The Star Wars franchise has featured the fictitious
"Death Star," which can shoot powerful beams of
radiation across space. The Universe, however,
produces phenomena that often surpass what science
fiction can conjure.
The Pictor A galaxy is one such impressive object.
This galaxy, located nearly 500 million light years from
Earth, contains a supermassive black hole at
its center. A huge amount of gravitational energy is
released as material swirls towards the event
horizon, the point of no return for infalling
material. This energy produces an enormous beam, or
jet, of particles traveling at nearly the speed of
light into intergalactic space.
To obtain images of this jet, scientists used NASA's Chandra
X-ray Observatory at
various times over 15 years. Chandra's X-ray data
(blue) have been combined with
from the Australia Telescope Compact Array (red) in
this new composite image.
By studying the details of the structure seen in
both X-rays and radio waves, scientists seek to gain
a deeper understanding of these huge collimated
The jet [to the right] in Pictor A is the one that
is closest to us. It displays continuous X-ray
emission over a distance of 300,000 light years. By
comparison, the entire Milky Way is
about 100,000 light years in diameter. Because of
its relative proximity and Chandra's ability to make
detailed X-ray images, scientists can look at
detailed features in the jet and test ideas of how
the X-ray emission is produced.
In addition to the prominent jet seen pointing to
the right in the image, researchers report evidence
for another jet pointing in the opposite direction,
known as a "counterjet". While tentative evidence
for this counterjet had been previously reported,
these new Chandra data confirm its existence. The
relative faintness of the counterjet compared to the
jet is likely due to the motion of the counterjet
away from the line of sight to the Earth.
The labeled image shows the location of the
supermassive black hole, the jet and the counterjet.
Also labeled is a "radio lobe" where the jet is
pushing into surrounding gas and a "hotspot" caused
by shock waves - akin to sonic booms from a
supersonic aircraft - near the tip of the jet.
The detailed properties of the jet and counterjet
observed with Chandra show that their X-ray emission
likely comes from electrons spiraling around
magnetic field lines, a process called synchrotron emission. In this case, the
electrons must be continuously re-accelerated as
they move out along the jet. How this occurs is not
The researchers ruled out a different mechanism for
producing the jet's X-ray emission. In that
scenario, electrons flying away from the black hole
in the jet at near the speed of light move through
the sea of cosmic background radiation (CMB) left
over from the hot early phase of the Universe after
the Big Bang. When a fast-moving electron
collides with one of these CMB photons, it can boost the photon's
energy up into the X-ray band.
The X-ray brightness of the jet depends on the power
in the beam of electrons and the intensity of the
background radiation. The relative brightness of the
X-rays coming from the jet and counterjet in Pictor
A do not match what is expected in this process
involving the CMB, and effectively eliminate it as
the source of the X-ray production in the jet.
A paper describing these results will be published
in the Monthly Notices of the Royal Astronomical
Society and is available online. The authors are
Martin Hardcastle from the University of
Hertfordshire in the UK, Emil Lenc from the
University of Sydney in Australia, Mark Birkinshaw
from the University of Bristol in the UK, Judith
Croston from the University of Southampton in the
UK, Joanna Goodger from the University of
Hertfordshire, Herman Marshall from the
Massachusetts Institute of Technology in Cambridge,
MA, Eric Perlman from the Florida Institute of
Technology, Aneta Siemiginowska from the
Harvard-Smithsonian Center for Astrophysics in
Cambridge, MA, Lukasz Stawarz from Jagiellonian
University in Poland and Diana Worrall from the
University of Bristol.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages
the Chandra program for NASA's Science Mission
Directorate in Washington. The Smithsonian
Astrophysical Observatory in Cambridge,
Massachusetts, controls Chandra's science and flight