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Hubble Views a Starry Ring world Born in a Head-On Collision

Target Name:  Cartwheel Galaxy
Spacecraft:  Hubble Space Telescope
Produced by:  Kirk Borne (STScI), and NASA
Copyright: Public Domain
Cross Reference:  STScI-PRC95-02
Date Released: 10 January 1995

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[Right] - A rare and spectacular head-on collision between two galaxies appears in this NASA Hubble Space Telescope true-color image of the Cartwheel Galaxy, located 500 million light-years away in the constellation Sculptor. The new details of star birth resolved by Hubble provide an opportunity to study how extremely massive stars are born in large fragmented gas clouds.

The striking ring-like feature is a direct result of a smaller intruder galaxy -- possibly one of two objects to the right of the ring -- that careened through the core of the host galaxy. Like a rock tossed into a lake, the collision sent a ripple of energy into space, plowing gas and dust in front of it. Expanding at 200,000 miles per hour, this cosmic tsunami leaves in its wake a firestorm of new star creation. Hubble resolves bright blue knots that are gigantic clusters of newborn stars and immense loops and bubbles blown into space by exploding stars (supernovae) going off like a string of firecrackers.

The Cartwheel Galaxy presumably was a normal spiral galaxy like our Milky Way before the collision. This spiral structure is beginning to re-emerge, as seen in the faint arms or spokes between the outer ring and bulls-eye shaped nucleus. The ring contains at least several billion new stars that would not normally have been created in such a short time span and is so large (150,000 light-years across) our entire Milky Way Galaxy would fit inside.

Hubble's new view does not solve the mystery as to which of the two small galaxies might have been the intruder. The blue galaxy is disrupted and has new star formation which strongly suggests it is the interloper. However, the smoother-looking companion has no gas, which is consistent with the idea that gas was stripped out of it during passage through the Cartwheel Galaxy.

[Top Left] - Hubble's detailed view shows the knot-like structure of the ring, produced by large clusters of new star formation. Hubble also resolves the effects of thousands of supernovae on the ring structure. One flurry of explosions blew a hole in the ring and formed a giant bubble of hot gas. Secondary star formation on the edge of this bubble appears as an arc extending beyond the ring.

[Bottom Left] - Hubble resolves remarkable new detail in the galaxy's core. The reddish color of this region indicates that it contains a tremendous amount of dust and embedded star formation. Bright pinpoints of light are gigantic young star clusters.

The picture was taken with the Wide Field Planetary Camera-2 on October 16, 1994. It is a combination of two images, taken in blue and near-infrared light.

Image use statement at the time this image was obtained.

All of the HST images available via WWW and ftp may be used without restriction as long as credit information accompanies the picture. Credit usually includes the principal scientist responsible for the data, AURA/STScI, NASA and/or ESA, the European Space Agency. Specific credit information may be found in the captions accompanying the images as plain text files. The captions are available via links from the Web pages as well as separate files in the gif directory on the ftp server.

Copyright © 1995-2016 by Calvin J. Hamilton. All rights reserved.