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Distant galaxy: HD1, red object in enlarged section
Photo: Harikane et al.
Astronomers have discovered what may be the oldest and most distant known galaxy.
It probably arose soon after the Big Bang, which marked the origin of the universe.
The galaxy, dubbed HD1, formed just over 300 million years after the Big Bang 13.8 billion years ago, the researchers said on Thursday.
According to their observations, HD1 was forming new stars at a breathtaking rate, about 100 a year.
Alternatively, the galaxy could also host one of the oldest known supermassive black holes.
Because light travels nearly 9.5 trillion kilometers in a year, observing objects as distant as HD1 is like looking back in time.
If the new data are confirmed, HD1 would surpass the oldest known galaxy GN-z11 by about 100 million years.
James Webb telescope should bring more clarity
The researchers used data from telescopes in Hawaii, Chile and the Spitzer Space Telescope.
They hope to get more clarity on the James Webb Telescope, which was launched by Nasa in December and is expected to be operational in a few months.
"The observable information on HD1 is limited and other physical properties remain a mystery, including its shape, mass and metallicity," said University of Tokyo astrophysicist Yuichi Harikane, lead author of a publication on the discovery in the Astrophysical Journal.
Metallicity refers to the proportion of materials other than the gases hydrogen and helium that were already present in the original universe.
"The difficulty is that we've almost pushed the limits of the capabilities of today's telescopes, both in terms of sensitivity and wavelength," added Harikane.
Galaxies are vast collections of stars and other matter held together by gravity, like the Milky Way, which includes our solar system.
The first galaxies, which formed about 100 to 150 million years after the Big Bang, were smaller and denser than today's, with significantly fewer stars.
Ten billion times more massive than the sun
According to the researchers, HD1, which has a mass about 10 billion times that of our Sun, could have been populated by stars from the very first generation.
These stars, called Population III, are believed to have been extremely massive, luminous, hot, and short-lived, composed almost entirely of hydrogen and helium.
“After the Big Bang, some regions of space were denser than others, and this attracted more matter over time.
This effect produced large concentrations of gas, some of which collapsed to form stars,” said Harvard-Smithsonian Center for Astrophysics astrophysicist Fabio Pacucci, lead author of a related study in the Monthly Notices of the Royal Astronomical Society Letters.
Elements other than hydrogen and helium were absent from the early stages of the universe, formed later within the first stars, and then spewed into the space between stars when they exploded at the end of their lives.
Extreme ultraviolet light
HD1, the researchers observed, glowed in the extreme ultraviolet.
Population III stars could emit more UV light than conventional stars.
HD1 possibly went through "a very abrupt star effect," Pacucci said.
Another explanation for the UV light could be a supermassive black hole within HD1, which would be about 100 million times more massive than our Sun, Pacucci added.
Several galaxies, including the Milky Way, contain such black holes at their centers.
So far, the oldest known galaxy of this type has been dated to around 700 million years after the Big Bang.
The first stars and galaxies paved the way for those that exist today.
“The first galaxies were millions of times the mass of the Milky Way and much denser.
You can think of them as building blocks in the construction of today's galaxies like our Milky Way,” said Avi Loeb, a theoretical physicist at Harvard University and a co-author of the study.
ak/Reuters