All known black holes weigh more than five suns, while all known neutron stars-born from lighter stars that stopped short of becoming black holes-weigh less than three suns. On that August day, the automatic system confidently declared that at least one of the objects that produced GW190814 fell into the “mass gap,” a wasteland, spanning three to five solar masses, seemingly bereft of black holes and neutron stars. The LIGO-Virgo collaboration’s algorithmic pipeline spits out a basic classification based on the shape of a wave, its duration and other factors almost instantly-Hanna’s team aims for under 20 seconds-so astronomers can immediately slew their telescopes in the celestial direction the wave came from. “The first thing I knew was that it was extremely significant,” Hanna says, “kind of off-the-charts loud.” His group specializes in rapid classification of LIGO events, so he immediately logged in to check the wave’s details. An “Off-The-Charts” SignalĬhad Hanna, a LIGO collaborator and astrophysicist at Pennsylvania State University, was celebrating his wedding anniversary with his wife when his phone went off. While the classification remains uncertain, this event, now known as GW190814, marks the beginning of a new era of astrophysical studies, with implications for how researchers understand Einstein’s general theory of relativity, the deaths of stars and the behavior of extreme matter. This may be the first such event detected with confidence and, after black hole–black hole mash-ups and mergers between two neutron stars, the third variety of collision detected by gravitational waves. Subsequent analysis recategorized the signal as a collision between a black hole and a neutron star, a stellar remnant in which gravity squeezes an entire sun’s mass into a ball the size of a city. An automatic first pass pegged it as resulting from an unprecedented merger between a pair of bodies too light to classify, sending astronomers scrambling to look for additional electromagnetic emissions from the event. and the Virgo Observatory in Italy at 21:11:18 UTC on August 14, 2019. The wave was detected by LIGO in the U.S. “My jaw dropped when I saw the data,” says Geoffrey Lovelace of California State University, Fullerton, a member of the Laser Interferometer Gravitational-wave Observatory (LIGO) Scientific Collaboration. This time, however, astrophysicists instantly knew that the observed event was special. An automated system sent out a preliminary alert 21 seconds later, vibrating smartphones and pinging laptops around the world.Ī few years after the Nobel Prize–winning first gravitational-wave detection, which stemmed from a pair of colliding black holes, such alerts had become commonplace. Their merger shook the fabric of space with a gravitational wave that swept through Earth on August 14, 2019, rippling through three pairs of carefully calibrated lasers designed to detect their passage.
Some 870 million years ago two dead stars became one.
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