In what was likely one of the most thoroughly observed astronomical events in history -- there
were over 70 observatories involved and one of the papers on it has literally thousands
of co-authors, scientists in the US and Europe jointly announced today that they caught a
neutron star merger in the act.
Known as GW 170817 it should simultaneously solve, or at least shed light on a number
of mysteries within astronomy, but ultimately creates a new one in the process.
Because so many observatories dropped everything and looked at this object, we have numerous
observations of the aftermath of the collision across the electromagnetic spectrum, but also
something very new and cutting edge, the LIGO/VIRGO collaboration saw the gravitational waves
from the incident.
Gravitational waves were predicted by General Relativity, but had not been seen until 2015,
and publicly announced only last year.
Essentially, they are ripples in space time created by major gravitational events, such
as the merger of two black holes.
All detections to date had been black holes merging, but GW170817 changed that.
It was a merger of neutron stars, and that seems to have resulted in an event known as
a kilonova.
The gravitational wave signal was very different than that of a black hole signal.
Firstly, it lasted way longer, about 100 seconds as opposed to the few seconds of black hole
mergers.
Secondly, its frequency increased across the detection.
This will have implications on studying the behavior of gravity itself, such as confirming
that gravity propagates at the speed of light, another prediction of Einstein.
Another implication here is on the subject of gamma ray bursts.
Associated with this event was a short gamma ray burst, GRB 170817A, which appeared about
1.7 seconds after the gravitational wave event.
Up until now, the source of short gamma ray bursts was not well understood, though merging
neutron stars were thought to be a strong candidate, but now the association is on much
more solid footing.
From visible light, which was detected about 11 hours after the gravitational waves, they
were able to determine where this merger occurred, which turned out to be the galaxy NGC 4993,
which is not that far away as far as galaxies go, about 130 million light-years.
But something else was detected that you might not expect in association with the kilonova.
The creation of elements in the universe heavier than iron were thought to be linked, at least
partially, with kilonovas.
That was not confirmed until now however.
In this case, the aftermath of the kilnova was an expanding cloud of heavy elements including
an estimated 10,000 earth masses of gold and platinum.
But now to the mystery this event created.
Scientists know what the masses of these neutron stars were, and post merger there should be
something left.
But it's not clear just what this object would be.
It would either be the heaviest known neutron star, or a very light black hole.
Thanks for listening!
I am futurist and science fiction author John Michael Godier and if you would like to help
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in-depth explorations into the interesting, weird and unknown aspects of this amazing
universe in which we live.
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