[ExI] we're baaaack!

[John Clark]

On Mon, Aug 19, 2019 at 7:13 PM <spike at rainier66.com> wrote:


>
>
> *>I don't expect the mailing list will go down henceforth, for Max has
> askedme to take over the cheerful task of seeing to it that it stays up.
> Thishonor and privilege is one I embraced after mulling it over for
> severalmilliseconds.*


Thanks Spike, you're a gentleman and a scholar!

*John I hope you will post the marvelous news you and I learned a few days
> ago from LIGO please.*
>

Be happy to. On August 14 2019 LIGO detected for the first time
Gravitational Waves coming from a Black Hole-Neutron Star merger; it was 870
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 because 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. So you can make 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

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 on the other
hand that would give us information about the nature of Neutronium and, other
than  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.

Astronomers Spy a Black Hole Devouring a Neutron Star
<https://www.scientificamerican.com/article/astronomers-spy-a-black-hole-devouring-a-neutron-star/>

John K Clark
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