News in Science

Ancient galaxy puts astronomers in a spin

Surprise find Astronomers have found a link between the earliest spiral galaxies and galactic collisions.

The discovery reported in the journal Nature, provides a new insight into how galaxies form.

They detected the ancient spiral named Q2343-BX442, while observing more than 300 distant galaxies with the Hubble space telescope.

Study co-author, Dr Alice Shapley from the University of California, Los Angeles, says BX442 is almost 11 billion light years away, dating to a time when the universe was just a quarter of its current age.

"The discovery is extremely rare, in fact it's the earliest grand design spiral ever seen," says Shapley.

"Grand design spirals, galaxies with well defined spiral arms such as the Milky Way, are relatively common in the local universe today. But we didn't think the conditions of the early universe would have allowed their formation."

Strange structures

"As you go back in time, galaxies look really messed up, clumpy and irregular, not symmetric," says Shapley.

"The vast majority of old galaxies look like train wrecks, so I was shocked when I saw this one was so different, and so beautiful."

Follow-up observations by Shapley and colleagues found it to be a thick disc of stars with lots of star burst activity occurring in its spiral arms.

"This is the same process seen in galaxies today," says Shapley.

But there were more surprises to come.

"We were amazed when we discovered this thing was rotating, and blown away when we found it was rotating at the same speed as the Milky Way is today."

Spiral origins

The data also shows the galaxy is merging with another.

"We think this is what's driving the formation of the spiral structure," says Shapley.

"Even now, many of the best known spiral galaxies in the nearby universe including the Whirlpool galaxy, Messier 81 and the Pinwheel Galaxy, appear to have satellite galaxies."

The Milky Way is orbited by at least three satellite galaxies, the Large and Small Magellanic Clouds and the Sagittarius dwarf galaxy.

Shapley and colleagues tested the idea, using computer simulations, finding spiral patterns are formed by mergers.

However the simulations also show these spiral structures may be fleeting, dissipating in just 100 million years.

"It means either the triggering mechanism is relatively rare or the duration of the spiral pattern is extremely short lived," says Shapley.

"We looked at over 300 early epoch galaxies and this is the only one we've found with spiral arms."

"One interpretation of the data is that spirals may not last that long."

"Yet when we look at the modern universe we see lots of spirals, so something has changed."