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Unique Dwarf Galaxy May Shed Light On The Early Universe

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Justine Alford

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827 Unique Dwarf Galaxy May Shed Light On The Early Universe
MIT, Anna Frebel. The Magellan Telescopes at Las Campanas Observatory, Chile.

Scientists have unearthed hints about the conditions present in the early universe by analyzing the unusual composition of an extremely faint “wimpy” dwarf galaxy called Segue 1. The findings have been published in The Astrophysical Journal.

Segue 1 is roughly 75,000 light years away from us and contains a meager 1,000 stars more or less, which is an impressively small number considering your “average” galaxy will often contain about 1 million. It’s also the faintest galaxy discovered so far. Curiously, it seems that the growth of this galaxy was stunted pretty early on in its evolution, leaving a rather primitive bundle of stars that therefore offer an insight into the evolution of galaxies relatively soon after the Big Bang.


“It tells us how galaxies get started” said Anna Frebel, lead author of the paper and an assistant professor of physics at the Massachusetts Institute of Technology (MIT). “It’s really adding another dimension to the stellar archeology, where we look back in time to study the era of the first star and first galaxy formation.”

The scientists used data collected by the Magellan Telescopes in Chile and the Keck Observatory in Hawaii in order to resolve the chemical composition of the brightest stars within this galaxy, which were six red giants. Red giants are very luminous yet relatively cool dying stars that are reaching the last stages of stellar evolution.

They found that the stars within this galaxy had a strikingly low metal content, and all of the elements present that are heavier than helium probably came from a single supernova explosion that took place shortly after the galaxy was born. After this explosion, gas became in short supply and there wasn’t enough to fuel the formation of more stars, and the galaxy stopped growing. According to Frebel, this lack of star formation is also why more of the heavy elements could not be produced.

More evidence for the apparent lack of star formation came from the observation that the galaxy also contained exceedingly low levels of neutron-capture elements, which are forged in intermediate-mass stars. “This galaxy tried to become a big galaxy, but it failed,” says Frebel.


Frebel also points out that Segue 1 is quite unlike other dwarf galaxies that have been investigated so far, since those are merely miniaturized galaxies. This galaxy, on the other hand, is arrested in terms of evolution and retains a primitive chemical composition.

The data is exciting since Segue 1 is the first of its kind to be discovered, and galaxies such as this may help to paint a more informative picture of the development of the universe. The team don’t know how rare these galaxies are just yet, so it could be a while before another is discovered. 


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