News in Science

Milky Way hangs by a cosmic thread

We are here Sitting like a bead on a cosmic thread, Australian astronomers have identified our galaxy's position in the large scale structure of the cosmos.

Dr Stefan Keller from the Research School of Astronomy and Astrophysics at the Australian National University and colleagues made the discovery while studying ancient balls of tightly packed stars called globular clusters.

Instead of being randomly distributed, the researchers found they were primarily located along a narrow plane around the Milky Way.

"It was a nice discovery and in some ways unexpected," says Keller.

"We were discussing news about the discovery that satellite dwarf galaxies around the Milky Way were spread along a single plane and we wondered if globular clusters did likewise. So I did a few calculations and found that they did indeed trace the same plane."

Pulling it all together

Keller says the filaments also link globular clusters and satellite galaxies.

"Instead of being collections of stars from our own galaxy, some globular clusters could be the remnants of other galaxies that have collided with and been consumed by the Milky Way through the process of galactic cannibalism," says Keller.

The findings reported on the pre-press physics blog arXiv.org and submitted for publication in Astrophysical Journal, support the hypothesis that the large scale structure of the cosmos consists of long filaments made up of galaxies, and vast voids millions of light years across which have virtually nothing in them.

"We're kind of sandwiched between two enormous voids which pin us into a filament linked at one end to the big Virgo galaxy cluster and to the Fornax galaxy cluster off to the other side," says Keller.

'Foam on the crest of a wave'

Keller says the structure of the filaments were most probably shaped by interactions between dark and ordinary matter.

"A consequence of the Big Bang and the dominance of dark matter is that ordinary matter is driven, like foam on the crest of a wave, into vast interconnected sheets and filaments stretched over the enormous cosmic voids,"

Keller says, "Gravity draws the material over these interconnecting filaments towards the largest lumps of matter, and our findings show the globular clusters and satellite galaxies of the Milky Way trace one of these filaments.