Figure 1. The left hand panel shows an actual observation of the
galaxy cluster MS 0735.6+7421, while on the right the background Hubble
image has instead been overlaid with a mock observation of the jet
(pink) and X-ray emission (blue) made from the simulation. Both images
show cavities excavated by the lobe inflation surround by X-ray bright
rims of dense gas (blue), which are filled by distorted jet material
(pink). Image credit: Hubble and Chandra Image: NASA, ESA, CXC, STScI,
and B. McNamara (University of Waterloo); Very Large Array Telescope
Image: NRAO, and L. Birzan and team (Ohio University); Simulated Data:
M. A. Bourne (University of Cambridge).
Figure 2. An artist’s impression of the jet launched by a
supermassive black hole, which inflates lobes of very hot gas that are
distorted by the cluster weather. Image credit: Institute of Astronomy,
University of Cambridge.
“Weather” in clusters of galaxies may explain a
longstanding puzzle, according to a team of researchers at the
University of Cambridge. The scientists used sophisticated simulations
to show how powerful jets from supermassive black holes are disrupted by
the motion of hot gas and galaxies, preventing gas from cooling, which
could otherwise form stars. The team publish their work in the journal
Monthly Notices of the Royal Astronomical Society.
Typical clusters of galaxies have several thousand member
galaxies, which can be very different to our own Milky Way and vary in
size and shape. These systems are embedded in very hot gas known as the
intracluster medium (ICM), all of which live in an unseen halo of
so-called ‘dark matter’.
A large number of galaxies have supermassive black holes in their centres, and these often have high speed jets of material stretching over thousands of light years that can inflate very hot lobes in the ICM.
The researchers, based at the Kavli Institute for
Cosmology and Institute of Astronomy performed state-of-the-art
simulations looking at the jet lobes in fine detail and the X-rays
emitted as a result. The model captures the birth and cosmological
evolution of the galaxy cluster, and allowed the scientists to
investigate with unprecedented realism how the jets and lobes they
inflate interact with a dynamic ICM.
They found that the mock X-ray observations of the
simulated cluster revealed the so-called “X-ray cavities” and “X-ray
bright rims” generated by supermassive black hole-driven jets, which
itself is distorted by motions in the cluster remarkably resemble those
found in observations of real galaxy clusters.
Dr Martin Bourne of the Institute of Astronomy in
Cambridge led the team. He commented: “We have developed new
computational techniques, which harness the latest high-performance
computing technology, to model for the first time the jet lobes with
more than a million elements in fully realistic clusters. This allows us
to place the physical processes that drive the liberation of the jet
energy under the microscope.”
As galaxies move around in the cluster, the simulation
shows they create a kind of ‘weather’, moving, deforming and destroying
the hot lobes of gas found at the end of the black hole jets. The jet
lobes are enormously powerful and if disrupted, deliver vast amounts of
energy to the ICM.
The Cambridge team believe that this cluster weather
disruption mechanism may solve an enduring problem: understanding why
ICM gas does not cool and form stars in the cluster centre. This
so-called “cooling flow” puzzle has plagued astrophysicists for more
than 25 years.
The simulations performed provide a tantalizing new
solution that could solve this problem. Dr Bourne commented: “The
combination of the huge energies pumped into the jet lobes by the
supermassive black hole and the ability of cluster weather to disrupt
the lobes and redistribute this energy to the ICM provides a simple and
yet elegant mechanism to solve the cooling flow problem.”
A series of next generation X-ray space telescopes will
launch into orbit over the next decade. These advanced instruments
should help settle the debate – and if intergalactic weather really does
stop the birth of stars.
Notes
The simulations have been performed on the STFC DiRAC HPC facilities which are part of the National e-Infrastructure. The research was funded by European Research Council, STFC and the Kavli Foundation. This work has been accepted by Monthly Notices of the Royal Astronomical Society: “AGN jet feedback on a moving mesh: lobe energetics and X-ray properties in a realistic cluster environment” by Martin A. Bourne, Debora Sijacki and Ewald Puchwein.
Science Contact
Dr Martin Bourne
Kavli Institute for Cosmology, Cambridge
Institute of Astronomy
Cambridge
Mob: +44 (0)7557380858
mabourne@ast.cam.ac.uk
Science Contact
Dr Martin Bourne
Kavli Institute for Cosmology, Cambridge
Institute of Astronomy
Cambridge
Mob: +44 (0)7557380858
mabourne@ast.cam.ac.uk
