Addressing a Gap in Our Knowledge of Black Holes

The merger of a black-hole binary
Simulated picture of the merger of a black-hole binary
SXS Lensing

One way for black holes to kind is in supernovae, or the deaths of large stars. However, our present data of stellar evolution and supernovae means that black holes with plenty between 55 and 120 solar plenty can’t be produced through supernovae. Gravitational-wave indicators from black hole mergers provide us an observational check of this “gap” in black hole plenty.

Black Hole Boundaries

Supernova SN 2016iet
The supernova SN 2016iet, which is perhaps one of the primary noticed pair-instability supernovae. The strains present the location of the instrument used to take spectra of the supernova.
Adapted from Gomez et al. 2019

You want a large star to go supernova to supply a black hole. Unfortunately, extraordinarily large stars explode so violently they depart nothing behind! This situation can happen with pair-instability supernovae, which occurs in stars with core plenty between 40 and 135 solar plenty. The “pair” in “pair-instability” refers back to the electron–positron pairs which are produced by gamma rays interacting with nuclei in the star’s core. Energy is misplaced in this course of, that means that there’s much less resistance to gravitational collapse.

As the star collapses additional, two issues can occur. If the star is sufficiently large, its core ignites in an explosion that tears the star aside, leaving no remnant. If the star is much less large, the core ignition causes the star to pulse and shed mass until it leaves the pair-production stage and its core collapses usually into black hole. The most large black hole that may be produced in this situation is roughly 55 solar plenty, forming the decrease finish of the black hole mass hole.

On the opposite aspect of the mass hole, it’s theoretically attainable for sure large stars to break down usually with out getting into the pair-production state, thus evolving into black holes with plenty better than 120 solar plenty. The distinctive factor about these large stars is that they’re low metallicity, containing virtually no parts which are heavier than helium.

So the underside line is that we’re unlikely to look at any black holes with plenty between 55 and 120 solar plenty. But how can we check this prediction? Gravitational-wave indicators are an possibility! Properties of merging black holes are coded into the gravitational waves produced by the merger, together with the black hole plenty. So, a latest research led by Bruce Edelman (University of Oregon) checked out our present catalog of black hole merger indicators to see if the mass hole would emerge from the info.

Mind the Gap, If There Is a Gap

A chart showing the likely masses of the black holes involved in the 46 mergers considered in this study.
The doubtless plenty of the black holes concerned in the 46 mergers thought-about in this research. The x-axis is the anticipated mass of one black hole and the y-axis is the anticipated mass of the opposite. Each contour represents a merger. However, the bolded green and purple mergers characterize the identical merger, GW190521, and correspond to values from two totally different research. The orange areas characterize the expected mass hole.
Adapted from Edelman et al. 2021

Edelman and collaborators used two established mannequin distributions of black hole plenty to strategy the issue. They additionally altered the fashions so the hole was explicitly allowed and so increased black hole plenty may very well be explored with out artificially inflating the speed of mergers above the hole. Edelman and collaborators then match their fashions to information from 46 binary black hole mergers noticed by the Laser Interferometer Gravitational-Wave Observatory and the Virgo interferometer.

Interestingly, the existence of the hole is quite ambiguous! One issue is the inclusion of the merger related to the sign GW190521, which was doubtless a excessive mass merger whose part black holes straddle the mass hole. If the hole doesn’t exist, it’s attainable that the sudden black holes are fashioned by the merging of smaller black holes. On the entire, this consequence factors to many avenues of research with regards to pair-instability supernovae and black hole formation!


“Poking Holes: Looking for Gaps in LIGO/Virgo’s Black Hole Population,” Bruce Edelman et al 2021 ApJL 913 L23.

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


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