More Gravity Waves Detected
LIGO Detects Gravitational Waves Detected for Third Time, Caltech
“The Laser Interferometer Gravitational-wave Observatory (LIGO) has made a third detection of gravitational waves, ripples in space and time, demonstrating that a new window in astronomy has been firmly opened. As was the case with the first two detections, the waves were generated when two black holes collided to form a larger black hole. The newfound black hole, formed by the merger, has a mass about 49 times that of our Sun. This fills in a gap between the masses of the two merged black holes detected previously by LIGO, with solar masses of 62 (first detection) and 21 (second detection).”
Was there a seismograph nearby to confirm that they weren’t detecting earthquakes?
Yes, the LIGO detectors have many seismometers to detect earthquakes.
Avoiding that sort of false detection is built into LIGO. They use measurements from two sites, about 3000 km apart. One in Louisiana and one in Washington state. An earthquake near one could give a false signal. But if there isn’t a similar signal at both sites, with the proper timing, amplitude and phase to match a gravitational wave, they automatically ignore it. The signal from colliding black holes also varies in frequency and amplitude, in a way an earthquake would not. Figuring out how to filter out earthquakes, or even passing trucks, has been the long-standing problem with gravitational wave detections. It looks like LIGO has finally figured out how to do it right.
Figuring out how to filter out terrestrial noise from the data stream is indeed important, but that is not the big change that led to detecting black hole mergers a year and a half ago. More important is keeping those signals from getting into the data stream in the first place. The upgrade from LIGO to Advanced LIGO included better isolation of the mirrors from ground motion. Reduction of thermal motion in the mirrors and photon shot noise were also parts of the upgrade, and about as essential to the detections.
I wonder how they tease out of the data the sizes of the colliding black holes? Masses of 62 and 21 are widely reported, but surely there’s a confidence interval in there? Why not, say, 60 and 23? I’ve not seen a layman-accessible explanation.
For that matter, how is the date of the event determined? The telescopes were bathed in the data for mere nanoseconds! (maybe pico seconds, actually), as the wave passed our back yard, on the way to…wherever.
So 62+21=83; and the mass of the emergent object is given as 49. As 83-49=34, does this mean that mass equivalent to 34 solar masses has been converted into energy?
The mind boggles.
Go look at the paper. See section IV, “Source Properties”.
https://journals.aps.org/pr…