|
| An artist’s depiction of a black hole spewing jets of matter: Stocktrek Images, Inc. / Alamy Stock Photo |
Supermassive black holes that beam powerful jets of matter towards Earth,
known as blazars, accelerate particles to extraordinarily high energies – and
astronomers have finally figured out how.
Astronomers may have solved a major mystery about the supermassive black
holes at the centres of some galaxies. A subset of these black holes called
blazars
blast out colossal jets
of matter towards Earth, and we may now know how the particles in those jets
reach such high energies.
Researchers have known about these jets for decades, but we have never been
able to look into the heart of a blazar before to see how it accelerates
particles. A new X-ray space telescope called the Imaging X-ray Polarimetry
Explorer (IXPE) has made this possible for the first time.
Yannis Liodakis
at the University of Turku in Finland and his colleagues used it to look at
a particularly bright blazar called Markarian 501.
“When we look at optical light and radio waves, we’re looking at the jet
itself, far away from where the acceleration takes place. And there, the
theoretical models basically all look the same,” says Liodakis. “But with
X-rays you can go super close to the accelerator, where the magic takes
place, and that is where we can discriminate between the models.”
There were two main models for how blazars accelerate particles: either via
interactions within the black hole’s magnetic field or via shock waves
propagating through the jets. The IXPE observations suggest it is shock
waves. These are probably created through simple turbulence in the jet, when
faster-moving plasma smashes into slower areas and gives up some of its
energy.
Previous observations have revealed strange knots of material moving around
in the jets, and these new observations hint that those may be caused by
shock waves. Observations of two other blazars showed similar behaviour, so
this same mechanism may explain particle acceleration in all blazars,
Liodakis says.
This is important because the
extreme areas around black holes
may someday serve as laboratories through which we can investigate
conditions much more extreme than scientists can create on Earth. The jets
alone accelerate particles to energies far higher than any human-made
collider can achieve.
“You can do very extreme particle physics, you can do tests of strong
gravity, all of these things that would expand our understanding of physics,
but before you do that you have to figure out exactly how these objects
work,” says Liodakis. “These are the first steps to doing that.”
Reference:
Liodakis, I., Marscher, A.P., Agudo, I. et al. Polarized blazar X-rays imply
particle acceleration in shocks. Nature 611, 677–681 (2022).
DOI: 10.1038/s41586-022-05338-0