that came up: “hive,” “asterisk,” “kitchen sink” and “sock drawer.”

Now, members of the LISA Study Team, after a grueling smackdown of several hundred possibilities, have compiled a list of their own 10 favorites (in no particular order): cacophony, graveyard, horde, perforation, swarm, colloquium, disaster, sieve, brood and doom.

“There were strong feelings about the results,” said Dr. Holley-Bockelmann, who lamented that a few of her own favorites — convergence, choir and void — hadn’t made the cut.

It all means nothing and everything.

Anybody who has ever been tormented in a schoolyard or a locker room knows that names, and nicknames, matter. I have never outgrown or outrun “Dennis the Menace,” and in college the similarity of my last name to the word “ovary” provoked much mirth around the fraternity house. Part of Donald Trump’s success on the campaign trail owed to his inimitable way of branding his opponents: Crooked Hillary, Lyin’ Ted, Low-Energy Jeb.

Names matter in science, too. Twenty years ago the astronomical community tore itself apart over the definition of the word “planet,” at least as it refers to bodies in our solar system. In the end, by an argument few understand, Pluto was demoted to the status of a dwarf planet.

But the name “black hole” is one of the great branding successes of modern science. Black holes are objects or realms in space-time where gravity is so great that not even light can escape. Their existence was effectively predicted in 1916, when the German physicist and astronomer Karl Schwarzschild solved Albert Einstein’s equations of the general theory of relativity for a single point mass, a star.

In the 1960s and ’70s, when such objects were first being found, some Russian theorists called them “frozen stars,” because of a quirk in relativity that makes time appear to slow down in a gravitational field. A star’s collapse — the prototypical origin of such a phenomenon — would appear to stop in time altogether at the edge of a black hole. It would never age, nor would we ever see it go over the edge of the “hole” into complete collapse from our point of view.

But if the star could see, it would observe itself falling freely past the edge and being crushed out of existence at the black hole’s center, where, according to Einstein’s equations, space, time and the laws of physics would cease to exist. This dire possibility — of physics predicting the end of physics — deserved attention, according to the late John Archibald Wheeler, a theoretical physicist at Princeton and the University of Texas at Austin.

Wheeler did not invent the name “black hole,” but it was he who seized on it after an audience member reportedly tossed it out during a talk Wheeler was giving on what he considered the greatest crisis in the history of physics. “Calling these things black holes was a master stroke,” Stephen Hawking, the Cambridge University astrophysicist, once told me. “They’re named black holes because they related to human fears of being destroyed or gobbled up.”

Hawking perhaps did the most to dispel that aura of doom and death when he discovered in 1974 that, at the far end of time, black holes would eventually release back into the cosmos all the energy and matter they had imprisoned.

But we are not yet at that phase of cosmic history. For the time being, black holes are dark, ravenous stars, strewing table scraps across space and lighting it up with their passive hunger. A black hole won’t chase you down like a shark it sits with its mouth open, like an eel in a coral reef, waiting for you to swim past.

A group of sharks is a shiver eels are a swarm. Black holes? Many of the suggestions from Times readers drew on the grim aspect.

“Abyss,” “crush,” “haunting” and “chasm” came up frequently. So did (less grimly) “Hawking,” after the man who did so much to understand them, as well as “riddle,” “mystery,” “mass” and “binge.” Other favorites: a “scream” of black holes, an “oblivion” and a “mosh pit.”

Some readers, playing on the idea of a multiplicity of holes, proposed a “colander,” a “doily,” a “lace” and a “warren.” One, responding to Dr. Holley-Bockelmann’s giggle, nominated “loon.”

Another proposed Argus Panoptes, a primordial giant in Greek mythology, whose body was covered with eyes. A third reached into Stephen King’s “Dark Tower” series to suggest a “thinny,” a weak spot in reality where the fabric between worlds has grown thin.

Inevitably, politics was on the minds of many. A suggestion to call a group of black holes a “Trump” was recommended by 125 other readers. “Congress” received multiple votes. (Presumably cooler heads will prevail among astronomers, who depend on federal funds to build their telescopes and conduct research.)

For what it’s worth, there is nothing official going on here. Nor will there be any prize for coming up with the winning name.

