APOD: GW190521: Unexpected Black Holes Collide (2020 Sep 08)

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Chris Peterson
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Re: APOD: GW190521: Unexpected Black Holes Collide (2020 Sep 08)

Post by Chris Peterson » Wed Sep 09, 2020 2:33 pm

LeighGus wrote: ↑
Wed Sep 09, 2020 2:27 pm
orin stepanek wrote: ↑
Tue Sep 08, 2020 12:19 pm
GW190521_Virgo_1080.jpg


Oh My!!! Kaboom! 🌪 If 2 black holes collide; would not that be like 2 strong magnets coming together???? Either banging together or sling themselves fast apart? ⁉️ 🤯
It seems to me that the comparison is not the same. The two magnets are directly approaching each other and are pulled directly in by the mutual attraction. The two black holes are orbiting each other. The orbits are just unstable enough that they spiral in toward each other and eventually scrape each other and merge. There is insufficient lateral energy for a slingshot to happen.

I do believe that slingshots can and do happen if the two black holes are not captured by each other into orbits. I wonder what the minimum parameters for a slingshot would be. I suppose it depends on their masses, relative velocities, angles of approach, and so on.
In all of these cases, the black holes started as binary stars. So they have always been in closed (elliptical) orbits, and there is no way for that to change without introducing a third massive body- something that is unlikely (outside, perhaps, a system with three close components to begin with).

In the case of a pair of unrelated black holes passing each other, it is exceedingly unlikely that their relative speeds would be below their escape velocities. That is, their orbits would be open (hyperbolic), and again, there is no way to change that without involving a third massive body. So virtually any interaction between a pair of unrelated black holes will result in a slingshot.
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orin stepanek
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Re: APOD: GW190521: Unexpected Black Holes Collide (2020 Sep 08)

Post by orin stepanek » Wed Sep 09, 2020 2:38 pm

LeighGus wrote: ↑
Wed Sep 09, 2020 2:27 pm
orin stepanek wrote: ↑
Tue Sep 08, 2020 12:19 pm
GW190521_Virgo_1080.jpg


Oh My!!! Kaboom! 🌪 If 2 black holes collide; would not that be like 2 strong magnets coming together???? Either banging together or sling themselves fast apart? ⁉️ 🤯
It seems to me that the comparison is not the same. The two magnets are directly approaching each other and are pulled directly in by the mutual attraction. The two black holes are orbiting each other. The orbits are just unstable enough that they spiral in toward each other and eventually scrape each other and merge. There is insufficient lateral energy for a slingshot to happen.

I do believe that slingshots can and do happen if the two black holes are not captured by each other into orbits. I wonder what the minimum parameters for a slingshot would be. I suppose it depends on their masses, relative velocities, angles of approach, and so on.
I do a lot imaginative thinking! :roll: :mrgreen:
Orin

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Re: APOD: GW190521: Unexpected Black Holes Collide (2020 Sep 08)

Post by BDanielMayfield » Wed Sep 09, 2020 3:37 pm

LeighGus wrote: ↑
Wed Sep 09, 2020 2:27 pm
orin stepanek wrote: ↑
Tue Sep 08, 2020 12:19 pm
GW190521_Virgo_1080.jpg


Oh My!!! Kaboom! 🌪 If 2 black holes collide; would not that be like 2 strong magnets coming together???? Either banging together or sling themselves fast apart? ⁉️ 🤯
It seems to me that the comparison is not the same. The two magnets are directly approaching each other and are pulled directly in by the mutual attraction. The two black holes are orbiting each other. The orbits are just unstable enough that they spiral in toward each other and eventually scrape each other and merge. There is insufficient lateral energy for a slingshot to happen.

I do believe that slingshots can and do happen if the two black holes are not captured by each other into orbits. I wonder what the minimum parameters for a slingshot would be. I suppose it depends on their masses, relative velocities, angles of approach, and so on.
Also consider cases of more than two bodies. In cases with three, two are often pulled into a tighter orbit while the third is hurled away. This is also how we use planetary flyby gravity assist maneuvers to accelerate space probes. There is always an "equal and opposite" exchange of momentum in such "slingshots".
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Re: APOD: GW190521: Unexpected Black Holes Collide (2020 Sep 08)

Post by neufer » Wed Sep 09, 2020 4:48 pm

Click to play embedded YouTube video.
LeighGus wrote: ↑
Wed Sep 09, 2020 2:03 pm

If a human were close enough to a black hole merger event, say within a light year or closer, would the human eye perceive spacial distortions from the gravity waves?

... if one was looking at the black holes through a telescope from close range, what would one see? What if one turned the telescope 180° away to look at stars in the local distance, what would we see?
With frequencies of ~100Hz the circularly polarized quadrupolar waves would have ~3,000 km wavelengths such that the circular motions seen at the outskirts of the video at the left would be similar (but rotate in a counter clockwise fashion).
Art Neuendorffer

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Re: APOD: GW190521: Unexpected Black Holes Collide (2020 Sep 08)

Post by Joe Walker » Wed Sep 09, 2020 6:37 pm

I'm trying to understand how the stars in the star cluster move up and down (or in a circle like an orbit around a point in space) as they are riding the gravitational waves. I estimate that they could be moving about 20,000,000 miles from peak to trough (or front to back) and at a frequency of 2,000 Hz (from the LIGO recording). Since they are gaseous wouldn't they just be smeared/obliterated? Or do gravitational waves move tremendous masses at near the speed of light and do no harm to the geometry of the masses? Thanks for any info.

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Chris Peterson
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Re: APOD: GW190521: Unexpected Black Holes Collide (2020 Sep 08)

Post by Chris Peterson » Wed Sep 09, 2020 6:49 pm

Joe Walker wrote: ↑
Wed Sep 09, 2020 6:37 pm
I'm trying to understand how the stars in the star cluster move up and down (or in a circle like an orbit around a point in space) as they are riding the gravitational waves. I estimate that they could be moving about 20,000,000 miles from peak to trough (or front to back) and at a frequency of 2,000 Hz (from the LIGO recording). Since they are gaseous wouldn't they just be smeared/obliterated? Or do gravitational waves move tremendous masses at near the speed of light and do no harm to the geometry of the masses? Thanks for any info.
The stars aren't moving. The light from the stars is being distorted so they appear to move from the viewpoint of the camera. Like looking at the distant landscape through a glass you're waving in front of your eyes.
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