Scientists say cosmic rays bombarding the earth do not come from where we thought, and we may have found their source.
For decades, researchers thought that the cosmic rays that come from the edge of the galaxy to Earth begin in stars that become supernovae. It happens when they get so big that they cannot support their own core, and explode.
Researchers can be sure that such cosmic rays reach us – and at such high speeds – as a result of experiments, including the high-altitude water Cherenkov (HAWC) observatory near Puebla, Mexico, which uses large metal tanks that burn water when struck by high-energy particles.
But scientists now say the high-energy particles do not appear to be from supernovae because they are not powerful enough to do so with the large amounts of energy observed. Although supernovae can destroy an entire solar system, they do not have the power to hit us with such energetic rays, the researchers say.
Instead, the fast cosmic rays appear to come from stellar clusters that act as accelerators and throw the particles with such intense amounts of energy across the galaxy, according to new research.
Papers describing the new findings, which researchers describe as a paradigm shift, have been published in Natural Astronomy and Astrophysical journal letters.
Although it is suspected that the rays come from the remains of supernovae, researchers say that they are theoretically difficult to explain, and there was no evidence that the very energetic cosmic rays come from such supernovae.
Researchers have already seen hints that it could be star clusters that are actually responsible. But they have now seen a confirmation that they are capable of doing so, in work looking at the Cygnus Cocoon, a ‘superbubble’ surrounding an area where massive stars are forming.
Such star-forming regions appear to be leading candidates for ‘PeVatrons’, the researchers say. (PeVatrons is the name for PeV accelerators, with petaelectron volts or PeVs being a marker of the amount of energy needed to move particles at such high velocities.)
“There were several other hints that star clusters could be part of the story,” Henrike Fleischhack, one of the study’s researchers, said in a statement. “Now we get confirmation that they are capable of going to the highest energy.”
Star clusters are made from the remains of a supernova. They are also known as stargazers, and consist of winds and junk clouds that gather in violent and extreme patches of space.
As their name suggests, they are filled with hundreds of stars assembled in a very limited amount of space: hundreds of massive objects, known as the spectral type O and type B, are collected in areas of just over 100 light-years.
It is between the stars that the cosmic rays are hurled across the universe.
“Spectral O stars are the most massive,” said Binita Hona, another of the many researchers in the new articles. “When their winds fluctuate with each other, shock waves form, this is where acceleration takes place.”