Scientists using the Dark Energy Spectroscopic Instrument (DESI) have completed two major tasks. They’ve compiled the largest ever sample of dwarf galaxies (systems contain up to a mere several billion stars, compared to the Milky Way’s estimated 2 billion to 400 billion) that host an actively feeding black hole. They’ve also recorded the largest collection of potential intermediate-mass black holes so far.
Both results are reported in The Astrophysical Journal and provide new insight into the formation and evolution of both galaxies and black holes. They are essentially early returns from DESI’s 5-year run, representing about 20 percent of the first year of data collected by the instrument.
Collecting Data on the Universe
Think of DESI as an ultra-long-range camera with super-fast shutter speed that can be pointed in every possible direction. It can measure light wavelengths from 5,000 galaxies every 20 minutes, using 5,000 robotic helpers to aim its fiber-optic eyes at the thousands of galaxies its users program it to shoot. Its ultimate purpose is to create the largest 3-D map of the Universe.
It turns out that 20 percent of DESI’s first year of data contains a lot of information. It includes the spectra of 410,000 galaxies, including roughly 115,000 dwarf galaxies. This collection of data will help astrophysicists better understand the interplay black hole evolution and dwarf galaxy evolution.
Black Hole Appetite and Energy
Black holes remain both mysterious in nature and difficult to find. Astrophysicists suspect that all massive galaxies contain a black hole at their centers. But they are less certain about the presence of black holes in dwarf galaxies, where they are even more difficult to spot — unless they are eating.
“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 (AGN),” Ragadeepika Pucha, a University of Utah research fellow who analyzed the DESI data, said in a press release. “This dramatic activity serves as a beacon, allowing us to identify hidden black holes in these small galaxies.”
Those AGN beacons led the team to identify about 2,500 candidate dwarf galaxies with them at their center. This represents four times as many AGNs than previous studies revealed. The implication is that there are many more dwarf galaxy black holes yet to be discovered.
Read More: A Binary Star Neighbors Our Galaxy's Supermassive Black Hole
The Lightweight Blackholes
The other portion of the project identified 300 intermediate-mass black hole candidates. Lightweight blackholes are less than 100 times the mass of our Sun, while supermassive ones are more than a million times that. Not much is known about the in-between ones.
Some astrophysicists theorize that intermediates are leftovers from the first black holes formed in the early Universe, as well as the seeds of supermassive ones. Until now, only about 100 to 150 intermediate-mass black holes have been identified.
The survey contained another surprise. Astrophysicists predict that black holes that have been found in dwarf galaxies will be of intermediate mass. But only 70 of the newly discovered intermediate-mass black hole candidates are also considered potential dwarf AGNs. This raises a host of new questions about how black holes form and evolve over time.
“For example, is there any relationship between the mechanisms of black hole formation and the types of galaxies they inhabit?” Pucha said in the release. “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.”
Read More: The Oldest Black Hole Could Wreak Havoc on a Faraway Galaxy
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
The Astrophysical Journal. 300 new intermediate-mass black holes plus 2500 new active black holes in dwarf galaxies discovered
NSF NOIRLab (U.S. National Science Foundation National Optical-Infrared Astronomy Research Laboratory). The Dark Energy Spectroscopic Instrument (DESI)
Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
