The Galactic Halo: Bright Stars & Dark Matter

Our Milky Way Galaxy may be indulging in galactic cannibalism, according to Dr. Kathryn Johnston of Institute of Advanced Study, Princeton. Johnston will report her findings today at a major symposium which has brought over a hundred of the world's leading astrophysicists to Canberra.

The Milky Way is surrounded by an entourage of 11 satellite galaxies, which orbit it just as the Moon orbits the Earth. They are subjected to immense tidal forces from the Galaxy, akin to those which raise the ocean tides in the Earth-Moon system. Unlike the Earth and Moon, however, the Milky Way's tidal forces can tear material from a satellite galaxy, possibly annihilating it altogether.

This has led astronomers to ask whether those satellites we see today are just the remains of a much larger number. 'The answer to this puzzle is of interest both for understanding the history of our own Milky Way, and for learning how galaxies may have formed in the first place,' Johnston claims.

Her research has shown that the debris of a destroyed satellite will form a distinctive stream of stars moving along the original orbit of the satellite. This persists for billions of years. The structure of these streams can be simply interpreted using Newton's laws, thus yielding evidence of the early history of our Milky Way Galaxy itself.

The best preserved fossil streams will be at large distances from our Galaxy, however, so the stars in them will be extremely faint.

Nevertheless, new ground-based and satellite telescopes should be able to observe these star streams within the next decade, providing confirmation as to whether Johnston's findings on galactic cannibalism are correct.

The Galactic Halo: Bright Stars and Dark Matter is an international meeting organised by Mount Stromlo and Siding Spring Observatories of the Australian National University. It runs over 17-21 August 1998 at the Australian Academy of Science in Canberra.

Kathryn Johnston studied Mathematics as an undergraduate at Cambridge University, and Astrophysics as a graduate student at the University of California in Santa Cruz, before moving to her current position as a postdoctoral researcher at the Institute for Advanced Study in Princeton. Her research focuses on the study of Galactic dynamics, with particular emphasis on the use of numerical simulations to understand and interpret observations.

Media Contacts:

Before 17 August 1998:

Professor John Norris	Dr. Don Faulkner	Mrs. Fiona Aplin
Ph: (02) 6279 8034	Ph: (02) 6249 0258	Ph: (02) 6249 0266
Fax: (02) 6249 0233	Fax: (02) 6249 0233	Fax: (02) 6249 0260
jen@mso.anu.edu.au	djf@mso.anu.edu.au	director@mso.anu.edu.au

During the Conference (17-21 August 1998):

Becker House			Ph: 014 685 255 (Fiona Aplin)
Australian Academy of Science			Fax: (02) 6247 5373 (attention: Don Faulkner)
Gordon Street
Canberra City ACT 2601

Fixed line for phone interviews: (02) 6248 8872
(but please arrange interviews on mobile number above)

Third Stromlo Symposium web site: http://msowww.anu.edu.au/~tss.

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