Post by Shadow on Jan 17, 2006 17:52:01 GMT -5
New Scientist Space
# 17:46 13 January 2006
# NewScientist.com news service
# Maggie McKee, Washington DC
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.
Calm after the storm
The outer ring, which is wider than our galaxy, the Milky Way, reveals the youngest wave of star formation because it shines in high-energy X-rays and ultraviolet light. "Usually a galaxy is brighter toward the centre, but the ultraviolet view indicates the collision actually smoothed out the interior of the galaxy, concentrating older stars and dust into the inner regions," says Appleton. "It's like the calm after the storm of star formation."
The image also reveals about a dozen bright X-ray sources (purple), thought to arise when gas falls towards a black hole. Most galaxies contain only one or two such sources. But Appleton says the Cartwheel is so rich in these sources because so many massive stars, from which black holes form, are forming and dying there.
# 17:46 13 January 2006
# NewScientist.com news service
# Maggie McKee, Washington DC
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.
Calm after the storm
The outer ring, which is wider than our galaxy, the Milky Way, reveals the youngest wave of star formation because it shines in high-energy X-rays and ultraviolet light. "Usually a galaxy is brighter toward the centre, but the ultraviolet view indicates the collision actually smoothed out the interior of the galaxy, concentrating older stars and dust into the inner regions," says Appleton. "It's like the calm after the storm of star formation."
The image also reveals about a dozen bright X-ray sources (purple), thought to arise when gas falls towards a black hole. Most galaxies contain only one or two such sources. But Appleton says the Cartwheel is so rich in these sources because so many massive stars, from which black holes form, are forming and dying there.