Credit X-ray: NASA/CXC/Univ. of Alberta/B.Tetarenko et al;
Optical: NASA/STScI; Radio: NSF/AUI/NRAO/Curtin Univ./J. Miller-Jones
Astronomers have identified the true nature of an unusual source in the Milky Way galaxy. As described in our latest press release, this discovery implies that there could be a much larger number of black holes in the Galaxy that have previously been unaccounted for.
The result was made by combining data from many different telescopes that detect various forms of light, each providing key pieces of information. These telescopes included NASA's Chandra X-ray Observatory,
the Hubble Space Telescope, NSF's Karl G. Jansky Very Large Array
(VLA), Green Bank Telescope, Arecibo Observatory, and the European Very
Long Baseline Interferometry Network.
The collaborative nature of this study is depicted in this
multi-panel graphic. The large panel shows a composite Chandra and
optical image of the globular cluster M15 located in our galaxy, where the X-ray
data are purple and the optical data are red, green and blue. The
source being studied here is bright in radio waves, as shown in the
close-up VLA image, but the Chandra data reveal it can only be giving
off a very small amount of X-rays.
This new study indicates this source, called VLA J213002.08+120904 (VLA J2130+12 for short), contains a black hole
a few times the mass of our Sun that is very slowly pulling in material
from a companion star. At this paltry feeding rate, VLA J2130+12 was
not previously flagged as a black hole since it lacks some of the
telltale signs that black holes in binary systems typically display.
Previously, most astronomers thought that VLA J2130+12 was probably a
distant galaxy. Precise measurements from the radio telescopes showed
that this source was actually well within our Galaxy and about five
times closer to us than M15. Hubble data identified the companion star
in VLA J2130+12 having only about one-tenth to one-fifth the mass of the
Sun.
The observed radio brightness and the limit on the X-ray brightness
from Chandra allowed the researchers to rule out other possible
interpretations, such as an ultra-cool dwarf star, a neutron star, or a white dwarf pulling material away from a companion star.
Because this study only covered a very small patch of sky, the
implication is that there should be many of these quiet black holes
around the Milky Way. The estimates are that tens of thousands to
millions of these black holes could exist within our Galaxy, about three
to thousands of times as many as previous studies have suggested.
A paper
describing these results appeared in the Astrophysical Journal. The
authors were Bailey Tetarenko (University of Alberta), Arash Bahramian
(Alberta), Robin Aranson (Alberta), James Miller-Jones (International
Center for Radio Astronomy Research), Serena Repetto (Technion), Craig
Heinke (Alberta), Tom Maccarone (Texas Tech University), Laura Chomiuk
(Michigan State Univsersity), Gregory Sivakoff (Alberta), Jay Strader
(Michigan State), Franz Kirsten (ICRAR), and Wouter Vlemmings (Chalmers
University of Technology).
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 VLA J2130+12:
Scale: Main image is 2.6 arcmin across (about 5.4 light years); inset image is 6 arcseconds across (about 0.2 light years)
Coordinates (J2000): RA 21h 21m 58s | Dec +12° 10’ 00.02"
Constellation: Pegasus
Observation Date: 12 pointings between Aug 2000 and Oct 2013
Observation Time: 63 hours 25 min (2 days 15 hours 25 min).
Obs. ID: 675, 1903, 2412, 2413, 4572, 9584, 11029, 11886, 11030, 13420, 13710, 14618
Instrument: ACIS
References: Tetarenko, B., 2016, ApJ (accepted); arXiv:1605.00270
Color Code: X-ray (Purple); Optical (Red, Green and Blue); Radio (Green)
Distance Estimate: About 7,200 light years
