Gravitational waves reveal collision of heavy and light black holes | Hacker News Reader

Gravitational waves reveal collision of heavy and light black holes

sciencemag.org

66 pointsjdnier17 comments

Are they saying that the frequency produced is the same as the note in the Elvis song or just that the ratio of the two notes in the song is the same as the ratio of the two frequencies detected?

I mean, I am not sure what the frequencies generated by orbiting black holes would be.. but ~260hz (middle C) sounds destructively fast to me so I'm guessing the latter. What is the orbital frequency likely to be here?

260hz is not unreasonable, black hole mergers are unimaginably violent.

https://youtu.be/9IdVyArDlZ4

yes but I'm imagining that when the orbital frequency gets to that kind of level, the end would be extremely imminent?

(for the remote observer anyway haha)

Yes, LIGO observes the actual merger.

They report two initial masses, the final mass of the merged black hole and what as a result was radiated in energy.

Yes, but it's only when the black holes get extremely close that they produce gravitational waves powerful enough for us to detect.

You're correct that for many years (millenia?) the black holes have been orbiting each other much more slowly. We can't detect that though.

I wonder what the right time scale is here. My gut reaction is million of years?

I believe it depends on the specifics of the merger, but my understanding is the reason black holes that orbit each other merge at all is because they bleed energy to gravitational waves. While they are at a reasonable distance, that's a very small amount of energy. I think some of these systems would be stable for billions of years.

Billions seemed too long to me, at that point you're talking about tenths of the lifetime of the universe!

That's the timescale the solar system is stable on.

Aw, sorry. I think I mis-interpreted your comment. I was thinking more of how long the system has been falling apart for. It didn't make sense to me that that could have been for billions of years, since the movement involved would be so slow?

Just for folks that aren't familiar pulsars are spinning stars that can hold themselves together up to at least ~1khz. Here's what the signal sounds like coming from a few different ones (incl. 600hz range) https://www.youtube.com/watch?v=gb0P6x_xDEU

`If the main frequency were a C on a piano, the overtone would be the next higher G—a perfect fifth, and the interval of the first two notes in the melody of Elvis Presley’s hit “I Can’t Help Falling in Love with You.”`

My read is that it's just saying that the first smaller frequency was the same ratio from the primary as G to C are in sound frequencies, so they're describing it as a similar interval as the first two notes, not as being literally the same tune.

Two slower frequencies can interfere and produce a much higher frequency in a phenomenon known as beating

It's actually the other way around. Beat frequencies can't exceed the frequency of either of the component frequencies.

Ah oops, I forgot about the factor of 2 in the denominator of the equation

A link to the paper would be appreciated if anyone has it.

It was a paid livestream of the virtual conference. Free slides available below.

http://meetings.aps.org/Meeting/APR20/Session/C06.2

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