Observations at Mount Stromlo Observatory near Canberra may have cracked the problem of 'dark matter' in our Galaxy - the unseen material astronomers have spent decades searching for - an international conference at the Academy of Science in Canberra will be told today.
A mainly Australian and US team has found objects that could account for about 50% of our Galaxy's unseen mass, team leader Dr. Charles Alcock of the US Lawrence Livermore National Laboratory will tell the conference.
"In time we may be able to account for all of it," said team member Professor Ken Freeman of Mount Stromlo Observatory.
The dark matter appears to be in lumps of about half the mass of the Sun.
"The favoured candidate is dim shrunken stars called 'white dwarfs'," Dr. Alcock said. "But there are problems with those. When white dwarfs form there's a lot of associated chemical 'pollution' in space, and we're not seeing that."
Primordial black holes are another possibility, says Professor Freeman. "To be the right mass they must have formed early in the life of the Universe, about ten microseconds after the Big Bang," he said.
Lying in a 'halo' around our Galaxy, the dark matter makes up 90% of the Galaxy's mass.
"We've known of this stuff for decades because of its gravitational effects," said Dr. Alcock. "But we didn't know if it existed as big dark star-sized lumps or exotic elementary particles."
The hypothetical star-sized lumps were christened MACHOs - MAssive Compact Halo Objects.
The MACHO team hunted down its prey through 'gravitational lensing'. When a MACHO passes in front of a background star the MACHO's gravitational field acts like a lens, magnifying the star's light. The MACHO team has recorded about 15 such events.
The observations were made with the historic Great Melbourne Telescope at Mount Stromlo Observatory. The telescope system can record the brightnesses of tens of millions of stars in a night. The background stars which the MACHOs magnified were in a small neighbouring galaxy called the Large Magellanic Cloud.
Terabytes of data have been recorded and analysed, first at the Lawrence Livermore National Laboratory and more recently with powerful computers installed at the telescope.
This huge data bank has been used for more than a hundred scientific papers.
Professor Freeman cautioned that MACHOs help to solve the dark matter problem for our Galaxy but not for the whole Universe. "There is a great deal of dark matter out there and there are many other things it could be," he said.
"Conventional cosmology still tells us that most of it is not ordinary (baryonic) matter."
The MACHO project has run for five years and will wind down after another two. Similar work has just been started by a French team using a telescope in Chile.
About the MACHO team:
Individual members: C. Alcock, R.A. Allsman, D. Alves, T.S. Axelrod, A.C. Becker, D.P. Bennett, K.H. Cook, A.J. Drake, K.C. Freeman, K. Griest, L.J. King, M.J. Lehner, S.L. Marshall, D. Minniti, B.A. Peterson, M.R. Pratt, P.J. Quinn, P.B. Stetson, C.W. Stubbs, W. Sutherland, A. Tomaney, T. Vandehei, D.L. Welch
Participating institutions:
* Lawrence Livermore National Laboratory, California * Center for Particle Astrophysics, University of California Berkeley * Supercomputing Facility, Australian National University * Department of Physics, University of California Davis * Mt. Stromlo and Siding Spring Observatories, Australian National University * Departments of Astronomy and Physics, University of Washington, Seattle * Department of Physics, University of Notre Dame * Department of Physics, University of California San Diego * Department of Physics, University of Sheffield * Departmento de Astronomia, Universidad Catolica, Santiago, Chile * Center for Space Research, MIT * European Southern Observatory * National Research Council, Canada * Department of Physics, University of Oxford * Departments of Physics and Astronomy, McMaster University, Canada
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.
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.
Back to the main meeting page.
For feedback on the Third Stromlo Symposium web pages, please email tss@mso.anu.edu.au.