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 radio data 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 blasts.
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 well understood
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 operations.
Fast Facts for Pictor A:
Scale: Image is 10 arcmin across (about 1.4 million light years)
Category: Quasars & Active Galaxies
Coordinates (J2000): RA 05h 19m 49.70s | Dec -45° 46' 45"
Constellation: Pictor
Observation Date: 14 pointings between Jan 2000 and Jan 2015
Observation Time: 128 hours 53 min (5 days 8 hours 53 min)
Obs. ID: 346, 3090, 4369, 12039, 12040, 11586, 14357, 14221, 15580, 15593, 14222, 14223, 16478, 17574
Instrument: ACIS
References: Hardcastle, M. et al., 2016, MNRAS, 455, 3526; arXiv:1510.08392
Color Code: X-ray (Blue), Radio (Red)
Distance Estimate: About 480 million light years (z=0.035)
Source: NASA’s Chandra X-ray Observatory
