For the third time, physicists have detected a gravitational wave: a tiny ripple in the fabric of space-time.
Like the two previous detections, it came from two colliding black holes, but this pair was much further away and may have been spinning in different directions.
The discovery, reported today in the journal Physical Review Letters, has important implications for our understanding of black holes, dark matter and the early Universe.
It was made on January 4 this year, when an international research team picked up the infinitesimal wobble produced by two black holes, 3 billion light-years away. They spiralled towards each other and eventually merged to form a bigger black hole 50 times the mass of the Sun.
Study co-author Professor Susan Scott said the signal offered fresh and intriguing insights.
"The black holes are not necessarily lined up," said Professor Scott, of the Australian National University, one of several Australian universities involved in the research.
In a binary system like this, the two black holes each rotate on their own axis, as well as circling each other in space.
According to Professor Scott, the new findings offer the first evidence that those individual spins might not always be aligned.
She said the discovery was "a very significant advancement" because it provided some insight into how double black hole systems evolved.
"It's also interesting because black holes of the types of masses that we've found could actually be black holes from the very early Universe and contribute significantly to the dark matter in the Universe," she said.
The gravitational wave was detected using the LIGO observatories 3,000 kilometres apart in Livingston, Louisiana and Hanford, Washington.
Each instrument uses laser beams to constantly measure the lengths of two perpendicular 4km pipes, with stunning accuracy; tiny, fleeting changes in length can reveal a passing gravitational wave.
In 2015 the same 1,000-strong team of scientists detected gravitational waves from black holes 1.3 billion and 1.4 billion light-years away. Those historic discoveries were confirmed and reported in 2016.
At 3 billion light-years, the new discovery is more than twice as distant.
Professor Scott said an upgrade to the LIGO instruments last year made it possible to see further back in time.
"We're constantly improving the sensitivity of the LIGO instrument and as we do that we can see further and further out into space and that means we can pick up more events because we are looking at a bigger volume of space," she said.
The race is now on to find gravitational waves from other sources such as double neutron stars, which are made when giant stars explode and their cores collapse.
"Neutron stars are the very densest types of stars we know about," Professor Scott said.
"We also want to detect single neutron stars that have some kind of minute mountain on top of them, and as they rotate they produce gravitational waves.
While Professor Scott is confident that those first two new sources may be detected soon, she said picking up gravitational waves from near the dawn of the Universe around 13.8 billion years ago "is still some time off".
"We really need to be able to improve the sensitivity further to do that," she said.
"LIGO doesn't tell us very well where the event is exactly," said Professor Scott, who is a member of the newly-formed ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav).
"We know its rough distance but we don't know exactly where on the sky it is."
She said Australian projects such as Skymapper, an optical telescope at Siding Spring, may help pinpoint the source.
Like the two previous detections, it came from two colliding black holes, but this pair was much further away and may have been spinning in different directions.
The discovery, reported today in the journal Physical Review Letters, has important implications for our understanding of black holes, dark matter and the early Universe.
It was made on January 4 this year, when an international research team picked up the infinitesimal wobble produced by two black holes, 3 billion light-years away. They spiralled towards each other and eventually merged to form a bigger black hole 50 times the mass of the Sun.
Study co-author Professor Susan Scott said the signal offered fresh and intriguing insights.
"The black holes are not necessarily lined up," said Professor Scott, of the Australian National University, one of several Australian universities involved in the research.
In a binary system like this, the two black holes each rotate on their own axis, as well as circling each other in space.
According to Professor Scott, the new findings offer the first evidence that those individual spins might not always be aligned.
She said the discovery was "a very significant advancement" because it provided some insight into how double black hole systems evolved.
"It's also interesting because black holes of the types of masses that we've found could actually be black holes from the very early Universe and contribute significantly to the dark matter in the Universe," she said.
The gravitational wave was detected using the LIGO observatories 3,000 kilometres apart in Livingston, Louisiana and Hanford, Washington.
Each instrument uses laser beams to constantly measure the lengths of two perpendicular 4km pipes, with stunning accuracy; tiny, fleeting changes in length can reveal a passing gravitational wave.
In 2015 the same 1,000-strong team of scientists detected gravitational waves from black holes 1.3 billion and 1.4 billion light-years away. Those historic discoveries were confirmed and reported in 2016.
At 3 billion light-years, the new discovery is more than twice as distant.
Professor Scott said an upgrade to the LIGO instruments last year made it possible to see further back in time.
"We're constantly improving the sensitivity of the LIGO instrument and as we do that we can see further and further out into space and that means we can pick up more events because we are looking at a bigger volume of space," she said.
The race is now on to find gravitational waves from other sources such as double neutron stars, which are made when giant stars explode and their cores collapse.
"Neutron stars are the very densest types of stars we know about," Professor Scott said.
"We also want to detect single neutron stars that have some kind of minute mountain on top of them, and as they rotate they produce gravitational waves.
While Professor Scott is confident that those first two new sources may be detected soon, she said picking up gravitational waves from near the dawn of the Universe around 13.8 billion years ago "is still some time off".
"We really need to be able to improve the sensitivity further to do that," she said.
How do we know where the waves are coming from?
Detecting a gravitational wave is one thing; pinpointing its source is another."LIGO doesn't tell us very well where the event is exactly," said Professor Scott, who is a member of the newly-formed ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav).
"We know its rough distance but we don't know exactly where on the sky it is."
She said Australian projects such as Skymapper, an optical telescope at Siding Spring, may help pinpoint the source.
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