Gravitational waves eject black hole from galaxy

https://www.nasa.gov/feature/goddard/2017/gravitational-wave-kicks-monster-black-hole-out-of-galactic-core/

by anigbrowl • 9 years ago

209 56 9 years ago

jarmitage• 9 years ago

What happens to a black hole-less galaxy?

analog31• 9 years ago

My guess is that it gains a new black hole as stuff coalesces at the center. This hunch comes from not much more than knowing what Newton predicted, which is that any system with more than two bodies is unstable, with outcomes that include ejecting a body, or two bodies colliding. The formation of stars in the first place is the result of such coalescence, so it's not unthinkable that the same thing will happen at the center of a galaxy full of stars.

M_Grey2• 9 years ago

Truthfully, most if not all large galaxies probably do have central supermassive black holes. Dwarf galaxies might not, but they're more like drifting clouds (and tend to be gobbled up by larger galaxies over time). It's just that there is no way to say with certainty that a BH is in the center of a galaxy when it isn't actively feeding, unless it's close enough for us to resolve the motions of individual stars in the core.

Remember also that there are large swaths of the sky we basically cannot observe in the 'Zone of Avoidance'.

sandworm1012• 9 years ago

If a galaxy is in a position to be lensing, or we can otherwise get a grip on its mass, then we can guess the BH if it isnt emitting enough. If the galaxy is dim but massive, black holes are likely.

gliese1337• 9 years ago

Not much. Relative to a star, central supermassive black holes are, well, super-massive. But relative to the total mass of the galaxy, or even just the core region, they aren't that big. The rest of the galaxy will just keep orbiting around its center of gravity, regardless of whether or not there happens to be a black hole there.

saagarjha3• 9 years ago

In what kind of galaxy is a 1 billion solar mass black hole not a significant portion of the mass?

idlewords2• 9 years ago

Made fun of by the other galaxies

gjm11• 9 years ago

Actual headline has "... out of galactic core". The black hole is still in the galaxy, though perhaps in 20 million years it will have escaped.

The involvement of gravitational waves is conjecture and the evidence for it is highly indirect (it all sounds pretty plausible to me, but what do I know?).

yodon2• 9 years ago

Gravitational waves are among the most difficult physical phenomena to detect directly, because of the very small size of the effects involved and the huge masses required to cause those small effects (one commonly encounters numbers like 10^-51 when doing gravitational wave calculations). The original experimental demonstration of gravitational waves was from analyzing the change in rotational frequency over time of an orbiting binary pulsar and computing that the energy loss in the system was precisely matched by the general relativistic prediction of energy radiated away in gravitational waves. The importance of this work was recognized with the Nobel Prize in Physics [0].

[0] http://www.astro.cardiff.ac.uk/research/gravity/tutorial/?pa...

ab5tract2• 9 years ago

Can someone please explain why such waves that supposedly have minimal/hard-to-detect effects are somehow valid explanations for pushing around black holes?

Meanwhile, electrical forces are clearly powerful and yet still neglected in the mainstream.

yodon2• 9 years ago

Amazing - the calculations in the article suggest gravitational waves emitted by a pair of colliding black holes can have sufficient energy to eject the combined object from the potential well of the galaxy.

M_Grey2• 9 years ago

It's a scale that's hard to grapple with, when the energy being carried away in those waves is far more than the mass of the Sun.

dogma11382• 9 years ago

This make me wonder if the galactic void is full of ejected black holes which will be nearly undetectable since the X-ray radiation comes from the accretion disk and the matter falling into the black hole. This mechanism could be potentially be another candidate for "dark matter".

jcarreiro• 9 years ago

This is a good observation, but gravitational lensing surveys have all but eliminated massive compact objects as a potential source of dark matter; see for example https://www.ncbi.nlm.nih.gov/pubmed/17359015.

saagarjha3• 9 years ago

Unrelated, but why is a paper on astrophysics on the NIH website?

dogma11382• 9 years ago

Gravitational lensing surveys coverage is pretty darn small so far it's also might not be appearant on the scales we are talking about there will need to be a pretty lucky alignment of a galaxy and a black hole given the space and relative size of both objects and the noticeable lense diameter I'm not sure that intergalactic lensing will be detectable as intragalactic ones which also are pretty rare.

sandworm1012• 9 years ago

Not undetectable. There is still gravity lensing. And black holes (the small ones) are still stars, or at least mass/matter that once was. That material still has a place in the equations for the evolution of stars in galaxies.

kakarot2• 9 years ago

Dark matter is an answer to a universal expansion problem that a small population of vigilante black holes couldn't really account for.

euyyn• 9 years ago

The merit of that hypothesis notwithstanding, you're confusing dark matter with dark energy.

yiyus• 9 years ago

It's pretty cool.

alnitak• 9 years ago

Imagine you are an Earth-level (0.7 on Kardashev's scale) civilisation on the path of this monster.

In fact, let's just imagine it were to happen in the Milky Way. What happens to us then?

tonmoy• 9 years ago

Seems like a VERY VERY low possibility. Even in case of two galaxies colliding, with 100s of billions of stars coming close to each other, the individual stars would barely feel a thing. http://curious.astro.cornell.edu/about-us/96-the-universe/ga...

flashman2• 9 years ago

(Napkin math time.) A black hole with 1 billion solar masses would pull Earth with a force equal to the Sun from half a light year away. It does the same thing to Uranus from a distance of 9.6 light years. It would have enough influence to disturb those orbits from much further away.

