On Aug. 14, 2019, a gravitational wave -- a massive ripple through the fabric of space-time -- washed over the Earth. The wave was detected by sophisticated, fine-tuned lasers in the U.S. and Italy. And it was astonishing.
The signal was one of the strongest ever seen by the gravitational wave scientists at the Laser Interferometer Gravitational-wave Observatory and Italy's Virgo observatory.
After an alert was sent out moments after detection, teams of astronomers across the world turned their telescopes to the point in space that the wave emanated from.
But their searches came up empty. No light, no X-rays, no infrared, no gamma rays.
The event was puzzling. And it became more puzzling as scientists began to pore over the data.
On Tuesday, researchers from the LIGO and Virgo collaborations detailed their full analysis of the gravitational wave detection, dubbed GW190814, in The Astrophysical Journal Letters. It's the first detailed study of the epic cosmic collision, and it only deepens the mystery.
"GW190814 is, I think, the first time we've observed gravitational waves where the source of the waves is genuinely puzzling," said Rory Smith, an astrophysicist at Monash University in Australia. "I've been in LIGO for just over 10 years now, and this is certainly one of the most exciting events we've seen."
The key to the research are the two LIGO facilities and the Virgo facility, which can detect gravitational waves.
Extreme astronomical objects like black holes and neutron stars send out waves across the cosmos when they collide. The facilities are essentially listening in to the sounds of massive cosmic beasts colliding with each other -- and then working backward to understand their physical characteristics.
Smith and his colleagues have been working on simulating these types of collisions using supercomputers, which help perform that back-calculation and can infer what the objects are, their likely masses and their whereabouts.
"We use fancy parallelized algorithms which can run our analyses on a supercomputer cluster containing many hundreds, or thousands of individual computers," he said. "Running the same analysis on your laptop would have taken around 50 to 100 years."
The observations show GW190814 pair collided around in a deep corner of space, 800 million light-years away. One half of the pair is definitely a black hole, about 23 times more massive than our sun. But its dancing partner is mysterious -- the other object is only around 2.6 times more massive than our sun, which puts it in a weird position.
"It's something that has not been seen before," said Hannah Middleton, an astrophysicist at the University of Melbourne. It could be a neutron star, that possibility is still on the table, but it might also be a black hole. Middleton says it is "a bit of a mystery" as to which... but it's also a slight problem.
"It's hard to explain how either a black hole or a neutron star could be around 2.6 solar masses," notes Smith.
Scientists have never detected a black hole that's so light. Neutron stars are not expected to be that heavy -- they collapse into black holes when they get too big. So the mysterious object seems to be some sort of Goldilocks star that doesn't fit our current understanding. Whatever it turns out to be, it will rewrite our knowledge on one of the two extreme objects.
-- This article originally appeared on CNET.com.