We have now seen the Milky Way galaxy through the lens of neutrinos thanks to data gathered by an observatory in Antarctica. It’s the first time that a particle, as opposed to various light wavelengths, has “painted” our galaxy.
Milky Way galaxy:
Researchers now have a fresh window into the universe thanks to the outcome, which was reported in Science. Cosmic rays, highly energetic charged particles, are hypothesised to have contributed to the production of neutrinos when they collided with other types of matter. There is a lot about cosmic rays that we still don’t understand due to the limitations of our detection technology. Neutrinos are a different method of analysing them as a result.
Since ancient times, people have conjectured that the Milky Way that we can see arcing across the night sky is made up of stars that resemble our Sun. It was realised in the 18th century that we were looking out at a flattened sheet of stars. It has barely been 100 years since we discovered that the Milky Way is one galaxy—or “island universe”—among 100 billion others.
A form of pulsing star known as a “Cepheid variable” was discovered in 1923 by American astronomer Edwin Hubble in the Andromeda “nebula” (a massive cloud of gas and dust). This gave a measurement of the separation between Earth and Andromeda, thanks to earlier research by Henrietta Swan Leavitt.
Milky Way galaxy:
This settled a long-running argument and fundamentally altered our understanding of our place in the cosmos by proving that Andromeda is an extremely distant galaxy similar to our own.
Milky Way galaxy:
letting windows open:
We have since viewed our galaxy in a variety of light wavelengths, including radio waves, different infrared bands, X-rays, and gamma-rays, as new astronomical windows have opened up to the sky. Now, neutrino particles, which are known as “ghost particles” due to their extremely low mass and weak interactions with other matter, allow us to observe our cosmic home.
In our galaxy, neutrinos are produced when cosmic rays strike interstellar matter. However, stars like the Sun, some supernovae, and possibly the majority of the high-energy phenomena we see in the universe, such gamma-ray bursts and quasars, also produce neutrinos. As a result, they can give us a picture of very energetic processes in our galaxy that is never before possible using only light.
A fairly peculiar “telescope” that is submerged several kilometres beneath the South Pole in the Antarctic ice cap was necessary for the latest breakthrough detection. A gigatonne of the incredibly translucent ice is placed under extreme pressure by the IceCube Neutrino Observatory in order to detect Cherenkov radiation, a type of energy.
Charged particles, which can move faster than light in ice but not in a vacuum, generate this feeble radiation. The atoms in the ice are struck by incoming neutrinos, which result from cosmic ray collisions in the galaxy, and produce the particles.
Along with neutrons, proton particles—which combined with a few other heavy nuclei make up the atomic nucleus—as well as a few electrons and heavy nuclei make up cosmic rays. These were found to be uniformly showering down on Earth from all directions around a century ago. Since the magnetic fields in the region between stars skew their travel directions, we are yet unsure of all of their sources.
in the ice’s depths:
As special indicators of cosmic ray interactions far inside the Milky Way, neutrinos can be used. However, the spectral particles are also produced when cosmic rays strike the atmosphere of the Earth. In order to distinguish between neutrinos of “astrophysical” origin, or those coming from alien sources, and those produced by cosmic ray collisions in our atmosphere, researchers utilising the IceCube data needed a technique to classify the neutrinos.
The study concentrated on a cascade-type of neutrino interaction in the ice. These produce roughly spherical light showers and increase the researchers‘ sensitivity to astrophysical Milky Way neutrinos. This is due to the fact that, despite being more difficult to reconstruct, a cascade yields a more accurate measurement of a neutrino’s energy than other kinds of interactions.
Using powerful machine learning algorithms, ten years of IceCube data analysis produced over 60,000 neutrino occurrences with energies greater than 500 gigaelectronvolts (GeV). Only around 7% of them were astronomical in origin, with the remaining neutrinos coming from a “background” source created by the Earth’s atmosphere.
At a level of statistical significance known as 4.5 sigma, the possibility that cosmic rays impacting the Earth’s atmosphere may be the cause of all neutrino occurrences was categorically ruled out. In other words, the likelihood that our result was a fluke is only approximately 1 in 150,000.
This doesn’t quite meet the typical 5 sigma threshold for making a claim of discovery in particle physics. On reasonable astrophysical grounds, such emission from the Milky Way is anticipated.
We will collect a lot more neutrino events with the future ten-fold-larger IceCube-Gen2 experiment, and the currently hazy image of our galaxy will transform into a detailed one that we have never seen before.
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