[Where do cosmic rays
come from?]
Scientists could be closer to finding out with 'hotspot'
discovery
A 'hotspot' was discovered near the Plough or Big Dipper
constellation
Lizzie Dearden Tuesday 08 July 2014
Astronomers could be closer to discovering the mysterious
source of cosmic rays after finding a “hotspot” beneath the Plough
constellation. Scientists at a University of Utah observatory found a
“disproportionate” number of the high-energy rays emitting from the area. Gordon
Thomson, a researcher at the Telescope Array cosmic ray observatory near Delta,
said: “This puts us closer to finding out the sources – but no cigar yet.
“All we see is a blob in the sky, and inside this blob there
is all sorts of stuff – various types of objects – that could be the source. “Now we know where to look.”
The observatory has the Northern Hemisphere’s largest cosmic
ray detector. This map of the northern sky shows cosmic ray concentrations,
with a “hotspot” with a disproportionate number of cosmic rays shown as the
bright red and yellow spot.
Between May 2008, and May 2013, it recorded 72 of the most
powerful cosmic rays to find the source. Nineteen came from the direction of
the hotspot but only 4.5 would have been expected if they came randomly from
all parts of the sky. The hotspot makes up 6 per cent of the northern sky and
is centered in the southwest corner of the constellation Ursa Major, which
includes the Big Dipper or Plough.
“The hotspot is a couple of hand widths below the Big Dipper’s
handle,” Mr Thomson said. An article on the “hotspot” discovery will be
published in the journal Astrophysical Journal Letters.
University of Utah physicists Gordon Thomson, Charlie Jui
and John Matthews discuss the Telescope Array cosmic ray observatory’s
discovery of a “hotspot” The study was carried out by 125
researchers in the Telescope Array
project, including scientists from Japan,
the United States, South Korea, Russia and Belgium.
Mr Thomson said many astrophysicists suspect ultrahigh-energy cosmic rays are
generated by active galactic nuclei,
or AGNs, where material is sucked into a supermassive black hole at the centre
of a galaxy, while other material is beamed away in a blazar.
Another popular theory is that the highest-energy cosmic rays come from some supernovas that emit
gamma rays bursts.
Lower-energy cosmic rays come
from the sun, other stars and exploding stars, but the source or sources of the
most energetic cosmic rays has been a mystery since they were discovered in
1912.
Despite being called rays, they are actually made up of particles. If an ultrahigh-energy cosmic ray could penetrate the atmosphere and hit
someone in the head, a single subatomic particle would feel like being hit in
the head by a fast-bowled cricket ball.
A scintillation detector at the Telescope Array cosmic ray
observatory A scintillation detector at the Telescope Array cosmic ray
observatory Observations by the Pierre Auger cosmic ray observatory in
Argentina provide evidence for a weaker
hotspot in the southern hemisphere.
If that proves real, Mr Thomson said cosmic rays in the northern and southern hotspots must
come from different sources. Physicists want to expand the size and thus
sensitivity of the Telescope Array in Utah to carry on the research.
See the Source
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