Gas whirlpool observed for the first time in early galaxies

The early galaxies observed by ALMA in the sky observed by Hubble (Image Hubble (NASA/ESA), ALMA (ESO/NAOJ/NRAO), P. Oesch (University of Geneva) and R. Smit (University of Cambridge))
The early galaxies observed by ALMA in the sky observed by Hubble (Image Hubble (NASA/ESA), ALMA (ESO/NAOJ/NRAO), P. Oesch (University of Geneva) and R. Smit (University of Cambridge))

An article published in the journal “Nature” describes the first observation of the movement of gas inside two small newborn galaxies about 13 billion light years away from Earth. A team led by the Dutch astronomer Renske Smit of the Kavli Institute of Cosmology at the University of Cambridge, UK, used the ALMA radio telescope to detect the processes underway in those early galaxies, verifying that the gas moves similarly to galaxies such as Milky Way. These results were also presented at the 231st meeting of the American Astronomical Society, which was held this week.

The observation of very distant galaxies is made difficult not only by the fact that their light is very dim but also by a sort of haze generated by the neutral hydrogen that existed in abundance in the early universe. Observations with optical telescopes are rendered almost completely ineffective by that problem but there are other electromagnetic frequencies such as those of the far infrareds that can be detected.

The antennas of the ALMA radio telescope are capable of capturing far infrareds and the analysis of those frequencies’ spectral “signature” allowed the researchers to establish the distance of the two galaxies object of the study and, for the first time, to see the internal gas movements. Before ALMA (Atacama Large Millimeter/submillimeter Array), inaugurated in March 2013, no instrument had the power and sensitivity to achieve such a result.

From the Earth we see the two galaxies, cataloged as COS-3018555981 and COS-2987030247, the way they were about 800 million years after the Big Bang so they could be some of the oldest galaxies in the universe. The observations revealed that the gas inside them spins with a whirlpool motion similar to that existing in mature galaxies such as the Milky Way.

These are galaxies that in the period we’re observing were small, about 20% of the Milky Way, a huge size for galaxies in the early universe. The pace of star formation is high, higher than that of other young galaxies, but the researchers predicted that.

In that early age gravity caused gas to flow rapidly into galaxies, with the result that a lot of new stars formed. A lot of gas means an abundance of massive stars, which consume their hydrogen very quickly and die after a few million years in supernovae that generate strong turbulence in their areas.

In essence, the researchers expected a more chaotic situation because the idea was that those galaxies had a lot of internal turbulence. Instead they show an order similar to that of the more mature galaxies. This discovery raises new questions about the evolution of galaxies and the observations carried out with ALMA mark the beginning of new studies of this kind.

Artist's impression of a whirlpool motion in an early galaxy (Image Institute of Astronomy, Amanda Smith)
Artist’s impression of a whirlpool motion in an early galaxy (Image Institute of Astronomy, Amanda Smith)

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