Nova outbursts are apparently a source for cosmic rays

Date:
April 14, 2022
Source:
Max Planck Institute for Physics
Summary:
The MAGIC telescopes have observed the nova RS Ophiuchi shining
brightly in gamma rays at extremely high energy. The Gamma rays
emanate from protons that are accelerated to very high energies
in the shock front following the explosion. This suggests that
novae are also a source of the ubiquitous cosmic radiation in
the universe which consists mainly of protons rich in energy,
which race through space at almost the speed of light.



FULL STORY ========================================================================== Light on, light off -- this is how one could describe the behavior of
the nova, which goes by the name RS Ophiuchi (RS Oph). Every 15 years
or so, a dramatic explosion occurs in the constellation of the Serpent
Bearer. Birthplaces of a nova are systems in which two very different
stars live in a parasitic relationship: A white dwarf, a small, burned-out
and tremendously dense star - - a teaspoon of its matter weighs about
1 ton -- orbits a red giant, an old star that will soon burn up.


==========================================================================
The dying giant star feeds the white dwarf with matter shedding its
outer hydrogen layer as the gas flows onto the nearby white dwarf. This
flow of matter continues, until the white dwarf over(h)eats itself. The temperature and pressure in the newly gained stellar shells become too
large and are flung away in a gigantic thermonuclear explosion. The dwarf
star remains intact and the cycle begins again -- until the spectacle
repeats itself.

Explosion in the high-energy range It had been speculated that such
explosions involve high energies. The two MAGIC telescopes recorded
gamma rays with the value of 250 gigaelectronvolts (GeV), among the
highest energies ever measured in a nova. By comparison, the radiation
is a hundred billion times more energetic than visible light.

MAGIC was able to make its observations following initial alerts from
other instruments measuring at different wavelengths. "The spectacular
eruption of the RS Ophiuchi shows that the MAGIC telescopes' fast response really pays off: It takes them no more than 30 seconds to move to a new target," said David Green, a scientist at the Max Planck Institute for
Physics and one of the authors of the paper.

Accelerated protons as a part of cosmic rays After the explosion, several
shock fronts propagated through the stellar wind from the Red Giant and
the interstellar medium surrounding the binary system.

These shock waves work like a giant power plant in which particles
are accelerated to near the speed of light. The combined measurements
suggest that the gamma rays emanate from energetic protons, nuclei of
hydrogen atoms.

"This also makes nova outbursts a source of cosmic rays," explains
David Green.

"However, they tend to play the role of local heroes -- meaning to only contribute to the cosmic rays in the close neighborhood. The big players
for cosmic rays are supernova remnants. The shock fronts created from
stellar explosions are far more violent compared to novae.

To fully understand the complicated interplay of violent events with
the interstellar medium in the Milky Way, more observations like those
reported now will be necessary. The MAGIC collaboration will therefore
continue to look for "restless" objects in our Galaxy and beyond.


========================================================================== Story Source: Materials provided by
Max_Planck_Institute_for_Physics. Note: Content may be edited for style
and length.


========================================================================== Related Multimedia:
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The_binary_star_system_RS_Ophiuchi:_Matter_flows_from_the_red_giant_onto
the_white_dwarf.

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Nature Astronomy, 2022; DOI: 10.1038/s41550-022-01640-z ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220414125109.htm

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