Cosmic rays bombarding Earth aren’t coming from where we thought, scientists say – and we may have found their source.
For decades, researchers have thought that the cosmic rays coming to Earth from the edges of the galaxy begin in stars that become supernovae. That happens when they get so big that they can’t support their own cores and explode.
Researchers can be sure that such cosmic rays will reach us – and at such speeds – thanks to experiments including the High-Altitude Water Cherenkov (HAWC) Observatory near Puebla, Mexico, which uses large metal water tanks that glow when they light up. hit by high-energy particles.
But scientists now say those high-energy particles don’t appear to be from supernovae because they aren’t powerful enough to do so with the vast amounts of energy that have been observed. Although supernovae can destroy an entire solar system, they don’t have the power to hit us with such energetic rays, the researchers say.
In fact, according to new research, the fast cosmic rays appear to come from star clusters that act as accelerators, ejecting the particles through the galaxy with such intense amounts of energy.
Papers describing the new findings, which researchers describe as a paradigm shift, are published in Nature astronomy and Astrophysical Journal Letters.
While the radiation is believed to come from the remnants of supernovae, researchers say it is theoretically difficult to explain, and there is no evidence that the highly energetic cosmic rays come from such supernovae.
Researchers had already seen evidence that it might be star clusters that were, in fact, responsible. But they have now seen confirmation of their ability to do so, in work that looked at the Cygnus Cocoon, a “super bubble” surrounding an area where massive stars are being formed.
Such star-forming regions appear to be prime candidates for “PeVatrons,” say the researchers. (PeVatrons is the name for PeV accelerators, where petaelectron volts, or PeVs, are a marker of the amount of energy required to move particles at such high speeds.)
“There are several other indications that star clusters may be part of the story,” Henrike Fleischhack, one of the study’s researchers, said in a statement. “Now we are getting confirmation that they are able to move to the highest energies.”
Star clusters are made from the remains of a supernova. Also known as star carriers, they consist of winds and debris clouds that gather in violent and extreme places in space.
As their name suggests, they are filled with hundreds of stars grouped together in a very limited number of space: hundreds of massive objects, known as spectral type O and type B, are collected in regions just over 100 light years across.
It is between those stars that the cosmic rays are hurled through the universe.
“Spectral type O stars are the most massive,” said Binita Hona, one of the many researchers on the new papers. “When their winds interact, shock waves are created, and that’s where acceleration takes place.”