Atomic hydrogen in a very distant galaxy

The researchers were able to catch the radiation of atomic hydrogen at a length of 21 cm, coming from a record-breaking distance. We can hear its signal from a distant galaxy only thanks to the gravitational lensing that enhances it.

Atomic hydrogen in a distant galaxy. Source: www.vzglyad.kg

Atomic hydrogen at record distance

Astronomers from McGill University in Canada and the Indian Institute of Science in Bangalore were able to catch the radiation of atomic hydrogen in a very distant galaxy using a giant meter-wave radio telescope.

Usually hydrogen enters the galaxy from its surroundings in the form of ionized gas. That is, the electrons in it are torn off from the nuclei of atoms. As the hydrogen settles in the star system, it turns into ordinary atomic gas.

Then the elementary hydrogen particles combine into molecules, cold gas-dust clouds are formed from them, and stars are born from them. But even before this happens, the hydrogen emits at a length of 21 cm.

Radiation lensing

The radiation that generates atomic hydrogen is a good indicator of the processes taking place in the galaxy. But it is usually too weak to catch it at a great distance.

Until now, the record was considered to be radiation at a length of 21 cm, which came from a galaxy for which the redshift index is z = 0.376. This parameter shows how much the lines in the radiation spectrum of the object are shifted to the red side as a result of the expansion of the Universe. It corresponds to a distance of 4.1 billion light years.

But the new record is much higher than the previous one. Here z =1.29, which corresponds to a distance of 8.8 billion light years. This became possible only thanks to the phenomenon of gravitational lensing. For the radiation of atomic hydrogen at a length of 21 cm, it was also observed for the first time. 

Gravitational lensing consists in the fact that if there is a massive object between the remote signal source and the observer, then its mass bends the radiation rays in the same way as it happens in a conventional lens. If they gather at one point somewhere near the scientists’ telescope, they will have the opportunity to see what would otherwise be difficult to see.

According to phys.org

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