Raisa Stebbins, the 32-year-old daughter of one of the LISA scientists, Tuck Stebbins, raised the etymological issue initially, Dr. Holley-Bockelmann said. “It was Raisa’s question that turned our Very Serious Meeting About LISA into a fun distraction,” she said. Hundreds of ideas poured in from friends and the internet.

In all, two dozen astronomers took part in the process, Dr. Holley-Bockelmann said. After much spirited discussion brought the list down to 16 strong contenders, the astronomers voted on them using a proportional ranked-choice voting algorithm, RankIt.

“There were only 26 voters,” Dr. Holley-Bockelmann said, “so then we had a discussion about small-number statistics and what happens in the algorithm when there are tie votes.”

The International Astronomical Union, the author of Pluto’s notorious demotion, controls naming rights for individual things in the sky, with far-reaching fussiness. For instance, the rules demand that straits connecting the seas of Titan be named for characters in Isaac Asimov’s classic “Foundation” series of science-fiction novels. But the group has no stance on black-hole conglomerations, said Marion Schmitz, a Caltech astronomer who is chair of the I.A.U. Commission 5 working group on designations.

“We don’t come up with designations unless there is an obvious conflict with existing designations or inappropriate suggestions,” Dr. Schmitz said in an email. Any name that is used in the literature is fine with the working group and the rest of the community, she said.

With that in mind, I propose that the naming process begin by changing the overarching theme from one of doom to one of creation, minding Hawking’s idea that black holes will eventually explode and return their energy to the universe. I would call them a “litter,” as in a litter of kittens.

We don’t know what the future of the universe is in any detail. A litter of black holes, as of the kind that was discovered in the star cluster NGC 6397, brims with possibility and mischief. They could do anything: merge into a giant black hole, or engage in spirited energetic interplay. Like kittens, they pose no threat to us — in their current incarnation, at least — and are a delight to watch at a safe distance.


Physicists have discovered that rotating black holes might serve as portals for hyperspace travel

Narrator: Black holes skirt the line between science fiction and science fact. On the one hand, scientists have seen real black holes in action, consuming unsuspecting stars that pass too close. But where reality ends and fiction takes over is at the edge of a black hole — a place called the event horizon, where no spacecraft has ever gone.

So, whatever happens beyond that boundary, inside of a black hole, is anyone's guess. Scientists agree that if you travel far enough into a black hole, gravity will eventually become so strong that it kills anything in its path. But sci-fi films are more optimistic, d epicting black holes as portals through space and time or gateways to other dimensions. And it turns out, some scientists now think the sci-fi buffs may be onto something. Black holes might be suitable for hyperspace travel, after all i t just takes the right kind of black hole.

At the center of every black hole is a point of infinite density, called a singularity. It's what gives black holes their strong gravitational pull. A nd for decades, scientists thought singularities were all the same, s o anything that passed the event horizon would be destroyed the same way: b y being stretched and pulled like an infinitely long piece of spaghetti.

But that all changed in the early 1990s when different research teams in Canada and the US discovered a second singularity c alled a "mass inflation singularity." It still has a strong gravitational pull, b ut it would only stretch you by a finite amount, and potentially NOT kill you in the process, meaning, you might survive the trip through a black hole. More specifically, through a large, rotating black hole, which is where these types of singularities exist.

Now, astronomers obviously can't travel through a black hole yet to test this theory. In fact, the best place to test this is at the supermassive black hole in the center of our home galaxy, the Milky Way, which is 27,000 light years away. Not conveniently close to the least.

Therefore, scientists instead run computer simulations to see what would happen if we did manage to reach an isolated, rotating black hole, a nd now, for the first time, a team of scientists at UMass Dartmouth and Georgia Gwinnett College has done exactly that.

Lior Burko: " You would feel a slight increase in temperature, but it would not be a dramatic increase. It's just that you don't have enough time to respond to the very strong forces. It would just go through you too quickly."

Narrator: He added that passing through a weak singularity is like quickly running your finger through a candle flame that's 1,000 degrees Celsius. If you hold your finger in the flame long enough, you'll get burned, b ut pass your finger through quickly, and you'll barely feel a thing. Similarly, if you pass through a weak singularity with the right speed and momentum, and at the right time, you may not feel much at all.

