Virgo Network catches another neutron star collision

Katie Ramirez
January 8, 2020

This latest detection, which took place in April 2019, sadly wasn't accompanied by any other signals, but it does add to our understanding of gravitational waves.

Scientists believe that one of the objects that took part in this collision is a neutron star, and it has a mass between 1.1 and 1.7 times the mass of the sun.

"The combined mass of this binary is much higher than what was expected", said Ben Farr, a LIGO team member based at the University of Oregon.

We don't know yet if GW190425 resulted in a small black hole or a big neutron star, but it - and the object produced by GW170817, which is also still unknown - could reveal some answers about this weird mass gap.

The announcement of the detection of gravitational waves in April was made on Monday at the meeting of the American Astronomical Society in Honolulu, Hawaii, after a study was submitted to "The Astrophysical Journal Letters".

The first detection of gravitational waves from the fiery collision of two neutron stars was made on August 17, 2017, by the LIGO Hanford observatory near Richland and its twin observatory in Louisiana.

The study, submitted to the Astrophysical Journal Letters, is authored by an worldwide team that comprises the LIGO Scientific Collaboration and the Virgo Collaboration, the latter of which is associated with the Virgo gravitational-wave detector in Italy.

According to a new study, astronomers have only discovered gravitational waves for the second time, which resulted from the violent fusion of two neutron stars.

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The signal was only detected by the Livingston detector because the other LIGO detector in Hanford was temporarily offline.

Black hole collisions, as first detected at LIGO Hanford in 2015 and since detected dozens of times, emit no light. This merger was not clearly visible in the Virgo data, but that fact provided key information that ultimately pinpointed the event's location in the sky. For comparison, the August 2017 event was narrowed to a region of just 16 square degrees, or 0.04 percent of the sky.

"This is our first published event for a single-observatory detection", says Caltech's Anamaria Effler, a scientist who works at LIGO Livingston Observatory.

Most of the detections made so far have been from pairs of black holes merging, but scientists have also observed black holes slurping up neutron stars, and in one case two neutron stars crashing into each other.

The masses of the two neutron stars in the binary are about two and 1.4 times the mass of the Sun, respectively.

Both neutron stars and black holes are the ultradense remains of a dead star, but we've never seen a black hole smaller than 5 times the mass of the Sun, or a neutron star larger than around 2.5 times the mass of the Sun.

"This leads to the intriguing possibilities that the old binary system we've discovered formed differently to those observed in the Milky Way and that neutron star binaries this massive may not be detectable by current telescope surveys". Although this was very unusual, it is nearly impossible that the two are black holes, since the black holes are at least five times the solar mass. "And this could have interesting implications for how the pair originally formed". The data from the 2019 event did not indicate which of these scenarios was more likely-more data and new models will be needed to explain the unexpectedly high mass.

This could help astronomers understand how binary neutron stars form.

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