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Most distant star-forming nebulae observed
Posted: 22 March

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A faraway galaxy has been discovered forming stars at a rate of 250 Suns per year in four star-forming nebulae that stretch hundreds of light years across. The discovery bolsters evidence that galaxies formed stars, and therefore grew in size, much more quickly in the past than they do today.

This three-stage composite image shows the galaxy cluster on the left in visible light – note that SMM J2135-0102 is not visible at this stage – and on the top right the APEX radio image of the galaxy laid on top of the visible light image, and on bottom right are the Submillimeter Array observations of the four star-forming regions. Image: ESO/APEX/M Swinbank et al/NASA/ESA/Hubble/SMA.

The galaxy, catalogued as SMM J2135-0102, is seen as it was 3.7 billion years after the big bang; i.e. its light has been travelling to us for about ten billion years (a redshift of 2.3). Galaxies so far away are usually incredibly faint, but this one was boosted by a handy gravitational lens – a cluster of galaxies that lies between us, magnifying the more distant galaxy’s light. It was first spotted at radio wavelengths by the Atacama Pathfinder Experiment (APEX) telescope at the European Southern Observatory in Chile, which saw glowing dust heated by the fires of star formation within the galaxy, and the star-forming regions themselves were actually observed directly in follow-up observations by the Submillimeter Array telescope in Hawaii.

An artistŐs impression of the galaxy, with contour lines showing the locations of the four star-forming regions as seen by the Submillimeter Array. Image: ESO/M Kornmesser/M Swinbank et al.

“With follow-up observations using the Submillimeter Array telescope we’ve been able to study the clouds where stars are forming in the Galaxy with great precision,” says Dr Mark Swinbank of Durham University, who led the discovery team. They found that the star-formation rate was far greater in SMM J2135-0102 than it is today in the Milky Way where ten solar masses worth of stars are formed per year, at the most. The four star-forming regions in SMM J2135-0102 are also far larger than typical stellar nurseries in our own Galaxy; placed side-by-side, the Orion Nebula would appear 100 times fainter, and at least three times as small.

Zooming in from the night sky view right up to the lensing cluster, and then on again into the dust emission observed by APEX and the ‘blobs’ of the star forming regions seen by the Submillimeter Array.

It is the second time in six months that Swinbank has announced the discovery of a distant galaxy that is forming stars at a rate of knots. Astronomers have long suspected that galaxies made stars more quickly when the Universe was still young, and that the formation of the most massive stars hit its peak about 10–11 billion years ago; the bigger the star-forming region, the more stars are born, and the more stars that are born the greater the chance of getting some really massive stars. Last month we reported that the reason that galaxies formed stars faster long ago was because they were experiencing larger influxes of gas through mergers. Studies of galaxies such as SMM J2135-0102 are crucial in helping us understand star formation better.

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