MeerKAT finds largest hydrogen atoms in distant galaxy

BY THE MEERKAT ABSORPTION LINE SURVEY TEAM

Scientists using the MeerKAT radio telescope to study a galaxy 7.3 billion light years away have unexpectedly found gas clouds made up of some of the largest hydrogen atoms in the Universe, Rydberg atoms.

It is the first time scientists observed these hydrogen atoms in a distant galaxy. What’s more, they believe the large atoms are spread throughout the galaxy in ionised interstellar gas clouds. The discovery could help researchers to understand the nature and evolution of interstellar gas in galaxies and how Rydberg atoms are formed in space. A paper on the discovery was recently published in The Astrophysical Journal

The light from a distant quasar (an extremely luminous active supermassive black hole at the centre of a galaxy), located 11.1 billion light years away in the constellation Sagittarius, was key to the discovery.

Quasar PKS1830-211 is one of the brightest radio sources in the sky since the high-power jet from its super massive black hole is pointed directly at Earth (meaning it is also known as a blazar). As light from the quasar travels towards Earth, it passes through the foreground galaxy – located 7.3 billion light years from us, between our planet and the quasar – illuminating molecular chemistry in the galaxy’s spiral arms. This rare alignment has allowed the large hydrogen atoms to be observed.

A Rydberg atom refers to an atom with an electron in a high energy state. Radio light amplifies the Rydberg atoms, and under just the right conditions, the atoms become naturally occurring lasers. Finding the conditions for this to occur in distant galaxies has been a long-standing mystery, but a new generation of state-of-the-art radio telescopes observing the Universe at centimetre to metre wavelengths are making it possible for the first time.

Large surveys that cover the sky using wide bandwidth receivers have high enough precision to look for spectral fingerprints from many wavelengths simultaneously. The MeerKAT Absorption Line Survey (MALS) led by Prof. Neeraj Gupta of the Inter-University Centre for Astronomy and Astrophysics (IUCAA), India, is one such survey.

Using the MeerKAT data processed at the dedicated high-performance computing setup at IUCAA, the MALS team found 44 fingerprints from Rydberg atoms and used them to study the physical and dynamic structures in the foreground galaxy.

“The Rydberg atoms could be coming from large clouds of gas that are ionised by the radiation from young massive stars. These atoms tell us that interstellar gas in this galaxy is much denser than what is found in the Milky Way,” said Dr Kimberly Emig, a Jansky Fellow at the US National Radio Astronomy Observatory (NRAO) and lead author of the paper.

“We were excited to discover these high-excitation hydrogen atoms in such a distant galaxy. It gives a new way to observe our Universe and possibly study the evolution of interstellar gas in galaxies over cosmic time. They could also help us to understand how interstellar gas drives and inhibits the activity of super massive black holes.”

The discovery also provides an exciting prelude to what will be possible with the SKAO.

“This first discovery demonstrates that, with the huge sensitivity of the future SKA telescopes, we will be able to detect many other sources in these spectral lines, or fingerprints, corresponding to the atom recombination [when an electron binds to a proton]. This will multiply our ability to detail the physical conditions of remote sources,” said Prof. Françoise Combes, astronomer at Paris Observatory and cochair of the SKA Extragalactic Spectral Line working group.

Read the paper: https://arxiv.org/abs/2301.03115

ABOVE: Light from the distant quasar (far left) travels through the foreground galaxy (centre) on its way to Earth, illuminating molecular chemistry in the galaxy’s spiral arms.

Image credits: ESA + K. Emig