Collision between black hole and ‘mysterious object’ puzzles astronomers

On August 14, 2019, a gravitational wave – a massive wave through the fabric of space-time – flooded the earth. The wave was captured by sophisticated, fine-tuned lasers in the United States and Italy. And it was amazing. While the lasers had previously recorded Collisions with black holes and Neutron star collisionsThey now proposed something unprecedented: a black hole that shattered into a neutron star.

The signal was one of the strongest ever seen by gravitational wave scientists at the laser interferometer gravitational wave observatory and the Italian Jungfrau Observatory. After an alarm went off shortly after the discovery, teams of astronomers around the world turned their telescopes to the point in space from which the wave emanated.

But their search was empty. No light, no X-rays, no infrared, no gamma rays.

The event was puzzling. And it got more puzzling when scientists started thinking about the data. On Tuesday, researchers from the LIGO and Virgo collaborations describe their full analysis of gravitational wave detection, called GW190814, in The Astrophysical Journal Letters. It is the first detailed study of the epic cosmic collision and only deepens the mystery.

“GW190814 is, I believe, the first time we have observed gravitational waves where the source of the waves is really puzzling,” said Rory Smith, astrophysicist at Monash University in Australia. “I’ve been with LIGO for a little over 10 years now and this is certainly one of the most exciting events we’ve ever seen.”

The key to the research are the two LIGO devices and the Virgo device, which can detect gravitational waves. Extreme astronomical objects such as black holes and neutron stars send waves across the cosmos when they collide. The facilities essentially listen to the sounds of massive cosmic beasts colliding – and then work backwards to understand their physical properties.

Smith and his colleagues have worked on simulating this type of collision using supercomputers. These help to carry out this recalculation and can infer the objects, their likely masses and their location.

“We use fancy parallelized algorithms to run our analyzes on a supercomputer cluster that contains many hundreds or thousands of individual computers,” he said. “It would have taken about 50 to 100 years to do the same analysis on your laptop.”

The observations show that the GW190814 pair collided in a deep corner of space, 800 million light years away. Half of the pair is definitely a black hole, about 23 times more massive than our sun. But his dance partner is mysterious – the other object is only about 2.6 times as massive as our sun, which puts it in a strange position.

“It’s something that has never been seen before,” said Hannah Middleton, astrophysicist at the University of Melbourne. It could Be a neutron star, this possibility is still on the table, but it could also be a black hole. Middleton says it’s “a bit puzzling” what … but it’s also a light Problem.

“It is difficult to explain how a black hole or neutron star can have around 2.6 solar masses,” notes Smith.

Scientists have never discovered such a light black hole. Neutron stars are not expected to be that heavy – they fall into black holes when they get too big. So the mysterious object appears to be a kind of goldilocks star that does not fit our current understanding. Whatever turns out, it will rewrite our knowledge of one of the two extreme objects.

Interestingly, when it is an ultra-heavy neutron star, Smith says, “maybe even new physics would be needed to explain this.” If it’s a bright black hole, our understanding of how and where the light-hungry cosmic beasts form will be rewritten. It is a win-win scenario for science.

GW190814 is only the second time that gravitational wave detection has identified a significant discrepancy in the mass of the objects. A collision between two black holes discovered on April 12, 2019 with the name GW190412 showed a mass difference of over 20 solar masses. These big differences are incredibly helpful: they allow researchers to test Einstein’s theory of general relativity. Both GW190814 and GW190412 fit Einstein’s predictions – so we haven’t broken physics (yet).

GW190814 is exceptionally rare. We have only seen one of these events in three years of observation and it will be a while before we find more. The LIGO and Virgo detectors have been switched off since March and end their last observation run due to the Corona virus Pandemic and won’t be back online until the end of next year.

“Our detectors are currently being updated to be more sensitive when they are turned on,” said Smith. “At this point, we are not only expecting more systems like GW190814, but probably also other unexpected sources of gravitational waves.”

That leaves a lot of room to explain the mysterious object. Is it a black hole? Is it a neutron star?

“Theorists are having a lot of fun trying to explain GW190814!” said Smith.

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