As for what happens once you get through to the other side, n o one really knows, but Burko has his own ideas. He says one possibility is that we'd arrive at some other remote part of our galaxy, potentially light years away from any planets or stars, b ut a second, and perhaps more intriguing, possibility is that we'd arrive in a different galaxy altogether. That's if you even make it that far.

Scientists say more research is needed before we're anywhere close to successfully traveling through a black hole. But when we are ready, one of the safest passageways might be the supermassive black hole at the center of our galaxy called Sagittarius A*, and it might just be our ticket out of the Milky Way.


Hungry black hole eats faster than thought possible

Astronomers have discovered a black hole that is consuming gas from a nearby star 10 times faster than previously thought possible.

The black hole -- known as P13 -- lies on the outskirts of the galaxy NGC7793 about 12 million light years from Earth and is ingesting a weight equivalent to 100 billion billion hot dogs every minute.

The discovery was published today in the journal Nature.

International Centre for Radio Astronomy Research astronomer Dr Roberto Soria, who is based at ICRAR's Curtin University node, said that as gas falls towards a black hole it gets very hot and bright.

He said scientists first noticed P13 because it was a lot more luminous than other black holes, but it was initially assumed that it was simply bigger.

"It was generally believed the maximum speed at which a black hole could swallow gas and produce light was tightly determined by its size," Dr Soria said.

"So it made sense to assume that P13 was bigger than the ordinary, less bright black holes we see in our own galaxy, the Milky Way."

When Dr Soria and his colleagues from the University of Strasbourg measured the mass of P13 they found it was actually on the small side, despite being at least a million times brighter than the Sun. It was only then that they realised just how much material it was consuming.

"There's not really a strict limit like we thought, black holes can actually consume more gas and produce more light," Dr Soria said.

Dr Soria said P13 rotates around a supergiant 'donor' star 20 times heavier than our own Sun.

He said the scientists saw that one side of the donor star was always brighter than the other because it was illuminated by X-rays coming from near the black hole, so the star appeared brighter or fainter as it went around P13.

"This allowed us to measure the time it takes for the black hole and the donor star to rotate around each other, which is 64 days, and to model the velocity of the two objects and the shape of the orbit," Dr Soria said.

"From this, we worked out that the black hole must be less than 15 times the mass of our Sun."

Dr Soria compared P13 to small Japanese eating champion Takeru Kobayashi.

"As hotdog-eating legend Takeru Kobayashi famously showed us, size does not always matter in the world of competitive eating and even small black holes can sometimes eat gas at an exceptional rate," he said.

Dr Soria said P13 is a member of a select group of black holes known as ultraluminous X-ray sources.

"These are the champions of competitive gas eating in the Universe, capable of swallowing their donor star in less than a million years, which is a very short time on cosmic scales," he said.


Black hole: What is a black hole? Could a black hole swallow the Sun? What is inside one?

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Black hole ripped star 'asunder' in NASA find says scientist

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A black hole is an almost impossibly dense object in space, exhibiting gravitational acceleration so strong even light cannot escape. Although black holes are undoubtedly mysterious, they are simply a consequence of how gravity works &ndash when enough mass is compressed into a small enough space, the resulting object rips the very fabric of space and time, becoming what is called a singularity.

Related articles

How are black holes formed?

A stellar-mass black hole, with a mass of tens of times the mass of the Sun, can likely form in seconds, after the collapse of a massive star.

These relatively small black holes can also be made through the merger of two dense stellar remnants called neutron stars.

A neutron star can also merge with a black hole to make a bigger black hole, or two black holes can collide.

Mergers like these also make black holes quickly, and produce ripples in space-time called gravitational waves.

More mysterious are the supermassive black holes found at the centre of galaxies.

It can take less than a billion years for one to reach a very large size, but it is unknown how long it takes them to form, generally.

Black hole:The black hole named Cygnus X-1 formed when a large star caved in (Image: NASA/CXC/M.Weiss)

Could a black hole swallow the Sun?

Supermassive black hole M87 lies 50 million light-years from our Earth and is one of the largest black holes discovered so far, thought to contain a mass equal to 6.6 billion of our suns.

