Riddle of cannibal black hole pairs solved ... nearly: Astroboffins explain all to El Reg

Astrophysicists are one step closer to understanding how pairs of merging black holes form in the far reaches of the cosmos. The dramatic melding of two black holes produced the first gravitational waves detected by the Earth-based Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). While these waves confirmed …

[Pen-y-gors]

Cosmic palaeontologist?

I love the concept!

But... it's rather rare for two such terrifying voids to smash into each other. -surely in an almost infinite universe, very rare events must be happening all the time?

[DropBear]

Re: Cosmic palaeontologist?

That may well be, but "signal strength" is still subject to distance to source, and as astonishingly sensitive as our "receiver" is, it's still barely picking it up - so we kinda need the event to be rather closer than infinity if we want a hope to detect it...

[Nick Kew]

Re: Cosmic palaeontologist?

almost infinite

Oh dear. Where to start?

How about "almost infinite is 0.00000000000000000000000000000% of infinite". That matters when it comes to probabilities.

Rare events and big spaces need quantifying to come up with meaningful conclusions.

[allthecoolshortnamesweretaken]

Re: Cosmic palaeontologist?

This calls for a re-make of Jurassic Park, only this time with black holes instead of dinosaurs.

[I am the liquor]

surely in an almost infinite universe, very rare events must be happening all the time?

You know how it is, a million-to-one chance will come up nine times out of ten.

[crimelovingfunster]

Re: surely in an almost infinite universe, very rare events must be happening all the time?

When did you last count to a million? I think you'll find a million to one chance happens six times out of ten...

[Loyal Commenter]

Re: Cosmic palaeontologist?

The universe may or may not be infinite. However, its age (since the big bang) is not infinite, and neither is the speed of light, meaning that the furthest we can actually see is a smidge under 14 billion light years.

[xehpuk]

Re: Cosmic palaeontologist?

The visible universe is much larger than its age. It explained by the expansion/inflation somehow.

[Alan Brown]

Re: Cosmic palaeontologist?

"surely in an almost infinite universe"

1: It's not infinite (the multiverse might be but our universe isn't)

2: These events are observed happening billions of lightyears away, therefore billions of years ago.

3: The universe was a lot smaller then, therefore more dense.

It looks like a lot of the supermassive blackhole formation which occurred happened in the early stages of the universe due to more gas around to form stars and it being less disturbed by starlight pressure, etc. (Oversimplifying massively)

:-)

[Chairo]

So that gravity wave came from ...

stellar black holes. I wonder what would be the gravity wave resulting of the merger of two supermassive black holes. Must be spectacular.

[A Non e-mouse]

If the two black holes start out as stars orbiting one another, wouldn't the first star to collapse into a black hole either destroy or suck in the second star?

[Tom 7]

re first star to collapse into

No - the gravitational field outside the event horizon does not change when a black hole forms. If fact you cant actually tell when a black hole forms - its normally associated with some form of supernova event and we assume a black hole has formed but - what with it being out of our purview and all that - we just have to assume there is one there.

[Justicesays]

Re: re first star to collapse into

In fact, normally the gravitational pull would become rather less overall, what with all the gas being blown off by the supernova event (in the case of mostly hydrogen/helium stars).

[Anonymous Coward]

"If the two black holes start out as stars orbiting one another, wouldn't the first star to collapse into a black hole either destroy or suck in the second star?"

As Tom 7 points out, the gravitational gradient outside the Event Horizon wouldn't change just as a result of collapsing and as Justicesays says, the collapsing star would lose mass, so, from the gravitational point of view, the other star would see a reduction in the gravitational field strength. Moreover, that out-flowing mass from the collapsing star would tend to push the other star further away.

I'd expect that the majority of BHs will have formed from White Dwarves or Neutron stars though, via accretion, than directly from massive stars, simply because there're a lot more WDs & NSs around than there are massive stars.

[Brewster's Angle Grinder]

I'd expect that the majority of BHs will have formed from White Dwarves or Neutron stars though, via accretion, than directly from massive stars, simply because there're a lot more WDs & NSs around than there are massive stars.

Material accreted onto a white dwarf generally produces a nova, as the material hits the surface and ignites. You can still up the mass. But if you manage to accrete enough ash, then it will blow up. (Type Ia supernova.)

Material falling onto a neutron should burn in the disk before it ever reaches the star. I'm not quite clear if you can nevertheless increase their mass.

But the vast majority of non-primordial black holes are formed by the core collapse of stars, with some formed by the merging or neutron stars.

[You aint sin me, roit]

So,,,

We have two mutually orbiting stars.

The first goes nova, producing a black hole at its core, blowing off considerable amounts of matter, but let's say it has mass X which wasn't too different from the original star.

The second probably has a bit of a wobble (possibly an understatement) and goes nova too, producing another black hole, let's say it has a mass Y.

The mass of the black holes isn't that different from the original stars, and they are in essentially their same mutual orbit. Suppose for some reason they slowly circle closer to each other, eventually spiralling in to collision...

How is that different from star one of mass X spiralling in to star two of mass Y?

Why do we need them to be black holes? Wouldn't two equally massive stars cause the same gravity waves that were detected?

[Francis Boyle]

Think of it like this:

You jump as high as you can. While you're in the air the Earth collapses into a black hole. Your landing is now going to be a bit harder than you expected. Well, it's not like that, as a famous black hole wrangler once said. But still, it's a bit like that, only more so, since you have two objects that have mass but aren't made of matter, so they can't actually collide but that doesn't stop them combining. . .

Yes, black holes are weird.

[Meph]

"How is that different from star one of mass X spiralling in to star two of mass Y?"

Armchair enthusiast reporting, so suitable disclaimer attached.

