APOD: When Black Holes Collide (2021 Apr 11)

[APOD Robot]

When Black Holes Collide

Explanation: What happens when two black holes collide? This extreme scenario occurs in the centers of many merging galaxies and multiple star systems. The featured video shows a computer animation of the final stages of such a merger, while highlighting the gravitational lensing effects that would appear on a background starfield. The black regions indicate the event horizons of the dynamic duo, while a surrounding ring of shifting background stars indicates the position of their combined Einstein ring. All background stars not only have images visible outside of this Einstein ring, but also have one or more companion images visible on the inside. Eventually the two black holes coalesce. The end stages of such a merger is now known to produce a strong blast of gravitational radiation, providing a new way to see our universe.

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[Antony Rawlinson]

The text says it's computer-generated. Can anyone say what real-life scale it represents, in terms of distance/size, mass and time?

[nam888id]

The text says it's computer-generated. Can anyone say what real-life scale it represents, in terms of distance/size, mass and time?

Other than the small one is 1/6 the mass of the larger one I do not know. However, this paper may be related though I do not have access to it. https://www.researchgate.net/publicatio ... al_methods

[JohnD]

How realistic is that simulation?

The event horizons of either BH are distorted as they rotate into each other. I believe that a spinning BH would distort into an oblate sphere, wider at the 'equator' so maybe. But at one stage, the smaller one separates off a smaller black area, as if it was split into two BHs with their own horizons! Surely not?!
JOhn

[orin stepanek]

Black holes; I got nothing to say! They leave me in aw! I saw the movie Event Horizon!https://youtu.be/ZmSLkiYwAbw

[Chris Peterson]

The text says it's computer-generated. Can anyone say what real-life scale it represents, in terms of distance/size, mass and time?

I believe this is a simulation of stellar mass black holes colliding. So the black holes are several solar masses, and their event horizons several tens of kilometers across.

[Ann]

Black holes; I got nothing to say! They leave me in aw! I saw the movie Event Horizon!https://youtu.be/ZmSLkiYwAbw

Black holes! I've got very little to say. And I didn't even see the movie Event Horizon.

But I will say this:

What gets me about today's APOD is the "silence" of the creation of the final, larger black hole collision product.

I'm thinking of the asteroid that hit the Earth and wiped out the dinosaurs, which was, all in all, such a really tiny cosmic event. That impact seemed to trigger all sorts of debris, plumes, flying boulders, tsunamis, vast gas clouds and all kinds of blinding lights and screeching sounds. By contrast, the final merger of the two black holes seems... eventless.

Ann

[Chris Peterson]

Black holes; I got nothing to say! They leave me in aw! I saw the movie Event Horizon!https://youtu.be/ZmSLkiYwAbw

Black holes! I've got very little to say. And I didn't even see the movie Event Horizon.

But I will say this:

What gets me about today's APOD is the "silence" of the creation of the final, larger black hole collision product.

I'm thinking of the asteroid that hit the Earth and wiped out the dinosaurs, which was, all in all, such a really tiny cosmic event. That impact seemed to trigger all sorts of debris, plumes, flying boulders, tsunamis, vast gas clouds and all kinds of blinding lights and screeching sounds. By contrast, the final merger of the two black holes seems... eventless.

Ann

Even though they say, "In space, no one can hear you scream", I think that in this case, were you as close as the viewpoint of this video, the gravitational waves (which can carry away several solar masses energy equivalent) might well be able to stimulate your hearing. You might actually hear this, given that the chirp generated by mergers of this size lie at least partly in the audio frequency range.

[Case]

What gets me about today's APOD is the "silence" of the creation of the final, larger black hole collision product.

As you probably know, the signal has been converted to audible wavelengths, to let us hear a ‘chirp’ sound of the merger.
https://www.ligo.caltech.edu/video/ligo20160211v2

[orin stepanek]

Does a black hole have any color; or is that a way to describe it?

[Chris Peterson]

Does a black hole have any color; or is that a way to describe it? :roll:

A black hole is presumed to act like a blackbody radiator with a temperature just above absolute zero, meaning its "color" is far out in the long wave radio spectrum (but way too dim for us to detect with our current technology).

[shaileshs]

I'm assuming whatever is shown inside Einestien ring/circle are the copy images of real stuff outside because of gravitational lensing. If yes, after the merger is complete, I was thinking all that stuff will be cleared (copy images removed).. No ?