A black hole this huge would have a very wide event horizon &ndash the edge from which nothing can escape.

Light from our Sun takes eight minutes to travel to Earth and four hours to travel to Neptune, the solar system&rsquos most distant planet.

M87&rsquos black hole has an event horizon about four times as large as Neptune&rsquos orbit, meaning it could theoretically swallow our solar system &ndash and our Sun &ndash whole.

Related articles

If black holes are &ldquoblack&rdquo, how do we know they exist?

A black hole invisible because their powerful pulls all light into the black hole's core.

However, scientists can see the effects of its strong gravity on the surrounding stars and gases.

If a star is orbiting a certain point in space, scientists can study the star's motion to find out if it is orbiting a black hole.

When a black hole and a star are orbiting close together, high-energy light is produced, capable of being detected by sensitive scientific instruments.

A black hole's gravity can sometimes be strong enough to suck a star&rsquos outer gases and grow a disk around itself called the accretion disk.

As gas from the accretion disk spirals into the black hole, the gas heats to very high temperatures and releases measurable X-ray energy.

Black hole: The Event Horizon Telescope captures a black hole at the centre of galaxy M87 (Image: Getty)

Black hole: Sagittarius A* weighs about 4 million times the mass of the Sun (Image: X-Ray: NASA/CXC/UMass/D. Wang et al. Radio: SARAO/MeerKAT)

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Will the entire Universe eventually be swallowed by a black hole?

A region where a black hole has exerts gravitational influence is quite limited compared to the size of a galaxy.

This applies even to supermassive black holes like the one sitting in the Milky Way&rsquos centre.

This black hole has probably already devoured most or all of the stars that formed nearby and stars further out are mostly safe from being pulled in.

Since this black hole already weighs a few million times the mass of the Sun, there will only be small increases in its mass if it swallows a few more Sun-like stars.

There is consequently little danger of Earth, located 26,000 light years away from the Milky Way's black hole, being pulled in.

Future galaxy collisions will cause black holes to grow in size, for example by merging of two black holes.

But collisions will not happen indefinitely because the Universe is infinite and expanding, meaning any sort of black hole runaway effect is highly unlikely.


Mini Black Holes Easier To Make Than Thought

Creating microscopic black holes using particle accelerators requires less energy than previously thought, researchers say.

If physicists do succeed in creating black holes with such energies on Earth, the achievement could prove the existence of extra dimensions in the universe, physicists noted.

Any such black holes would pose no risk to Earth, however, scientists added.

Black holes possess gravitational fields so powerful that nothing can escape, not even light. The holes normally form when the remains of a dead star collapse under their own gravity, squeezing their mass together.

A number of theories about the universe suggest the existence of extra dimensions of reality, each folded up into sizes ranging from as tiny as a proton to as big as a fraction of a millimeter. At distances comparable to the sizes of these extra dimensions, these models suggest gravity may become far stronger than normal. As such, atom smashers could cram enough energy together to generate black holes. [5 Reasons We May Live in a Multiverse]

When the most powerful particle accelerator in the world, the Large Hadron Collider, was coming online, scientists wondered if it might become a "black hole factory," generating a black hole as often as every second. Particles zip at high speeds around the 17-mile (27 kilometer) circular atom smasher before colliding into one another to create explosive energies. At its maximum, each particle beam the collider fires packs as much energy as a 400-ton train traveling at about 120 mph (195 km/h).

How to create a black hole

So far, researchers have detected no black holes at the Large Hadron Collider. Still, theoretical interest in this possibility remains alive. Now, using supercomputers, researchers simulating collisions among particles zipping near the speed of light have shown that black holes could form at lower energies than previously thought.

This new discovery is rooted in Einstein's theory of relativity. First, through his famous equation E = mc 2 , Einstein revealed that mass and energy are related. This means the greater the energy of a particle &mdash say, the faster a particle gets accelerated in a collider &mdash the greater its mass becomes.

Next, Einstein's theory explains that mass curves the fabric of space and time, generating the phenomenon known as gravity. As particles zip along within particle colliders, they warp space-timeand can focus energy much as glass lenses focus light.

