Starship Asterisk*

VictorBorun wrote: ↑Sat May 11, 2024 12:42 am

Chris Peterson wrote: ↑Fri May 10, 2024 11:08 pm

VictorBorun wrote: ↑Fri May 10, 2024 11:01 pm

Does a pair of BHs have to lose any of its total mass-energy to merge?
Can the two BHs just get closer (losing potenial energy and gaining kinetic energy) and then merge in a central collision?
It seems to me that a straight line collision would involve minimum of going around and radiating away one gravity wave after another…

Well, statistically I think a perfect straight line collision is effectively impossible. So it's just a theoretical construct. Still, you have accelerating masses, so they are radiating gravitational waves. But maybe not of a frequency or polarization that our detectors can deal with.

offtopic
Can a microscopic BH moving with a relativistically great velocity escape Hawking's evaporation and endure say from Bing Bang to nowadays?
In the cosmology reference system, a relativistic BH's mass-energy would be mostly kinetic energy.
Would such a BH radiate much energy in gravity waves?
Would it get slowed down by absorbing relic photons, intergalactic hydrogen and dark matter particles?

Chris Peterson wrote: ↑Fri May 10, 2024 11:08 pm

VictorBorun wrote: ↑Fri May 10, 2024 11:01 pm

Chris Peterson wrote: ↑Fri May 10, 2024 1:55 pm

Neither black hole lost mass. The individual precursor black holes merged to form a new black hole, and it has a higher mass than either of the precursors. The total mass difference reflects the conversion of gravitational potential energy (as the two precursors got closer) into kinetic energy, and that into gravitational waves.

Does a pair of BHs have to lose any of its total mass-energy to merge?
Can the two BHs just get closer (losing potenial energy and gaining kinetic energy) and then merge in a central collision?
It seems to me that a straight line collision would involve minimum of going around and radiating away one gravity wave after another…

Well, statistically I think a perfect straight line collision is effectively impossible. So it's just a theoretical construct. Still, you have accelerating masses, so they are radiating gravitational waves. But maybe not of a frequency or polarization that our detectors can deal with.

VictorBorun wrote: ↑Fri May 10, 2024 11:01 pm

Chris Peterson wrote: ↑Fri May 10, 2024 1:55 pm

agardini wrote: ↑Fri May 10, 2024 9:07 am Hello everybody,

I have a question about the BHs' masses.
I imagined that nothing could escape from a BH (except perhaps by Hawking radiation) but it seems that part of the mass of a couple of merging BHs is radiated as GW.
I suspect that the energy emitted as GW comes from the kinetic/gravitational/rotational energy of the BHs rather than from their "rest mass" but I am not fully sure.
Can anyone elaborate on point?
Thanks

Neither black hole lost mass. The individual precursor black holes merged to form a new black hole, and it has a higher mass than either of the precursors. The total mass difference reflects the conversion of gravitational potential energy (as the two precursors got closer) into kinetic energy, and that into gravitational waves.

Does a pair of BHs have to lose any of its total mass-energy to merge?
Can the two BHs just get closer (losing potenial energy and gaining kinetic energy) and then merge in a central collision?
It seems to me that a straight line collision would involve minimum of going around and radiating away one gravity wave after another…

Chris Peterson wrote: ↑Fri May 10, 2024 1:55 pm

agardini wrote: ↑Fri May 10, 2024 9:07 am Hello everybody,

I have a question about the BHs' masses.
I imagined that nothing could escape from a BH (except perhaps by Hawking radiation) but it seems that part of the mass of a couple of merging BHs is radiated as GW.
I suspect that the energy emitted as GW comes from the kinetic/gravitational/rotational energy of the BHs rather than from their "rest mass" but I am not fully sure.
Can anyone elaborate on point?
Thanks

Neither black hole lost mass. The individual precursor black holes merged to form a new black hole, and it has a higher mass than either of the precursors. The total mass difference reflects the conversion of gravitational potential energy (as the two precursors got closer) into kinetic energy, and that into gravitational waves.

JohnD wrote: ↑Fri May 10, 2024 11:03 am While the bare physics have to be right, and the simulation flawless, I was underwhelmed by the video - surely such an event will be accompanied by more fireworks, with accretion disks and jets exploding?

And thank you to Ann for telling me of the "Final Parsec Problem". I found this:
"When two galaxies merge, they often produce a supermassive black hole binary (SMBHB) at their center. Numerical simulations with cold dark matter show that SMBHBs typically stall out at a distance of a few parsecs apart, and take billions of years to coalesce. This is known as the final parsec problem. We suggest that ultralight dark matter (ULDM) halos around SMBHBs can generate dark matter waves due to gravitational cooling. These waves can effectively carry away orbital energy from the black holes, rapidly driving them together. To test this hypothesis, we performed numerical simulations of black hole binaries inside ULDM halos. Our results imply that ULDM waves can lead to the rapid orbital decay of black hole binaries."

