Conditions favorable for gravitational wave-emitting mergers of massive black holes exist in the outer gas disks of big spiral galaxies, according to a study by Rochester Institute of Technology astronomer Sukanya Chakrabarti and co-authors.
This Hubble image shows the spiral galaxy Messier 83. Image credit: NASA / ESA / Hubble Heritage Team / STScI / AURA / W. Blair, STScI & JHU / Carnegie Institution of Washington / Las Campanas Observatory / NOAO.
“This study winds back time on massive black holes by analyzing their visible precursors — supernovae with collapsing cores,” the astronomers said.
“The slow decay of these massive stars creates bright signatures in the electromagnetic spectrum before stellar evolution ends in black holes.”
Using data from the Lick Observatory Supernova Search, they compared the supernovae rate in outer spiral galaxies with that of known hosts (dwarf/satellite galaxies) and found comparable numbers for typical spiral outskirts and typical dwarf galaxies, roughly two core-collapse supernovae per millennium.
“Low levels of elements heavier than hydrogen and helium found in dwarf/satellite galaxies create favorable conditions for massive black holes to form and create binary pairs,” Dr. Chakrabarti said.
“A similar galactic environment in the outer disks of spiral galaxies also creates likely hunting grounds for massive black holes.”
“If these core-collapse supernovae are the predecessors to the binary black holes detected by LIGO, then what we’ve found is a reliable method of identifying the host galaxies of LIGO sources.”
“Because these black holes have an electromagnetic counterpart at an earlier stage in their life, we can pinpoint their location in the sky and watch for massive black holes.”
Published in the Astrophysical Journal Letters, the findings complement the team’s 2017 study, which showed that the outer parts of spiral galaxies could contribute to LIGO detection rates.
The regions form stars at a comparable rate to dwarf galaxies and are low in heavy element content, creating a conducive home for massive black holes.
The current study isolates potential candidates within these favorable galactic environments.
“We see now that these are both important contributors. The next step is to do deeper surveys to see if we can improve the rate,” Dr. Chakrabarti said.
“This work may help us determine which galaxies to be on the lookout for electromagnetic counterparts of massive black holes,” added co-author Brennan Dell, a recent graduate from the Rochester Institute of Technology.
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Sukanya Chakrabarti et al. 2018. The supernova rate beyond the optical radius. ApJL, in press; arXiv: 1807.07585
