Credit X-ray: NASA/CXC/NRAO/D.-C.Kim; Optical: NASA/STScI;
Illustration: NASA/CXC/M.Weiss
Supermassive holes are generally stationary objects, sitting at the centers of most galaxies. However, using data from NASA's Chandra X-ray Observatory and other telescopes, astronomers recently hunted down what could be a supermassive black hole that may be on the move.
This possible renegade black hole, which contains about 160 million times the mass of our Sun, is located in an elliptical galaxy about 3.9 billion light years
from Earth. Astronomers are interested in these moving supermassive
black holes because they may reveal more about the properties of these
enigmatic objects.
This black hole may have "recoiled," in the terminology used by
scientists, when two smaller supermassive black holes collided and merged
to form an even larger one. At the same time, this collision would have
generated gravitational waves that emitted more strongly in one
direction than others. This newly formed black hole could have received a
kick in the opposite direction of those stronger gravitational waves.
This kick would have pushed the black hole out of the galaxy's center,
as depicted in the artist's illustration.
The strength of the kick depends on the rate and direction of spin of
the two smaller black holes before they merge. Therefore, information
about these important but elusive properties can be obtained by studying
the speed of recoiling black holes.
Astronomers found this recoiling black hole candidate by sifting through X-ray
and optical data for thousands of galaxies. First, they used Chandra
observations to select galaxies that contain a bright X-ray source and
were observed as part of the Sloan Digital Sky Survey (SDSS). Bright
X-ray emission is a common feature of supermassive black holes that are
rapidly growing.
Next, the researchers looked to see if Hubble Space Telescope
observations of these X-ray bright galaxies revealed two peaks near
their center in the optical image. These two peaks might show that a
pair of supermassive black holes is present or that a recoiling black
hole has moved away from the cluster of stars in the center of the
galaxy.
If those criteria were met, then the astronomers examined the SDSS
spectra, which show how the amount of optical light varies with
wavelength. If the researchers found telltale signatures in the spectra
indicative of the presence of a supermassive black hole, they followed
up with an even closer examination of those galaxies.
After all of this searching, a good candidate for a recoiling black
hole was discovered. The left image in the inset is from the Hubble
data, which shows two bright points near the middle of the galaxy. One
of them is located at the center of the galaxy and the other is located
about 3,000 light years away from the center. The latter source shows
the properties of a growing supermassive black hole and its position
matches that of a bright X-ray source detected with Chandra (right image
in inset). Using data from the SDSS and the Keck telescope in Hawaii,
the team determined that the growing black hole located near, but
visibly offset from, the center of the galaxy has a velocity that is
different from the galaxy. These properties suggest that this source may
be a recoiling supermassive black hole.
The host galaxy of the possible recoiling black hole also shows some
evidence of disturbance in its outer regions, which is an indication
that a merger between two galaxies occurred in the relatively recent
past. Since supermassive black hole mergers are thought to occur when
their host galaxies merge, this information supports the idea of a
recoiling black hole in the system.
Moreover, stars are forming at a high rate in the galaxy, at several
hundred times the mass of the Sun per year. This agrees with computer
simulations, which predict that star formation rates may be enhanced for
merging galaxies particularly those containing recoiling black holes.
Another possible explanation for the data is that two supermassive
black holes are located in the center of the galaxy but one of them is
not producing detectable radiation because it is growing too slowly. The
researchers favor the recoiling black hole explanation, but more data
are needed to strengthen their case.
A paper describing these results was recently accepted for publication in The Astrophysical Journal and is available online.
The first author is Dongchan Kim from the National Radio Astronomy
Observatory in Charlottesville, Virginia. 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 CXO J101527.2+625911:
Scale: Inset images are 10 arcsec across (about 163,000 light years)
Category: Quasars & Active Galaxies, Black Holes
Coordinates (J2000): RA 10h 15m 27.2s | Dec +62° 59' 11.5"
Constellation: Ursa Major
Observation Date: 1 pointing in Apr 2008
Observation Time: 0 hours 51 minutes 40 seconds
Obs. ID: 9203
Instrument: ACIS
References: Kim, D.-C. et al., 2017, ApJ [in print]; arXiv: 1704.05549v1
Distance Estimate: About 3.9 billion light years (z=0.3504)
Source: NASA’s Chandra X-ray Observatory
