A group of stars lurking in the Andromeda galaxy challenges the basic concept of how stars form.
Summary: The Radeb University team accidentally observed a globular cluster in the Andromeda galaxy, known as RBCEXT8, with an iron abundance of 1/3 of the lowest known iron abundance galaxy before, and metals are generally believed to be the basis for galaxy formation, but this result challenges existing theories of galaxy formation.
(Illustration: This image taken by the NASA/ESA Hubble Space Telescope is the largest and sharpest ever taken of the Andromeda galaxy, also known as M31.) Source: NASA)
In the early universe, ancient stars appeared in swarms.
Globular clusters of hundreds of thousands of ancient stars are tightly arranged into a single sphere and orbit the core of the galaxy.
In October 2019, while investigating globular clusters in the Andromeda galaxy, astronomers stumbled upon a cluster that didn't look quite right.
This strange group of stars has an astonishingly low level of heavy metals, and it is common sense that it is precisely this material that powers star formation.
A study published Thursday in the journal Science detailed the findings.
Soren Larsen is an associate professor at Radboud University and the lead author of the new study. He has been studying the composition of globular clusters for years, studying how galaxies form and evolve over time.
Last October, while Larson and his team were waiting for data from different research targets, they decided to randomly choose a different cluster to observe. But their inadvertent move had unexpected results.
(Illustration: RBC EXT8.) Image source: Aladin)
Larson said that because the results were so shocking, they had to check repeatedly to see if it was true.
The globular cluster that Larson and his colleagues picked is called RBC EXT8, and it is located in the Andromeda galaxy. Located only 2.5 million light-years from our Milky Way, Andromeda is our closest galaxy, and if nothing else, the Milky Way and the Andromeda galaxy will one day collide.
Scientists have found that the cluster's heavy metal content is about 800 times lower than that of the Sun. Its metal content is three times lower than the globular clusters with "minimum metal abundance" previously recorded. The discovery is rethinking how much of this heavy metal is needed to create stars.
(Illustration: This cluster is called RBC EXT8.) Observations suggest that it is the most metal-deficient globular cluster observed to date. That is, it lacks the "heavier" or more complex elements that stars make internally as they move through their lifetime. Source: ESASky en CFHT/ Astronomie.nl.)
In terms of past experience, heavy metals are considered to be chemical elements heavier than hydrogen and helium and relatively dense. They are essential fuels for star formation, especially at the high rates required to form globular clusters. But the observations of these clusters are confusing.
"Our findings suggest that in the early universe, massive globular clusters could have formed only by gases that contained only small amounts of elements other than hydrogen and helium," Larson said. "We have to try to understand how to form these huge clusters of stars with very small amounts of heavy metal elements."
Essentially, the data challenges astronomers' understanding of large populations of stars — suggesting that scientists are missing something in their theories of star formation. Now, the team is looking for other clusters that may have similar properties.
(Milky Way mosaic shot in Chile with a fisheye lens.) The Milky Way rises at a high inclination in the dark night sky, and the Milky Way's satellite galaxy, the Magellanic Cloud, appears near the left edge. Source: Wikipedia)
"We've found one," Larson said. "Now we hope to find more similar samples so that we can more systematically understand the principle behind this."
Scientists look at star formation in order to better understand how galaxies form. One theory is that galaxies were originally small nebulae of stars and dust that merged with other nebulae over time to eventually form a galaxy like the Milky Way.
"We still don't know how galaxies and stars in galaxies form," Larson said. "There are still many details to add."
(Illustration: Globular cluster M54.) Source: Wikipedia)
Globular clusters (GCs) are dense, gravitationally bound systems of thousands to millions of stars. They preferentially relate to the oldest components of galaxies, so measurements of their composition can give us insight into the formation of chemical elements in galaxies in the early universe. We report large summation nebulae with very little heavy element content in the Andromeda Galaxy (M31). Its iron abundance is about 800 times lower than that of the Sun and about three times lower than previous globular nebulae with the least known iron content. It is also severely deficient in magnesium. These measurements challenge the minimum metal abundance values previously required to form globular nebulae, and the theoretical expectation that a large globular nebula would not be possible at such a low metallic abundance.
BY: Inverse
FY: Gigi Wei
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