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Monday August 21, 2017

Exploding Stars and Stripes

Thursday March 24, 2011

Exploding Stars and Stripes

Your Source for University News
Pattern of X-ray ‘stripes’ in supernova remnant could explain how cosmic rays are produced

NEW BRUNSWICK,
N.J. – The discovery of a pattern of X-ray “stripes” in the remains of an
exploded star may provide the first direct evidence that a cosmic event can
accelerate particles to energies a hundred times higher than achieved by the
most powerful particle accelerator on Earth.

Tycho low energy

Chandraobservation of the Tycho supernova remnant. Low-energy X-rays (red) show expanding debris from thesupernova explosion and high energy X-rays (blue) show the blast wave, a shellof extremely energetic electrons. These high-energy X-rays show a pattern ofX-ray 'stripes.'

This result comes
from a very long observation of the Tycho supernova remnant with NASA's Chandra
X-ray Observatory
. It could explain how some of the extremely energetic
particles bombarding the Earth, called cosmic rays, are produced.

“We've seen lots
of intriguing structures in supernova remnants, but we’ve never seen stripes
before,” said Kristoffer Eriksen, a postdoctoral researcher at Rutgers
University who led the study.  “This made
us think very hard about what's happening in the blast wave of this powerful
explosion.” This latest study from Chandra provides support for a theory about
how magnetic fields can be dramatically amplified in such blast waves.

In this theory,
the magnetic fields become highly tangled and the motions of the particles very
turbulent near the expanding supernova shock wave at the front edge of the
supernova remnant.  High-energy charged
particles can bounce back and forth across the shock wave repeatedly, gaining
energy with each crossing. Theoretical models of the motion of the most
energetic particles – which are mostly protons – are predicted to leave a
messy network of holes and dense walls corresponding to weak and strong regions
of magnetic fields, respectively.

The X-ray stripes
discovered by the Chandra researchers are thought to be regions where the
turbulence is greater and the magnetic fields more tangled than surrounding
areas, and may be the walls predicted by the theory.  Electrons become trapped in these regions and
emit X-rays as they spiral around the magnetic field lines.

However, the
regular and almost periodic pattern of the X-ray stripes was not predicted by
the theory.

Tycho high energy

High-energy X-rays show a pattern of X-ray'stripes' (prominently visible at the right edge of the image) never previously seen in asupernova remnant.

“It was a big
surprise to find such a neatly arranged set of stripes,” said co-author Jack
Hughes, professor of physics and astronomy at Rutgers. “We were not expecting
so much order to appear in so much chaos. It could mean that the theory is
incomplete, or that there's something else we don't understand.”

Assuming that the
spacing between the X-ray stripes corresponds to the radius of the spiraling
motion of the highest energy protons in the supernova remnant, the spacing
corresponds to energies about 100 times higher than reached in the Large Hadron
Collider. These energies equal the highest energies of cosmic rays thought to
be produced in our Galaxy.

Because cosmic
rays are composed of charged particles, like protons and electrons, their
direction of motion changes when they encounter magnetic fields throughout the
galaxy. So, the origin of individual cosmic rays detected on Earth cannot be
determined.

Supernova
remnants have long been considered a good candidate for producing the most
energetic cosmic rays in our Galaxy.  The
protons can reach energies that are hundreds of times higher than the highest
energy electrons, but since they do not radiate efficiently like the electrons,
direct evidence for the acceleration of cosmic ray protons in supernova
remnants has been lacking.

These results
also support the prediction that magnetic fields in interstellar space are greatly
amplified in supernova remnants, but the difference between the observed and
predicted structures means that other interpretations cannot be ruled out.

“We were excited
to discover these stripes because they might allow us to directly track, for
the first time, the origin of the most energetic particles produced in our
galaxy,” said Eriksen. “But, we're not claiming victory yet."

Tycho illustration

X-ray stripes are thought to be regionswhere the turbulence is greater and the magnetic fields more tangled thansurrounding areas. Electrons become trapped in these regions andemit X-rays as they spiral around the magnetic field lines. Regions with enhanced turbulence and magneticfields were expected in supernova remnants, but the motion of the most energeticparticles - mostly protons - was predicted to leave a messy network of holesand dense walls corresponding to weak and strong regions of magnetic fields,respectively.

The Tycho
supernova remnant is named for the famous Danish astronomer Tycho Brahe, who
reported observing the supernova in 1572. 
Scientists think the explosion occurred when a white dwarf star grew in
mass and exceeded its weight limit, forming a so-called Type Ia supernova. The
Tycho remnant is located in the Milky Way, about 13,000 light years from Earth.

“Supernova
remnants are our best cosmic laboratories for understanding how nature
accelerates the highest energy cosmic rays,” said Roger Blandford of Stanford
University, a noted expert in this field who was not involved with these
findings.  “These careful measurements
provide a very strong clue as to what actually happens at these giant shock
fronts.”

These results
were published in the February 20th, 2011 issue of The Astrophysical Journal
Letters. The other co-authors are Carles Badenes from Tel-Aviv
University and the Weizmann Institute of Science in Israel, Robert Fesen from
Dartmouth College, NH, Parviz Ghavamian from Space Telescope Science Institute,
Baltimore, MD, David Moffett, from Furman University, Greenville, SC, Paul
Plucinsky from Harvard-Smithsonian Center for Astrophysics (CfA), Cambridge,
MA, Cara Rakowski from the Naval Research Laboratory, Washington, DC, Estela M.
Reynoso from the Institute of Astronomy and Space Physics and University of
Buenos Aires, Argentina and Patrick Slane from CfA.

NASA's Marshall Space
Flight Center in Huntsville, Ala., manages the Chandra program for NASA's
Science Mission Directorate in Washington. The Smithsonian Astrophysical
Observatory controls Chandra's science and flight operations from Cambridge,
Mass.

More information,
including images and other multimedia, can be found at:

Chandra X-Ray Observatory

NASA Chandra X-Ray Observatory Misson

Media Contact: Megan Watzke, Chandra X-Ray Center
617-496-7998
E-mail: mwatzke@cfa.harvard.edu

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