A gigantic observatory buried in the Antarctic ice has helped scientists trace elusive particles called neutrinos back to their origins at the heart of a nearby galaxy—offering a new way to study a supermassive black hole shrouded from view.
According to a new study published Thursday in the journal Science, neutrinos are accelerating towards Earth from the center of a spiral-shaped galaxy known as Messier 77, which is about 47 million light years from Earth. There, a matter- and radiation-dense region surrounds a black hole many millions times as massive as our sun.
The celestial heart of Messier 77 is situated in such a way that the dust and gas circulating around the black hole obscure the object when it is viewed from Earth using typical methods such as telescopes that rely on optical light.
“We’re seeing the galaxy a little bit sideways, and because we’re looking at it sideways, the black hole is hiding behind material that is orbiting near it,” said Ignacio Taboada, a professor of physics at the Georgia Institute of Technology and spokesperson for the international collaboration that conducted the research.
But neutrinos—the most abundant, energetic particles in the universe—pass through such gas and dust unaffected because they rarely interact with anything, including magnetic fields, matter or gravity. This ghostly aspect offers scientists an unprecedented means of probing processes happening around the previously hidden black hole, including how it accelerates the superhot, charged gas and matter in the vicinity, the researchers said.
“Neutrinos are a different way to look at the universe. And every time that you look at the universe in a new way, you learn something that you could not have learned with the old methods,” said Dr. Taboo.
Neutrinos preserve the information that was imprinted when they were generated at their sources, including their energies, according to Hans Niederhausen, a postdoctoral associate at Michigan State University who participated in the research. That same energy is brought to Earth along with the neutrinos.
Now that they know where certain neutrinos came from, the researchers are studying them to better understand where within Messier 77 the interactions happen that create and accelerate these particles—and the behavior and nature of the black hole itself, Dr. Niederhausen said.
They also plan to comb the cosmos for other neutrinos from galaxies with active supermassive black holes similar to Messier 77. This galaxy “gives us a very good idea where to look next,” he added.
The neutrino-detecting telescope used in the study, known as the IceCube Neutrino Observatory, is buried in a billion tons of ice around the US Amundsen-Scott South Pole Station. As neutrinos pass through the Earth, they occasionally collide with atoms in the ice. The observatory’s more than 5,000 basketball-sized sensors detect byproducts of those rare collisions and send that data to computers at the surface.
The $279 million observatory, mainly funded by the National Science Foundation, was completed in 2011 and detects roughly 100,000 neutrinos a year. Nearly all those neutrinos are created by processes in our atmosphere, but a few hundred or so neutrinos detected annually originate from outside our solar system—known as astrophysical neutrinos.
Because neutrinos penetrate matter and pass through unaffected, they unerringly travel in a straight line from their point of creation. So, by plotting an astrophysical neutrino’s direction of travel through the ice, researchers can reconstruct its path back across the universe to its source.
Nearly 400 scientists at more than 50 institutions make up the international IceCube collaboration, which analyzed data collected by the observatory between 2011 and 2020 to identify 79 neutrinos that originated from Messier 77.
That IceCube is finding individual objects that are the sources of astrophysical neutrinos is “absolutely amazing,” said Dr. Yoshi Uchida, a professor of physics at Imperial College London who was not involved in the study. “After running for 10 years, it’s turning the observation of neutrinos into another source of information.”
Dr. Taboada said he thinks IceCube will continue to get more neutrinos originating from this galaxy. Those future detections could not only help parse out additional details about Messier 77’s supermassive black hole, but could help answer the “oldest question in astronomy,” according to Francis Halzen, a University of Wisconsin-Madison physicist and principal investigator of IceCube.
Scientists have known about the existence of cosmic rays—streams of high-energy protons and atomic nuclei which travel at near-light speeds and create electromagnetic radiation and showers of subatomic particles when they hit Earth’s atmosphere—for more than a century. But the origin of these rays, and what mechanism speeds them up and sends them in our direction, remains elusive.
“Something in the universe gave them a ginormous kick to make them go that fast,” Dr. Niederhausen said of cosmic rays.
Neutrinos are a byproduct of those cosmic rays’ interactions with the matter and radiation surrounding high-energy objects like supermassive black holes, so Drs. Halzen and Taboada said tracing the ghostly particles back to their beginnings could help solve the origins of cosmic rays, too.
Write to Aylin Woodward at [email protected]
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