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UK astronomers detect swirling gas in earliest galaxies

10 January 2018


An international team of astronomers, led by the UK, have looked back to a time soon after the Big Bang and have witnessed in never-before-seen detail some of the earliest galaxies to have formed in the Universe.

These ‘newborn’ galaxies – observed as they appeared nearly 13 billion years ago – spun like a whirlpool, similar to our own Milky Way. This is the first time that it has been possible to detect movement in galaxies at such an early point in the Universe’s history.

The team, part funded by STFC and led by Dr Renske Smit from the University of Cambridge, used the ESO Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to open a new window onto the distant Universe, and have for the first time been able to identify normal star-forming galaxies at a very early stage in cosmic history.

Smit and her colleagues used ALMA to observe two small newborn galaxies, as they existed just 800 million years after the Big Bang. The Universe at that time, however, was filled with an obscuring ‘haze’ of neutral hydrogen gas, which makes it difficult to see the formation of the very first galaxies with optical telescopes. By analysing the spectral ‘fingerprint’ of the far-infrared light collected by ALMA, they were able to establish the distance to the galaxies and, for the first time, see the internal motion of the gas that fuelled their growth.

The researchers found that the gas in these newborn galaxies swirled and rotated in a whirlpool motion, similar to our own galaxy and other, more mature galaxies much later in the Universe’s history. Despite their relatively small size – about five times smaller than the Milky Way – these galaxies were forming stars at a higher rate than other young galaxies, but the researchers were surprised to discover that the galaxies were not as chaotic as expected.

“In the early Universe, gravity caused gas to flow rapidly into the galaxies, stirring them up and forming lots of new stars – violent supernova explosions from these stars also made the gas turbulent,” said Smit. “We expected that young galaxies would be dynamically ‘messy’, due to the havoc caused by exploding young stars, but these mini-galaxies show the ability to retain order and appear well regulated. Despite their small size, they are already rapidly growing to become one of the ‘adult’ galaxies similar to the one we live in today.”

The data from this project on small galaxies paves the way for larger studies of galaxies during the first billion years of cosmic time.

For more information, visit the Cambridge University news page.

For more on ALMA, visit the ESO web site.

Science and Technology Facilities Council Switchboard: 01793 442000