Brazilian astronomers using data from NASA’s Wide-field Infrared Survey Explorer have discovered two clusters of stars forming at the very edge of our Milky Way Galaxy.

Our galaxy has a barred spiral shape, with arms of stars, gas and dust winding out from a central bar.

Viewed from the side, it would appear relatively flat, with most of the material in a disc and the central regions.

Stars form inside massive and dense clumps of gas in so-called giant molecular clouds that are mainly located in the inner part of the galactic disc. With many clumps in a single molecular cloud, most stars are born together in clusters.

The astronomers led by Dr Denilso Camargo of the Federal University of Rio Grande do Sul in Porto Alegre, Brazil, not only found giant molecular clouds thousands of light years above and below the galactic disc, but that one of them unexpectedly contained two clusters of stars, named Camargo 438 and Camargo 439.

This is the first time scientists have found stars being born in such a remote location in our Galaxy.

“A stellar nursery in what seems to be the middle of nowhere is quite surprising,” said Dr Peter Eisenhardt of NASA’s Jet Propulsion Laboratory in Pasadena, the project scientist for the WISE mission, who was not involved in the study.

“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,” Dr Camargo said.

The newfound clusters are within the molecular cloud HRK 81.4-77.8.

This cloud is thought to be two million years old and is around 16,000 light years beneath the galactic disk, an enormous distance away from the usual regions of star formation.

The astronomers believe there are two possible explanations.

In the first case, the Chimney Model, violent events such as supernova explosions eject dust and gas out of the galactic disk. The material then falls back, in the process merging to form giant molecular clouds.

The other idea is that the interaction between the Galaxy and its satellites – the Large and Small Magellanic Clouds – may have disturbed gas that falls into the Galaxy, again leading to the creation of molecular clouds and stars.

“Our work shows that the space around the Galaxy is a lot less empty that we thought,” noted Dr Camargo, who is the first author of a paper published in the journal Monthly Notices of the Royal Astronomical Society.

_____

D. Camargo et al. Discovery of two embedded clusters with WISE in the high Galactic latitude cloud HRK 81.4−77.8. MNRAS 448 (2): 1930-1936; doi: 10.1093/mnras/stv092