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
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