According to scientists who
participated in the study, the new results have resolved a crucial
informational gap about the mass of atomic gas in galaxies and give a complete
picture of what these galaxies were made of.
A new study by a team of
astronomers located in Pune challenges all accepted theories by finding
that galaxies that formed during the early Universe were predominantly
constituted of neutral hydrogen gas, which is in stark contrast to the
composition of newer galaxies.
The conclusions are based on a
computed average result from observation of around 11,000 galaxies that were
formed around 9 billion years ago.
To reach these conclusions,
researchers Nissim Kanekar, Jayaram Chengalur, and Aditya
Chowdhury of the National Centre for Radio Astrophysics (NCRA),
Pune, under the Tata Institute of Fundamental Research (TIFR), examined
510 hours of data from the Giant Metrewave Radio Telescope (GMRT) - CATz1
survey.
Stars and either atomic or
molecular hydrogen make up galaxies in general. Atomic hydrogen cools and
transforms into molecular hydrogen throughout the galaxy's existence.
As it continues to collapse, stars, as we know them today, are created.
According to astronomers, the gas
deposits of these young galaxies compacted and changed over 9
billion years to create many galaxies, including the Milky Way. But as
scientists pointed out, it was star mass, not gas, that predominated. For
instance, the majority of the gas in a highly evolved galaxy would have been
consumed if it had kept on producing stars for a very long time. According to
the researchers, such galaxies would have a greater mass contained in their
stars than in actual gas.
We discovered that the galaxies
that formed 9 billion years ago were 70% atomic hydrogen and 16% mass condensed
in stars. While 2/3 of the material of galaxies today is contained in their
stars, 1/3 of the total conventional mass (dark matter included) is made up of
atomic hydrogen gas. According to Aditya Chaudhury, the study's
principal author, only 6% of all matter in the universe is made up of molecules,
including dark matter. The findings were published in the Astrophysical
Journal Letters.
According to Nissim Kanekar,
senior scientist at NCRA and co-author of the study, the new discoveries have
finally resolved the crucial missing information regarding the mass of atomic
gas in galaxies.
The first indications that these
galaxies are substantially different from galaxies now come from recent
discoveries of molecular gas in early galaxies, he added. According to him, the molecular gas in early
galaxies "has proved that the molecular gas is comparable to the stars
in mass."
The researchers claim that a
galaxy's evolutionary stage can be determined by the proportions of its atomic
and molecular gas and star stuff.
Researchers typically examine the
hydrogen atom's 21 cm wavelength spectral line to determine the mass of atomic
hydrogen gas. But with ground-based telescopes, the 21 cm spectral line
originating from far-off galaxies is incredibly feeble. Therefore, the
researchers coupled this data with in-depth observations made over specific sky
regions during the GMRT-CATz1 survey, which was conducted between 2018
and 2020.
According to Jayaram Chengalur,
director of TIFR and a co-author of the paper, the latest work resolves
a long-running argument regarding the composition of the early galaxies by
painting a complete picture of what these galaxies were formed of.
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