Cosmic particle accelerator at its limit
Gamma ray observatory H.E.S.S. reveals a cosmic particle acceleration
process in unprecedented detail

Date:
March 10, 2022
Source:
Deutsches Elektronen-Synchrotron DESY
Summary:
With the help of special telescopes, researchers have observed a
cosmic particle accelerator as never before. Observations made with
the gamma ray observatory H.E.S.S. in Namibia show for the first
time the course of an acceleration process in a stellar process
called a nova, which comprises powerful eruptions on the surface
of a white dwarf. A nova creates a shock wave that tears through
the surrounding medium, pulling particles with it and accelerating
them to extreme energies.

Surprisingly, the nova 'RS Ophiuchi' seems to cause particles to
accelerate at speeds reaching the theoretical limit, corresponding
to ideal conditions.



FULL STORY ==========================================================================
With the help of special telescopes, researchers have observed a cosmic particle accelerator as never before. Observations made with the gamma
ray observatory H.E.S.S. in Namibia show for the first time the course
of an acceleration process in a stellar process called a nova, which
comprises powerful eruptions on the surface of a white dwarf. A nova
creates a shock wave that tears through the surrounding medium, pulling particles with it and accelerating them to extreme energies. Surprisingly,
the nova "RS Ophiuchi" seems to cause particles to accelerate at speeds reaching the theoretical limit, corresponding to ideal conditions. The
research has been published in the journal Science.


========================================================================== White dwarves are burned-out old stars that have collapsed in on
themselves and develop into extremely compact objects. Novae events occur,
for example, when a white dwarf is in a binary system with a large star,
and the white dwarf gathers material from its more massive companion due
to its gravity. Once the gathered material goes over a critical level, it
spurs a thermonuclear explosion on the surface of the white dwarf. Some
novae are known to repeat. RS Ophiuchi is one of these recurrent novae;
there is an explosion on its surface every 15 to 20 years. "The stars
forming the system are at approximately the same distance from each
other as the Earth and the Sun," explains Alison Mitchell, researcher
at Friedrich-Alexander-Universita"t Erlangen-Nu"rnberg and principal investigator of the H.E.S.S Nova programme. "When the nova exploded in
August 2021, the H.E.S.S. telescopes allowed us to observe a galactic
explosion in very-high-energy gamma rays for the first time," she
continues.

The research group observed that the particles were accelerated to
energies several hundreds of times higher than previously observed
in novae.

Additionally, the energy released as a result of the explosion was
transformed extremely efficiently into accelerated protons and heavy
nuclei, such that the particle acceleration reached the maximum speeds calculated in theoretical models. According to Ruslan Konno, one of the
lead authors of the study and a doctoral candidate at DESY in Zeuthen,
"The observation that the theoretical limit for particle acceleration
can actually be reached in genuine cosmic shock waves has enormous
implications for astrophysics. It suggests that the acceleration
process could be just as efficient in their much more extreme relatives, supernovae." During the eruption of RS Ophiuchi, the researchers were
able for the first time to follow the development of the nova in real
time, allowing them to observe and study cosmic particle acceleration
as if they were watching a film.

The researchers were able to measure high-energy gamma rays up to one
month after the explosion. "This is the first time we have ever been able
to carry out observations like this, and it will allow us to gain even
more accurate future insights into how cosmic explosions work," explains
Dmitry Khangulyan, a theoretical astrophysicist at Rikkyo University in
Tokyo, Japan. "We may, for example, discover that novae contribute to the ever-present sea of cosmic rays and therefore have a considerable effect
on the dynamics of their immediate surroundings." Cosmic rays are immense showers of energetic subatomic particles that come from every direction
in space at the same time, and which have an unclear exact origin.

Specific telescopes were required for these measurements. The
H.E.S.S. facility (which stands for High Energy Stereoscopic
System) in Namibia consists of five Cherenkov telescopes that are
used to investigate gamma rays from space. A new, highly sensitive state-of-the-art camera -- known as FlashCam -- was recently installed
in the largest telescope. The FlashCam design is currently being further developed for the next generation gamma-ray observatory, the Cherenkov Telescope Array (CTA). "The new camera has been in use since late 2019,
and this measurement shows just how much potential the latest generation
of cameras has," explains Simon Steinmassl, a doctoral candidate at the
Max Planck Institute for Nuclear Physics in Heidelberg, who was involved
in analysing the camera data.

The telescopes were pointed towards the nova at very short notice
after amateur astronomers first reported the nova to the astrophysics community. The success of the observation was due in no small part to the
rapid reaction of the researchers and the wider astronomical community,
paving the way for extensive subsequent observations. H.E.S.S. Director
Stefan Wagner, a professor at the regional observatory in Heidelberg,
explains, "Over the next few years, research using the CTA telescopes
will show whether this type of nova is special." In addition, researchers
now have a clearer idea of what to look for.

This gives rise to a number of new possibilities for gaining a better understanding and being better able to explain events linked to
novae. "This measurement is a further success in gamma-ray astronomy
and an encouraging sign that we will be able to study many more cosmic explosions with H.E.S.S. and gamma-ray telescopes of the future."

========================================================================== Story Source: Materials provided by
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style and length.


========================================================================== Related Multimedia:
*
Artist's_impression_of_the_RS_Ophiuchi_Nova_outburst_and_what_follows ========================================================================== Journal Reference:
1. The H.E.S.S. collabroation. Time-resolved hadronic particle
acceleration
in the recurrent nova RS Ophiuchi. Science, 2022 DOI: 10.1126/
science.abn0567 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220310143755.htm

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