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The Cosmic Ties that Bind Us

The results of a computer simulation of a cold dark matter universe.

The results of a computer simulation of a cold dark matter universe. Ordinary matter, in the form of stars and gas, is held to the dark matter via gravity and flows along filaments towards the largest local mass. The alignment of satellite galaxies around the Milky Way and Andromeda galaxies is a direct consequence of the filamentary nature of the universe.

By Stefan Keller

Astronomers have found a filament of ancient stars and galaxies that joins us to neighbouring clusters of galaxies and beyond to the vast interconnected universe.

Stefan Keller is a Research Fellow at the Research School of Astronomy and Astrophysics of the Australian National University, where he is the Operational Scientist for the SkyMapper telescope.

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Globular clusters hold hundreds of thousands of stars in a compact ball hundreds of light years across. From their colours and brightness these stars tell us that they are old – the majority formed at the same time as the Milky Way some 13 billion years ago.

Some globular clusters, however, are younger by several billion years than the majority. Understanding the creation of such star clusters has proven a problem.

The galaxy is known to have settled into its current disk-like shape at this time. This is expected to have drawn in the gas required to form such star clusters.

A study I have been conducting at the Australian National University (ANU) with Gary Da Costa and Dougal Mackey suggests a solution that is not of our galaxy. When we examined the distribution of the younger globular clusters around the Milky Way we saw that these clusters extend out to much greater distances compared with their older counterparts. Furthermore, the younger globular clusters are not scattered randomly about the Milky Way. Rather, they are confined to a plane that meets the disk of our galaxy almost face-on (Fig. 1).

The Milky Way has a flotilla of small satellite galaxies. When the arrangement in space of these satellites was examined, we found that these objects too are in a plane. Our findings show that the plane described by the Milky Way’s satellite...

The full text of this article can be purchased from Informit.