For many years, humans have looked up at the collection of stars and planets shining in the night sky that make up the Milky Way. However, the Milky Way is now being observed for the first time in a new way.
Scientists said recently that they have produced an image of the Milky Way not based on light. Instead, the image is based on subatomic particles called neutrinos.
Scientists discovered the high-energy neutrinos in ice deep below Antarctica's surface. They then traced their source back to locations in the Milky Way. It is the first time these particles have been observed arising from our galaxy.
This observation of the galaxy is different from what can be seen with our own eyes, or even instruments that measure other electromagnetic sources like radio waves, microwaves, or X-rays.
The image does not contain stars or planets or other things observable because of their light. Rather they are observable because of the neutrinos originating in the galaxy. The neutrinos may be from explosive star deaths called supernovas.
The neutrinos were discovered over a period of 10 years at the IceCube Neutrino Observatory. It is part of a U.S. scientific research station at the South Pole. The researchers used more than 5,000 sensors covering an area the size of a small mountain.
"This observation is groundbreaking. It established the galaxy as a neutrino source. Every future work will refer to this observation," said Georgia Tech physicist Ignacio Taboada. He is the spokesperson for the IceCube research.
Neutrinos are electrically neutral. They are not affected by even the strongest magnetic field and rarely interact with matter. That is why they are also called the "ghost particle." As neutrinos travel through space, they pass clear through matter like stars, planets, and even people.
"Just as light goes without stopping through glass, neutrinos can go through everything, including the whole planet Earth," Taboada said.
Naoko Kurahashi Neilson is a physicist at Drexel University in Philadelphia. She is a member of the research team that published its findings in the publication Science. Neilson said neutrinos are elementary particles, meaning they are not made up of anything smaller.
“They are not the building blocks of stuff, like electrons and quarks are, but they are created in nuclear processes,” she said.
Many parts of the universe are impossible to observe using light alone. The ability to use particles like neutrinos in astronomy makes for a more complete examination.
Neutrinos are produced by the same sources as cosmic rays, the highest-energy particles ever observed. But cosmic rays, as electrically charged particles, cannot be traced directly back to their source. Strong magnetic fields in space change their path. But the direction from which neutrinos arrive points directly to their original source.
The researchers used machine learning to help determine which neutrinos originated in our galaxy and which originated elsewhere.
How the neutrinos originated is up for debate.
"This is now the key question,” said IceCube lead scientist Francis Halzen. “Neutrinos only originate in sources where cosmic rays are produced …The key question is where these cosmic rays originate," Halzen said.
"The most likely source of neutrinos and cosmic rays in our galaxy, are the remains of past supernova explosions,” Taboada added. “But this is unproven so far."
I’m Dan Novak.