[Chris Peterson]

I'm assuming whatever is shown inside Einestien ring/circle are the copy images of real stuff outside because of gravitational lensing. If yes, after the merger is complete, I was thinking all that stuff will be cleared (copy images removed).. No ?

Not sure what you mean. The video ends with the merger complete, so you can see what the background star field looks like at the end.

[johnnydeep]

How realistic is that simulation?

The event horizons of either BH are distorted as they rotate into each other. I believe that a spinning BH would distort into an oblate sphere, wider at the 'equator' so maybe. But at one stage, the smaller one separates off a smaller black area, as if it was split into two BHs with their own horizons! Surely not?!
JOhn

Yeah, those "secondary black blobs" left me guessing as well, but the paper the linked YouTube video points to explains it (or tries to - a lot is beyond me). They call them "eyebrows" and explain them as "shadows". From page six of paper https://arxiv.org/pdf/1410.7775v1.pdf:

Merging Black Holes "Eyebrow"

[rcdavison@orbitalmaneuvers.com]

Holy APOD! You threw me for a loop with the 'dynamic duo' link!

I totally expected the original dynamic duo:

Great post!

RC Davison

[JohnD]

Thank you, johnnydeep!
I didn't think to look in the literature for a commentary on the video!
So! The split-off BHs are more lke the gravitational lens doubling star images, or the Einstein ring. A gravitational illusion!

JOhn

[Ann]

Black holes; I got nothing to say! They leave me in aw! I saw the movie Event Horizon!https://youtu.be/ZmSLkiYwAbw

Black holes! I've got very little to say. And I didn't even see the movie Event Horizon.

But I will say this:

What gets me about today's APOD is the "silence" of the creation of the final, larger black hole collision product.

I'm thinking of the asteroid that hit the Earth and wiped out the dinosaurs, which was, all in all, such a really tiny cosmic event. That impact seemed to trigger all sorts of debris, plumes, flying boulders, tsunamis, vast gas clouds and all kinds of blinding lights and screeching sounds. By contrast, the final merger of the two black holes seems... eventless.

Ann

Even though they say, "In space, no one can hear you scream", I think that in this case, were you as close as the viewpoint of this video, the gravitational waves (which can carry away several solar masses energy equivalent) might well be able to stimulate your hearing. You might actually hear this, given that the chirp generated by mergers of this size lie at least partly in the audio frequency range.

Click to play embedded YouTube video.

Thanks, Chris. I guess what gets me the most is not the lack of sound, but the lack of debris. But that's black holes for you.

Enjoy the video of a simple simulation of the explosion of the progenitor star of the Crab Nebula. In space no one can hear you explode, that's true.

But there was sure as heck a lot of debris when the star that would become the Crab Nebula (and its pulsar) blew itself to smithereens. Black holes though, they just put on weight, and barely even burp when they do so.

(Except when they blow a really nasty jet when enjoying a snack.)

No Weight Watchers in the Universe can help them reduce, unless the Hawking radiation works the way it should.

Ann

[Antony Rawlinson]

The text says it's computer-generated. Can anyone say what real-life scale it represents, in terms of distance/size, mass and time?

I believe this is a simulation of stellar mass black holes colliding. So the black holes are several solar masses, and their event horizons several tens of kilometers across.

Does the event horizon coincide with the black circles on the video? Sorry, I'm not very knowledgable about black holes, and I'm a bit surprised that they're on the scale of only tens of km.

[Chris Peterson]

The text says it's computer-generated. Can anyone say what real-life scale it represents, in terms of distance/size, mass and time?

I believe this is a simulation of stellar mass black holes colliding. So the black holes are several solar masses, and their event horizons several tens of kilometers across.

Does the event horizon coincide with the black circles on the video? Sorry, I'm not very knowledgable about black holes, and I'm a bit surprised that they're on the scale of only tens of km.

Yes. The black hole itself is infinitesimally small, but we see the finite sized event horizon.

[Antony Rawlinson]

The text says it's computer-generated. Can anyone say what real-life scale it represents, in terms of distance/size, mass and time?

I believe this is a simulation of stellar mass black holes colliding. So the black holes are several solar masses, and their event horizons several tens of kilometers across.

