Cosmic Jellyfish

I love this! photo/image from GALEX/Chandra/Hubble/Spitzer

A cosmic jellyfish appears to pulse with light in this multi-wavelength image of the Cartwheel galaxy, compiled from images taken by four space telescopes.

The galaxy probably came by its distinctive shape when a small galaxy – possibly one of the objects at bottom-left of the image – collided with it head-on 100 million years ago. The crash set off ripples in the large galaxy's gas that led to concentric rings of star birth.

"It's like dropping a stone into a pond, only in this case, the pond is the galaxy and the wave is the compression of gas," explains Phil Appleton of the California Institute of Technology in Pasadena, US. "Each wave represents a burst of star formation – the youngest stars are found in the outer ring."

Astronomers dated this star formation by studying the wavelengths of light emitted by each region of the galaxy. This image represents those wavelengths by colour, with purple representing X-rays measured by the Chandra Space Telescope, blue representing ultraviolet light measured by the GALEX spacecraft, green representing visible light observed with the Hubble Space Telescope, and red denoting infrared light recorded by the Spitzer Space Telescope.