Data collected by an observatory in Antarctica has yielded our first view Galaxy The Milky Way through the lens of neutrino particles. This is the first time that we have seen our galaxy “colored” by a single particle rather than by different wavelengths of light.
The results, published in Science, provide researchers with a new window on the universe. Neutrinos are believed to be produced, in part, by the collision of high-energy, charged particles called cosmic rays with other matter. Because of the limitations of our detection equipment, we still don’t know much about cosmic rays. Therefore, neutrinos are another way to study them.
It has been hypothesized since ancient times that the galaxy we see moving across the night sky contains stars like ours. Sunday, It was recognized as a flat slab in the 18th century. Stars Which we are seeing from inside. it’s only been 100 years since we found out that the Milky Way is actually one GALAXYor “island universe”, one of a hundred billion others.
In 1923, American astronomer Edwin Hubble identified a type of pulsating star called a “Cepheid variable”, then known as Andromeda.nebula(a huge cloud of dust and gas). Thanks to the earlier work of Henrietta Swan Leavitt, it provided a measure of distance Earth to Andromeda.
This revealed that Andromeda is a distant galaxy just like our own, settling a long-standing debate and completely changing our perception of our place in the universe.
Thereafter, as new astronomical windows opened in the sky, we saw our galactic home in many different wavelengths of light – in radio waves, in various infrared bands, in X-rays and in gamma-rays. Now, we can see our cosmic abode in neutrino particles, which have very low mass and interact very weakly with other matter – hence the 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 also by most of the high-energy events we observe in the universe such as gamma-ray bursts and quasars. Therefore, they can provide us with an unprecedented view of the highly energetic processes in our galaxy – a view that we cannot obtain using light alone.
The new breakthrough required a strange “telescope” that is hidden several kilometers deep in the Antarctic ice cap beneath the South Pole. The IceCube neutrino observatory uses a gigatonne of ultra-transparent ice under enormous pressure to detect a form of energy called Cherenkov radiation.
This light radiation is emitted by charged particles, which can travel faster than light in ice (but not in a vacuum). The particles are created by incoming neutrinos, which come from cosmic ray collisions in the galaxy, that collide with atoms in the ice.
Cosmic rays are mainly proton particles (they together with neutrons make up atomic nuclei), along with some heavier nuclei and electrons. About a century ago, it was discovered that they rain down on the earth equally from all directions. We do not yet know with certainty all their sources, because their directions of travel are controlled by the magnetic fields in the interstellar space.
deep in the snow
Neutrinos can act as unique tracers of cosmic ray interactions in the depths of a galaxy. However, ghostly particles are also produced when cosmic rays collide with Earth’s atmosphere. So researchers using the IceCube data needed a way to distinguish between neutrinos of “astrophysical” origin — those originating from extraterrestrial sources — and neutrinos created by cosmic ray collisions within our atmosphere.
The researchers focused on a type of neutrino interaction in the ice called a cascade. These result in a nearly circular rain of light and give researchers a better level of sensitivity to astrophysical neutrinos from the Milky Way. This is because cascades provide a better measure of the energy of neutrinos than other types of interactions, even though they are harder to reconstruct.
Ten years of analysis of IceCube data using sophisticated machine learning techniques yielded approximately 60,000 neutrino events with energies above 500 gigaelectronvolts (GeV). Of these, only about 7% were of astronomical origin, the rest being due to “background” sources of neutrinos that originate in Earth’s atmosphere.
The hypothesis that all neutrino events could be caused by cosmic rays hitting Earth’s atmosphere was definitively rejected at a level of statistical significance called 4.5 sigma. Put another way, our result has only about 1 in 150,000 chance of being accidental.
This is slightly less than the traditional 5 sigma standard for claiming a discovery in particle physics. However, such emission from the Milky Way is expected on solid astronomical grounds.
With the upcoming expansion of the experiment – IceCube-Gen2 will be ten times larger – we will get many more neutrino events and the current blurry picture will turn into a detailed view of our galaxy that we’ve never had before.