
Black holes and neutron stars merge unseen in dense star clusters - dnetesn
https://phys.org/news/2020-05-black-holes-neutron-stars-merge.html
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JoeAltmaier
Interesting reading! But I take issue with the title. The article says

    
    
       "Laser Interferometer Gravitational Waves Observatory" (LIGO) in the USA, are able to detect these waves.
    

So not unseen, in as they've been seen :)

Curiously, its the fact that there was no visible light, that suggests it was
this particular collision. Vs two black holes or two neutron stars. So I guess
an indirect observation. Boy are astrophysicists clever!

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detritus
If we don't perceive this event using the electromagnetic spectrum, is it fair
to state that it remains un'seen' as such?

We need a verb for gravitational perception!

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eganist
I mean, events that are _seen_ are a subset of events that are _observed._ So
with that in mind, _" observed"_ is probably sufficient.

Another example: you can observe a fire by smelling it.

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badrabbit
Could gravitational waves be faster than Light/EM? Faster than c event?

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whatshisface
They're not faster than C, but they could outrun a beam of light if there was
some stuff hanging out in space and raising the index of refraction. In
relativity the C limit is geometric, in the same way that "you can't make an
apple bigger by rotating it around in your hands" is geometric.

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ncmncm
Not only can, but do.

The intergalactic medium (IGM) is very diffuse, but not pure vacuum. The
difference in arrival time of light and gravitational waves from an event
billions of light years distant could help measure the density of the IGM.

Incidentally, while it is very cold, the IGM is plasma, so obeys plasma fluid-
dynamic laws, which is why the clouds seen at the ends of Active Galactic
Nucleus jets, millions of light years across, can be visibly turbulent.

