From UCSC: ” Novel search strategy advances the hunt for primordial black holes”

UC Santa Cruz

UC Santa Cruz

February 21, 2018
Tim Stephens

Some theories of the early universe predict density fluctuations that would have created small “primordial black holes,” some of which could be drifting through our galactic neighborhood today and might even be bright sources of gamma rays.

Researchers analyzing data from the Fermi Gamma-ray Space Telescope for evidence of nearby primordial black holes have come up empty, but their negative findings still allow them to put an upper limit on the number of these tiny black holes that might be lurking in the vicinity of Earth.

NASA/Fermi Gamma Ray Space Telescope

NASA’s Fermi Gamma-ray Space Telescope is a powerful space observatory that opens a wide window on the universe. Primordial black holes are a potential source of gamma rays, the highest-energy form of light. (Illustration credit: NASA)

“Understanding how many primordial black holes are around today can help us understand the early universe better,” said Christian Johnson, a graduate student in physics at UC Santa Cruz who developed an algorithm to search data from Fermi’s Large Area Telescope (LAT) for the signatures of primordial black holes. Johnson is a corresponding author of a paper on the findings that has been accepted for publication in The Astrophysical Journal.

Low-mass black holes are expected to emit gamma rays due to Hawking radiation, a theoretical prediction from the work of physicist Stephen Hawking and others. Hawking showed that quantum effects can give rise to particle-antiparticle pairs near the event horizon of a black hole, allowing one of the particles to fall into the black hole and the other to escape. The result is that the black hole emits radiation and loses mass.

A small black hole that isn’t absorbing enough from its environment to offset the losses from Hawking radiation will steadily lose mass and eventually evaporate entirely. The smaller it gets, the brighter it “burns,” emitting more and more Hawking radiation before exploding in a final cataclysm. Previous searches for primordial black holes using ground-based gamma-ray observatories have looked for these brief explosions, but Fermi should be able to detect the “burn phase” occurring over a period of several years.

A limitation of the Fermi search was that it could only extend a relatively short distance from Earth (a small fraction of the distance to the nearest star). The advantage of looking nearby, however, is that primordial black holes could be distinguished from other sources of gamma rays by their movement on the sky.

“It’s like looking at the sky at night and trying to decide if something is an airplane or a star,” Johnson explained. “If it’s an airplane, it will move, and if it’s a star it will stay put.”

Any primordial black holes still around today would have started out much larger and have been gradually losing mass for billions of years. To detect one with Fermi, it would have to have reached the final burn phase during the roughly four-year observation period of the study. Over a period of a few years, it would go from undetectably dim to extremely bright, and would burn brightly for several years before exploding, Johnson said.

“Even though we didn’t detect any, the non-detection sets a limit on the rate of explosions and gives us better constraints than previous research,” he said.

In addition to Johnson, the other corresponding authors of the paper include Steven Ritz, professor of physics and director of the Santa Cruz Institute of Particle Physics at UCSC; and Stefan Funk and Dmitry Malyshev at the Erlangen Centre for Astroparticle Physics in Germany. Other members of the Fermi-LAT Collaboration also contributed to this work and are coauthors of the paper.

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UCO Lick Shane Telescope
UCO Lick Shane Telescope interior
Shane Telescope at UCO Lick Observatory, UCSC

Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

UC Santa Cruz campus
The University of California, Santa Cruz, opened in 1965 and grew, one college at a time, to its current (2008-09) enrollment of more than 16,000 students. Undergraduates pursue more than 60 majors supervised by divisional deans of humanities, physical & biological sciences, social sciences, and arts. Graduate students work toward graduate certificates, master’s degrees, or doctoral degrees in more than 30 academic fields under the supervision of the divisional and graduate deans. The dean of the Jack Baskin School of Engineering oversees the campus’s undergraduate and graduate engineering programs.

UCSC is the home base for the Lick Observatory.

Lick Observatory's Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building
Lick Observatory’s Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building

Search for extraterrestrial intelligence expands at Lick Observatory
New instrument scans the sky for pulses of infrared light
March 23, 2015
By Hilary Lebow
The NIROSETI instrument saw first light on the Nickel 1-meter Telescope at Lick Observatory on March 15, 2015. (Photo by Laurie Hatch) UCSC Lick Nickel telescope

Astronomers are expanding the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light at UC’s Lick Observatory. A new instrument, called NIROSETI, will soon scour the sky for messages from other worlds.

“Infrared light would be an excellent means of interstellar communication,” said Shelley Wright, an assistant professor of physics at UC San Diego who led the development of the new instrument while at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics.

Wright worked on an earlier SETI project at Lick Observatory as a UC Santa Cruz undergraduate, when she built an optical instrument designed by UC Berkeley researchers. The infrared project takes advantage of new technology not available for that first optical search.

Infrared light would be a good way for extraterrestrials to get our attention here on Earth, since pulses from a powerful infrared laser could outshine a star, if only for a billionth of a second. Interstellar gas and dust is almost transparent to near infrared, so these signals can be seen from great distances. It also takes less energy to send information using infrared signals than with visible light.

UCSC alumna Shelley Wright, now an assistant professor of physics at UC San Diego, discusses the dichroic filter of the NIROSETI instrument. (Photo by Laurie Hatch)

Frank Drake, professor emeritus of astronomy and astrophysics at UC Santa Cruz and director emeritus of the SETI Institute, said there are several additional advantages to a search in the infrared realm.

“The signals are so strong that we only need a small telescope to receive them. Smaller telescopes can offer more observational time, and that is good because we need to search many stars for a chance of success,” said Drake.

The only downside is that extraterrestrials would need to be transmitting their signals in our direction, Drake said, though he sees this as a positive side to that limitation. “If we get a signal from someone who’s aiming for us, it could mean there’s altruism in the universe. I like that idea. If they want to be friendly, that’s who we will find.”

Scientists have searched the skies for radio signals for more than 50 years and expanded their search into the optical realm more than a decade ago. The idea of searching in the infrared is not a new one, but instruments capable of capturing pulses of infrared light only recently became available.

“We had to wait,” Wright said. “I spent eight years waiting and watching as new technology emerged.”

Now that technology has caught up, the search will extend to stars thousands of light years away, rather than just hundreds. NIROSETI, or Near-Infrared Optical Search for Extraterrestrial Intelligence, could also uncover new information about the physical universe.

“This is the first time Earthlings have looked at the universe at infrared wavelengths with nanosecond time scales,” said Dan Werthimer, UC Berkeley SETI Project Director. “The instrument could discover new astrophysical phenomena, or perhaps answer the question of whether we are alone.”

NIROSETI will also gather more information than previous optical detectors by recording levels of light over time so that patterns can be analyzed for potential signs of other civilizations.

“Searching for intelligent life in the universe is both thrilling and somewhat unorthodox,” said Claire Max, director of UC Observatories and professor of astronomy and astrophysics at UC Santa Cruz. “Lick Observatory has already been the site of several previous SETI searches, so this is a very exciting addition to the current research taking place.”

NIROSETI will be fully operational by early summer and will scan the skies several times a week on the Nickel 1-meter telescope at Lick Observatory, located on Mt. Hamilton east of San Jose.

The NIROSETI team also includes Geoffrey Marcy and Andrew Siemion from UC Berkeley; Patrick Dorval, a Dunlap undergraduate, and Elliot Meyer, a Dunlap graduate student; and Richard Treffers of Starman Systems. Funding for the project comes from the generous support of Bill and Susan Bloomfield.

Please help promote STEM in your local schools.


Stem Education Coalition

UCSC is the home base for the Lick Observatory.