Largest Black Hole Measured

porkpickle tips us to a BBC article on the quasar OJ287, a binary object containing largest black hole yet discovered, weighing in at 18 billion times the mass of Sol. Researchers were able to estimate its mass due to the presence of a smaller black hole in orbit around it. When the smaller companion's orbit intersects OJ287's accretion disk, once every 12 years, it triggers a burst of radiation that was detected by the Spitzer Space Telescope. More detail and a diagram are available on the Turku University site.

that's a lot

[ILuvRamen]

I'll save you all the time of googling this cuz I know you wanna know too. There's 200-400 billion stars in the milky way for example but most are bigger than our sun I think. So 18 billion solar masses is A LOT of stars to suck up in one galaxy. Geeze the think probably looks like a big donut by now.

Re:that's a lot

[Anonymous Coward]

My googling says its even more impressive (http://curious.astro.cornell.edu/question.php?number=31) 100 billion stars in the Milky Way and most are smaller than the sun, so 18 billion makes it very greedy indeed!

Re:eh? I don't get it?

[AmaDaden]

It think they are not 100% sure about the whole "a black hole is a singularity" thing.

quantum mechanics .... does not allow objects to have zero size--so quantum mechanics says the center of a black hole is not a singularity but just a very large mass compressed into the smallest possible volume.

from http://en.wikipedia.org/wiki/Black_hole [wikipedia.org]

Re:eh? I don't get it?

[pclminion]

A black hole has an event horizon. This horizon has a very well-defined size.

Re:so is Rosie orbiting Oprah, or vice versa?

[ImYY4U]

oops again, Rosie's not black!

Re:eh? I don't get it?

[moderatorrater]

The event horizon is often considered the size of a black hole since nothing could ever leave that space.

Re:The Mass of a Hole?

[Mantaar]

A "black hole" is not a hole like in your cheese - it's just a very sloppy term for an actual object with a higher-than-usual mass. So high, that it swallows all the light it might emit otherwise and thus appears to be totally black. Due to it's (assumed) look it's been dubbed a "black hole", though it's not really a hole - and it probably wouldn't be too dark around it, too...

The Hawking Evaporation or just random stuff that's falling into it (gas, particles) should emit a considerable amount of light. Within the Event Horizon, of course, everything's pitch dark. So, the thing should actually look like a Space Donut.

Re:Ask slashdot

[ArcherB]

Is there a theoretical limit to the size of a black hole?

While I can't give you numbers since I'm going from memory, but there used to be a theoretical limit to black hole size. This was before "Super Massive Black Holes" were discovered in the center of every galaxy. Super Massive Black Holes are much more massive than the previous theoretical limit and were thought to be impossible so many astronomers were claiming that such a thing was couldn't exist while others were saying, "Oh yeah? Then why don't you put down the chalk, professor, and come down to my observatory and tell me what that big-ass black gravity thing is in the middle of our galaxy!" (Of course, they couldn't really see it, but you get the point)

I think astronomers are reluctant to guess at a size limit now as they don't want another discovery to make them look like asses.

gridwars

[doti]

This story makes me want to play gridwars2 [marune.de] again.

And again, and again...

That's incredible!

[renfrow]

Using this illustration [astro.utu.fi] and my trusty piece of paper straight edge, I estimate the long axis of the orbit to be 21000 AU and the minor axis to be 16000 AU. Using Ramunjan's Approximation [wikipedia.org] for the circumference of the elliptical orbit and converting to light years [glyphweb.com], I guesstimate the circumference of the orbit to be ~1.99 (call it 2) light years.

For a 12 year orbital period this means that the orbiting black hole is AVERAGING 1/6c (~49965km/sec, call it 50k km/sec)... meaning at periquaserion it's really booking! Much faster than The Dash!

Tom.

Re:Tag as Sun!Sol

[AbsoluteXyro]

We're pretty used to referring to Sol as "the sun" but the truth is, a sun is a thing and there are many of them. It is silly to call ours THE sun, because it clearly isn't. In actually, it is ONE OF the suns. Sol is our sun's Latin name. Similarly, Luna is our moon's Latin name.

Re:eh? I don't get it?

[BobGod8]

Actually it's way more complicated than that. Only non-rotating black holes could ever truly be point masses. Any angular momentum creates complicated tidal effects near the center, resulting in a non-point-mass. Carried further, the "singularity" expands until the point where it would effectively reach the event horizon itself, resulting in a naked singularity, which some calculations have shown can have actual size. Adding further rotation will (to a point), actually change the size of the "singularity". Of course, this is all moot, since that's not at all what the article was talking about, but that's my .02$.

Re:Ask slashdot

[Ambitwistor]

While I can't give you numbers since I'm going from memory, but there used to be a theoretical limit to black hole size.

There has never been a theoretical limit to the size of a generic black hole. (Technically, the observable universe could be in a giant black hole.) But back when people thought the only way a black hole could form was from the collapse of a single star, there was a practical limit on the size of an astrophysical black hole: if it forms from stellar collapse, it can't be more massive than the most massive stars. Everyone recognized that black holes can get larger by swallowing more mass, but it was a long time before people seriously considered the possibility of supermassive black holes actually existing.

