New observations with ESO’s Very Large Telescope (VLT) of the remains of a thousand-year-old supernova have revealed clues to the origins of cosmic rays. For the first time the observations suggest the presence of fast-moving particles in the supernova remnant that could be the precursors of such cosmic rays.
In the year 1006 a new star was seen in the southern skies and widely
recorded around the world. It was many times brighter than the planet Venus
and may even have rivaled the brightness of the Moon. It was so bright
at maximum that it cast shadows and it was visible during the day. More
recently astronomers have identified the site of this supernova and
named it SN 1006.
They have also found a glowing and expanding ring of material in the
southern constellation of Lupus (The Wolf) that constitutes the remains
of the vast explosion.
It has long been suspected that such supernova remnants may also be
where some cosmic rays — very high energy particles originating outside
the Solar System
and travelling at close to the speed of light — are formed. But until
now the details of how this might happen have been a long-standing
mystery.
A team of astronomers led by Sladjana Nikolić (Max Planck Institute for Astronomy,
Heidelberg, Germany has now used the VIMOS instrument on the VLT to
look at the one-thousand-year-old SN 1006 remnant in more detail than
ever before. They wanted to study what is happening where high-speed
material ejected by the supernova is ploughing into the stationary
interstellar matter — the shock front. This expanding high-velocity
shock front is similar to the sonic boom produced by an aircraft going
supersonic and is a natural candidate for a cosmic particle accelerator.
For the first time the team has not just obtained information about
the shock material at one point, but also built up a map of the
properties of the gas, and how these properties change across the shock
front. This has provided vital clues to the mystery.
The results were a surprise — they suggest that there were many very
rapidly moving protons in the gas in the shock region. While these are
not the sought-for high-energy cosmic rays themselves, they could be the
necessary “seed particles”, which then go on to interact with the shock
front material to reach the extremely high energies required and fly
off into space as cosmic rays. These protons are called suprathermal as
they are moving much quicker than expected simply from the temperature
of the material.
“This is the first time we were able to take a detailed look at what
is happening in and around a supernova shock front," Nikolić explained.
"We found evidence that there is a region that is being heated in just
the way one would expect if there were protons carrying away energy from
directly behind the shock front.”
The study was the first to use an integral field spectrograph to
probe the properties of the shock fronts of supernova remnants in such
detail. The team now is keen to apply this method to other remnants.
This is achieved using a feature of VIMOS called an integral field unit,
where the light recorded in each pixel is separately spread out into
its component colours and each of these spectra recorded. The spectra
can then be subsequently analysed individually and maps of the
velocities and chemical properties of each part of the object created.
“This kind of novel observational approach could well be the key to
solving the puzzle of how cosmic rays are produced in supernova
remnants,” concludedcCo-author Glenn van de Ven of the Max Planck
Institute for Astronomy.
The results are appearing in the 14 February 2013 issue of the journal Science.
Source: The Daily Galaxy via ESO
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