Markarian 1018
Credit X-ray: NASA/CXC/Univ of Sydney/R.McElroy et al, Optical: ESO/CARS Survey
Astronomers may have solved the mystery of the peculiar volatile behavior of a supermassive black hole at the center of a galaxy. Combined data from NASA's Chandra X-ray Observatory and other observatories suggest that the black hole is no longer being fed enough fuel to make its surroundings shine brightly.
Many galaxies have an extremely bright core, or nucleus, powered by
material falling toward a supermassive black hole. These so-called "active galactic nuclei" or AGN, are some of the brightest objects in the Universe.
Astronomers classify AGN into two main types based on the properties
of the light they emit. One type of AGN tends to be brighter than the
other. The brightness is generally thought to depend on either or both
of two factors: the AGN could be obscured by surrounding gas and dust,
or it could be intrinsically dim because the rate of feeding of the
supermassive black hole is low.
Some AGN have been observed to change once between these two types
over the course of only 10 years, a blink of an eye in astronomical
terms. However, the AGN associated with the galaxy Markarian 1018 stands
out by changing type twice, from a faint to a bright AGN in the 1980s
and then changing back to a faint AGN within the last five years. A
handful of AGN have been observed to make this full-cycle change, but
never before has one been studied in such detail. During the second
change in type the Markarian 1018 AGN became eight times fainter in X-rays between 2010 and 2016.
After discovering the AGN's fickle nature during a survey project
using ESO's Very Large Telescope (VLT), astronomers requested and
received time to observe it with both NASA's Chandra X-ray Observatory
and Hubble Space Telescope. The accompanying graphic
shows the AGN in optical light from the VLT (left) with a Chandra image
of the galaxy's central region in X-rays showing the point source for
the AGN (right).
Data from ground-based telescopes including the VLT allowed the
researchers to rule out a scenario in which the increase in the
brightness of the AGN was caused by the black hole disrupting and
consuming a single star. The VLT data also cast doubt on the possibility
that changes in obscuration by intervening gas cause changes in the
brightness of the AGN.
However, the true mechanism responsible for the AGN's surprising
variation remained a mystery until Chandra and Hubble data was analyzed.
Chandra observations in 2010 and 2016 conclusively showed that
obscuration by intervening gas was not responsible for the decline in
brightness. Instead, models of the optical and ultraviolet light
detected by Hubble, NASA's Galaxy Evolution Explorer (GALEX) and the
Sloan Digital Sky Survey in the bright and faint states showed that the
AGN had faded because the black hole was being starved of infalling
material. This starvation also explains the fading of the AGN in X-rays.
One possible explanation for this starvation is that the inflow of
fuel is being disrupted. This disruption could be caused by interactions
with a second supermassive black hole in the system. A black hole
binary is possible as the galaxy is the product of a collision and
merger between two large galaxies, each of which likely contained a
supermassive black hole in its center.
The list observatories used in this finding also include NASA's
Nuclear Spectroscopic Telescope Array (NuSTAR) mission and Swift
spacecraft.
Two papers, one with the first author of Bernd Husemann (previously
at ESO and currently at the Max Planck Institute for Astronomy) and the
other with Rebecca McElroy (University of Sydney), describing these
results appeared in the September 2016 issue of Astronomy &
Astrophysics journal.
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 Markarian 1018:
Scale: Main image is 2.64 arcmin across (about 440,000 light years)
Category: Quasars & Active Galaxies
Coordinates (J2000): RA 02h 06m 15.99s | Dec 00° 17' 29.20"
Constellation: Cetus
Observation Date: 27 Nov 2010, 25 Feb 2016
Observation Time: 13 hours 53 min.
Obs. ID: 12868, 18789
Instrument: ACIS
References: McElroy, R. et al, 2016, A&A 593, L8; arXiv:1609.04423; Husemann, B. et al, 2016, A&A 593, L9; arXiv:1609.04425
Color Code: X-ray (Purple); Optical (Red, Green, Blue)
Distance Estimate: About 590 million light years (z=0.043)
Source: NASA’s Chandra X-ray Observatory
