Posted: October 09, 2008
By combining observations at different wavelengths from telescopes on the ground and in space, astronomers have taken a fresh look at the history of star formation in a galaxy residing in the Small Magellanic Cloud.
NGC 346 is the brightest star forming region in the Small Magellanic Cloud, an irregular dwarf galaxy that orbits the Milky Way at a distance of 210,000 light years. "NGC 346 is a real astronomical zoo," says Dimitrios Gouliermis of the Max Planck Institute for Astronomy in Heidelberg, Germany. "When we combined data at various wavelengths, we were able to tease apart what's going on in different parts of this intriguing region."
This colourful portrait of NGC 346 shows that stellar formation is triggered by both wind and radiation from massive stars. Radiation triggered star formation has occurred in the centre of the image, with compressed material visible as the arc-shaped red-orange filament. Wind triggered formation is at play in the isolated pink blob at the top of the image and to the right of the stellar 'bubble' surrounding the bright white stars. Image: NASA/JPL-Caltech/ESA/ESO/MPIA.
The colourful portrait was made by combining infrared, visible and X-ray light from NASA's Spitzer Space Telescope, ESO's New Technology Telescope (NTT) and the European Space Agency's XMM-Newton orbiting X-ray telescope, respectively. The visible-light images allowed astronomers to resolve glowing gas while the multi-wavelength image reveals new insights into the mechanisms of stellar formation.
The image reveals that small stars are scattered throughout the whole of NGC 346, with the most massive stars residing in its centre. It is thought that these massive stars and most of the small ones formed at the same time out of one dense cloud, while other less massive stars were created later through a process called ‘triggered star formation’. This results from intense radiation from massive stars that eat away at the surrounding dusty cloud, triggering the expansion of gas and creating shock waves that compress nearby dust and gas into new stars, in this case within the region bound by red-orange filaments in the centre of the image.
But another set of younger low-mass stars in the region, seen as a pinkish blob at the top of the image, cannot be explained by this mechanism. "We were particularly interested to know what caused this seemingly isolated group of stars to form," says Gouliermis. The multi-wavelength data holds the answer: the trigger was a very massive star that blasted apart in a supernova explosion about 50,000 years ago. But instead of radiation, fierce winds from the dying star slammed the gas and dust together, forcing the creation of new stars.
While the remains of this massive star cannot be seen in the image, a ghostly reminder can be seen as a bubble surrounding the large white spot (which is actually a trilogy of stars) with a blue halo in the upper left of the image.
The finding demonstrates that both wind- and radiation-induced triggered star formation are at play in the same cloud, showing astronomers that stellar nurseries are far more complicated than originally thought, and comprising different competitive or collaborative mechanisms.