Young galaxy puts a spin on old models

From an arid and isolated plateau in the Atacama Desert, a radio telescope has spied a baby galaxy in the infant universe – and surprisingly, it’s rotating.

Astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to peer back to a time when the universe was just seven percent of its current age, aiming to explore the nature of the first generation of galaxies.

In two separate papers, the team reports finding a galaxy just 1/100th of the size of our Milky Way – about 2–3 billion times the mass of our Sun. But more interestingly, the galaxy is rotating.

Traditional models of how galaxies form and evolve predict that the gas in young galaxies should be turbulent and chaotic, before settling down to spin like a whirlpool as they age. But this new observation adds to the handful of young, rotating galaxies discovered over the past few years, sending theories of galaxy evolution into a spin.

These other galaxies were much brighter and larger, so to spot this fainter galaxy, the team had to use a natural “magnifying glass”.

“Many of the galaxies that existed in the early Universe were so small that their brightness is well below the limit of the current largest telescopes on Earth and in space, making [it] difficult to study their properties and internal structure,” explains Nicolas Laporte, co-author from the University of Cambridge. “However, the light coming from the galaxy, named RXCJ0600-z6, was highly magnified by gravitational lensing, making it an ideal target for studying the properties and structure of typical baby galaxies.”

Gravitational fields can distort light, just like water distorts the view of objects beneath its surface. The intense gravity of massive objects can therefore act like a giant lens, magnifying the light of fainter, more distant galaxies behind them.

In this study, ALMA surveyed 33 galaxy clusters. One of them – with the mass of 1000 trillion times our Sun – allowed the team to spot a galaxy in its early form – that it, as it was just 900 million years after the Big Bang (12.9 billion years ago).

The astronomers then combined other observations from the Hubble Space Telescope and ESO’s Very Large Telescope – as well as a theoretical model – to “undo” the distortion of the gravitational lens and see the galaxy as it actually was.

“Our study demonstrates, for the first time, that we can directly measure the internal motion of such faint, less massive galaxies in the early universe and compare it with the theoretical predictions,” says Kotaro Kohno, co-author from the University of Tokyo.

The baby galaxy will be studied further by the James Webb Space Telescope, the infrared successor to Hubble to be launched later in the year.

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