Thanks for this and the clarification, but can you or someone else say what the timescale of the animation is? Is it meant to be real-time?

[neufer]

Observed black holes with a glory ring at ~3 Schwarzschild radii

---

When Black Holes Collide

Explanation: The black regions indicate the event horizons of the dynamic duo, while a surrounding ring of shifting background stars indicates the position of their combined Einstein ring. All background stars not only have images visible outside of this Einstein ring, but also have one or more companion images visible on the inside. Eventually the two black holes coalesce.

Note: the black regions within glory rings at ~3 Schwarzschild radii indicate ones own distorted view of smaller (~1 Schwarzschild radii) event horizons as seen from a distance of 15 Schwarzschild radii.

(From a distance of 15 Schwarzschild radii you would hear yourself scream from the gravitational radiation.)

<<This is a physically accurate gravitational lensing visualization of the last few orbits of a binary black hole merger. The camera is above the orbital plane of the merger, looking down. The mass ratio is 3 to 1. The large black hole has a dimensionless spin of 0.7, whereas the small hole's dimensionless spin is 0.3, with both spins in arbitrary directions. This is case 4 of Phys. Rev. D, 88:124010, Dec 2013,
1309.3605.>>

What would a binary black hole merger look like?

Andy Bohn, Fran ̧cois Hebert, William Throwe, Darius Bunandar, Katherine Henriksson, Mark A. Scheel, and Nicholas W. Taylor
Center for Radiophysics and Space Research, Cornell University, Ithaca, New York 14853, USA
Theoretical Astrophysics 350-17, California Institute of Technology, Pasadena, California 91125, USA
MIT Kavli Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
(Dated: October 30, 2014)

In this paper, we focus on the question of what an observer in the vicinity of a BBH would actually see as the black holes orbit, spiral inward, and merge. This is in contrast to most BBH visualizations, in which the positions or horizons of the two black holes are simply shown as a function of time in some coordinate system. We instead compute the paths of light rays that enter the observer’s eye or camera to find what would actually be seen. Further more, this path must be computed in the fully time-dependent spacetime, as the orbital velocities for a black-hole binary are typically large enough that the system cannot be approximated as time-independent during the time taken by the photons to travel across it.

FIG. 4. Lensing caused by various analytic spacetimes. For all panels, we use [an artificial background at infinity] as a background. The camera has a 60◦ field of view and is at a distance of 15 Schwarzschild radii from the origin measured using Kerr-Schild coordinates. The bottom row shows two views of the Kerr spacetime, with dimensionless spin.

[johnnydeep]

The text says it's computer-generated. Can anyone say what real-life scale it represents, in terms of distance/size, mass and time?

I believe this is a simulation of stellar mass black holes colliding. So the black holes are several solar masses, and their event horizons several tens of kilometers across.

Thanks for this and the clarification, but can you or someone else say what the timescale of the animation is? Is it meant to be real-time?

I've looked far and wide, but I can't find a specific answer to that. I'm sure it depends on the masses of the two black holes, and perhaps also their spins. All I know is that it starts slowly and the last stages are sub-second. There are vague hints at https://en.wikipedia.org/wiki/Binary_black_hole :

Lifecycle
Inspiral
The first stage of the life of a binary black hole is the inspiral, a gradually shrinking orbit. The first stages of the inspiral take a very long time, as the gravitation waves emitted are very weak when the black holes are distant from each other. In addition to the orbit shrinking due to the emission of gravitational waves, extra angular momentum may be lost due to interactions with other matter present, such as other stars.

As the black holes’ orbit shrinks, the speed increases, and gravitational wave emission increases. When the black holes are close the gravitational waves cause the orbit to shrink rapidly.

The last stable orbit or innermost stable circular orbit (ISCO) is the innermost complete orbit before the transition from inspiral to merger.

Merger
This is followed by a plunging orbit in which the two black holes meet, followed by the merger. Gravitational wave emission peaks at this time.

Ringdown
Immediately following the merger, the now single black hole will “ring”. This ringing is damped in the next stage, called the ringdown, by the emission of gravitational waves. The ringdown phase starts when the black holes approach each other within the photon sphere. In this region most of the emitted gravitational waves go towards the event horizon, and the amplitude of those escaping reduces. Remotely detected gravitational waves have a fast reducing oscillation, as echos of the merger event result from tighter and tighter spirals around the resulting black hole.

