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Looking back in time to see the birth of ancient stars


With the help of gravitational lensing and complex calculations, astronomers can see stars forming in the early universe.


The blue arc at left is actually three separate images of the same background galaxy, distorted and magnified by gravitational lensing. On the right is a reconstructed image of what the galaxy would look like without distortion.
NASA, ESA, and T. Johnson

Even the Hubble Space Telescope has limits. However, clever astronomers are always looking to push past them.

A team of American researchers scanning through arcs of light in Hubble observations realised that one such arc was in fact three separate images of a galaxy seen edge-on, smeared out, magnified and replicated due to gravitational lensing by a giant cluster of galaxies between it and Earth.

The galaxy, known as SDSS J1110+6459, is some 11 billion light-years from Earth, so we see it as it was a mere 2.7 billion years after the Big Bang. This would normally be too distant and too far back in time – they are the same thing, to astronomers – for Hubble to see clearly.

However, the gravitational lensing made the image of the galaxy 30 times larger than it would otherwise be. By combining the three images and using some fancy computer processing to undo the distortion caused by the gravitational lensing, the astronomers were able to reconstruct an image about 10 times sharper than what Hubble could normally see at that distance.

“When we saw the reconstructed image we said, ‘Wow, it looks like fireworks are going off everywhere,’” said astronomer Jane Rigby of NASA’s Goddard Space Flight Center in Maryland.

The reconstructed image revealed two dozen clumps of newborn stars, each spanning about 200 to 300 light-years. This contradicted theories suggesting that star-forming regions in the distant, early universe were much larger, 3,000 light-years or more in size.

Without the magnification boost of the gravitational lens, the disk galaxy would have appeared perfectly smooth and unremarkable to Hubble.

The research is published in the Astrophysical Journal Letters.

Curated content from the editorial staff at Cosmos Magazine.
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