A giant telescope built beneath the South Pole’s ice has detected neutrinos from our galaxy, the Milky Way, for the first time. The finding is confirmation of a phenomenon that has been expected for years and implies that there are unknown bodies in our own cosmic neighborhood that are capable of producing the most energetic particles in the universe.
Neutrinos are the most common particles in the cosmos. About 100 billion of them pass through our bodies every second without us noticing. These ghostly particles have no electrical charge and little mass. The vast majority of neutrinos traverse the earth from side to side without leaving a trace. However, a select few interact with an atom and produce a flash of blue light that allows their origin to be determined.
The IceCube telescope is a one-cubic-kilometer mass of Antarctic ice that houses more than 5,000 spherical detectors capable of detecting the flashes that neutrinos leave in their wake. In 2013, the observatory detected the first two neutrinos outside of our galaxy. Epi and Blas were baptized, ushering in a new era in astronomy, although it has not been possible to determine their exact origins.
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A few dozen more neutrinos were captured in 2017 and 2022, identifying the first two sources outside our galaxy: two black holes that could fit millions of stars like the Sun. In the first case, the neutrinos had been traveling there at almost the speed of light for more than 4 billion years from the distant galaxy TXS 0506+065. In the second case, they came from Messier 77, a galaxy only 47 million light-years from our solar system.
Neutrinos are associated with cosmic rays – the jets of charged particles that are the most energetic in the universe. In 1993 a telescope in Utah (USA) captured the strongest known particle of this type. It was moving at almost the speed of light and its energy was a million times higher than that of the world’s most powerful particle accelerator, the LHC. At first it was called WTF-Signal (initials of what the fuck!, in English), but eventually it was named OMG (Oh my God). Astrophysicists use the large neutrino detectors to try to find out where cosmic rays come from.
On that occasion, IceCube detected hundreds of neutrinos originating from the center of our galaxy, about 25,000 light-years away, with an energy 10,000 times greater than that of a particle accelerator, explains Ignacio Taboada, spokesman for the IceCube telescope. “Detecting these galactic neutrinos should be the easiest, but turns out the Milky Way doesn’t produce many. We finally managed to capture them, so we know that there are also objects in our cosmic environment that can produce them,” stresses Taboada, a researcher of Venezuelan origin who has been working on IceCube since its construction, in 2010. The Discovery is published today in Science magazine, reference of the best world science.
Representation of the Milky Way with galactic neutrino signals.IceCube
The IceCube mass is below the US Amundsen-Scott base at the South Pole, where the average temperature is 50 degrees below zero. During the six-month Antarctic winter, when it is always night, only two people remain at the base to keep the IceCube running. A team of more than 300 scientists from more than 12 countries can now access the data in real time.
For today’s discovery, an artificial intelligence was developed that analyzed a billion neutrino signals captured between 2011 and 2022 and selected the few hundred that originated from the Milky Way. Juanan Aguilar, an Albacete-based astroparticle physicist and part of the IceCube team, explains that “previously, less accurate statistical models were used to analyze the signals detected by the telescope.” to clean up the generated noise and leave only “the signals coming from the interior of the galaxy”.
The Milky Way is shaped like a flattened spiral, like a cookie, and the signals appear to be coming straight from the edge. The IceCube data shows that there is a kind of fuzzy cloud of neutrinos that stretches across the galactic center. In addition, there can be one or more point sources for neutrinos. One of them may be Sagittarius A*, a black hole with the mass of four million Sun-like stars crouching at the very center of the galaxy. It’s also possible that there are other unknown objects that produce cosmic rays and neutrinos, such as a black hole swallowing a nearby star.
Astroparticle physicist Ignacio Taboada, at the Amundsen-Scott base at the South Pole.IT
“The IceCube finding shows that there must be huge particle accelerators in our own galaxy,” comparable to those previously discovered in other more or less distant galaxies, summarizes Francisco Salesa, scientist at the Institute of Corpuscular Physics in Valencia. In the same month, the Antares neutrino detector, located under the Mediterranean Sea off the coast of Toulon (France), detected a galactic neutrino signal. “The reliability of this signal was two sigma, which means there was a 100% chance that the signal was an error,” explains Salesa. “The IceCube observation has 4.5 sigma, an error probability of 10 million.” It’s much more reliable, but it’s not enough to claim a discovery, which requires five sigma — a one in 3.5 million chance.
A global race to identify the origin of galactic neutrinos is now beginning. IceCube, which is mainly driven by the United States, will continue to operate for several more years and could make it. However, since it is in the southern hemisphere, the center of the galaxy is directly overhead, causing a lot of noise created by other elementary particles generated in the atmosphere, the sun, and other objects. Currently under construction is KM3Net, a new underwater telescope in the Mediterranean Sea with two sites, Arca and Orca, near Toulon and Sicily (Italy). Being in the northern hemisphere, Earth will act as a filter and theoretically be able to pinpoint the origin of the elusive galactic neutrinos much better.
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