Nearby galaxy is a “fossil” from the early universe


Share post:

New work from a team of scientists including Carnegie’s Josh Simon analyzed the chemical elements in the faintest known galaxy, called Segue 1, and determined that it is effectively a fossil galaxy left over from the early universe.

Nearby galaxy is a “fossil” from the early universe
On the left, Segue 1 (note that you can’t see the galaxy); on the right, the stars 
that are part of Segue 1 are circled [Credit: Marla Geha Yale University]

Astronomers hoping to learn about the first stages of galaxy formation after the Big Bang use the chemical composition of stars to help them unravel the histories of the Milky Way and other nearby galaxies. Using these chemical analysis techniques, the team was able to categorize Segue 1’s uniquely ancient composition. Their work is published by Astrophysical Journal.

Stars form from gas clouds and their composition mirrors the chemical composition of the galactic gas from which they were born. Only a few million years after stars begin burning, the most-massive stars explode in titanic blasts called supernovae. These explosions seed the nearby gas with heavy elements produced by the stars during their lifetimes. The very oldest stars consist almost entirely of the two lightest elements, hydrogen and helium, because they were born before ancient supernova explosions built up significant amounts of heavier elements.

In most galaxies, this process is cyclical, with each generation of stars contributing more heavy elements to the raw material from which the next set of stars will be born. But not in Segue 1 — in contrast to all other galaxies, the new analysis shows that Segue 1’s star formation ended at what would ordinarily be an early stage of a galaxy’s development. Segue 1 likely failed to progress further because of its unusually tiny size.

“Our work suggests that Segue 1 is the least chemically evolved galaxy known,” Simon said. “After the initial few supernova explosions, it appears that only a single generation of new stars were formed, and then for the last 13 billion years the galaxy has not been creating stars.”

Nearby galaxy is a “fossil” from the early universe
The Magellan Telescopes at Las Campanas Observatory, Chile, where some of the
 new research on the Segue 1 galaxy was conducted [Credit: Anna Frebel]

Because it has stayed in the same state for so long, Segue 1 offers unique information about the conditions in the universe shortly after the Big Bang. Other galaxies have undergone multiple supernova explosions since their formation. The first supernovae to blow up, from the most massive stars, produce elements like magnesium, silicon, and calcium. Later explosions of smaller stars primarily make iron. Segue 1’s uniquely low iron abundance relative to other elements shows that its star formation must have stopped before any of the iron-forming supernovae occurred.

This truncated evolution means that the products of the first explosions in Segue 1 have been preserved. Intriguingly, very heavy elements like barium and strontium are nearly absent from Segue 1’s stars.

“The heaviest elements in this galaxy are at the lowest levels ever found,” said Anna Frebel of the Massachusetts Institute of Technology, the leader of the team. “This gives us clues about what those first supernovae looked like.”

Studying individual stars in dwarf galaxies can be difficult and Segue 1, which orbits our own Milky Way, is particularly puny, containing only about a thousand stars. Just seven stars in the entire galaxy are in the red giant phase of their lives, making them bright enough for modern telescopes to detect the features astronomers use to measure the abundance of each chemical element. Three of the seven red giants have heavy element abundances more than 3,000 times lower than that of the Sun, highlighting the primitive nature of the galaxy.

“Having found such a fossil galaxy is of enormous importance to astronomy, because it provides a new window into the first galaxies,” Frebel said.

Along with Simon and Frebel, the other author of the study was Evan Kirby of the University of California, Irvine. The team used one of Carnegie’s 6.5 meter Magellan telescopes in Chile to observe five of the Segue 1 stars, while one was studied with the 10 meter Keck I telescope in Hawaii. The final star was identified and measured by a competing team using the European Southern Observatory’s 8.2 meter Very Large Telescope, also in Chile.

Source:  Carnegie Institution  [May 01, 2014]



Related articles

Another stunning Archaeopteryx fossil found in Germany

Archaeopteryx is one of the world's most iconic prehistoric animals - a dinosaur caught in the midst of...

Climate change will bring greater biodiversity to world seas

Tropical marine animals that currently thrive in warm habitats around the equator will have to spread north and...

Iron Age settlement hailed ‘most significant’ find

An Iron Age settlement unearthed in Devon has been described as one of the most important finds of...

Meltwater from Tibetan glaciers floods pastures

Glaciers are important indicators of climate change. Global warming causes mountain glaciers to melt, which, apart from the...

Theatre of ancient Telmessos undergoing restoration

Restoration has begun at southwestern province of Muğla’s Fethiye district to revive the ancient theater at Telmessos. The Telmessos...

Rescue digs in Portugal ahead of dam construction

Archaeological works that have been going on for two years in the region of the Lower Sabor River...

Antarctic life – highly diverse, unusually structured

In a comprehensive assessment of Antarctic biodiversity, published in Nature this week, scientists have revealed the region is...

Whales only recently evolved into giants when changing ice, oceans concentrated prey

The blue whale, which uses baleen to filter its prey from ocean water and can reach lengths of...