Redefining a Heavy Collision

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. Hurt (IPAC)

A brand new examine means that essentially the most huge merger of black holes detected by LIGO/Virgo might have included a shocking light-weight.

Echoes of a Surprising Merger

In May 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 instructed that the individuals on this cosmic collision had been ~85 and ~66 occasions the mass of the Sun, and that they fashioned a closing black hole of ~142 solar lots — an unexpectedly heavy end result 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 lots of the totally different elements of noticed compact binary mergers. GW190521, high heart, is extra huge than every other binary merger we’ve noticed.
LIGO-Virgo / Northwestern U. / Frank Elavsky & Aaron Geller

But GW190521 raised eyebrows for an additional motive as effectively: the estimated lots of the 2 merging black holes fell between 65 and 120 solar lots, a area referred to as the pair-instability mass hole. This vary of lots ought to be inherently off-limits for black holes born from collapsed stars, based mostly on our present understanding of stellar evolution processes.

While there are a lot of hypotheses about how mass-gap black holes may probably type, two scientists have targeted on an alternate angle: what if we had been merely unsuitable in our estimate of GW190521’s part lots?

Checking Our Assumptions

How can we measure part lots from a gravitational-wave sign? Decades of theoretical analysis have produced a huge array of mannequin alerts for mergers with totally different parameters. By evaluating the noticed gravitational-wave sign to the assorted fashions, we will calculate which of them match greatest. But this comparability depends on what are referred to 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 pair 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 University Hannover, Germany) reanalyze the gravitational-wave sign for GW190521 utilizing a totally different 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 much like that discovered by the LIGO collaboration — and one other, through which the part black holes are ~16 and ~170 solar lots. This second possibility turns into much more closely favored when the authors analyze the gravitational-wave sign concurrently with an electromagnetic flare which will have been related to the merger.

An Uneven Pair?

What does this end result inform us? The lots in Nitz and Capano’s second answer 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 through which one part is considerably bigger than the opposite. This sign then offers an thrilling milestone and a chance to study extra concerning the several types of dramatic collisions that happen in our galaxy.

Citation

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


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


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