The first view of the Milky Way seen through neutrino particles

Data collected by an Antarctic observatory has produced our first view of the Milky Way galaxy through the lens of neutrino particles. This is the first time that our galaxy has been “colored” by a particle rather than different wavelengths of light.

The result, published in Science, gives researchers a new window into space. Neutrinos are thought to be produced in part by high-energy, charged particles called cosmic rays colliding with other matter. Because of the limitations of our detection equipment, we still don’t know much about cosmic rays. So neutrinos are another way to study them.

The Milky Way we see in the night sky has long been believed to be made up of stars like our Sun. In the 18th century, it was recognized that it is a flattened plate of stars that we see from the inside. It’s only been 100 years since we learned that the Milky Way is actually a galaxy, or “island universe,” one of a hundred billion others.

The Milky Way as seen with neutrinos. IceCube Collaboration / US National Science Foundation (Lily Le and Sean Johnson) / ESO (S. Brunier)

In 1923, American astronomer Edwin Hubble identified a type of pulsating star called a “Cepheid variable” in what was then known as the Andromeda “nebula” (a huge cloud of dust and gas). Thanks to previous work by Henrietta Swan Leavitt, it provided a measurement of the distance from Earth to Andromeda.

It showed that Andromeda is a distant galaxy like our own, settling a long-standing debate and completely reshaping our understanding of our place in the universe.

Openable windows

As new astronomical windows have opened in the sky, we have seen our galactic home in many different wavelengths of light—radio waves, various infrared bands, X-rays, and gamma rays. We can now see our cosmic home in neutrino particles, which have very little mass and interact only very weakly with other matter, hence their nickname “ghost particles”.

Neutrinos are emitted from our galaxy when cosmic rays collide with interstellar matter. However, neutrinos are also produced by stars like the Sun, some exploding stars or supernovae, and probably most of the high-energy phenomena we observe in the universe, such as gamma-ray bursts and quasars. As such, they can give us unprecedented insight into the highly energetic processes in our galaxy, a view we can’t get using light alone.

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