Thanks, Michael. That was of interest. It was actually the first place I heard about this result (I wasn't at the AAS meeting), thought I've been hearing plenty about it since from colleagues who think it's killed one of my pet theories.
It's very neat that the maximum spin rate has been raised from 642Hz to 716Hz, but I think they are overplaying the implications. Oh well, that's how you get published in a journal like Science. By the way, a copy of their paper is now available here.
Previous studies of accretion-powered pulsars predicted that things could be found up to the mid-700s (in Hz), so 716 isn't that surprising. It'll probably bump up the estimates of the high-frequency cutoff a bit, but it won't change the fact that there is a big gap between the observed maximum spin frequency and the theoretical predictions, most of which are over 1000Hz. That gap is one of the arguments for gravitational radiation operating in some substantial population of rapidly rotating neutron stars.
Which brings me to the other big thing they are claiming, that this looks bad for the r-modes of neutron stars as sources of gravitational radiation. It doesn't actually change the picture much. If you have a star accreting at a very low rate, it can be cold enough that various viscous mechanisms can kill the instability. In this paper they only mentioned one, which probably isn't the dominant one. (They didn't seem too familiar with the gravitational waves literature overall.) So if you have a star accreting for a very long time at a very low rate, it can be spun up to 716Hz or even more without triggering gravitational wave emission from the r-modes.
Hmm, that was more technical than I usually like to get here, but I had to get it off my chest.
The bottom line is: This particular star doesn't look like a good source of gravitational waves, but it doesn't put the damper on gravitational wave emission in general as these guys are claiming.
Fast-spinning neutron star smashes speed limit
)
Nice one. That'll make for a revision. It's spins at over 4000rpm!
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Michael Karlinsky
)
Michael Karlinsky wrote:
Thanks, Michael. That was of interest. It was actually the first place I heard about this result (I wasn't at the AAS meeting), thought I've been hearing plenty about it since from colleagues who think it's killed one of my pet theories.
It's very neat that the maximum spin rate has been raised from 642Hz to 716Hz, but I think they are overplaying the implications. Oh well, that's how you get published in a journal like Science. By the way, a copy of their paper is now available here.
Previous studies of accretion-powered pulsars predicted that things could be found up to the mid-700s (in Hz), so 716 isn't that surprising. It'll probably bump up the estimates of the high-frequency cutoff a bit, but it won't change the fact that there is a big gap between the observed maximum spin frequency and the theoretical predictions, most of which are over 1000Hz. That gap is one of the arguments for gravitational radiation operating in some substantial population of rapidly rotating neutron stars.
Which brings me to the other big thing they are claiming, that this looks bad for the r-modes of neutron stars as sources of gravitational radiation. It doesn't actually change the picture much. If you have a star accreting at a very low rate, it can be cold enough that various viscous mechanisms can kill the instability. In this paper they only mentioned one, which probably isn't the dominant one. (They didn't seem too familiar with the gravitational waves literature overall.) So if you have a star accreting for a very long time at a very low rate, it can be spun up to 716Hz or even more without triggering gravitational wave emission from the r-modes.
Hmm, that was more technical than I usually like to get here, but I had to get it off my chest.
The bottom line is: This particular star doesn't look like a good source of gravitational waves, but it doesn't put the damper on gravitational wave emission in general as these guys are claiming.
Hope this helps,
Ben