Cartwheel Galaxy : supersonic comet-like objects in heart of galaxy 26/11/1996
Researchers analyzing the Hubble Space Telescope's dramatic images of the Cartwheel galaxy have discovered immense comet-like clouds of gas speeding at nearly 700,000 mph through the galaxy's core.
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Image Credit: Hubble images: Curt Struck and Philip Appleton (Iowa State University), Kirk Borne (Hughes STX Corporation), and Ray Lucas (STScI), and NASA; VLA radio telescope image: Jim Higdon (Australia Telescope National Facility's Paul Wild Observatory; Cerro Tololo picture was taken by Victor Blanco.  
Researchers analyzing the Hubble Space Telescope's dramatic images of the Cartwheel galaxy have discovered immense comet-like clouds of gas speeding at nearly 700,000 mph through the galaxy's core.

[Image on left] - The Cartwheel is part of a group of four galaxies, as shown in this collage of images from ground-based optical and radio telescopes and the Hubble Space Telescope's Wide Field and Planetary Camera 2. Located 500 million light-years away in the constellation Sculptor, the galaxy (located near the bottom right corner) looks like a wagon wheel. The galaxy's nucleus is the bright object in the center; the spokes are wisps of material connecting the nucleus to the outer ring of young stars. The galaxy's unusual configuration was created by a nearly head-on collision with a smaller galaxy about 200 million years ago.

The stream of green material between the Cartwheel and the galaxy near the top left corner is neutral hydrogen gas taken in radio wavelengths by the Very Large Array radio telescope in New Mexico. The bridge of neutral hydrogen may be related to the comet-like and spoke-like structures seen in the Cartwheel galaxy's nucleus.

[Image on right]- The Cartwheel's nucleus is shown in this Hubble Space Telescope color-coded image. The comet-like knots of gas are mostly confined to the core's left side. They are the blue knots arranged in a semi-circular pattern around the center of the nucleus. The "heads" are a few hundred light-years across; the tails are more than 1,000 light-years long, the longest of which is nearly 5,000 light-years. The structures look like comets because they probably were spawned by a collision between high-speed and slower-moving material. This collision created an arrowhead-shaped pattern called a bow shock, which is similar to the wake of a boat speeding across a lake.

The collage was composed from images taken by the Very Large Array radio telescope in New Mexico, Cerro Tololo Inter-American Observatory in Chile, and the Hubble Space Telescope's Wide Field and Planetary Camera 2. The right-hand image was taken October 16 and 17, 1994 by the Wide Field and Planetary Camera 2.

 
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