More gravitational waves detected
Scientists have collected a second burst of gravitational waves sweeping through the Earth.
The warping of space-time was sensed on Christmas Day in the US at the Advanced LIGO laboratories – the same facilities that made the historic first detection in September last year.
Back then, the waves came from two huge coalescing black holes.
This new set of waves, likewise, is ascribed to a black hole merger – but a smaller one.
Reporting the event in the journal Physical Review Letters, the international collaboration that operates LIGO says the two objects involved had masses that were 14 and eight times that of our Sun.
The data indicates the union produced a single black hole of 21 solar masses, meaning they radiated pure energy to space equivalent to the mass of one star of Sun size.
It is this energy, in the form of gravitational waves, that was sensed in the laser interferometers of the LIGO labs in Livingston, Louisiana, and Hanford, Washington State, at 22:38 Eastern Standard Time on 25 December (03:38 GMT, 26 Dec; Boxing Day in Europe).
According to UK collaboration member Prof Bernard Schutz of Cardiff University, making a second detection proves the first was not just an isolated event, and that Advanced LIGO really does have the capability to open up a new cosmic realm to investigation.
“It shows the first event wasn’t just a fluke. It shows that the Universe is filled with black holes spiralling in together and merging and giving off these huge bursts of gravitational waves quite regularly. It’s a violent Universe,” he told BBC News.
It has been one big celebration since scientists fulfilled their decades-long quest in September by detecting the warping of space generated from the merger of black holes 29 and 36 times our Sun’s mass.
Key LIGO pioneers have been lauded with prizes, and there are very short odds now on the achievement being crowned with a Nobel in October.
But the researchers involved say the effort was never about just the one detection; the dream has always been to use the routine observation of gravitational waves to learn new things about the cosmos. And that is apparent in the latest result.
Because of their lighter mass, the Christmas Day black holes spent more time – about a second – in the sensitive band of the LIGO instruments. The data captures the last 27 revolutions the black holes make around each other.
This has allowed scientists to glean insights about the objects not possible in September, including the realisation that at least one of the progenitor holes was spinning
Theorists have always said black holes should spin, but this is very strong observational evidence for the phenomenon.
“One of the black holes was spinning with the dimensionless number of 0.2,” Prof Gabriela González from Louisiana State University, US, told reporters.
“We measure between zero (not spinning) and one (maximally spinning). We can also measure the spin of the final black hole but we expect that black hole to have a spin (because of the merger); we don’t know about the original black holes and that’s astrophysical information that informs the scenarios for how black holes form.”
“The data indicates the union produced a single black hole of 21 solar masses, meaning they radiated pure energy to space equivalent to the mass of one star of Sun size.”
“It shows that the Universe is filled with black holes spiralling in together and merging and giving off these huge bursts of gravitational waves quite regularly. It’s a violent Universe,”
that it is..