Cluster of stars found forming at edge of Milky Way

© NASA/JPL

If alien life existed on the planets orbiting these stars, they would have views of a portion, or all, of the galactic disk.

A cluster of stars forming at the edge of our very own Milky Way galaxy has been discovered by a team of Brazilian astronomers using data collected from the NASA Wide-field Infrared Survey Explorer (WISE), the US space agency announced on Friday.

These stars live on the edge

"A stellar nursery in what seems to be the middle of nowhere is quite surprising," said Peter Eisenhardt, the project scientist for the WISE mission at the Jet Propulsion Laboratory (JPL) in Pasadena. "But surprises turn up when you look everywhere, as the WISE survey did."

The team of astronomers responsible for the discovery, led by Denilso Camargo of the Federal University of Rio Grande do Sul in Porto Alegre, have published their findings in a recent issue of the journal .

The Milky Way has a barred spiral shape, with arms of stars, dust and gas emerging from a central bar, the researchers explained. When it is viewed from the side, the galaxy appears to be relatively flat, with the majority of the material in a disk and in the central area.

Stars form within dense clumps of gas in what are known as giant molecular clouds (GMCs). These GMCs are primarily located in the inner part of the galactic disk, and with many clumps within each of these clouds, the majority of stars are born together in clusters.

Carmargo's team analyzed infrared survey images provided from WISE and found GMCs located thousands of light years above and below the galactic disk. They also found that one of them contained two clusters of stars, marking the first time that researchers had ever discovered stars forming in such a remote location of the galaxy.

The new clusters are located in the molecular cloud HRK 81.4-77.8, which is believed to be approximately two million years old and roughly 16,000 light years beneath the galactic disk - a tremendous distance from the traditional regions of star formation, according to the researchers. The clusters have been given the names Camargo 438 and 439.

Cluster explanation

According to Carmago, there are two possible explanations for the phenomenon. In the first, supernova explosions and other violent events eject dusk and gas out of the galactic disk. That material then falls back, merges, and forms GMCs. In the second, the GMCs formed from gas that was disturbed by interaction with the galaxy and the Magellanic Clouds.

The first explanation, also known as the "chimney model," would need several hundred massive stars to have exploded as supernovae over the course of several generations, creating a so-called "superwind" that forced HRK 81.4-77.8 into its present position, the authors explained.

The bubbles created by these explosions would, over millions of years, themselves compress materials, forming an increasing number of stars and fuelling the ejection of material in a type of "galactic fountain," they added. Eventually, the gas and dust would fall back down onto the disk.

"Our work shows that the space around the Galaxy is a lot less empty that we thought," Carmago said in a statement. "The new clusters of stars are truly exotic. In a few million years, any inhabitants of planets around the stars will have a grand view of the outside of the Milky Way, something no human being will probably ever experience."

"Now we want to understand how the ingredients for making stars made it to such a distant spot. We need more data and some serious work on computer models to try to answer this question," the astronomer added.