This illustration of the region surrounding our Solar System shows the estimated location of the two-million-year-old supernova, lying close to the galactic magnetic field, that may have been the source for some high-energy cosmic rays observed today. Credit: Michael Kachelrieß, Norwegian University of Science and Technology (NTNU)
High-energy protons, nuclei, and other particles are constantly showering down on Earth’s atmosphere from space, but the origins of these cosmic rays is unknown. One possibility is that the cosmic rays come from supernovae, although the evidence for this claim is limited. Now by analyzing the cosmic ray energy spectrum, scientists have been able to deduce that some high-energy cosmic rays may have originated from a 2 million yo supernova located ~100 trillion miles away.
Supernova of the same age and distance has also been proposed as the source of rare iron isotopes buried in the Earth’s ocean crusts. The 2 different sets of data—cosmic rays and iron isotopes—both seem to point to the same exploding star as their source.
It’s difficult to extract information about the sources of cosmic rays from observations. This is partly because the galactic magnetic field that permeates empty space interferes with the cosmic ray trajectories, which makes the cosmic ray energy intensity nearly uniform. In addition, there are likely multiple sources of cosmic rays, and the signals from all of these sources overlap in the cosmic ray spectrum, which makes it difficult to extract signatures of individual sources.
However, cosmic ray energy spectrum may still have some “memory” of individual sources, which could be encoded in small features eg why there are more than expected positrons (antielectrons) above a certain energy level.
“Traditionally in cosmic ray physics, one uses the approximation that the sources of cosmic rays are smoothly distributed in time and space,” Prof Kachelrieß. “Our paper and the related work show that this approximation should be abandoned… it is important to take into account that cosmic rays are accelerated in events which happen only about once per century in our galaxy.”
The data also provide a way to constrain the parameters of this source: a source that was older or younger than ~2 million yrs, or a source that was nearer or further away than 100 trillion miles, inconsistent with the observed spectra. One possibility that the data rules out, for example, is that these high-energy cosmic rays originated from a “superbubble,” a region of space that is “blown” by massive star formation and large numbers of supernovae. The only plausible model of the cosmic ray source, according to the data, is an individual supernova.
“We are continuing to refine our model for the cosmic ray propagation, extending it, for example, to lower energies,” Kachelrieß said. “This may have also an impact on the predictions of antimatter fluxed from dark matter annihilations or decays. Moreover, we will try with collaborators to calculate the effect of cosmic rays from this local supernova on the Earth’s atmosphere.”
http://phys.org/news/2015-11-cosmic-rays-two-million-year-old-supernova.htmljCp
Recent Comments