Galaxy Segue 1 study suggests it is a fossil from the early universe

The portion of sky in which astronomers found the Segue 1 dwarf galaxy. 

Credit: Marla Geha/W.M. Keck Observatory.

A trio of space researchers studying the galaxy Segue 1 has found that its red giant stars are made mostly of hydrogen and helium, with very few heavy elements, suggesting the galaxy stopped evolving not long after its formation.

In their paper uploaded to the preprint sever arXiv (and soon to be published in Astrophysical Journal) the team describes observation data they've obtained regarding the galaxy and why what they've found might mean Segue 1 is the oldest observable galaxy in the night sky.

Scientists have known about Segue 1 for some time, it's both close to us (just 75,000 light years away) and very small, with just few hundred stars.

In this new effort, Anna Frebel with MIT, Joshua Simon with Carnegie Mellon University and Evan Kirby with the University of California studied the makeup of red giants in Segue 1 and found they are made up mostly of hydrogen and helium.

This implies that the stars came about due to the explosions of massive stars, prior research has shown that it's smaller star explosions that result in new stars forming heavy with metals (because the smaller stars create the heavier elements).

Prior research has also shown that higher mass stars tend to blow up at a much younger age than low mass stars.

Also when stars explode in general, they release material that winds up being used in new star formation. As the process repeats, more stars with heavy metals are created.

But not Segue 1, for some reason the evolution process simply stopped, leaving the galaxy in very nearly the same condition it was shortly after forming.

Why this happened is a mystery, though there is one theory, it's based on reionization.

Reionisation theory suggests that shortly after the universe was born, ionized gasses began to cool allowing the formation of atoms and eventually stars.

Those stars eventually blew up releasing radiation that served as fuel for more reionisation.

New stars cannot form from ionized gasses, of course, so if certain parts of space had stars that caused a lot of reionisation, the creation of new stars would have been impossible, the evolution of such a galaxy would simply stop.

Thus far, Segue 1 is the only such galaxy to have been found, but if the reionisation theory is correct, it's likely there are many more, researchers just can't see them because they are too far away.

More information: Segue 1: An Unevolved Fossil Galaxy from the Early Universe, arXiv:1403.6116 [astro-ph.GA] arxiv.org/abs/1403.6116

NASA Cassini Titan Research: Ice On A Hydrocarbon Lake

This artist's concept envisions what hydrocarbon ice forming on a liquid hydrocarbon sea of Saturn's moon Titan might look like. 

A new model from scientists on NASA's Cassini mission suggests that clumps of methane-and-ethane-rich ice could float under some conditions. They are shown here as the lighter-colored clusters.

A new paper by scientists on NASA's Cassini mission finds that blocks of hydrocarbon ice might decorate the surface of existing lakes and seas of liquid hydrocarbon on Saturn's moon Titan.

The presence of ice floes might explain some of the mixed readings Cassini has seen in the reflectivity of the surfaces of lakes on Titan.

"One of the most intriguing questions about these lakes and seas is whether they might host an exotic form of life," said Jonathan Lunine, a paper co-author and Cassini interdisciplinary Titan scientist at Cornell University, Ithaca, N.Y.

"And the formation of floating hydrocarbon ice will provide an opportunity for interesting chemistry along the boundary between liquid and solid, a boundary that may have been important in the origin of terrestrial life."

Titan is the only other body besides Earth in our solar system with stable bodies of liquid on its surface. But while our planet's cycle of precipitation and evaporation involves water, Titan's cycle involves hydrocarbons like ethane and methane.

Ethane and methane are organic molecules, which scientists think can be building blocks for the more complex chemistry from which life arose.

Cassini has seen a vast network of these hydrocarbon seas cover Titan's northern hemisphere, while a more sporadic set of lakes bejewels the southern hemisphere.