Koo, Bak, Park et al, Final parsec problem of black hole mergers and ultralight dark matter, Astrophysics, https://doi.org/10.48550/arXiv.2311.03412

Chris Peterson wrote: ↑Fri May 10, 2024 6:33 pm

johnnydeep wrote: ↑Fri May 10, 2024 6:29 pm

Chris Peterson wrote: ↑Fri May 10, 2024 6:25 pm

I don't think there are any missing words. When a mass is allowed to move in a gravitational field, its velocity increases, which represents a conversion of gravitational potential energy to kinetic energy. Right? And any accelerating mass generates gravitational waves ("acceleration" can be tricky here, involving reference frames, but the basic concept should be pretty clear). So a tiny bit of energy is actually taken out of the moving mass, slowing it down. That's why black holes spiral into each other. But the amount is far below what we have the technology to measure, except for these special cases of massive bodies merging.

That sentence still isn't parsing for me: Is it "gravitational potential energy gets converted to kinetic energy, [which can also?, which always? and?] gets converted to gravitational waves all the time"?

Gravitational waves are a form of energy that is radiated from an accelerating mass. That energy is being "stolen" from the kinetic energy of that moving mass. If you wave your hand around you are radiating gravitational waves from it.

johnnydeep wrote: ↑Fri May 10, 2024 6:29 pm

Chris Peterson wrote: ↑Fri May 10, 2024 6:25 pm

johnnydeep wrote: ↑Fri May 10, 2024 6:12 pm

Can you clear up that statement for me? Any missing words for example?

I don't think there are any missing words. When a mass is allowed to move in a gravitational field, its velocity increases, which represents a conversion of gravitational potential energy to kinetic energy. Right? And any accelerating mass generates gravitational waves ("acceleration" can be tricky here, involving reference frames, but the basic concept should be pretty clear). So a tiny bit of energy is actually taken out of the moving mass, slowing it down. That's why black holes spiral into each other. But the amount is far below what we have the technology to measure, except for these special cases of massive bodies merging.

That sentence still isn't parsing for me: Is it "gravitational potential energy gets converted to kinetic energy, [which can also?, which always? and?] gets converted to gravitational waves all the time"?

Chris Peterson wrote: ↑Fri May 10, 2024 6:25 pm

johnnydeep wrote: ↑Fri May 10, 2024 6:12 pm

Chris Peterson wrote: ↑Fri May 10, 2024 6:06 pm

In the mundane world, gravitational potential energy gets converted to kinetic energy, gets converted to gravitational waves all the time. Like when you drop a rock. But it takes something as massive as merging black holes or neutron stars to produce strong enough gravitational waves for our existing technology to detect them.

Can you clear up that statement for me? Any missing words for example?

I don't think there are any missing words. When a mass is allowed to move in a gravitational field, its velocity increases, which represents a conversion of gravitational potential energy to kinetic energy. Right? And any accelerating mass generates gravitational waves ("acceleration" can be tricky here, involving reference frames, but the basic concept should be pretty clear). So a tiny bit of energy is actually taken out of the moving mass, slowing it down. That's why black holes spiral into each other. But the amount is far below what we have the technology to measure, except for these special cases of massive bodies merging.

johnnydeep wrote: ↑Fri May 10, 2024 6:12 pm

Chris Peterson wrote: ↑Fri May 10, 2024 6:06 pm

johnnydeep wrote: ↑Fri May 10, 2024 5:46 pm

Kinetic energy can get converted into gravitational energy? In the mundane world, kinetic energy clearly can get converted into heat (a bullet hitting
a steel plate for example), but does it also get converted to GWs (however miniscule an amount that might result in)?

In the mundane world, gravitational potential energy gets converted to kinetic energy, gets converted to gravitational waves all the time. Like when you drop a rock. But it takes something as massive as merging black holes or neutron stars to produce strong enough gravitational waves for our existing technology to detect them.

Can you clear up that statement for me? Any missing words for example?

Chris Peterson wrote: ↑Fri May 10, 2024 6:06 pm

johnnydeep wrote: ↑Fri May 10, 2024 5:46 pm

Chris Peterson wrote: ↑Fri May 10, 2024 1:55 pm

Neither black hole lost mass. The individual precursor black holes merged to form a new black hole, and it has a higher mass than either of the precursors. The total mass difference reflects the conversion of gravitational potential energy (as the two precursors got closer) into kinetic energy, and that into gravitational waves.

