The rumours were true. Another gravitational wave – a ripple in space itself – has been detected. This time they were created when two neutron stars smashed into each other.
This is the fourth time a gravitational wave signal has been seen, more than 100 years since Albert Einstein predicted their existence, and it’s been two years since LIGO’s incredible first detection. It is also the first time the signal has been seen from neutron stars, with the first three detections coming from pairs of black holes.
If the acronym LIGO isn’t in your repertoire, it stands for Laser Interferometer Gravitational-Wave Observatory. It’s essentially a large-scale physics experiment, where astrophysicists convene to monitor and observe gravitational waves. LIGO is funded by the National Science Fund (NSF), and holds the distinction of being the largest and most ambitious project to be funded by the body. It was conceived of, constructed, and is operated by two mediocre academic institutions known Caltech and MIT.
This latest signal was detected by two advanced LIGO sensors in the US, and, for the first time, by sensors in Europe, namely the Virgo detector near Pisa, Italy. This three-way detection meant researchers were able to more accurately determine the source of the gravitational waves, and independently confirm the initial 2015 discovery.
Virgo isn’t as accurate, or to use the correct term, as sensitive as LIGO but the combination of all three magnified the precision by a factor of 10.
Virgo was completed in 2003. It features a €300 million interferometer with 3-kilometer-long arms and was funded by the French National Center for Scientific Research (CNRS) and the Italian National Institute of Nuclear Physics (INFN). Researchers from both the LIGO and Virgo projects joined a data-sharing agreement in 2007 and then in August, Virgo joined LIGO in the search for gravitational waves.
This latest announcement had been foretold. At the end of August, J Craig Wheeler, an astrophysicist at the University of Texas, took to Twitter to announce: “Rumor of exciting new LIGO source”. Three days later, he confirmed “New LIGO. Source with optical counterpart. Blow your sox off!”
Explaining more about the latest detection, Christopher Berry from the University of Birmingham, wrote: “On 14 August, we found a signal. A signal that was observable in all three detectors. Virgo is less sensitive than the LIGO instruments, so there is no impressive plot that shows something clearly popping out, but the Virgo data do complement the LIGO observations, indicating a consistent signal in all three detectors.”
Images: NASA Goddard Space Flight Center, used under Creative Commons
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