If Intermediate-Mass Black Holes (IMBHs) are real, astronomers expect to find them in dwarf galaxies and globular clusters. There’s tantalizing evidence that they exist but no conclusive proof. So far, there are only candidates.
The Dark Energy Spectroscopic Instrument (DESI) has found 300 additional candidate IMBHs.
Logic says that IMBHs should exist. We know of stellar-mass black holes, and we know of supermassive black holes (SMBHs). Stellar-mass black holes have between five and tens of solar masses, and SMBHs have at least hundreds of thousands of solar masses. Their upper limit is not constrained. Astrophysicists think these black holes are linked in an evolutionary sequence, so it makes sense that there’s an intermediate step between the two. That’s what IMBHs are, and their masses should range from about 100 to 100 thousand solar masses. IMBHs could also be relics of the very first black holes to form in the Universe and the seeds for SMBHs.
The problem is that there are no confirmed instances of them.
Omega Centauri, the brightest globular cluster in the Milky Way, is one of the prime candidates for an IMBH. There’s an ongoing scientific discussion about the cluster and the potential IMBH in its center. Stars in the cluster’s center move faster than other stars, indicating that a large mass is present. Some scientists think it’s an IMBH, while others think it’s a cluster of stellar-mass black holes.
Other evidence for IMBHs comes from a gravitational wave detection in 2019. The wave was generated by two black holes merging. The pair of black holes had masses of 65 and 85 solar masses, and the resulting black hole had 142 solar masses. The other 8 solar masses were radiated away as gravitational waves.
By adding 300 more IMBH candidates to the list, DESI may be nudging us toward a definitive answer about the existence of these elusive black holes.
The 300 new candidates are presented in a paper soon to be published in The Astrophysical Journal. It’s titled “Tripling the Census of Dwarf AGN Candidates Using DESI Early Data” and is available at arxiv.org. The lead author is Ragadeepika Pucha, a postdoctoral researcher at the University of Utah.
The 300 candidate IMBHs are the largest collection to date. Until now, there were only 100 to 150 candidates. This is a massive leap in the amount of available data, and future research will no doubt rely on it to make progress on the IMBH issue.
“Our wealth of new candidates will help us delve deeper into these mysteries, enriching our understanding of black holes and their pivotal role in galaxy evolution.”
Ragadeepika Pucha, University of Utah
The new candidates were identified in DESI’s early data release, which contains data from 20% of DESI’s first year of operations. The data included more than just IMBH candidates. DESI also found about 115,000 dwarf galaxies and spectra from about 410,000 galaxies, a huge number.
The data allowed lead author Pucha and her colleagues to explore the relationship between the evolution of dwarf galaxies and black holes.
Despite their extreme masses, black holes are difficult to find. Their presence is inferred from their effect on their environment. In their presence, stars are accelerated to high velocities. Fast-moving stars were one of the clues showing that the Milky Way has an SMBH.
Astronomers are pretty certain that all massive galaxies like ours host an SMBH in their centers, but this certainty fades when it comes to dwarf galaxies. Dwarf galaxies are so small that our instruments struggle to observe them in detail. Unless the black hole is actively feeding.
When a black hole is actively consuming material, it is visible as an active galactic nucleus (AGN.) AGNs are like beacons that alert astronomers to the presence of a black hole.
“When a black hole at the center of a galaxy starts feeding, it unleashes a tremendous amount of energy into its surroundings, transforming into what we call an active galactic nucleus,” lead author Pucha said in a press release. “This dramatic activity serves as a beacon, allowing us to identify hidden black holes in these small galaxies.”
The team found 2,500 dwarf galaxies containing an active galactic nucleus, an astonishing number. Like the new IMBH candidates, this is the largest sample ever discovered. The researchers determined that 2% of the dwarf galaxies hosted AGN, a big step up from the 0.5% gleaned from other studies.
“This increase can be primarily attributed to the smaller fibre size of DESI compared to SDSS <Sloan Digital Sky Survey>, which aids with the identification of lower luminosity AGN within the same magnitude and redshift range,” the authors explain in their paper.
Astronomers think that black holes found in dwarf galaxies should be within the intermediate-mass range. However, only 70 of the newly discovered IMBH candidates overlap with dwarf AGN candidates. This is unexpected and raises yet more questions about black holes, how they form, and how they evolve within galaxies.
“For example, is there any relationship between the mechanisms of black hole formation and the types of galaxies they inhabit?” Pucha said. “Our wealth of new candidates will help us delve deeper into these mysteries, enriching our understanding of black holes and their pivotal role in galaxy evolution.”
DESI is only getting started. These discoveries were made with only a small portion of data from the instrument’s first year of operation, and there are several more years of operation to come.
“The anticipated increase in the sample of dwarf AGN candidates over the next five years with DESI will accelerate studies of AGN in dwarf galaxies,” the authors write in their research. “The statistical sample of dwarf AGN candidates will be invaluable for addressing several key questions related to galaxy evolution on the smallest scales, including accretion modes in low-mass galaxies and the co-evolution of galaxies and their central BHs,” they conclude.
- Press Release: DESI Uncovers 300 New Intermediate-Mass Black Holes Plus 2500 New Active Black Holes in Dwarf Galaxies
- Research: Tripling the Census of Dwarf AGN Candidates Using DESI Early Data
- Research: Properties and Astrophysical Implications of the 150 M? Binary Black Hole Merger GW190521
- Research: New constraints on the central mass contents of Omega Centauri from combined stellar kinematics and pulsar timing
The post DESI Found 300 Candidate Intermediate Mass Black Holes appeared first on Universe Today.
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