Re:Question about gravity

[Ambitwistor]

Other people have answered your question (radiation cannot escape from inside the horizon, but it can still generate a static external field), but here [ucr.edu] is a FAQ with more detail, including the quantum picture.

Re:orbiting blackholes?

[Ambitwistor]

It is highly unlikely that a black hole would have planets orbiting it, as the planets would have insufficient mass to keep from simply falling in to the black hole,

If the Sun collapsed into a black hole, its gravitational pull on the Earth wouldn't change.

that is to say the overwhelming mass of the black hole would place the barycenter of the black hole and any accompanying planet well inside the event horizon,

Maybe you're talking about supermassive black holes, but if you're talking about black holes in solar systems, formed from collapsed stars, that's not true. A black hole is not "overwhelmingly massive"; it generally has less mass than the star it formed from, since some mass may be lost during the collapse. (Unless it gains a lot more later ...)

Furthermore, as the Earth-Sun barycenter is well outside the Sun's Schwarzschild radius, it would be outside the event horizon of a solar-mass black hole, too. Not that the location of the barycenter even matters to the stability of the orbit.

There are exoplanets — the first discovered, actually — known to orbit neutron stars, which are only 10-20 km in radius. There's no reason why planets couldn't orbit black holes too.

Re:Ask slashdot

[Cassini2]

The Eddington limit [wikipedia.org] appears to limit the size of a star. At one point in time, it was thought that black holes formed from the collapse of stars. Later on, it was concluded that supermassive black holes are very good at feeding on neighboring stars, and thus supermassive black holes could form. The Wikipedia page on Black Hole Parameters [wikipedia.org] has an explanation.

Re:orbiting blackholes?

[Ambitwistor]

The existence of a single solar mass black hole has nothing to do with any of the facts I stated. They hold no matter what the mass of the black hole, so long as it's not comparable in size to the planet's orbit itself.

(FYI, the smallest known black hole candidates are about 3 solar masses, with a size of about 18 km in diameter, i.e., about half the size of a neutron star.)

Re:eh? I don't get it?

[Anonymous Coward]

That's misleading, and I'm guessing you don't really understand what you're describing. A rotating black hole (aka every black hole, to some extent), is still a singularity (no need for quotation marks, it still has zero volume) despite not being a point. It's a ring with zero cross-sectional area, sort of like an infinitely thin thread arranged in a circle.

Furthermore, this thread is based on quibbling over semantics without really understanding what the author quite validly meant. The "black hole" aspect of a singularity is a description of the effects of its event horizon, which of course scales with mass. A more massive black hole is by definition larger then a less massive black hole. Someone mod this up so this misunderstanding can be cleared up for more people.

Re:Question about gravity

[Ambitwistor]

One hypothesis of gravity is that it is an exchange of 'gravitons'. If this hypothesis is indeed correct, then it does indeed make sense to ask how these gravitons can escape a black hole. And I don't know the answer to that.

Static gravitational fields are mediated by virtual gravitons, which can travel at any speed, including faster than light. However, you cannot use them to transmit information, i.e., changes in the field from inside the horizon.

With this image, it is spacetime that bends so there's no meaningful question for how gravity 'escapes' from it.

Right. Classically you can see that the exterior field does not depend on the interior field, and that gravitational radiation generated inside the hole can't get out.

Re:eh? I don't get it?

[jgarra23]

How large can a singularity be?

I mean, if they used the word "massive" I'd get it. But large?

I believe they are measuring the event horizon, not the singularity.

Re:Question about gravity

[Ambitwistor]

If I used my magic obliterator to magically make the sun disappear, would Earth go flying off into space at the same moment or would it continue to orbit the missing sun for the 8 minutes it would take the last rays of light to reach us?

The latter.

This is where they say gravitons come in as a particle that conveys gravity which doesn't make any sense.

Why doesn't it make any sense? Photons are particles which convey electric and magnetic forces, do you have a problem with them too?

Anyway, you don't need to appeal to graviton particles to answer the above question. Even in classical general relativity, the answer is still "8 minutes later", since that's how long for gravitational waves of spacetime curvature, traveling at the speed of light, take to reach the Earth.

Re:that's a lot

[Lijemo]

I'll save you all the time of googling this cuz I know you wanna know too. There's 200-400 billion stars in the milky way for example but most are bigger than our sun I think. So 18 billion solar masses is A LOT of stars to suck up in one galaxy. Geeze the think probably looks like a big donut by now.

Actually, my understanding is that the most common stars in the galaxy are Red Dwarfs, and thus smaller than our sun. (Yup, NASA confirms: http://planetquest.jpl.nasa.gov/glossary/red_dwarf.html [nasa.gov])

Re:Tag as Sun!Sol

[illogique]

why many suns? it's more like they are many stars and our star is name the sun!
similarly, the moon is the name of the Earth natural satellite