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Have astronomers found a new class of tiny black hole?
Black holes are the cosmic champions of hide-and-seek. Einstein predicted they existed in 1916, but it took over 100 years before a telescope as wide as the world snapped the first picture of a black hole. They're elusive beasts, avoiding detection because they swallow up light. Even so, astronomers can see the tell-tale signs of black holes in the universe by studying different forms of radiation, like X-rays. So far, that's worked -- and a huge number of black holes have been discovered by looking for these signs.
However, an entirely new detection method, pioneered by researchers at The Ohio State University, suggests there may be a whole population of black holes we've been missing.
The findings, published in the journal Science on Nov. 1, detail the discovery of a black hole orbiting the giant star 2MASS J05215658+4359220 (J05215658, for short) using data from Earth-based telescopes and Gaia satellite observations. The team shows J05215658 is being orbited by a massive unseen companion -- and they suspect it might be an entirely new class of black holes.
A noninteracting low-mass black hole–giant star binary system, Science (DOI: 10.1126/science.aau4005)
(Score: 5, Informative) by Immerman on Monday November 04 2019, @02:41PM (16 children)
The article makes it sound like there's something unusual or at least unexpected about a black-hole binary system where the black hole isn't devouring material from the star, but for the life of me I can't think of why that would be. I mean, how many binary star systems do we see out there where the stars are exchanging significant amounts of material? Very few, percentage wise. And a black hole will be significantly less massive than the star it used to be, which means it will be drawing in significantly less material at a given distance.
It seems like every discussion f black holes assumes that they're some sort of all-devouring gravitational monsters - which completely overlooks the fact that, mergers notwithstanding, they're less gravitationally powerful than the stars that birthed them at a given distance - the extreme gravity only starts to comes into play when you're already so close to the center of mass that you would have been completely inside the old star. If the sun suddenly collapsed into a black hole, the Earth wouldn't be devoured - at worst it would continue in its orbit unaffected (aside from freezing), more likely the sun would lose a whole lot mass in the collapse/explosion, and the Earth would move further away as a result.(well, assuming it wasn't vaporized by the blast)
(Score: 2) by RS3 on Monday November 04 2019, @02:47PM (1 child)
Maybe they're dark matter, feeding on dark matter?
(Score: 3, Interesting) by Immerman on Monday November 04 2019, @08:25PM
You joke (I hope), but tiny black holes are actually one of the candidates for dark matter that haven't been completely ruled out yet.
Assuming dark matter is in fact some exotic non-interacting material though - it would be almost impossible to create a black hole out of the stuff. It just can't clump together enough to form dense objects like rocks, much less black holes. When two bits of normal matter rush towards each other, they collide, both slowing down while the excess kinetic energy is converted to heat. That's how stars and planets form - repeated collisions slow down clouds of dust and gas until they coalesce into a single object.
Dark matter can't do that - collisions are an electromagnetic interaction, and dark matter doesn't respond to electromagnetism. If it did, it wouldn't be invisible, we would at least be able to see it absorbing or scattering light that passes through it, as we can with clouds of dust or gas. Two dark matter particles rush towards each other, they're going to pass right through each other without interacting and continue on there merry way to distant parts unknown. Unless there's some other fundamental forces at work that we've never had any hint of because they only apply to dark matter - and there's precious little theoretical basis to assume that.
(Score: 2) by ikanreed on Monday November 04 2019, @03:08PM
Newly observed is new in a way.
(Score: 0) by Anonymous Coward on Monday November 04 2019, @03:27PM
It was unexpected to find these intermediate masses because they have to merge with other black holes or swallow stars to do it. Repeatedly, when such encounters should be rare.
(Score: 3, Interesting) by bzipitidoo on Monday November 04 2019, @04:28PM (4 children)
I have read that there's a gap in our knowledge between the largest known neutron stars, at approximately 2.5 to 3 solar masses, and the smallest known black holes, at approximately 5 solar masses. What kind of object is in between? A black hole, or a neutron star? Or could it be that there's some instability at that particular mass and density, and ther eare no such objects?
So this may be it, these extremely compact objects of about 4 solar masses do exist, and they are black holes, not neutron stars. I would also guess theory predicted it. It also makes sense that it is a black hole, because they are so difficult to observe, and that's why we haven't seen anything. Of course, until an example is found, one can never be completely sure. If the headline is an exaggeration, it's not by much.
(Score: 3, Informative) by HiThere on Monday November 04 2019, @05:20PM
Neutron stars are also quite difficult to observe, when they don't have an axis that causes their radio signals to periodically sweep across our observation. And that means almost all of them. And the older ones are expected to be pretty quiet anyway.
So the difficulty of observation doesn't allow one to choose between black hole and neutron star. The choice has to have been either on theoretical grounds, or on "what will grab the headlines". (I do notice that even in the summary they qualify with the term "might".)