When two particles collide, each one can focus the energy of the other. If scientists use models based on classical relativity that exclude notions of extra dimensions, "one might expect black hole formation at one-third the energy" than previously expected, researcher Frans Pretorius, a theoretical physicist at Princeton University, told LiveScience.

Still, conventional physics suggest it would take a quadrillion, or a million-billion, times more energy to form a microscopic black hole than the Large Hadron Collider is capable of, so even a third of that is beyond human reach. Scenarios based on extra dimensions could have black holes form at a lower energy, "but they make no concrete predictions on what it should be," Pretorius said.

Risk-free black holes

As frightening as black holes might seem, if particle accelerators on Earth can generate them, such infinitesimal entities pose no risk to the planet.

"The one common misconception about the small black holes that may form at the Large Hadron Collider is that they would swallow the Earth," Pretorius said. "With about as much confidence as we can say anything in science, this is completely impossible."

To start with, theoretical physicist Stephen Hawking calculated all black holes should lose mass over time, giving it off as so-called Hawking radiation. Tiny black holes should shrink via such evaporation faster than they grow by gobbling up matter, dying within a fraction of a second, before they could engorge on any significant amount of matter.

Even if one assumes Hawking is wrong and that black holes are more stable than that, the tiny black holes would pose no danger. Because the microscopic black holes would be created within a particle accelerator, they should keep enough speed to escape from Earth's gravity. Moreover, if any get trapped, they are so tiny it would take each one more than the current age of the universe to destroy even a milligram of Earth matter.

"These black holes would be too small to consume any significant amount of matter," Pretorius said.

Pretorius and his colleague William East detailed their findings online March 7 in the journal Physical Review Letters.


Black hole basics

Upon first arriving at a black hole, you will most likely be struck by how utterly, completely…boring it is. The black hole itself is simply a fathomless black orb hanging out somewhere in the distance. Black holes don’t really do anything except sit there and gravitate. In fact, they’re famously easy to miss: Unless they’re actively feeding on material or coincidentally bending/blocking the view to a star in the background, you simply can’t see them. Once you know one is there, though, you can start to have some fun.

The size of the orb is determined by the black hole’s mass in a famous equation first derived by German astronomer Karl Schwarzschild, and the radius of that orb is named after him (the Schwarzschild radius). The smallest black holes have Schwarzschild radii no bigger than Manhattan the largest ones could encompass our entire Solar System.

The orb itself represents the event horizon of the black hole. This is the region where the inward pull of gravity becomes so strong that nothing, not even light, can escape. While gravitating objects are constantly pulling spacetime towards them, black holes pull so intensely that, at the event horizon, spacetime itself rushes in faster than the speed of light. If you want to escape, you have to fight against that extreme current of spacetime. Since you can’t, you’re trapped.

Beyond the weirdness of the event horizon, however, there’s nothing strange about orbiting a black hole.

That’s because gravity is just gravity. Your gravitational attraction to the Sun, for example, depends entirely on the mass of the Sun. Same for a black hole. You could replace our Sun with a one-solar-mass black hole and the orbits of the planets would be completely unperturbed (sure, all the plants would die and everything would freeze from the lack of light, but that’s a different problem).

As long as you are far enough away from the black hole itself, nothing seems out of the ordinary. You can maintain a stable orbit around a black hole for eternity if you wanted to. And thankfully for anyone wanting to take up residence there, we can calculate what “far enough away” really is. It’s called the innermost stable circular orbit (ISCO), which is pretty much exactly what the name implies. For a simple, non-rotating black hole, it’s three times the Schwarzschild radius. Within that distance, stable circular orbits are impossible, and you either have to eject yourself to the freedom of empty space or allow yourself to plummet below the event horizon.

For a more realistic situation where the black hole is rotating, the ISCO is much harder to calculate, and depends on how quickly the black hole is rotating and whether your orbit is going with the spin of the black hole (prograde) or against it (retrograde). In general, though, as long as you’re more than 10 times the Schwarzschild radius away from the black hole, you’re good.


Could anything consume a small black hole? - Astronomy

Disclaimer: This material is being kept online for historical purposes. Though accurate at the time of publication, it is no longer being updated. The page may contain broken links or outdated information, and parts may not function in current web browsers. Visit chandra.si.edu for current information.

