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LIGO and Virgo made 5 likely gravitational wave detections in a month

Spacetime ripples came from colliding black holes, neutron stars and maybe a new kind of event

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1:41pm, May 2, 2019
neutron star merging with black hole

NEW TYPE?  Scientists from the LIGO and Virgo experiments may have spotted spacetime ripples from a brand new source: a neutron star melding with a black hole (illustrated in a computer simulation).

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Gravitational wave sightings are now a weekly occurrence.

It took decades of work to find the first set of ripples in spacetime, detected in 2015 (SN: 3/5/16, p. 6). But now, just a month after reviving the search with newly revamped detectors, scientists with the LIGO and Virgo gravitational wave observatories have already made five potential sightings of the tiny, elusive tremors.

“The entire astrophysics community is very excited,” astrophysicist Jess McIver of the LIGO Laboratory at Caltech said during a telephone news conference May 2. “We’re quickly building up a catalog of events.”

Analysis of the detections is in the early stages, and will need to be confirmed by further work. But one event in particular has piqued interest as possibly the first-ever sighting of a black hole colliding with a neutron star, the dense remnant of a dead star.

For the first time, LIGO — the U.S.-based Advanced Laser Interferometer Gravitational-Wave Observatory — and Virgo, based in Italy, are publicly announcing candidate gravitational wave signals as they happen, rather than reporting them after they’ve been established.

Picking up

In just one month, scientists have already spotted 5 possible gravitational wave events, plotted here as a function of their approximate distance from Earth. That’s compared to 11 events from all previous observations combined. Most detections are from merging black holes, but neutron star mergers (red) are also in the mix. And one event (yellow) might be a mash up between a black hole and a neutron star.

Gravitational wave detections by LIGO and Virgo are becoming more frequent

Researchers also spotted three possible instances of black holes colliding, the most commonly detected source of gravitational waves. In previous searches, LIGO and Virgo have found a total of 10 such events (SN: 1/19/19, p. 10).

And on April 25, for the second time ever, scientists observed waves that were apparently from two merging neutron stars. Astronomers around the world searched for light from the crash, which could help illuminate how elements such as gold are produced in the universe (SN: 11/11/17, p. 6). But no definite light show from the blast has yet been detected.

A day later, physicists detected the enticing potential merger of a black hole and neutron star. Although the detection could be a false alarm, astronomers are trying to pinpoint light from that cataclysm as well. Observing such a coalescence could help uncover the properties of the mysterious, ultradense material that makes up a neutron star or reveal how fast the universe is expanding.

Citations
Further Reading

E. Conover. The LIGO and Virgo gravitational wave detectors are back on. Science News Online, April 1, 2019.

E. Conover. Scientists’ collection of gravitational waves just got a lot bigger. Science News. Vol. 195, January 19, 2019, p. 10.

E. Conover. Neutron star collision showers the universe with a wealth of discoveries. Science News. Vol. 192, November 11, 2017, p. 6.

A. Grant. Gravity waves from black holes verify Einstein’s prediction. Science News. Vol. 189, March 5, 2016, p. 6.

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