Astronomers have found evidence for a faded electron cloud "coming back to life," much like the mythical phoenix, after two galaxy clusters collided. This "radio phoenix," so-called because the high-energy electrons radiate primarily at radio frequencies, is found in Abell 1033. The system is located about 1.6 billion light years from Earth.
By combining data from NASA's Chandra X-ray Observatory,
the Westerbork Synthesis Radio Telescope in the Netherlands, NSF's Karl
Jansky Very Large Array (VLA), and the Sloan Digital Sky Survey (SDSS),
astronomers were able to recreate the scientific narrative behind this
intriguing cosmic story of the radio phoenix.
Galaxy clusters are the largest structures in the Universe held together by gravity. They consist of hundreds or even thousands of individual galaxies, unseen dark matter,
and huge reservoirs of hot gas that glow in X-ray light. Understanding
how clusters grow is critical to tracking how the Universe itself
evolves over time.
Astronomers think that the supermassive black hole
close to the center of Abell 1033 erupted in the past. Streams of
high-energy electrons filled a region hundreds of thousands of light
years across and produced a cloud of bright radio emission. This cloud
faded over a period of millions of years as the electrons lost energy
and the cloud expanded.
The radio phoenix emerged when another cluster of galaxies slammed
into the original cluster, sending shock waves through the system. These
shock waves, similar to sonic booms
produced by supersonic jets, passed through the dormant cloud of
electrons. The shock waves compressed the cloud and re-energized the
electrons, which caused the cloud to once again shine at radio
frequencies.
A new portrait of this radio phoenix is captured in this multi wavelength image
of Abell 1033. X-rays from Chandra are in pink and radio data from the
VLA are colored green. The background image shows optical observations
from the SDSS. A map of the density of galaxies, made from the analysis
of optical data, is seen in blue. Mouse over the image above to see the
location of the radio phoenix.
The Chandra data show hot gas in the clusters, which seems to have
been disturbed during the same collision that caused the re-ignition of
radio emission in the system. The peak of the X-ray emission is seen to
the south (bottom) of the cluster, perhaps because the dense core of gas
in the south is being stripped away by surrounding gas as it moves. The
cluster in the north may not have entered the collision with a dense
core, or perhaps its core was significantly disrupted during the merger.
On the left side of the image, a so-called wide-angle tail radio galaxy
shines in the radio. The lobes of plasma ejected by the supermassive
black hole in its center are bent by the interaction with the cluster
gas as the galaxy moves through it.
Astronomers think they are seeing the radio phoenix soon after it had
reborn, since these sources fade very quickly when located close to the
center of the cluster, as this one is in Abell 1033. Because of the
intense density, pressure, and magnetic fields near the center of Abell
1033, a radio phoenix is only expected to last a few tens of millions of
years.
A paper describing these results was published in a recent issue of
the Monthly Notices of the Royal Astronomical Society and a preprint is available online.
The authors are Francesco de Gasperin from the University of Hamburg,
Germany; Georgiana Ogrean and Reinout van Weeren from the
Harvard-Smithsonian Center for Astrophysics; William Dawson from the
Lawrence Livermore National Lab in Livermore, California; Marcus
Brüggen and Annalisa Bonafede from the University of Hamburg, Germany,
and Aurora Simionescu from the Japan Aerospace Exploration Agency in
Sagamihara, Japan.
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 Abell 1033:
Scale: Image is about 17 arcmin across (about 7.5 million light years)
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 10h 31m 33.70s | Dec +35° 04' 33.96"
Constellation: Leo Minor
Observation Date: 19 and 21 Feb 2013
Observation Time: 17 hours 35 min.
Obs. ID: 15084, 15614
Instrument: ACIS
References: de Gasperin, F. et al, 2015, MNRAS (accepted); arXiv:1501.00043
Color Code: X-ray (Pink); Optical (Red, Green, Blue); Radio (Green); Density Map (Blue)
Distance Estimate: About 1.62 billion light years (z=0.1259)
Source: NASA’s Chandra X-ray Observatory