How Black Holes Both Consume and Eject Material

January 5, 2005 ::

Chandra X-ray Image of MS 0735.6+7421
With the announcement of the most powerful eruption ever witnessed in the Universe in the galaxy cluster MS 0735.6+7421, astronomers are seeing that how supermassive black holes eject matter is just as interesting as how they consume it.

This discovery, as is often the case, leads to more questions: How can black holes eject so much energy and material? Have similar eruptions been seen, or is this some sort a cosmic loner? What does it teach us about supermassive black holes and about the galaxies where they reside?

To begin with, it sounds illogical that black holes could even generate massive eruptions. After all, hasn't it always been said that nothing, not even light, can escape a black hole? This remains true, but only when matter passes inside the "event horizon" of a black hole. This is a black hole's point of no return, when nothing is capable of escaping from its intense gravity. In other words, it's what puts the "black" in "black holes."

But, knowing the size of the feast does not identify its contents and astronomers are not sure what was swallowed by the black hole in MS 0735. One possibility is that it comes from the enormous reservoir of hot gas visible in the Chandra image. If the hot gas in the inner part of the galaxy cluster was able to cool down quickly enough, it could collapse onto the black hole in vast amounts. In this scenario, as the sinking gas fed the swirling disk around the black hole, energy released through the erupting jets would then reheat the remaining gas in the cluster. As the energy from the eruption dies down, the gas would start cooling again until this whole process repeats itself.

This scenario could help address a mystery in the life cycle of galaxies. That's because astronomers expect, without the black hole as a heat source, the hot gas near the center of the cluster should keep cooling until it eventually forms many, many new stars. The problem is that astronomers are not finding this excess of stars. Therefore, it may turn out that what these black holes eat might be the key to understanding several different fields of astrophysics: the evolution of supermassive black holes and the evolution of galaxies and the clusters they inhabit. The dining habits of black holes may influence all three of these fields.

How does the powerful eruption in MS 0735 compare with events seen in other galaxy clusters? Sometimes the Chandra images show no evidence at all for energetic events. But, recent Chandra observations have shown evidence for extremely powerful eruptions in both Hercules A and Hydra A (with masses of 170 million and 50 million Suns swallowed respectively). The size, energy and power of the cavities in MS 0735 are the largest of the three, but the others are not far behind.

The large size of these cosmic meals comes as a surprise. A recent study suggests that other large black holes have grown very little in the recent past, and that only smaller black holes are still growing quickly. These three black holes have had the ultimate super-sized meals, just when everyone was ready to believe that they are on starvation diets.

Size Comparison of MS 0735.6+7421 & Perseus Cluster
A much less powerful system of cavities is found in the Perseus cluster. This cluster earned widespread recognition because Chandra determined that the black hole is generating the deepest "note" detected in the Universe. More than just being impressive acoustically, these sound waves are more good evidence for the cycle of cooling, black hole-jet eruptions, heating of gas, followed by more cooling, etc.

The cavities in Perseus required large amounts of energy to form, but they are puny compared to the ones in MS 0735. The cavities in MS 0735 are over 10 times larger in physical size and they are expected to get bigger, unlike with Perseus. Even more impressively, about 250 times more energy was required to generate the MS 0735 cavities. All of this is not to say that the supermassive black hole in Perseus is a wimp, just that it has a very different diet: a lot of small, evenly spaced meals instead of occasional feasts.

An obvious follow-up question arises: what do we know about the sound in MS 0735? The sound waves in Perseus are generated when the expanding cavities slow down below the speed of sound and push against the cluster gas. In MS 0735, the cavities are still growing at supersonic speeds, despite their colossal size.

Animation of Eruption from Supermassive Black Hole
Sound waves may eventually be generated when the cavities slow down. If the eruption near the supermassive black hole repeated itself then the resulting "note" would potentially be far deeper than the one in Perseus. However, no tell-tale ripples are visible in the Chandra image.

Because the cavities are so large in MS 0735, they extend almost to the edge of the observed extent of the hot gas cloud in this cluster. Outside the cavities the X-rays are so faint that even extremely long observations with Chandra might never detect any ripples due to sound waves. In a sense the eruption may simply be too powerful to allow a detection of MS 0735's note.