...

Observation
The first observation of stellar mass binary black holes merging, GW150914, was performed by the LIGO detector.[15][22][23] As observed from Earth, a pair of black holes with estimated masses around 36 and 29 times that of the Sun spun into each other and merged to form a 62 solar mass black hole (approximate) on 14 September 2015, at 09:50 UTC.[24] Three solar masses were converted to gravitational radiation in the final fraction of a second, with a peak power 3.6×10⁵⁶ ergs/second (200 solar masses per second),[15] which is 50 times the total output power of all the stars in the observable universe.[25] The merger took place 440+160
−180 megaparsecs from Earth,[26] between 600 million and 1.8 billion years ago.[22] The observed signal is consistent with the predictions of numerical relativity.[2][3][4]

I suspect the final few orbits take milliseconds, so this video is very likely extremely slowed down! There's probably a more specific answer here - https://www.black-holes.org/explore/movies - but I haven't found it yet. There are some possible answers at Quora, but take them with a grain of salt.

EDIT: I see neufer posted while I was typing mine up, though I'm not sure if he was trying to answer the timeline question or not. But perhaps his implication is that because relativistic time dilation effects are extreme during the merger, a timeline is meaningless? But surely, for those outside the immediate vicinity, there would be some valid time taken for stellar mass blackholes to appear to merge over the last, oh, 100 km of separation?

[neufer]

I believe this is a simulation of stellar mass black holes colliding. So the black holes are several solar masses, and their event horizons several tens of kilometers across.

Thanks for this and the clarification, but can you or someone else say what the timescale of the animation is? Is it meant to be real-time?

I've looked far and wide, but I can't find a specific answer to that. I'm sure it depends on the masses of the two black holes, and perhaps also their spins. All I know is that it starts slowly and the last stages are sub-second. I suspect the final few orbits take milliseconds, so this video is very likely extremely slowed down!

EDIT: I see neufer posted while I was typing mine up, though I'm not sure if he was trying to answer the timeline question or not. But perhaps his implication is that because relativistic time dilation effects are extreme during the merger, a timeline is meaningless? But surely, for those outside the immediate vicinity, there would be some valid time taken for stellar mass blackholes to appear to merge over the last, oh, 100 km of separation?

The first measurement of a gravitational wave event

---

My post was about the fact that we are only observing Black Hole "mirages" about ~3 times larger than the event horizons themselves. Hence, the intense final stages of merging event horizons would be obscured to us in this visualization.

The first observed orbit in the APOD video, however, might represent a ~0.05 second full orbit of the first observed LIGO quadruple gravitation wavelength pair (i.e., 0.30 to 0.35 seconds )

This would suggest a slow motion reduction of about 1/60 speed such that the entire 12 second APOD video represents ~0.2 seconds of real time.

[johnnydeep]

Thanks for this and the clarification, but can you or someone else say what the timescale of the animation is? Is it meant to be real-time?

I've looked far and wide, but I can't find a specific answer to that. I'm sure it depends on the masses of the two black holes, and perhaps also their spins. All I know is that it starts slowly and the last stages are sub-second. I suspect the final few orbits take milliseconds, so this video is very likely extremely slowed down!

EDIT: I see neufer posted while I was typing mine up, though I'm not sure if he was trying to answer the timeline question or not. But perhaps his implication is that because relativistic time dilation effects are extreme during the merger, a timeline is meaningless? But surely, for those outside the immediate vicinity, there would be some valid time taken for stellar mass blackholes to appear to merge over the last, oh, 100 km of separation?

The first measurement of a gravitational wave event

---

My post was about the fact that we are only observing Black Hole "mirages" about ~3 times larger than the event horizons themselves. Hence, the intense final stages of merging event horizons would be obscured to us in this visualization.

The first observed orbit in the APOD video, however, might represent a ~0.05 second full orbit of the first observed LIGO quadruple gravitation wavelength pair (i.e., 0.30 to 0.35 seconds )

This would suggest a slow motion reduction of about 1/60 speed such that the entire 12 second APOD video represents ~0.2 seconds of real time.

Thanks for the numbers, but where are you getting the values from? Are they implied by knowing the gravitational wavelength oscillation amplitude shown in the pic?

EDIT: d'oh! The time scale on the pic wasn't showing up for me on the enlarged pic! I now see it on the post pic.