On the 17th August 2017 a gravitational wave
signal was detected on Earth by the LIGO and Virgo
gravitational wave detectors. The signal came
from two neutron stars, each the size of a
city and between one to one and a half times
heavier than the sun, when they crashed into
each other over 130 million light years away.
The signal lasted nearly 100 seconds, making
it the longest, closest and most accurately
located gravitational wave signal detected
so far. But what makes this detection really
special is that for the first time ever electromagnetic
observations were made that coincided with
the signal. Nearly two seconds after the neutron
stars crashed into each other, a fireball
of gamma rays was released, as the stars formed
one ultradense object. Almost 11 hours later
a kilonova occured, where material left over
from the collision, that glows with light,
was blasted into space. From this detection
5 new discoveries were made: Gravitational
waves travel at the speed of light, the expansion
rate of the universe called the Hubble constant
was measured, information about the structure
of a neutron star was unveiled, merging neutron
stars are sources for short gamma ray bursts,
and finally, my favourite - colliding neutron
stars are the factories for the heavier elements,
such as gold, in the universe.