One would suspect that even though the nominal mass of both objects is broadly the same, the acceleration towards impact (once at least one of the singularities crosses the event horizon of the other) is likely to be significantly higher than if two stars of comparable mass decided to bump in to each other.

I'm only guessing, but I know enough to know that the speed (velocity?) of the impact contributes to the overall outcome at least as much as the size of the objects.

[Paul Smith]

“A paleontologist, who has never seen a living dinosaur, can figure out how the dinosaur looked and lived from its skeletal remains. In a similar way, we can analyze the mergers of black holes, and use these observations to figure out how those stars interacted during their brief but intense lives.”

Tosh and fiddlesticks! Paleontologists have come up with the the most incredibly dumb and far stretched explanations to fit the bones they found and have often been very slow to admit, let alone correct their mistakes. The worlds favourite dinosaur after the T-Rex? The Brontosaurus? It doesn't exist!

[allthecoolshortnamesweretaken]

But, but - that would mean that Anne Elk was wrong and her theory about Brontosauruses is false... surely not?

[Loyal Commenter]

Fact Check

Laydeez and gentlemen, I give you, The Brontosaurus.

[Paul Smith]

Re: Check your "Fact Check"

From the same wiki page [quote]Palaeontologist Donald Prothero criticized the mass media reaction to this study as superficial and premature, concluding:

Until someone has convincingly addressed the issue, I'm going to put "Brontosaurus" in quotes and not follow the latest media fad, nor will I overrule Riggs (1903) and put the name in my books as a valid genus.[29][/quote]

What you know of as a "Brontosaurus" is just a sub-type of Apatosaurus, and any drawings or models you have seen probably have the wrong head on it.

[Alan Brown]

"A paleontologist, who has never seen a living dinosaur"

Apart from the ones with feathers :-)

[Any mouse Cow turd]

Where's the Editor?

"Their results were published Wednesday in Nature Communications".

- Come on chaps, the results were published ON Wednesday. Please sort out your grammar.

[Joerg]

They solved nothing. Just fairy tales.

They solved nothing. Just fairy tales.

They don't have a clue of what they are talking about. Unless they got spaceships to go in the area and see with their own eyes what is there then it is just fairy tales. They even officially don't have any probe there to see a damn thing.

[LionelB]

Re: They solved nothing. Just fairy tales.

Are you sure your arse is different from your elbow? Better send a probe up there.

You don't really get science, do you?

[Anonymous Coward]

ermm .... to be fair

The g-wave data is giving you a handful of scalar values - the massas of the 2 BH. Plus... dunno... angular momentum and spins,, charge ?? And the frequecy of hese events, over the years, once we get more hits.

Constructing a model of the stellar formation and relative motions will be vastly underconstrained .. i.e. they could come up with any array of scenarios matching a few experimentally known parameters. A la Popper - how robustly will their theory be tested. Maybe predicting the . But typically, papers of this type will be followed by more papers of this type, all tweaked as the g-wave data trickles though. So, no hard target prediction for robust testing.

[Patrician]

Re: They solved nothing. Just fairy tales.

So you have no understanding of how science works?

[Rich 11]

Re: They solved nothing. Just fairy tales.

Unless they got spaceships to go in the area and see with their own eyes what is there then it is just fairy tales.

I expect you're also one of those people who refuses to believe that any historical event took place unless you were there to see it with your own eyes.

[LionelB]

Re: They solved nothing. Just fairy tales.

I expect you're also one of those people who refuses to believe that any historical event took place unless you were there to see it with your own eyes.

... while trees fall silently in deserted forests ...

(Couldn't be arsed to go full haiku.)

[Loyal Commenter]

Re: They solved nothing. Just fairy tales.

It must be wonderful to exist in a world where science, mathematics, and rational deduction play no part, and where 1+1=potato.

[G R Goslin]

What???

Saying "stars were probably formed almost completely from hydrogen and helium." is a bit pointless. That goes for all stars, ours included. The proportion of elements other than hydrogen and helium is very small. . The other elements are only significant to us, because virtually all the hydrogen and helium has gone from our environment

[Rich 11]

Re: What???

Saying "stars were probably formed almost completely from hydrogen and helium." is a bit pointless.

Not really. Stellar metallicity has an effect on stellar evolution.

[Alan Brown]

Re: What???

"Stellar metallicity has an effect on stellar evolution."

Given that most of these supermassive babies seem to have formed in the first couple of billion years of the universe's eveolution it's unlikely there would be much metal in the gas clouds that they formed from.

Some trace amounts of lithium perhaps, but that's about all.

[Alistair]

Upcoming events on the horizon.

"it's rather rare for two such terrifying voids to smash into each other"

I can think of a couple of terrifying voids that are about to at least run into one another. However, I doubt they'll be giving off gravitational waves. I suspect that they will just be giving off creepy vibes.

Having spent some time discussing solar evolution with the youngest (He's a 'fact based' bedtime story type. We've read all sorts of science books ...) we made it to 'what are black holes' and one of the first questions he asked was 'what would happen if two really big ones could grab each other'. There is a rather well detailed PHD on this .... scary thing was he found it on the interwebz before I did. And managed to read most of it (although the maths in the proofs are still way beyond him <and me too in some cases>, he now has a reason to work at math) just needing some translation for the more exotic language elements.

I'm inclined to suggest that if this is what it took to trigger something we could detect, then we still have a long way to go with G wave detection equipment. I suspect (personally) that we'll have to redefine a couple of cosmological constants *just a wee bit* at some point and suddenly some weird affect will fall out that will enhance what we already know and will explain (Gravity/Dark matter/Dark Energy) gaps. This is the way these things have happened in the past, and we'll find the bit we're missing sometime. yay for some progress to add to the pile.