NGC 4696
Credit: X-ray: NASA/CXC/MPE/J.Sanders et al.;
Optical: NASA/STScI; Radio: NSF/NRAO/VLA
At the center of the Centaurus galaxy cluster, there is a large elliptical galaxy called NGC 4696. Deeper still, there is a supermassive black hole buried within the core of this galaxy.
New data from NASA's Chandra X-ray Observatory and other telescopes has revealed details about this giant black hole, located some 145 million light years
from Earth. Although the black hole itself is undetected, astronomers
are learning about the impact it has on the galaxy it inhabits and the
larger cluster around it.
In some ways, this black hole resembles a beating heart that pumps
blood outward into the body via the arteries. Likewise, a black hole can
inject material and energy into its host galaxy and beyond.
By examining the details of the X-ray
data from Chandra, scientists have found evidence for repeated bursts
of energetic particles in jets generated by the supermassive black hole
at the center of NGC 4696. These bursts create vast cavities in the hot
gas that fills the space between the galaxies in the cluster. The bursts
also create shock waves, akin to sonic booms produced by high-speed airplanes, which travel tens of thousands of light years across the cluster.
This composite image contains X-ray data from Chandra (red) that reveals the hot gas in the cluster, and radio data
from the NSF's Karl G. Jansky Very Large Array (blue) that shows
high-energy particles produced by the black hole-powered jets. Visible
light data from the Hubble Space Telescope (green) show galaxies in the
cluster as well as galaxies and stars outside the cluster.
Cavity
processing scale: This image shows a larger field of view than the main
composite image above and is about 122,000 light years across. This
image has also been rotated slightly clockwise to the main composite
image above.
Astronomers employed special processing to the X-ray data (shown
above) to emphasize nine cavities visible in the hot gas. These cavities
are labeled A through I in an additional image, and the location of the
black hole is labeled with a cross. The cavities that formed most
recently are located nearest to the black hole, in particular the ones
labeled A and B.
The researchers estimate that these black hole bursts, or "beats",
have occurred every five to ten million years. Besides the vastly
differing time scales, these beats also differ from typical human
heartbeats in not occurring at particularly regular intervals.
A different type of processing of the X-ray data (shown above)
reveals a sequence of curved and approximately equally spaced features
in the hot gas. These may be caused by sound waves generated by the
black hole's repeated bursts. In a galaxy cluster, the hot gas that
fills the cluster enables sound waves — albeit at frequencies far too
low for the human hear to detect — to propagate. (Note that both images
showing the labeled cavities and this image are rotated slightly
clockwise to the main composite.)
The features in the Centaurus Cluster are similar to the ripples seen in the Perseus cluster of galaxies.
The pitch of the sound in Centaurus is extremely deep, corresponding to
a discordant sound about 56 octaves below the notes near middle C. This
corresponds to a slightly higher (by about one octave) pitch than the
sound in Perseus. Alternative explanations for these curved features
include the effects of turbulence or magnetic fields.
The black hole bursts also appear to have lifted up gas that has been enriched in elements generated in supernova
explosions. The authors of the study of the Centaurus cluster created a
map showing the density of elements heavier than hydrogen and helium.
The brighter colors in the map show regions with the highest density of
heavy elements and the darker colors show regions with a lower density
of heavy elements. Therefore, regions with the highest density of heavy
elements are located to the right of the black hole. A lower density of
heavy elements near the black hole is consistent with the idea that
enriched gas has been lifted out of the cluster's center by bursting
activity associated with the black hole. The energy produced by the
black hole is also able to prevent the huge reservoir of hot gas from
cooling. This has prevented large numbers of stars from forming in the
gas.
A paper describing these results was published in the March 21st 2016
issue of the Monthly Notices of the Royal Astronomical Society and is available online. The first author is Jeremy Sanders from the Max Planck Institute for Extraterrestrial Physics in Garching, Germany.
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 NGC 4696:
Scale: Image is about 2.2 arcmin across (about 93,000 light years)
Category: Black Holes, Normal Galaxies & Starburst Galaxies
Coordinates (J2000): RA 12h 48m 48.90s | Dec -41° 18′ 44.40
Constellation: Centaurus
Observation Date: 15 pointings between May 2000 and June 2014
Observation Time: 216 hours 29 min (9 days 29 min)
Obs. ID: 504, 505, 4190, 4191, 4954, 4955, 5310, 16223-16225, 16534, 16607-16610
Instrument: ACIS
References: Sanders, J. et al., 2016, MNRAS, 457, 82; arXiv:1601.01489
Color Code: X-ray (Red); Optical (Green); Radio (Blue)
Distance Estimate: About 145 million light years
Source: NASA’s Chandra X-ray Observatory
