A signal like none before

Apr 23, 2020 | Black Holes (Stellar)

A signal like none before
Binary black hole merger where the two black holes have distinctly different masses of about 8 and 30 times that of our Sun. CREDIT: N. Fischer, H. Pfeiffer, A. Buonanno (Max Planck Institute for Gravitational Physics), Simulating eXtreme Spacetimes project

Even though things here on earth are slowing to a punctuated shelter-in-place, the universe just keeps doing its thing, spewing out events at its regular and random cadence. While most observatories on the ground have shut down, their observations from their most recent runs are still being processed. This means that while there will be some future dead time when no results are coming our way, we haven’t hit that point yet because there is a lag between when observations are made and when they are analyzed and published. This lag means that while the LIGO gravitational wave detectors are currently shut down, we have a cool new result about a GW that was detected last year: GW190412. Just a year after it’s detection, a new paper posted on arxiv.org describes how an 8 Solar Mass and 30 solar mass pair of black holes merged into a new and greater black hole. Until now, the majority of LIGO’s BH-BH detections have been similarly sized black holes merging with a characteristic “Woooop” which increases in pitch without a lot of harmonics. With these asymmetric masses, the waves have overtones, more like how one string on a guitar will create overtones over a sympathetically resonating guitar cavity. Different shaped cavities, or in this case different sized distortions in space time, resonate differently, and we can see these resonances in the LIGO detections. This kind of an asymmetric observation isn’t unexpected: Black holes should come in a variety of sizes. This is just the first time we’ve seen this, and firsts are good, because they confirm the universe works the way we expect. In this case, the huge difference in mass between the two black holes indicates this may be a multi-generational merger, with the 30 solar mass black hole originating through the merger of other smaller black holes. This is, after all, the story of our universe – smaller things forever merging into larger and larger objects. GW190412 is just 1 of 56 events in the most recent observing run performed by LIGO. We all look forward to seeing what is lurking in those other 55 events. Some will likely turn out to be something here on Earth jiggling the system, but others… well… we’re just going to have to wait for those publications to see.

More:

LIGO and Virgo detectors catch first gravitational wave from binary black hole merger with unequal masses (Albert Einstein Institute)

GW190412: Observation of a Binary-Black-Hole Coalescence with Asymmetric Masses (ArXiv.org)

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