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CosmosUp | October 3, 2022

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AGC 198691 Galaxy Provide A Glimpse of Early Universe’ Conditions

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AGC 198691, a dwarf blue galaxy, located in the nearby neighborhood provide some of the best links to the conditions present in the infant universe, astronomers says.

AGC 198691, discovered in 2013 as part of the Arecibo Legacy Fast ALFA survey, is a blue compact dwarf galaxy located about 30 million light-years away from us in the constellation Leo Minor.

Its a small galaxy with a diameter of just 1,000 light years, that’s 100 times smaller than our galaxy. The brightest stars in AGC 198691 are giant blue stars which is why this galaxy itself appears blue in color.

Nicknamed Leoncino (“little lion”), AGC 198691 is unique and extremely rare galaxy due to it’s low level of heavy elements; it is actually the most metal-poor galaxy ever detected in a gravitationally bound system of stars present in the local universe.

The importance of the extremely metal-deficient (XMD) galaxiesRight after the Big Bang, the universe did not contain any heavy metals thus the first galaxies were metal-poor, “metals” refers to any element other than hydrogen or helium.

The study of these systems, so-called extremely metal-deficient (XMD) galaxies, is considered of special importance. The XMD galaxies provide some of the best links to the conditions present in the infant universe.

They offer a great opportunity to learn about star formation and the properties of massive stars, as well as providing measurements of primordial abundances at the time of the Big Bang.

Up today, only 4 such galaxies are known in the local universe: the blue compact dwarf galaxy I Zw 18, the starburst galaxy SBS 0335–052W, the irregular galaxy DDO 68 and the dwarf galaxy Leo P. Unfortunately, observations of such extremely low metallicity systems are exceptionally uncommon. This is why the discovery of AGC 198691 is so important.

Finding the most metal-poor galaxy ever is exciting since it could help contribute to a quantitative test of the Big Bang,

said one of the researchers, John J. Salzer.

There are relatively few ways to explore conditions at the birth of the Universe, but low-metal galaxies are among the most promising.

 The team of researchers, led by Alec Hirschauer at the University of Indiana, has published the article online on March 11 in the arXiv website.

AGC 198691 The most poor-metal galaxy known to date

Hirschauer and his colleagues conducted spectroscopic observations to obtain spectra of this nearby dwarf galaxy. To accomplish this task, astronomers used two Arizona-based telescopes: the new high-throughput KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m and the Blue Channel spectrograph on the MMT 6.5-m telescope.

Their observations enable the measurement of the temperature-sensitive line and hence the determination of a “direct” oxygen abundance for AGC 198691, thus revealing that this system is exceptionally metal-poor.

The dwarf galaxy AGC 198691 beat the galaxy that had previously been the record-holder – called SBS 0335–052W – with an estimated 29% lower metal abundance overall.

We’re eager to continue to explore this mysterious galaxy,

said Salzer

Low-metal-abundance galaxies are extremely rare, so we want to learn everything we can.

The team plans for future observations of this system. They intend to carry out an analysis of helium abundance of AGC 198691 with the Large Binocular Telescope in Arizona:

While the spectra in the current study were not suitable for providing an estimate of the helium abundance in this galaxy, we suggest that future observations would very likely be fruitful in yielding an estimate of the primordial helium abundance,

the researchers write in the paper.


  1. Ron Cole

    Or maybe it’s low in metals because that’s just what it is, unrelated to it’s age or the age of the Universe. Or maybe light from metals deteriorates for reasons not yet known over such a great distance and time.

    I think this science is wonderful but I also think drawing any conclusions from it are way too premature. I would leave the door more widely open on the very possible large difference between what is seen and what is reality. I say that because I’m old enough to remember the expectation that Jupiter’s *four* moons would all be boring and very much like our own Moon. Egg meet face.

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