#astronomy Fixing a cosmic (ray) thriller – Astronomy Now

March 14, 2021 - Comment

An infrared picture of mud clouds within the Cocoon nebula captured by NASA’s retired Spitzer Area Telescope. An overlay (in inexperienced to yellow to purple) signifies rgions of gamma-ray emissions the place cosmic rays could also be generated. Picture: TeV: Binita Hona (HAWC Collaboration), IR: Hora et. al, Spitzer’s Rising Legacy, ASP Convention Sequence, 2010,



An infrared picture of mud clouds within the Cocoon nebula captured by NASA’s retired Spitzer Area Telescope. An overlay (in inexperienced to yellow to purple) signifies rgions of gamma-ray emissions the place cosmic rays could also be generated. Picture: TeV: Binita Hona (HAWC Collaboration), IR: Hora et. al, Spitzer’s Rising Legacy, ASP Convention Sequence, 2010, P. Ogle, ed.

Typical knowledge holds that high-energy cosmic rays crashing into Earth’s ambiance on the pace of sunshine, triggering showers of cascading particles, are generated in highly effective supernova blasts.

Not so quick, researchers say.

Because it seems, supernovae, which do certainly generate high-energy gamma rays, usually are not highly effective sufficient to elucidate the petaelectronvolt (PeV) energies noticed with probably the most excessive cosmic ray occasions. As an alternative of supernovae, new analysis suggests, star clusters that includes carefully packed kind O and sort B stars are accountable, appearing as so-called PeVatron accelerators.

“Cosmic rays under PeV power are believed to return from our galaxy, however the query is what are the accelerators that may produce them?” mentioned crew chief Petra Huentemeyer, professor of physics at Michigan Technological College.

Group member Henrike Fleischhack, a researcher at Catholic College/NASAGSFC/CRESST II, mentioned supernovae “do speed up cosmic rays, however they don’t seem to be in a position to get to highest energies. There have been a number of … hints that star clusters could possibly be a part of the story. Now we’re getting affirmation that they’re able to go to highest energies.”

Star clusters made up of suns born within the wake of supernova blasts can characteristic large kind O and sort B stars packed by the tons of in areas as “small” as 30 parsecs (108 gentle years) throughout.

“Spectral kind O stars are probably the most large,” mentioned Binita Hona, a current graduate of Michigan Technological College. “When their winds work together with one another, shock waves kind, which is the place acceleration occurs.”

Cosmic rays created in supernova blasts can’t be confined lengthy sufficient to succeed in the energies seen in probably the most excessive examples. However highly effective magnetic fields in star clusters can do exactly that.

“Supernova remnants have very quick shocks the place the cosmic ray might be accelerated. Nonetheless, they don’t have the kind of lengthy confinement areas,” mentioned Sabrina Casanova on the Institute of Nuclear Physics Polish Academy of Sciences in Krakow. “That is what star clusters are helpful for. They’re an affiliation of stars that may create disturbances that confine the cosmic rays and make it potential for the shocks to speed up them.”

The analysis, revealed in two papers in Nature Astronomy and Astrophysical Journal Letters, is predicated on 1,343 days of measurements utilizing the Excessive-Altitude Water Cherenkov – HAWC – observatory close to Puebla, Mexico. Physicists at HAWC hint cosmic rays by measuring the secondary rays generated when gamma rays from deep house hit Earth’s ambiance.

“When gamma rays work together with the ambiance, they generate secondary particles in particle showers,” mentioned doctoral scholar Dezhi Huang. “When particle showers are detected at HAWC, we will measure the bathe and the cost of secondary particles. We use the particle cost and time info to reconstruct info from the first gamma.”

The researchers plan to work with the Southern Vast-field Gamma-ray Observatory (SWGO), now within the planning phases, to search for extra candidate star clusters within the southern sky.



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