In a distant, distant galaxy called MACS1149-JD1, located 13.28 billion light years away, astronomers have found oxygen, which, in their opinion, could appear there just 500 million years after the Big Bang. Scientists who wrote an article about the discovery in the journal Nature say that it is the earliest discovery of oxygen on the scale of the age of the Universe. Moreover, the galaxy discovered by researchers has become the most distant galaxy with a reliably determined distance. Models show that the first stars began to form in it over 13.5 billion years ago.
After the Big Bang, complex processes took place in the Universe - first quarks, hadrons and other subatomic particles were born, and after them the first atoms appeared, which became part of the primary stellar matter. When hydrogen recombination took place and the universe began to cool, it plunged into the "dark ages". At that time, the first stars were not yet lit and quasars were not born - active galactic nuclei with a supermassive black hole inside. This era ended with the "cosmic dawn" - the emergence of the ancient galaxies that we register today. Their search is important in order to determine how the evolution of the Universe and basic chemical elements took place.
An international team of astronomers led by Takuya Hashimoto of Sanyo University in Osaka observed the very distant galaxy MACS1149-JD1 with the ALMA telescope and discovered a very faint glow of ionized oxygen. Due to the expansion of the Universe, the wavelength of the initially infrared radiation has increased more than tenfold during its travel in space. The source's redshift indicated that the signal recorded by scientists was emitted 13.3 billion years ago, or just 500 million years after the Big Bang. This is the longest distance ever recorded for oxygen, and its presence indicates that earlier generations of stars must also exist in this galaxy.
In addition to the oxygen emissions recorded at ALMA, the researchers also noticed weaker hydrogen emissions with the VLT. The distance to the galaxy determined from these observations is consistent with that obtained from the oxygen line. Thus, MACS1149-JD1 turns out to be the most distant galaxy with a reliably determined distance and the most distant galaxy ever observed on ALMA or VLT.
The first enlarged image shows which galaxy MACS1149-JD1 was seen by the ESO's VLT; the second is how the Hubble Space Telescope saw this galaxy. The white outlines show the zones of ionized oxygen seen by the ALMA telescope.
“We see this galaxy in an era when the universe was only 500 million years old - and it turns out that at that time it was already inhabited by mature stars,” explains Nicolas Laporte, second author of the article.
"We can use this galaxy to probe an earlier, completely unknown period in space history."
For some time after the Big Bang, there was no oxygen in the Universe: it appeared as a result of fusion processes in the bowels of the first stars and then, when supernova explosions occurred, it was scattered in space. Oxygen registration in MACS1149-JD1 shows that just 500 million years after the beginning of the universe, these early generations of stars have already formed and managed to produce enough oxygen. To find out when the first luminaries began to emerge, the researchers reconstructed the early history of MACS1149-JD1 from infrared data obtained by the Hubble and Spitzer telescopes. It turned out that the observed brightness of the galaxy is well explained by a model where the beginning of star formation dates back to an epoch only 250 million years after the Big Bang. Moreover, today it is believedthat the "dark ages" came 377 million years after the birth of the Universe - that is, it should be assumed that MACS1149-JD1 began to form in the era of recombination.
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Thus, MACS1149-JD1 makes scientists wonder when the first galaxies originated. The age of the object they discovered indicates that they existed long before the era at which we are now able to register them.
In the past, the most distant oxygen was found in a galaxy that was born 700 million years after the Big Bang. Its amount, according to researchers' estimates, turned out to be about ten times less than the observed amount of oxygen in the Sun.
Nikolay Khizhnyak
