A binary star as a cosmic particle accelerator
Evidence of very high-energy gamma radiation from Eta Carinae

Date:
July 1, 2020
Source:
Deutsches Elektronen-Synchrotron DESY
Summary:
Scientists have identified the binary star Eta Carinae as a new kind
of source for very high-energy (VHE) cosmic gamma-radiation. Eta
Carinae is located 7500 lightyears away in the constellation
Carina in the Southern Sky and, based on the data collected,
emits gamma rays with energies up to 400 gigaelectronvolts (GeV),
some 100 billion times more than the energy of visible light.



FULL STORY ========================================================================== Scientists have identified the binary star Eta Carinae as a new kind of
source for very high-energy (VHE) cosmic gamma-radiation. Eta Carinae is located 7500 lightyears away in the constellation Carina in the Southern
Sky and, based on the data collected, emits gamma rays with energies
up to 400 gigaelectronvolts (GeV), some 100 billion times more than the
energy of visible light.


==========================================================================
With a specialised telescope in Namibia a DESY-led team of researchers
has proven a certain type of binary star as a new kind of source for
very high- energy cosmic gamma-radiation. Eta Carinae is located 7500 lightyears away in the constellation Carina (the ship's keel) in the
Southern Sky and, based on the data collected, emits gamma rays with
energies all the way up to 400 gigaelectronvolts (GeV), some 100 billion
times more than the energy of visible light. The team headed by DESY's
Stefan Ohm, Eva Leser and Matthias Fu"ssling is presenting its findings,
made at the gamma-ray observatory High Energy Stereoscopic System
(H.E.S.S.), in the journal Astronomy & Astrophysics. An accompanying
multimedia animation explains the phenomenon. "With such visualisations
we want to make the fascination of research tangible," emphasises DESY's Director of Astroparticle Physics, Christian Stegmann.

Eta Carinae is a binary system of superlatives, consisting of two blue
giants, one about 100 times, the other about 30 times the mass of our
sun. The two stars orbit each other every 5.5 years in very eccentric elliptical orbits, their separation varying approximately between
the distance from our Sun to Mars and from the Sun to Uranus. Both
these gigantic stars fling dense, supersonic stellar winds of charged
particles out into space. In the process, the larger of the two loses a
mass equivalent to our entire Sun in just 5000 years or so. The smaller
one produces a fast stellar wind travelling at speeds around eleven
million kilometres per hour (about one percent of the speed of light).

A huge shock front is formed in the region where these two stellar
winds collide, heating up the material in the wind to extremely high temperatures. At around 50 million degrees Celsius, this matter radiates brightly in the X-ray range. The particles in the stellar wind are not
hot enough to emit gamma radiation, though. "However, shock regions
like this are typically sites where subatomic particles are accelerated
by strong prevailing electromagnetic fields," explains Ohm, who is the
head of the H.E.S.S. group at DESY. When particles are accelerated this rapidly, they can also emit gamma radiation. In fact, the satellites
"Fermi," operated by the US space agency NASA, and AGILE, belonging to
the Italian space agency ASI, already detected energetic gamma rays of
up to about 10 GeV coming from Eta Carinae in 2009.

"Different models have been proposed to explain how this gamma radiation
is produced," Fu"ssling reports. "It could be generated by accelerated electrons or by high-energy atomic nuclei." Determining which of these
two scenarios is correct is crucial: very energetic atomic nuclei account
for the bulk of the so-called Cosmic Rays, a subatomic cosmic hailstorm striking Earth constantly from all directions. Despite intense research
for more than 100 years, the sources of the Cosmic Rays are still not exhaustively known. Since the electrically charged atomic nuclei are
deflected by cosmic magnetic fields as they travel through the universe,
the direction from which they arrive at Earth no longer points back to
their origin. Cosmic gamma rays, on the other hand, are not deflected. So,
if the gamma rays emitted by a specific source can be shown to originate
from high-energy atomic nuclei, one of the long-sought accelerators of
cosmic particle radiation will have been identified.

"In the case of Eta Carinae, electrons have a particularly hard time
getting accelerated to high energyies, because they are constantly being deflected by magnetic fields during their acceleration, which makes
them lose energy again," says Leser. "Very high-energy gamma radiation
begins above the 100 GeV range, which is rather difficult to explain
in Eta Carinae to stem from electron acceleration." The satellite data
already indicated that Eta Carinae also emits gamma radiation beyond
100 GeV, and H.E.S.S. has now succeeded in detecting such radiation up
to energies of 400 GeV around the time of the close encounter of the
two blue giants in 2014 and 2015. This makes the binary star the first
known example of a source in which very high-energy gamma radiation is generated by colliding stellar winds.

"The analysis of the gamma radiation measurements taken by H.E.S.S. and
the satellites shows that the radiation can best be interpreted as
the product of rapidly accelerated atomic nuclei," says DESY's PhD
student Ruslan Konno, who has published a companion study, together
with scientists from the Max Planck Institute for Nuclear Physics in Heidelberg. "This would make the shock regions of colliding stellar
winds a new type of natural particle accelerator for cosmic rays." With H.E.S.S., which is named after the discoverer of Cosmic Rays, Victor
Franz Hess, and the upcoming Cherenkov Telescope Array (CTA), the next-generation gamma-ray observatory currently being built in the
Chilean highlands, the scientists hope to investigate this phenomenon
in greater detail and discover more sources of this kind.

"I find science and scientific research extremely important," says
Nicolai, who sees close parallels in the creative work of artists and scientists. For him, the appeal of this work also lay in the artistic
mediation of scientific research results: "particularly the fact that
it is not a film soundtrack, but has a genuine reference to reality," emphasizes the musician and artist.

Together with the exclusively composed sound, this unique collaboration of scientists, animation artists and musician has resulted in a multimedia
work that takes viewers on an extraordinary journey to a superlative
double star some 7500 light years away.


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


========================================================================== Journal References:
1. H. Abdalla et al. Detection of very-high-energy g-ray emission
from the
colliding wind binary e Car with H.E.S.S.. Astronomy & Astrophysics,
2020; 635: A167 DOI: 10.1051/0004-6361/201936761
2. R. White, M. Breuhaus, R. Konno, S. Ohm, B. Reville,
J.A. Hinton. Gamma-
ray and X-ray constraints on non-thermal processes in e Carinae.

Astronomy & Astrophysics, 2020; 635: A144 DOI: 10.1051/0004-6361/
201937031 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200701100106.htm

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