4 ms·
No, the distinction between BH and NS can be made by just looking at the shape of the gravitational wave (stress as a function of time). A BH and a NS of the sa
by jessriedel 6y ago
No, the distinction between BH and NS can be made by just looking at the shape of the gravitational wave (stress as a function of time). A BH and a NS of the same mass will have different densities, so they produce very different ripples as they merge.
Of course, this can be corroborated with electromagnetic observations. But, to my knowledge, not all NS-NS mergers are witnessed in telescopes for various technical limitations.
- astro123 6y agoI don't think that is right, though I'm not a GW expert so please tell me if I'm wrong. I think they know the difference just by looking at the mass. i.e. we think it is hard to form black holes smaller than ~3.3ish solar masses and we don't think neutron stars can be more massive than 2.2 solar masses. This is why we get articles like [1] where there is an issue when we think we've found something between those numbers. And yes, the foolproof way of checking whether a NS was involved is to follow up with telescopes. But the constraints on position from GW aren't always good and so you can't always find it. [1] https://www.sciencemag.org/news/2020/06/gravitational-waves-reveal-lightest-black-hole-ever-observed https://www.sciencemag.org/news/2020/06/gravitational-waves-...
- jessriedel 6y agoYikes, on reflection I think you're right. Sorry about that. Thanks for the correction!
- jessriedel 6y agoOk, I'm actually only 90% wrong! It turns out that there is in fact some information about the BH-NS distinction in the gravitational signal itself, but it is very weak and hasn't been detected yet. It is expected to be detected in the future though. https://twitter.com/di_goldene_pave/status/1322322977984143360 https://twitter.com/di_goldene_pave/status/13223229779841433...
- astro123 6y agoI didn't know about that, that's really cool! Thanks for letting me know.