Quasar jets are particle accelerators thousands of light-years long


Date:
June 17, 2020
Source:
CNRS
Summary:
An international collaboration bringing together over 200 scientists
from 13 countries has shown that the very high-energy gamma-ray
emission from quasars is not concentrated in the region close to
their central black hole but in fact extends over several thousand
light-years along jets of plasma. This discovery shakes up current
scenarios for the behaviour of such plasma jets.



FULL STORY ==========================================================================
An international collaboration bringing together over 200 scientists from
13 countries has shown that the very high-energy gamma-ray emission from quasars, galaxies with a highly energetic nucleus, is not concentrated
in the region close to their central black hole but in fact extends over several thousand light-years along jets of plasma. This discovery shakes
up current scenarios for the behaviour of such plasma jets. The work,
published in the journal Nature on June 18th, 2020, was carried out
as part of the H.E.S.S collaboration, involving in particular the CNRS
and CEA in France, and the Max Planck society and a group of research institutions and universities in Germany.


==========================================================================
Over the past few years, scientists have observed the Universe using
gamma rays, which are very high-energy photons. Gamma rays, which form
part of the cosmic rays that constantly bombard the Earth, originate from regions of the Universe where particles are accelerated to huge energies unattainable in human-built accelerators. Gamma rays are emitted by a
wide range of cosmic objects, such as quasars, which are active galaxies
with a highly energetic nucleus. The intensity of the radiation emitted
from these systems can vary over very short timescales of up to one
minute. Scientists therefore believed that the source of this radiation
was very small and located in the vicinity of a supermassive black hole,
which can have a mass several billion times that of the Sun's. The
black hole is thought to gobble up the matter spiralling down into it
and eject a small part of it in the form of large jets of plasma, at relativistic speeds, close to the speed of light, thus contributing to
the redistribution of matter throughout the Universe.

Using the H.E.S.S. Observatory in Namibia, an international astrophysics collaboration observed a radio galaxy (a galaxy that is highly luminous
when observed at radio wavelengths) for over 200 hours at unparalleled resolution.

As the nearest radio galaxy to Earth, Centaurus A is favourable to
scientists for such a study, enabling them to identify the region emitting
the very high- energy radiation while studying the trajectory of the
plasma jets. They were able to show that the gamma-ray source extends
over a distance of several thousand light-years. This extended emission indicates that particle acceleration does not take place solely in the
vicinity of the black hole but also along the entire length of the plasma
jets. Based on these new results, it is now believed that the particles
are reaccelerated by stochastic processes along the jet. The discovery
suggests that many radio galaxies with extended jets accelerate electrons
to extreme energies and might emit gamma-rays, possibly explaining the
origins of a substantial fraction of the diffuse extragalactic gamma
background radiation.

These findings provide important new insights into cosmic gamma-ray
emitters, and in particular about the role of radio galaxies as
highly efficient relativistic electron accelerators. Due to their
large number, it would appear that radio galaxies collectively make
a highly significant contribution to the redistribution of energy in
the intergalactic medium. The results of this study required extensive observations and optimized analysis techniques with H.E.S.S., the most sensitive gamma-ray observatory to date. Next-generation telescopes
(Cherenkov Telescope Array, or CTA) will no doubt make it possible to
observe this phenomenon in even greater detail.


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


========================================================================== Journal Reference:
1. The H.E.S.S. Collaboration. Resolving acceleration to very high
energies
along the jet of Centaurus A. Nature, 2020 DOI:
10.1038/s41586-020-2354-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200617150027.htm

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