http://chandra.harvard.edu/photo/2016/ngc5128/
NGC 5128
Credit: NASA/CXC/UA/J.Irwin et al.
This image shows the location of a remarkable source that dramatically flares in X-rays
unlike any ever seen. Along with another similar source found in a
different galaxy, these objects may represent an entirely new
phenomenon, as reported in our latest press release [link to PR].
These two objects were both found in elliptical galaxies, NGC 5128 (also known as Centaurus A) shown here and NGC 4636. In this Chandra X-ray Observatory image of NGC 5128, low, medium, and high-energy X-rays are colored red, green, and blue, and the location of the flaring source is outlined in the box to the lower left.
Both of these mysterious sources flare dramatically - becoming a
hundred times brighter in X-rays in about a minute before steadily
returning to their original X-ray levels about an hour later. At their
X-ray peak, these objects qualify as ultraluminous X-ray sources (ULXs)
that give off hundreds to thousands of times more X-rays than typical
X-ray binary systems where a star is orbiting a black hole or neutron star.
Five flares were detected from the source located near NGC 5128, which is at a distance of about 12 million light years
from Earth. A movie showing the average change in X-rays for the three
flares with the most complete Chandra data, covering both the rise and
fall, is shown in the inset.
The source associated with the elliptical galaxy NGC 4636, which is
located about 47 million light years away, was observed to flare once.
The only other objects known to have such rapid, bright, repeated
flares involve young neutron stars such as magnetars, which have
extremely powerful magnetic fields. However, these newly flaring sources
are found in populations of much older stars. Unlike magnetars, the new
flaring sources are likely located in dense stellar environments, one
in a globular cluster and the other in a small, compact galaxy.
When they are not flaring, these newly discovered sources appear to
be normal binary systems where a black hole or neutron star is pulling
material from a companion star similar to the Sun. This indicates that
the flares do not significantly disrupt the binary system.
While the nature of these flares is unknown, the team has begun to
search for answers. One idea is that the flares represent episodes when
matter pulled away from a companion star falls rapidly onto a black hole
or neutron star. This could happen when the companion makes its closest
approach to the compact object in an eccentric orbit. Another
explanation could involve matter falling onto an intermediate-mass black
hole, with a mass of about 800 times that of the Sun for one source and
80 times that of the Sun for the other.
This result is describing in a paper appearing in the journal Nature
on October 20, 2016. The authors are Jimmy Irwin (University of
Alabama), Peter Maksym (Harvard-Smithsonian Center for Astrophysics),
Gregory Sivakoff (University of Alberta), Aaron Romanowsky (San Jose
State University), Dacheng Lin (University of New Hampshire), Tyler
Speegle, Ian Prado, David Mildebrath (University of Alabama), Jay
Strader (Michigan State University), Jifeng Lui (Chinese Academy of
Sciences), and Jon Miller (University of Michigan).
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 5128:
Scale: Main image is 16.7 arcmin across (about 58,000 light years); Inset image is 1 arcmin across (about 3,500 light years)
Category: Quasars & Active Galaxies
Coordinates (J2000): RA 13h 25m 52.7s | Dec -43° 05' 46.00"
Constellation: Centaurus
Observation Date: 21 pointings between 05 Dec 1999 and 29 Aug 2012
Observation Time: 229 hours 57 min (9 days 13 hours 57 min).
Obs. ID: 316, 962, 2978, 3965, 7797-7799, 7800, 8489, 8490, 10722, 10723, 10724-10726, 11846, 11847, 12155, 12156, 13303, 13304
Instrument: ACIS
Also Known As: Centaurus A, Cen A
References: Irwin, J. et al, 2016, Nature (in press)
Color Code: X-ray (Red, Green, Blue)
Distance Estimate: 12 million light years
Source: NASA’s Chandra X-ray Observatory
