It looks like we've made another profit for gravitational wave astronomy. A new gravitational wave detection is the best candidate yet for an unprecedented kind of cosmic collision – the elusive fusion between a black hole and a neutron star.
The event, named S190814bv, was captured by the LIGO and Virgo interferometers on August 14 at 11 minutes past 21:00 UTC. And after initial analysis, there is a 99 percent chance that it is a neutron star black hole kaboom.
Even as you read this, scientists stare into space over data, looking for the light that the neutron star may have left behind as it is absorbed into the black hole.
"It's like the night before Christmas," astronomer Ryan Foley from the University of California at Santa Cruz told ScienceAlert. "I'm just waiting to see what's under the tree."
Since this amazing first gravitational wave detection – a collision between two black holes with star mass – was announced in February 2016, the field has only gotten stronger. The technology is so sophisticated that collisions between two neutron stars can be detected – objects that are much less massive than black holes.
Both neutron stars and black holes are the ultra-dense remnants of a dead star, but we have never seen a black hole smaller than five times the mass of the sun or greater than 2.5 times the mass of the sun.
But a collision between a black hole and a neutron star escaped us. One discovery seemed to have been an event earlier this year, but chances were only 13 percent. And the signal-to-noise ratio was so low that astronomers did not track it.
This is not the case with S190814bv. The signal is very strong and the astronomers are excited – if it's really a collision between a neutron star and a black hole, it's the first time such a binary system has ever been seen.
This would mean that such hitherto hypothetical binary systems are actually possible. We could even get clues to their origins – did they form themselves as binaries, lived, grew and died together? Or has the black hole caught a passing neutron star in its orbit?
Believe it or not, we can learn that from the gravitational wave signal – waves in space-time caused by a massive collision, like a stone falling into a pond – if it's strong enough. Indications of the formation of the binary are encoded in the waveform along with the masses of each object, their speed and acceleration.
"From the gravitational wave signal one can obtain information about the rotations of the individual objects and their orientation in relation to the axis to the orbit. " the physicist Peter Veitch from the University of Adelaide in Australia and OzGrav (the Australian branch of the LIGO Scientific Collaboration) to ScienceAlert.
"[We’re] Check that the rotation rotations of the individual objects are aligned with each other, which might indicate that they were originally in a binary system. For example, if a compact object was detected by something other than fused galaxies, it is expected that these objects will have different rotations pointing in different directions. "
Foley and his colleagues are currently investigating a galaxy in the Keck Observatory that is about 900 million light-years away. There they believe that the signal could have originated. They are looking for electromagnetic radiation that could result from colliding with a neutron star.
And of course there is the burning question: What do neutron star entrails look like?
"We'd like to see a black hole break a neutron star when they come together," says Australian Scottish physicist Susan Scott of the Australian National University and OzGrav.
"This would give us important information about the material that makes up the densest stars in the universe – neutron stars – which remains a very open question in this area."
If no electromagnetic radiation is detected, it may mean that astronomers are simply looking in the wrong place. Or it could mean that the electromagnetic radiation is too weak to be detected.
This could also mean that no neutron star is involved – which would be very interesting because the signal indicates that the smaller object has less than three times the mass of the sun. If it's not a neutron star, it's perhaps the smallest black hole we've ever discovered.
Or it could mean that the dynamics between a neutron star and a black hole, when they converge into a slightly larger black hole, is even stranger than we knew.
"I like to think (for the moment) that if a black hole is much more massive than a neutron star, then the neutron star will be torn apart as it merges Within the event horizon of the black hole! In this case, even if a lot of light is generated, no one escapes the black hole so we can see it, "Foley told ScienceAlert.
"That's as close to science fiction as it gets."