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| An artist's impression of a nova being observed by the HESS telescope (in the foreground). (Image credit: DESY/H.E.S.S., Science Communication Lab) |
A burned-out stellar core produced a shockwave that pushed particles to
their theoretical speed limit, scientists have reported.
Astronomers used a gamma-ray observatory in Namibia called the High Energy
Stereoscopic System (HESS) to show how an eruption creates a shock wave that
accelerates material around it super-fast speeds. The research focused on RS
Ophiuchi, a nova that erupts every 15 to 20 years — most recently, in 2021.
RS Ophiuchi's system includes one normal star and one white dwarf, the cold
dense core that remains after a star explodes. The white dwarf pulls matter
off the star, and when the stellar corpse has swallowed enough material, it
produces the eruption scientists call a nova. As the nova erupts, the
resulting shock wave collides through the surrounding area, pulling
particles along with it and creating an accelerator that turns out to be
incredibly powerful.
"When the nova exploded in August 2021, the HESS telescopes allowed us to
observe a galactic explosion in very-high-energy gamma rays for the first
time," noted principal investigator Alison Mitchell, researcher at
Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany, in a statement
Thursday (March 10).
Notably, particles at RS Ophiuchi reached rates hundreds of times faster
than scientists have ever observed at other novas. The acceleration was so
powerful that the particles reached the maximum speed predicted in
theoretical models, the team behind the new research noted.
"The observation that the theoretical limit for particle acceleration can
actually be reached in genuine cosmic shock waves has enormous implications
for astrophysics," co-author Ruslan Konno, a doctoral candidate at Deutsches
Elektronen-Synchrotron in Germany, said in the same statement. "It suggests
that the acceleration process could be just as efficient in their much more
extreme relatives, supernovas."
Supernovas are stellar explosions generated when the most massive stars run
out of fuel and are in fact the process that creates white dwarfs like the
one in RS Ophiuchi.
In addition to tracking the eruption as it progressed, the researchers were
able to measure high-energy gamma-rays from the RS Ophiuchi nova up to a
month after the explosion. Such observations are the first of their kind,
according to the statement.
The RS Ophiuchi nova may not be the largest explosion out there, but for
scientists these observations are particularly special, made possible only
by a cutting-edge camera that HESS installed on one of its telescopes in
late 2019. The newness of the technology means scientists aren't yet sure
how rare this type of event is.
The HESS observations also relied on amateur astronomers swiftly reporting
their sightings of the nova to professional counterparts, according to the
statement.
The researchers said that the study has implications not only for novas and
supernovas, but perhaps also for better understanding the origin story of
cosmic rays. Cosmic rays are energetic explosions that appear to come from
every direction in space, making their source difficult to trace, but having
studied the RS Ophiuchi nova, the researchers have a hunch that this type of
nova might play a role.
A study based on the research was published on Thursday (March 10) in
Science.
Reference:
Time-resolved hadronic particle acceleration in the recurrent Nova RS
Ophiuchi, Science (2022).
DOI: 10.1126/science.abn0567
Tags:
Space & Astrophysics