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Redefining a Heavy Collision – Sky & Telescope

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Black hole collision (art)
Artist’s impression of the collision of two black holes that produced the gravitational-wave sign GW190521.
LIGO / Caltech / MIT / R. Harm (IPAC)

A brand new research means that probably the most large merger of black holes detected by LIGO/Virgo might have included a stunning light-weight.

Echoes of a Stunning Merger

In Might 2019, a collision of two black holes shook spacetime, registering within the LIGO and Virgo gravitational-wave detectors because the heaviest black-hole merger found but. Initial analysis of GW190521 urged that the contributors on this cosmic collision had been ~85 and ~66 occasions the mass of the Solar, and that they shaped a closing black gap of ~142 photo voltaic plenty — an unexpectedly heavy consequence that lands within the elusive class of intermediate-mass black holes.

Masses in the Stellar Graveyard
The quickly increasing “stellar graveyard”, a plot of the plenty of the completely different parts of noticed compact binary mergers. GW190521, prime middle, is extra large than every other binary merger we’ve noticed.
LIGO-Virgo / Northwestern U. / Frank Elavsky & Aaron Geller

However GW190521 raised eyebrows for an additional purpose as properly: the estimated plenty of the 2 merging black holes fell between 65 and 120 photo voltaic plenty, a area generally known as the pair-instability mass hole. This vary of plenty must be inherently off-limits for black holes born from collapsed stars, primarily based on our present understanding of stellar evolution processes.

Whereas there are numerous hypotheses about how mass-gap black holes might doubtlessly type, two scientists have centered on another angle: what if we had been merely mistaken in our estimate of GW190521’s part plenty?

Checking Our Assumptions

How can we measure part plenty from a gravitational-wave sign? A long time of theoretical analysis have produced an enormous array of mannequin alerts for mergers with completely different parameters. By evaluating the noticed gravitational-wave sign to the assorted fashions, we will calculate which of them match greatest. However this comparability depends on what are known as priors — a set of assumptions that go into the evaluation and have an effect on the result.

The observed gravitational-wave signal of GW190521
The noticed gravitational-wave sign of GW190521 in every of the three detectors (black), plotted with two best-fit fashions: one for when the part mass ratio is between 1 and a couple of (blue) and one for a mass ratio between 2 and 25 (orange).
Nitz & Capano 2021

In a latest publication, scientists Alexander Nitz and Collin Capano (Max Planck Institute for Gravitational Physics and Leibniz College Hannover, Germany) reanalyze the gravitational-wave sign for GW190521 utilizing a unique set of priors and constraints than the unique evaluation accomplished by the LIGO collaboration.

Nitz and Capano discover that their evaluation admits two doable options for GW190521: one just like that discovered by the LIGO collaboration — and one other, during which the part black holes are ~16 and ~170 photo voltaic plenty. This second possibility turns into much more closely favored when the authors analyze the gravitational-wave sign concurrently with an electromagnetic flare that will have been related to the merger.

An Uneven Pair?

What does this consequence inform us? The plenty in Nitz and Capano’s second resolution each lie exterior of the pair-instability mass hole, neatly resolving the paradox beforehand created by this merger.

If the authors’ interpretation is right, then GW190521 would symbolize the primary detected intermediate-mass-ratio inspiral — a kind of merger during which one part is considerably bigger than the opposite. This sign then supplies an thrilling milestone and a possibility to be taught extra in regards to the several types of dramatic collisions that happen in our galaxy.


“GW190521 Might Be an Intermediate-mass Ratio Inspiral,” Alexander H. Nitz and Collin D. Capano 2021 ApJL 907 L9. doi:10.3847/2041-8213/abccc5

This submit initially appeared on AAS Nova, which options analysis highlights from the journals of the American Astronomical Society.


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