My wild guess would be neutron stars, but perhaps they've got grounds to thing a neutron star couldn't be that heavy.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 3, Informative) by Immerman on Monday November 04 2019, @09:05PM (2 children)
I believe the "2.5 solar mass limit" on neutron stars is a theoretical limit - we know roughly how dense neutronium must be, and we know how strong the weak nuclear forces is. Combine the two, and you get an upper mass limit before the weak nuclear force is no longer strong enough to keep a body from collapsing under its own gravity.
There might be some possibility for quark stars above that limit though - the theory is still pretty crude as to how exactly the physics would work on a star-sized quantum object.
Of course, we're still not 100% certain that black holes actually exist either. As one example, a slight reformulation of Relativity to treat the energy in gravitational fields the same as all other energy fields (which generate their own gravitational field based on the field's energy density) would mean that gravity well would asymptotically approach a maximum "depth", leveling out a little before an event horizon could form due to the gravitational "pullback" from the intense energy stored in the surrounding gravitational field, no matter how much material you put in one place. In which case it wouldn't matter that there are no known forces strong enough to resist gravity, because gravity almost disappears when very close to an ultra-dense object. And you'd have some sort of degenerate-matter soup sloshing around on the almost-flat bottom of an extremely deep gravity well. If the resulting "dark hole" were massive enough it might even be possible for exotic "normal" matter to exist at the bottom*
*One of the curious properties of a black hole, is that its effective density (mass divided by the volume enclosed within the event horizon) shrinks rapidly with mass - for a mass M the density is about (1.8x10^16 g/cm3) x (Msun / M)^2 (according to a quick search). A huge number for "normal" black holes, but something massive like Saggitarius A* at the center of our galaxy, at 2.6 million solar masses that falls to about 2.6kg/cm^3. Still about 200x denser than lead, but 10^14x less dense than neutronium. Assuming that gravity actually plateaus at least a little outside where the event horizon would form, the average density of the material at the bottom would be no greater than that.
(Score: 2) by FatPhil on Monday November 04 2019, @11:39PM (1 child)
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 3, Interesting) by Immerman on Tuesday November 05 2019, @12:47AM
That is true. Personally I suspect the gulf has something to do with more massive black holes having an easier time stealing material from passing star systems. If we can only see them when they're eating, and have no reason to believe they eat regularly, then it would stand to reason that the black holes we can see will overwhelmingly be the ones that are big enough to have an easy time capturing material from other star systems when they pass nearby. And even then it'll only be captured in orbit - it probably needs several planets to stir things up enough for debris to end up on a collision course with the tiny pinprick of a black hole a few miles across so that it can be devoured.
(Score: 3, Interesting) by FatPhil on Monday November 04 2019, @11:18PM (6 children)
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 4, Interesting) by Immerman on Tuesday November 05 2019, @12:32AM (2 children)
The climate change would be *everything* to do with what's there at the focus - or more specifically, what's suddenly NOT there. Namely, a massive fusion furnace flooding our planet with warming radiation. :-D
They can accumulate new material, but they will do so at a much slower rate than they did as a star, since interstellar debris can slingshot much closer to the center of mass without hitting anything before eternally departing on a hyperbolic "orbit" (and non-interstellar debris was probably only a few percent of the original mass of the star). Of course, as a star it was also belching out material at a phenomenal rate, which typically more than counteracts any net accumulation. Still, in order to be devoured by a black hole, you first have to hit it - and in turning into a black hole our sun would shrink from, 865,000 miles across, to only about 6, shrinking the area of the "bullseye" (and thus the impact rate) by a factor of about 20 billion. And orbital dynamics make actually hitting the sun already an extremely unlikely event.
I would fully expect the vast majority of black holes to be almost completely inert - it's only collisions with interstellar gas clouds and other star systems that would ever feed them more than a tiny trickle of material - and even those are unlikley to feed it much - a sun-mass black hole passing through our solar system would devastate the orbits of the planets, but it's very unlikely that it would manage to capture any material that didn't lie *directly* within that 6-mile wide path. Everything else would slingshot around it - quite possibly being torn apart into gravel and launched out of our solar system, but almost certainly not being captured in orbit around the black hole, since it all started out with escape velocity from the black hole's perspective.
(Score: 2) by FatPhil on Tuesday November 05 2019, @12:59AM (1 child)
regarding slingshotting - there will also be increased spaghettification from such closer approaches, so not all of it will be able to fly by hyperbolically, comets are seemingly quite crumbly, for example.
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 2) by FatPhil on Tuesday November 05 2019, @01:18AM
was being nagged to stop SN-ing and turn off the monitor at the time...
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 2) by Reziac on Tuesday November 05 2019, @02:41AM (2 children)
Well, our orbit might wobble less, because a teeny little black hole might not slosh around so much as the sun's innards do.
And there is no Alkibiades to come back and save us from ourselves.
(Score: 2) by FatPhil on Tuesday November 05 2019, @09:47AM
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 2) by takyon on Tuesday November 05 2019, @10:00AM
Don't forget the even greater effect in the solar system: radiation pressure [wikipedia.org].
The difference would be much greater for smaller objects and those closer to the Sun, and "comet" trajectories would be affected even more due to the newfound lack of outgassing.
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