Kinetic energy can get converted into gravitational energy? In the mundane world, kinetic energy clearly can get converted into heat (a bullet hitting
a steel plate for example), but does it also get converted to GWs (however miniscule an amount that might result in)?

In the mundane world, gravitational potential energy gets converted to kinetic energy, gets converted to gravitational waves all the time. Like when you drop a rock. But it takes something as massive as merging black holes or neutron stars to produce strong enough gravitational waves for our existing technology to detect them.

Chris Peterson wrote: ↑Fri May 10, 2024 1:55 pm (Perhaps we should read this as an indicator that the "mundane world" is much less mundane than it superficially appears!)

johnnydeep wrote: ↑Fri May 10, 2024 5:46 pm

Chris Peterson wrote: ↑Fri May 10, 2024 1:55 pm

agardini wrote: ↑Fri May 10, 2024 9:07 am Hello everybody,

I have a question about the BHs' masses.
I imagined that nothing could escape from a BH (except perhaps by Hawking radiation) but it seems that part of the mass of a couple of merging BHs is radiated as GW.
I suspect that the energy emitted as GW comes from the kinetic/gravitational/rotational energy of the BHs rather than from their "rest mass" but I am not fully sure.
Can anyone elaborate on point?
Thanks

Neither black hole lost mass. The individual precursor black holes merged to form a new black hole, and it has a higher mass than either of the precursors. The total mass difference reflects the conversion of gravitational potential energy (as the two precursors got closer) into kinetic energy, and that into gravitational waves.

Kinetic energy can get converted into gravitational energy? In the mundane world, kinetic energy clearly can get converted into heat (a bullet hitting
a steel plate for example), but does it also get converted to GWs (however miniscule an amount that might result in)?

Chris Peterson wrote: ↑Fri May 10, 2024 1:55 pm

agardini wrote: ↑Fri May 10, 2024 9:07 am Hello everybody,

I have a question about the BHs' masses.
I imagined that nothing could escape from a BH (except perhaps by Hawking radiation) but it seems that part of the mass of a couple of merging BHs is radiated as GW.
I suspect that the energy emitted as GW comes from the kinetic/gravitational/rotational energy of the BHs rather than from their "rest mass" but I am not fully sure.
Can anyone elaborate on point?
Thanks

Neither black hole lost mass. The individual precursor black holes merged to form a new black hole, and it has a higher mass than either of the precursors. The total mass difference reflects the conversion of gravitational potential energy (as the two precursors got closer) into kinetic energy, and that into gravitational waves.

Chris Peterson wrote: ↑Fri May 10, 2024 1:55 pm

agardini wrote: ↑Fri May 10, 2024 9:07 am Hello everybody,

I have a question about the BHs' masses.
I imagined that nothing could escape from a BH (except perhaps by Hawking radiation) but it seems that part of the mass of a couple of merging BHs is radiated as GW.
I suspect that the energy emitted as GW comes from the kinetic/gravitational/rotational energy of the BHs rather than from their "rest mass" but I am not fully sure.
Can anyone elaborate on point?
Thanks

Neither black hole lost mass. The individual precursor black holes merged to form a new black hole, and it has a higher mass than either of the precursors. The total mass difference reflects the conversion of gravitational potential energy (as the two precursors got closer) into kinetic energy, and that into gravitational waves.

agardini wrote: ↑Fri May 10, 2024 9:07 am Hello everybody,

I have a question about the BHs' masses.
I imagined that nothing could escape from a BH (except perhaps by Hawking radiation) but it seems that part of the mass of a couple of merging BHs is radiated as GW.
I suspect that the energy emitted as GW comes from the kinetic/gravitational/rotational energy of the BHs rather than from their "rest mass" but I am not fully sure.
Can anyone elaborate on point?
Thanks

Guest wrote: ↑Fri May 10, 2024 8:21 am According to the mathematics that I learned, 36 + 31 = 67, which is 4 (four) more than 63, not 3 more.
Of course, this could easily be a matter of rounding issues. But then, if the actual figures were known with greater precision, it would have been quite possible to supply those numbers instead of the ones that were given.
For instance: 35.7 + 30.7 = 66.4, and if the final mass would be 63.4, then the difference would indeed be precisely 3 solar masses while all the other "named " masses would round to the values that were actually given.

The way it is formulated in the APOD, there's an entire solar mass missing, presumably "gone fishing" or some such. Sloppy housekeeping, that.

BBC Sky at Night wrote:

In order to spiral towards one another, the two black holes must first shed energy.

To start with, that energy is transferred to surrounding material, including gas and dust.

Except when the galactic black holes get within a parsec of each other – just over three lightyears – it seems there’s no longer enough ‘stuff’ to shed energy to.

This has become known as the Final Parsec Problem.