In 1912, physicist Victor Hess discovered that Earth is continuously hit by energetic particles coming from outer space, which he called cosmic rays. Since then, astronomers have been hunting for the source responsible for spreading these powerful particles.
Scientists seem to have found the answer. Two new studies published on July 6 in the magazine Science, described how a team of physicists found that one of the sources of cosmic rays is a special type of galaxy called blazar. The blazar has supermassive black holes at the center of them that rip apart matter into its constituent parts, and then blast subatomic particles off into space.
The discovery was made possible when the IceCube Neutrino Observatory, located in the South Pole, detected a subatomic particle that is present in cosmic rays, called neutrino. This neutrino was rare, carrying an energy of more than 100 Tera electron volts – about 10 times the energy reachable by particles inside the most powerful accelerators on Earth.
Neutrinos are crucial for understanding our universe because it is possible to trace them back to their origins. Not only do they fly long distances and from otherwise impenetrable spots like the cores of stars at virtually the speed of light, but by not having an electrical charge they are not affected by interstellar and intergalactic magnetic fields. Neutrinos go as straight through the universe as Einsteinian gravity will allow.
Beyond possibly confirming blazars as a source of high-energy cosmic rays, the studies strengthen the possibility of using neutrinos as a kind of telescope for objects beyond our solar system. That’s important because we still know so little cosmic rays.
The beginning of the multimessenger astronomy era
This discovery, together with the detection of gravitational waves by the LIGO telescope, marks the beginning of a new discipline of astronomy, called multimessenger astronomy.
Almost everything we know about the cosmos today, we have learned by observing different forms of light –infrared, ultraviolet, radio, X-ray and gamma-ray radiation. However, this electromagnetic radiation is only one of four different messengers from the universe, along with neutrinos, cosmic rays and gravitational waves. The new discipline of multimessenger astronomy tries to combine signals of different messengers to create a new, more complete view of the cosmos.