Highest-energy cosmic rays originate in star clusters, not supernovae (earthsky.org)
Posted by Theresa Wiegert in Space | March 17, 2021
New research solves a decades-long riddle: from where do the highest-energy cosmic rays originate? Even supernovae – exploding stars – can’t explain them. Now it seems these sorts of cosmic rays may come from clusters of young, hot, massive stars.
Astronomers have long assumed that supernova explosions are responsible for cosmic rays – which are high-energy particles – zipping through space at the speed of light and regularly bombarding Earth from various directions in the galaxy. But supernovae can’t explain cosmic rays with the highest energies. Even a supernova powerful enough to light up our entire Milky Way galaxy isn’t strong enough to propel cosmic rays to the enormous energies that earthly observatories measure. A new study – announced on March 11, 2021 – suggests that clusters of young, hot, massive stars act as natural particle accelerators, capable of accelerating the particles to the energy levels required for the highest-energy cosmic rays.
The High-Altitude Water Cherenkov (HAWC) observatory – a collection of large high-tech water tanks on a mountainside in Mexico – detected the cosmic rays coming from Cygnus OB2, a birthplace of massive stars located inside a vast superbubble in the direction of the constellation Cygnus (within what’s called the Cygnus Cocoon, in the neighborhood of the Cocoon Nebula). A large team of scientists published the paradigm-shifting research – cosmic rays of the highest energies from a star cluster, not a supernova – in the peer-reviewed journal Nature Astronomy this month.
Team member Patrick Harding, an astrophysicist at Los Alamos National Laboratory who uses HAWC for his research, said in a statement
The origin of the highest-energy cosmic rays in the galaxy has been an open question in astrophysics for more than 60 years. Very few regions of the galaxy have both the power to produce high-energy particles and the necessary environments to boost those particles to the petaelectronVolt (PeV) energies that are seen in the highest-energy cosmic rays. And most of the expected regions to produce the particles have been ruled out in recent years by high-energy observatories.
Sometimes called stellar cradles, star clusters like Cygnus OB2 are thought to be formed in the aftermath of supernova explosions. So, in essence, the high-energy cosmic rays are still connected to supernovae, albeit not formed in an explosion. Cygnus OB2 primarily contains two different types of large, massive, short-lived stars known as spectral type O and type B stars. These are large, hot, and white and blue in color. In a region only about 108 light-years across, there are hundreds of these O and B stars.
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https://earthsky.org/space/highest-energy-cosmic-rays-originate-in-star-clusters-not-supernovae
