Gamma ray observatory H.E.S.S. reveals a cosmic particle acceleration process in unprecedented detail
From: Deutsches Elektronen-Synchrotron DESY, a
Research Centre of the Helmholtz Association
March 10, 2022 -- 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-Universität Erlangen-Nürnberg 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.”
About H.E.S.S.
The High Energy
Stereoscopy System (H.E.S.S.) is an array of five imaging atmospheric Cherenkov
telescopes for studying cosmic gamma rays. The observatory is operated through
an international collaboration. The telescopes are located in Namibia, near the
Gamsberg mountain, in a region known for its excellent optical properties. Four
H.E.S.S. telescopes went into operation in 2002/2003, the much larger fifth
telescope known as H.E.S.S. II is operational since July 2012 and
extends the energy coverage towards lower energies, as well as further
improving sensitivity. More than 230 researchers from 41 institutes
in 15 different countries are involved in H.E.S.S.
https://www.desy.de/news/news_search/index_eng.html?openDirectAnchor=2249&two_columns=0
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