An extraordinary ribbon of hot gas trailing behind a galaxy like a
tail has been discovered using data from NASA's Chandra X-ray
Observatory, as described in our latest press release.
This ribbon, or X-ray tail, is likely due to gas stripped from the
galaxy as it moves through a vast cloud of hot intergalactic gas. With a
length of at least 250,000 light years,
it is likely the largest such tail ever detected. In this new
composite image, X-rays from Chandra (blue) have been combined with data
in visible light from the Isaac Newton Group of Telescopes (yellow) in the Canary Islands, Spain.
The tail is located in the galaxy cluster Zwicky 8338, which is almost 700 million light years from Earth. The length of the tail is more than twice the diameter of the entire Milky Way
galaxy. The tail contains gas at temperatures of about ten million
degrees, about twenty million degrees cooler than the intergalactic gas,
but still hot enough to glow brightly in X-rays that Chandra can
detect.
The researchers think the tail was created as a galaxy known as
CGCG254-021, or perhaps a group of galaxies dominated by this large
galaxy, plowed through the hot gas in Zwicky 8338. The pressure exerted
by this rapid motion caused gas to be stripped away from the galaxy.
In images from Chandra and the NSF's Karl Jansky Very Large Array
(not shown in composite), the galaxy CGCG254-021 appears to be moving
towards the bottom of the image with the tail following behind. There is
a significant gap between the X-ray tail and the galaxy, the largest
ever seen. The significant separation between the galaxy and the tail
might be evidence that the gas has been completely stripped off the
galaxy.
Astronomers were also able to learn more about the interactions of
the system by carefully examining the properties of the galaxy and its
tail. The tail has a brighter spot, referred to as its "head". Behind
this head is the tail of diffuse X-ray emission. The gas in the head may
be cooler and richer in elements heavier than helium than the rest of
the tail. In front of the head there are hints of a bow shock, similar
to a shock wave formed by a supersonic plane and in front of the bow
shock is the galaxy CGCG254-021.
Independent research involving observations at infrared wavelengths
indicates that CGCG254-021 has the highest mass of all galaxies in
Zwicky 8338. The infrared observations, together with models for how
galaxies evolve, also imply that among the galaxies in the cluster,
CGCG254-021 had by far the highest rate of stars forming in the recent
past. However, there is no evidence for new star formation, possibly
because gas has been depleted in forming the tail.
The paper describing these results was published in the November 2015
issue of Astronomy and Astrophysics and is also available online. The
authors of the paper are Gerrit Schellenberger and Thomas Reiprich from
the University of Bonn in Germany. 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. Swift is managed by NASA's Goddard Space Flight
Center in Greenbelt, Maryland.
Fast Facts for Zwicky 8338:
Scale: Image is 3.6 arcmin across (about 700,000 light years)
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 18h 11m 26.75s | Dec +49° 49' 47.35"
Constellation: Hercules
Observation Date: 04 Jan 2013
Observation Time: 2 hours 13 min.
Obs. ID: 15163
Instrument: ACIS
References: Schellenberger, G. et al, 2015, A&A, 583, L2; arXiv:1510.03708
Color Code: X-ray: Blue; Optical: Yellow
Distance Estimate: About 680 million light years
Source: NASA’s Chandra X-ray Observatory
