ROYAL ASTRONOMICAL SOCIETY PRESS INFORMATION NOTE
16th April 2009
EMBARGOED UNTIL 0001 BST, 22ND APRIL 2009
Ref.: RAS PN 09/26 (NAM 13)

Issued by:

Dr Robert Massey
Press and Policy Officer
Royal Astronomical Society
Burlington House
Piccadilly
London W1J 0BQ
Tel: +44 (0)20 7734 3307 / 4582
Mob: +44 (0)794 124 8035
E-mail: rm@ras.org.uk

and

Anita Heward
Press Officer
Royal Astronomical Society
Mob: +44 (0)7756 034 243
E-mail: anitaheward@btopenworld.com

RAS website: http://www.ras.org.uk

EWASS meeting press room (20th – 23rd April only)
Tel:
+44 (0)1707 285530
+44 (0)1707 285640
+44 (0)1707 285781
+44 (0)1707 285587

EWASS home page: http://www.jenam2009.eu (map of campus at http://www.star.herts.ac.uk/ewass)

EWASS press page: http://www.star.herts.ac.uk/ewass/press

RAS PN 09/26 (NAM 13, EMBARGOED): TIME FOR A NEW THEORY OF GRAVITATION? SATELLITE GALAXIES CHALLENGE NEWTONIAN MODEL

The high speed of stars and apparent presence of ‘dark matter’ in the satellite galaxies that orbit our Milky Way Galaxy presents a direct challenge to Newton’s theory of gravitation, according to physicists from Germany, Austria and Australia. Professor Pavel Kroupa of the University of Bonn’s Argelander-Institut fuer Astronomie (AlfA) will discuss the results of the team’s two studies in a presentation on Wednesday 22nd April at the European Week of Astronomy and Space Science conference at the University of Hertfordshire.

Together with scientists at the University of Vienna and the Australian National University in Canberra, the AlfA team looked at the small dwarf galaxies that orbit the Milky Way. Some of these contain only a few thousand stars and so are relatively faint and difficult to find. Standard cosmological models predict the presence of hundreds of these companions around most of the larger galaxies, but up to now only 30 have been observed around the Milky Way.

The team of scientists looked at the distribution of these satellite dwarf galaxies and discovered they were not where they should be. “There is something odd about their distribution”, explains Professor Kroupa. “They should be uniformly arranged around the Milky Way, but this is not what we found.” The astronomers discovered that the eleven brightest of the dwarf galaxies lie more or less in the same plane - in a kind of disk shape - and that they revolve in the same direction around the Milky Way (in the same way as planets in the Solar System revolve around the Sun).

Professor Kroupa and the other physicists believe that this can only be explained if today’s satellite galaxies were created by ancient collisions between young galaxies. Team member and former colleague Dr Manuel Metz, now at the Deutsches Zentrum fuer Luft- and Raumfahrt, also worked on the study. “Fragments from early collisions can form the revolving dwarf galaxies we see today” comments Dr Metz. But he adds that this introduces a paradox. “Calculations suggest that the dwarf satellites cannot contain any dark matter if they were created in this way. But this directly contradicts other evidence. Unless the dark matter is present, the stars in the galaxies are moving around much faster than predicted by Newton’s standard theory of gravitation.”

Dr Metz continues, “The only solution is to reject Newton’s theory. If we live in a Universe where a modified law of gravitation applies, then our observations would be explainable without dark matter.”

With this evidence, the team share the convictions of a number of groups around the world who believe that some of the fundamental principles of physics have been incorrectly understood. If their ideas are correct, it will not be the first time that Newton’s theory of gravitation has been modified. In the 20th century it happened when Einstein introduced his Special and General Theories of Relativity and again when quantum mechanics was developed to explain physics on sub-atomic scales. The anomalies detected by Dr. Metz and Professor Kroupa and their collaborators imply that where weak accelerations predominate, a ‘modified Newtonian dynamic’ may have to be used. If the scientists are right then this has far-reaching consequences for our understanding of the Universe we live in.

The two studies will appear in papers in Monthly Notices of the Royal Astronomical Society and the Astrophysical Journal.

CONTACTS

Professor Dr. Pavel Kroupa
Argelander-Institut fuer Astronomie der Universitaet Bonn
Tel: +49 (0)228 73 6140
Mob: +49 177 9566127
E-mail: pavel@astro.uni-bonn.de

Dr. Manuel Metz
Deutsches Zentrum fuer Luft- und Raumfahrt (DLR)
Tel: +49 (0)228 447 511
Mob: +49 171 1457213
E-mail: manuel.metz@dlr.de

Helene Murphy
Media & PR Officer
University of Hertfordshire
Tel: +44 (0)1707 28 4095
E-mail: h.1.murphy@herts.ac.uk

IMAGES

An image of the Draco satellite dwarf galaxy is available from http://www.astro.uni-bonn.de/~mischa/gallery_ccd/draco.html

Credit: Mischa Schirmer, University of Bonn

NOTES FOR EDITORS

THE EUROPEAN WEEK OF ASTRONOMY AND SPACE SCIENCE

More than 1000 astronomers and space scientists will gather at the University of Hertfordshire for the European Week of Astronomy and Space Science (EWASS), incorporating the 2009 Royal Astronomical Society National Astronomy Meeting (RAS NAM 2009) and the European Astronomical Society Joint Meeting (JENAM 2009). The meeting runs from 20th to 23rd April 2009.

EWASS is held in conjunction with the UK Solar Physics (UKSP) and Magnetosphere Ionosphere and Solar-Terrestrial Physics (MIST) meetings. The conference includes scientific sessions organised by the European Organisation for Astronomical Research in the Southern Hemisphere (ESO) and the European Space Agency (ESA).

EWASS is principally sponsored by the Royal Astronomical Society (RAS), the Science and Technology Facilities Council (STFC) and the University of Hertfordshire, Hatfield.

THE ROYAL ASTRONOMICAL SOCIETY

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.