At this time of year, there are lots of gatherings often decorated with festive lights. When galaxies get together, there is the chance of a spectacular light show as is the case with NGC 2207 and IC 2163
Located about 130 million light years from Earth, in the constellation of Canis Major, this pair of spiral galaxies has been caught in a grazing encounter. NGC 2207 and IC 2163 have hosted three supernova explosions in the past 15 years and have produced one of the most bountiful collections of super bright X-ray lights known. These special objects - known as "ultraluminous X-ray sources" (ULXs) - have been found using data from NASA's Chandra X-ray Observatory.
As in our Milky Way galaxy, NGC 2207 and IC 2163 are sprinkled with many star systems known as X-ray binaries, which consist of a star in a tight orbit around either a neutron star or a "stellar-mass" black hole.
The strong gravity of the neutron star or black hole pulls matter from
the companion star. As this matter falls toward the neutron star or
black hole, it is heated to millions of degrees and generates X-rays.
ULXs have far brighter X-rays than most "normal" X-ray binaries. The
true nature of ULXs is still debated, but they are likely a peculiar
type of X-ray binary. The black holes in some ULXs may be heavier than
stellar mass black holes and could represent a hypothesized, but as yet
unconfirmed, intermediate-mass category of black holes.
This composite image of NGC 2207 and IC 2163 contains Chandra data in pink,
optical light data from the Hubble Space Telescope in red, green, and
blue (appearing as blue, white, orange, and brown), and infrared data
from the Spitzer Space Telescope in red.
The new Chandra image contains about five times more observing time
than previous efforts to study ULXs in this galaxy pair. Scientists now
tally a total of 28 ULXs between NGC 2207 and IC 2163. Twelve of these
vary over a span of several years, including seven that were not
detected before because they were in a "quiet" phase during earlier
observations.
The scientists involved in studying this system note that there is a
strong correlation between the number of X-ray sources in different
regions of the galaxies and the rate at which stars are forming in these
regions. The composite image shows this correlation through X-ray
sources concentrated in the spiral arms of the galaxies, where large
amounts of stars are known to be forming. This correlation also suggests
that the companion star in the binary systems is young and massive.
Colliding galaxies like this pair are well known to contain intense
star formation. Shock waves - like the sonic booms from supersonic
aircraft - form during the collision, leading to the collapse of clouds
of gas and the formation of star clusters. In fact, researchers estimate
that the stars associated with the ULXs are very young and may only be
about 10 million years old. In contrast, our Sun is about halfway
through its 10-billion-year lifetime. Moreover, analysis shows that
stars of various masses are forming in this galaxy pair at a rate
equivalent to form 24 stars the mass of our sun per year. In comparison,
a galaxy like our Milky Way is expected to spawn new stars at a rate
equivalent to only about one to three new suns every year.
A paper describing these results has been accepted for publication in The Astrophysical Journal and is available online.
The authors of the paper are Stefano Mineo of the Harvard-Smithsonian
Center for Astrophysics in Cambridge, MA; Saul Rappaport from the
Massachusetts Institute of Technology (MIT) in Cambridge, MA; Alan
Levine from MIT; David Pooley from Sam Houston State University in
Huntsville, TX; Benjamin Steinhorn from Harvard Medical School in
Boston, MA, and Jeroen Homan from MIT.
Fast Facts for NGC 2207 and IC 2163:
Scale: Image is 5 arcmin across (about 180,000 light years)
Category: Normal Galaxies & Starburst Galaxies
Coordinates (J2000): RA 06h 16m 22.10s | Dec -21° 22' 21.80"
Constellation: Canis Major
Observation Date: 4 pointings between Jul 2010 and Aug 2013
Observation Time: 17 hours 20 min
Obs. ID: 11228, 14799, 14914, 14915
Instrument: ACIS
References: Mineo, S. et al, 2014, ApJ, 797, 91; arXiv:1410.2472
Color Code: X-ray (Pink), Optical (Red, Green, Blue), Infrared (Red)
Distance Estimate: About 130 million light years
Source: NASA’s Chandra X-ray Observatory
