Cosmic telephoto lens shows intense, early star formation

Recently discovered galaxy gives detailed view of stellar birth in the young universe

Thanks to some gravitational sleight of hand, astronomers have obtained their sharpest view yet of individual star-making factories in a distant galaxy, 10 billion light-years from Earth. The study reveals that the concentration of new stars in these giant clouds of gas and dust is 100 times higher than that of similar regions in the Milky Way today.

INTERGALACTIC BLOWUP This false-color composite image shows the foreground galaxy cluster (center of left image) that acts as a gravitational lens, the magnified view of the remote galaxy SMM J2135-0102 (top right image, in red) and individual star-forming clouds in the galaxy (bottom right). The magnification of the distant galaxy by the foreground cluster creates a mirage, doubling the actual number of star-forming clouds. M. Swinbank et al./Nature, ESO, APEX; NASA, ESA, SMA

STARS BIRTH A fortuitous alignment of celestial objects allowed astronomers to snap their sharpest image to date of star-making regions in a galaxy about 10 billion light-years from Earth. Large bright clouds in this artist’s rendering of the distant galaxy SMM J2135-0102 are sites of vigorous star formation. M. Kornmesser/ESO

Mark Swinbank of the Institute for Computational Cosmology at Durham University in England and his colleagues were able to home in on star birth regions only 300 light-years across because of a chance alignment with a massive cluster of nearer galaxies that lies along the same line of sight but much closer to Earth. Because heavy objects bend light, the massive foreground cluster acts like a telephoto lens, enlarging the more distant galaxy 16-fold. Swinbank and his collaborators report their findings in a Nature article posted online March 21.

The astronomers discovered the galaxy, SMMJ2135-0102, using the submillimeter-wavelength Atacama Pathfinder Experiment Telescope in northern Chile. Follow-up observations with the Submillimeter Array on Hawaii’s Mauna Kea produced the sharp images that revealed four star-forming blobs in the galaxy. The smallest blob is about 300 light-years across, and most of the patches are about three times bigger than those in the galaxy Arp 220, a rare example of intense star formation in the universe today.

Observing at submillimeter wavelengths — which lie between infrared and radio waves on the electromagnetic spectrum — was critical for assessing the true star formation rate, because the radiation easily penetrates dusty, star-forming regions, notes Swinbank. Visible light emitted by stars is absorbed by surrounding dust and re-emitted at submillimeter and infrared wavelengths. That’s why “it is virtually impossible to derive accurate star-formation rates from optical imaging alone,” comments Fabian Walter of the Max Planck Institute of Astronomy in Heidelberg, Germany.

Previous lower-resolution studies, both in visible light and at submillimeter wavelengths, have found vigorous star formation in galaxies even more distant from Earth, which hail from even further back in time. “All of these results are pointing at the same picture: much more intense star formation in the distant universe than we expected, given how stars form locally,” says Swinbank.

The galaxy SMMJ2135-0102, observed as it appeared when the universe was about 3 billion years old, comes from the era when cosmic star formation was at its peak. James Dunlop of the University of Edinburgh suggests that such galaxies formed stars so abundantly because the galaxies still had plenty of gas — the raw material for making stars — and the gravity of the galaxies had had enough time to pull the gas together into cold, compact regions. Before about 10 billion years ago, gravity hadn’t yet drawn enough clumps of gas together, while at later times most galaxies had already run out of gas, he suggests.

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