The August 14 Black Hole - Neutron Star merger

[John Clark]

Yesterday August 14 2019 LIGO detected for the first time Gravitational Waves coming from a Black Hole-Neutron Star merger; it was 900 million light years away. They detected something like this a few months ago but were only 13% confident it was real, this time the signal was much stronger and they're 99% confident. They've narrowed the source down to a square 23 degrees on a side, so far they haven't detected any electromagnetic waves from it but have just started looking. This type of merger produces a cleaner signal that is easier to analyze than when two Black Holes merge and can provide a more rigorous test of General Relativity, and if you could spot a few dozen of these sort of mergers it could give us the best value yet of the Hubble constant which has been in dispute lately and perhaps tell us if we're heading for the Big Rip or not.

LIGO and Virgo spotted the first black hole swallowing up a neutron star

John K Clark

[Lawrence Crowell]

I am not sure how this is cleaner, for there is a lot of material dynamics that is complicated. Black hole coalescence is a pure vacuum problem. It is though interesting still. 

LC 

[John Clark]

On Fri, Aug 16, 2019 at 1:32 PM Lawrence Crowell <goldenfield...@gmail.com> wrote:

>> Yesterday August 14 2019 LIGO detected for the first time Gravitational Waves coming from a Black Hole-Neutron Star merger; it was 900 million light years away. They detected something like this a few months ago but were only 13% confident it was real, this time the signal was much stronger and they're 99% confident. They've narrowed the source down to a square 23 degrees on a side, so far they haven't detected any electromagnetic waves from it but have just started looking. This type of merger produces a cleaner signal that is easier to analyze than when two Black Holes merge and can provide a more rigorous test of General Relativity, and if you could spot a few dozen of these sort of mergers it could give us the best value yet of the Hubble constant which has been in dispute lately and perhaps tell us if we're heading for the Big Rip or not.  John K Clark

LIGO and Virgo spotted the first black hole swallowing up a neutron star

> I am not sure how this is cleaner, for there is a lot of material dynamics that is complicated. Black hole coalescence is a pure vacuum problem. It is though interesting still.

If a big thing and a small thing merge you could make certain approximations that wouldn't work if the two things were of equal size, and if the Black Hole was large enough the tidal forces wouldn't be strong enough to break up a Neutron Star until after it passed through the Event Horizon so the material dynamics of the star would have no effect on the signal that we see. If the Black Hole was smaller then the Neutron Star would break up on our side of the Event Horizon making the signal more complex, but that would give us information about the nature of Neutronium and, other than with glitches with Pulsars caused by starquakes, it is the only way we have to compare theory with reality because we can't make Neutronium in a lab.

 John K Clark

[Lawrence Crowell]

I suppose that makes sense, but a small on large black hole coalescence would seem to be to be cleaner. 

When neutron stars collide they may splash out neutron masses the size of baseballs on up. These might be called mini-neutron stars. This so called neutronium, a term I think is out of use, is probably a liquid and I used the old liquid drop model of the nuclei to estimate this. 

LC