A new map of the universe, drawn with cosmic neutrinos

Original to This story Featured in Quanta Magazine.

Of the 100 trillion neutrinos that pass through you every second, most come from the Sun or Earth’s atmosphere. But a small group of particles – those moving much faster than the rest – moved here from powerful sources farther away. For decades, astrophysicists have sought to determine the origin of these “cosmic” neutrinos. Now, the IceCube Neutrino Observatory has finally collected enough of them to reveal telltale patterns of where they come from.

In a paper published in June in SciencesThe team has revealed the first map of the Milky Way in neutrinos. (Our galaxy is usually mapped with photons, particles of light.) The new map shows a diffuse haze of cosmic neutrinos emanating from all over the Milky Way, but curiously no individual sources stand out. “It’s a mystery,” said Francis Halzen, who drives the IceCube.

The findings follow a study conducted by IceCube also last fall SciencesHe was the first to link cosmic neutrinos to a single source. It showed that a large portion of the cosmic neutrinos detected by the observatory so far came from the core of an “active” galaxy called NGC 1068. In the glowing core of the galaxy, matter is streaming into a central supermassive black hole, somehow creating cosmic neutrinos. In treatment.

“It’s really fun,” said Kate Schulberg, a neutrino physicist at Duke University who was not involved in the research. “They have already identified a galaxy. This is something the entire neutrino astronomy community has been trying to do forever.”

Identifying the sources of cosmic neutrinos opens the possibility of using the particle as a new probe of fundamental physics. Researchers have shown that neutrinos can be used to open cracks in the prevailing Standard Model of particle physics, and even test quantum descriptions of gravity.

However, determining the origin of at least some cosmic neutrinos is only a first step. Little is known about how these particles are generated by the activity surrounding some supermassive black holes, and the evidence so far points to multiple processes or conditions.

The long-awaited original

Despite their abundance, neutrinos typically streak across the Earth without leaving a trace; A very large detector had to be built to detect enough of them to perceive patterns in the directions they were coming from. The IceCube, built 12 years ago, consists of kilometer-long strings of detectors drilled deep into the Antarctic ice. Each year, IceCube detects approximately a dozen high-energy cosmic neutrinos that stand out clearly against the fog of atmospheric and solar neutrinos. More sophisticated analyzes could extract additional candidate cosmic neutrinos from the rest of the data.

Astrophysicists know that such energetic neutrinos can only be created when fast-moving atomic nuclei, known as cosmic rays, collide with material somewhere in space. Very few places in the universe have magnetic fields strong enough to push cosmic rays to sufficient energies. Gamma-ray bursts, ultra-bright flashes of light that occur when some stars go supernova or when neutron stars collide with each other, have long been thought to be one of the most plausible options. The only real alternative was active galactic nuclei, or AGNs, galaxies whose central supermassive black holes spew particles and radiation as matter falls into them.