Astronomers have now tallied up more gravitational wave sightings than they can count on their fingers.
Scientists with the LIGO and Virgo gravitational wave observatories report four new sets of these ripples in spacetime. Those additions bring the total count to 11, the researchers say in a study published December 3 at arXiv.org, marking major progress since the first gravitational wave detection 2015 (SN: 3 / 5 / 16, p. 6).
All but one of the 11 sets of waves were stirred up in violent collisions of two black holes. The one remaining detection, reported in October 2017, instead came from the smashup of two stellar corpses called neutron stars (SN: 11 / 11 / 17, p. 6).
The observations are beginning to reveal how often such waves jiggle the cosmos, and the properties of the shadowy cosmic figures that unleash the ripples. For example, the data hint that black holes may have merged more frequently earlier in the universe’s history, the researchers report in a second study posted December 3 at arXiv.org. The team also concluded that few mergers involve black holes bigger than about 50 times the sun’s mass.
“There’s real strong evidence that those [larger] black holes are missing,” says LIGO member Daniel Holz, an astrophysicist at the University of Chicago. Some theoretical physicists had predicted such a dearth of bulky black holes, based on the physics of stellar explosions that produce the cosmic chasms.
Record-breaking black holes produced one of the new sets of spacetime shivers. The combined mass of the colliding behemoths was the largest yet spotted, with one black hole weighing in at about 50 times the mass of the sun, and the other at 34 times the sun’s mass. Those ripples also originated farther away than any previous detection: about 9 billion light-years from Earth, give or take a few billion. “It stands out in every possible way,” says physicist Emanuele Berti of Johns Hopkins University, who was not involved with the research. “It’s super interesting.”
LIGO’s two detectors — located in Hanford, Wash., and Livingston, La., — and Virgo, near Pisa in Italy, are shuttered for upgrades until next spring. Improvements to the equipment could triple the number of gravitational wave sightings, Holz says. “We’re going to get a whole bunch more.”