SPT-CLJ2344-4243 - Phoenix Cluster
Credit:
X-ray: NASA/CXC/MIT/M.McDonald et al;
Optical: NASA/STScI; Radio: TIFR/GMRT
Galaxy clusters
are often described by superlatives. After all, they are huge
conglomerations of galaxies, hot gas, and dark matter and represent the
largest structures in the Universe held together by gravity.
Galaxy clusters tend to be poor at producing new stars in their
centers. They generally have one giant galaxy in their middle that forms
stars at a rate significantly slower than most galaxies - including our
Milky Way. The central galaxy contains a supermassive black holeroughly a thousand times more massive than the one at the center of our galaxy.
Without heating by outbursts from this black hole, the copious amounts
of hot gas found in the central galaxy should cool, allowing stars to
form at a high clip. It is thought that the central black hole acts as a
thermostat, preventing rapid cooling of surrounding hot gas and
impeding star formation.
New data provide more details on how the galaxy cluster SPT-CLJ2344-4243, nicknamed the Phoenix Cluster for the constellation
in which it is found, challenges this trend. The cluster has shattered
multiple records in the past: In 2012, scientists announced that the
Phoenix cluster featured the highest rate of cooling hot gas and star
formation ever seen in the center of a galaxy cluster, and is the most
powerful producer of X-rays of all known clusters. The rate at which hot gas is cooling in the center of the cluster is also the largest ever observed.
New observations of this galaxy cluster at X-ray, ultraviolet, and optical wavelengths by NASA's Chandra X-ray Observatory,
the Hubble Space Telescope, and the Clay-Magellan telescope located in
Chile, are helping astronomers better understand this remarkable object.
Clay-Magellan's optical data reveal narrow filaments from the center of
the cluster where stars are forming. These massive cosmic threads of
gas and dust, most of which had never been detected before, extend for
160,000 to 330,000 lights years.
This is longer than the entire breadth of the Milky Way galaxy, making
them the most extensive filaments ever seen in a galaxy cluster.
These filaments surround large cavities - regions with greatly
reduced X-ray emission - in the hot gas. The X-ray cavities can be seen
in this composite image that shows the Chandra X-ray data in blue and
optical data from the Hubble Space Telescope (red, green, and blue). For
the location of these "inner cavities", mouse over the image.
Astronomers think that the X-ray cavities were carved out of the
surrounding gas by powerful jets of high-energy particles emanating from
near a supermassive black hole in the central galaxy of the cluster. As
matter swirls toward a black hole, an enormous amount of gravitational
energy is released.
Combined radio and X-ray observations of
supermassive black holes in other galaxy clusters have shown that a
significant fraction of this energy is released as jets of outbursts
that can last millions of years. The observed size of the X-ray cavities
indicates that the outburst that produced the cavities in SPT-
CLJ2344-4243 was one of the most energetic such events ever recorded.
Radio & Optical Image of Phoenix Cluster
Credit
X-ray: NASA/CXC/MIT/M.McDonald et al;
Optical: NASA/STScI; Radio: TIFR/GMRT
However, the central black hole in the Phoenix cluster is suffering
from somewhat of an identity crisis, sharing properties with both "quasars",
very bright objects powered by material falling onto a supermassive
black hole, and "radio galaxies" containing jets of energetic particles
that glow in radio waves, and are also powered by giant black holes.
Half of the energy output from this black hole comes via jets
mechanically pushing on the surrounding gas (radio-mode), and the other
half from optical, UV and X-radiation originating in an accretion disk
(quasar-mode). Astronomers suggest that the black hole may be in the
process of flipping between these two states.
X-ray cavities located farther away from the center of the cluster,
labeled as "outer cavities", provide evidence for strong outbursts from
the central black hole about a hundred million years ago (neglecting the
light travel time to the cluster). This implies that the black hole may
have been in a radio mode, with outbursts, about a hundred million
years ago, then changed into a quasar mode, and then changed back into a
radio mode.
It is thought that rapid cooling may have occurred in between these
outbursts, triggering star formation in clumps and filaments throughout
the central galaxy at a rate of about 610 solar masses per year. By
comparison, only a couple new stars form every year in our Milky Way
galaxy. The extreme properties of the Phoenix cluster system are
providing new insights into various astrophysical problems, including
the formation of stars, the growth of galaxies and black holes, and the
co-evolution of black holes and their environment.
A paper describing these results, led by Michael McDonald
(Massachusetts Institute of Technology), has been accepted for
publication in The Astrophysical Journal and is available online.
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 Phoenix Cluster:
Scale: Image is about 1.2 arcmin across (about 1.5 million light years)
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 23h 44m 42.00s | Dec -42 42 52.60
Constellation: Phoenix
Observation Date: 3 pointings between Sep 2011 and Aug 2014
Observation Time: 36 hours 23 min (1 days 12 hours 23 min).
Obs. ID: 13401, 16135, 16545
Instrument: ACIS
Also Known As: SPT-CLJ2344-4243
References: arXiv:1508.05941
Color Code: X-ray (Blue); Optical (Red, Green, Blue)
Distance Estimate: About 5.7 billion light years; z=0.596