So if something similar entered our galactic neighbourhood, we would notice changes in the proper motion of stars closer to it, discrepancies between the planets' predicted and actual positions, and (possibly before anything else) predictable errors in GPS timing (since this is probably the most commonly-encountered system depending on accurate knowledge of speed, time and gravity).

grigjd33• 9 years ago

While the point you are aiming for is correct, your "napkin math" is wrong and ignores the equivalence principle.

tlogan• 9 years ago

I wonder whether this even also displaced dark matter.

And if both dark matter and black hole are displaced will galaxy just disintegrate?

strainer2• 9 years ago

This has curious similarity with errors which can appear in basic n-body simulations, where excessively close interactions can break orbits by throwing bodies too far from circumstances in one timestep to the next.

In n-body simulation the 'point gravity' objects are kind of mathematical singularities which never collide because they have no size. The integration time-step gives them a kind of radius or gradient of proximity where very large errors occur, where virtual energy can be added or lost.

I read in these cases of true black hole collision, the shedding of energy through gravitational waves is the main cause of their orbits decay - without making the waves, the holes could circle each other for a very long time. Presumably energy&momentum is maintained over the collision of the two astrophysical non-point singularities, unlike the basic n-body excessive gravitation phenomenon.

The full details of what actually happens during the collision/overlap of black-hole 'calculation radii' are surely mysterious.

z3t4• 9 years ago

this is also my experience with simulated gravity and galaxy systems. i guess newton physics alone would be enough to make a body flung out if it comes close enough. and i guess a merge is close enough.

i was working on a space mmo and after leaving the server running for weeks some body would always be flyng away with crazy speed.

strainer2• 9 years ago

The newtonian model itself doesn't produce this behaviour as it is continuous, so however much bodies accelerate towards each other they can decelerate just as much once they have passed. In n-body simulation the continuous model is 'squeezed' into time-slices, where bodies can accelerate towards each other in one time-slice and in the next be too far past each other to slow each other down again.

Seemingly in the real astrophysical world, blackholes will free-fall towards each other by their masses 'dragging' on spacetime, causing deep perturbations in spacetime (as gravity waves). Eventually there is a 'merge' as you called it, an operation during which the resulting merged body can get a directed kick from the persisting spacetime perturbations, one powerful enough to eject it from a galaxy.

In the real world, overall it is expected energy and momentum is not defied during this merge operation, it seems remarkable considering how exceptional and energetic these events appear.

edit ...on second thoughts, this 'merge event' produces GRAVITATIONAL PROPULSION - sorry for the caps but I think they might be justified.

abecedarius• 9 years ago

In Newtonian gravity you need at least three bodies to arrange an ejection: two of them start orbiting more tightly, to counterbalance the third one flying out to infinity. (IIRC this happens a lot in globular clusters, and simulations like yours.) With just two bodies you get only Newton's solutions, the conic sections.

dgudkov• 9 years ago

The whole idea of it reminds me the gliders in Conway's Game of Life.

cglider• 9 years ago

For those interested in seeing the metaphor http://jsfiddle.net/ankr/tgjLA

Sniffnoy• 9 years ago

What I'm wondering is, if this is the explanation, why don't we see this more often? Plenty of galaxies have formed from mergers, right? So the question is, how much of a difference between the black holes does there need to be for this to occur? The video seems to imply only a small one, in which case one might expect this to be a common occurrence. So why haven't we seen this before? Or is that not the case?

jschwartzi2• 9 years ago

Because we would need to be looking. The sky is so very vast, and our imaging equipment needs to look at such a small part in order to resolve the galaxies beyond our own.

narag• 9 years ago

Is it possible to create a "sail" or a "surf board" to get propulsion from this waves?

AnimalMuppet3• 9 years ago

If the black hole got propulsion from this wave, I'm pretty sure it's not hard at all. You just have to be in the vicinity - no special shape or structure required.

ProAm• 9 years ago

The narrator of that video was really annoying. NASA needs to step up its PR game if they want these videos to have impact or go remotely 'viral'

JumpCrisscross• 9 years ago

What is the probability that the ejected black hole (if it is indeed such a thing) goes on to spawn a new galaxy?

Black holes are likely responsible for galaxy formation and evolution [1]. Since new black holes don't spin up from the void, I had assumed this meant all the galaxies to ever be formed have been formed (excluding effects of mergers). This, however, produces a new origin method (even if extraordinarily low-probability).

[1] http://www.roe.ac.uk/~pnb/papers/bh_nature.pdf

AlexCoventry3• 9 years ago

How does a gravitational wave impart momentum to a mass it passes through?

jschwartzi2• 9 years ago

By warping spacetime. It's the same thing that causes us to fall toward Earth. The presence of Earth's mass warps spacetime, and thus the Earth imparts momentum on us.

AlexCoventry3• 9 years ago

Anywhere I can look for a more detailed explanation of the process by which a gravitational wave imparts momentum, though? It seems like the mechanism must be quite different from the geodesics in a constant gravitational field.

Gravitational waves eject black hole from galaxy

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