Alpbach summer school on fundamental physics in space

Peter Bender, JILA, University of Colorado, Boulder

Each year a Summer School in an area of space science is held in the picturesque mountain village of Alpbach, Austria. Erwin Schroedinger frequently spent time in the summer in Alpbach, and the main lecture room in the Congress House there bears his name. This year, the space science subject chosen was Fundamental Physics in Space. The school was organized and supported by the Austrian Federal Ministry of Science and Transport, the Austrian Space Agency, the European Space Agency, the national space authorities of the ESA member states, and the European Science Foundation. The Chairman was Johannes Ortner from the Austrian Space Agency.

About 50 graduate students from nine European countries took part in the Summer School. There were 25 lectures presented by scientists interested in fundamental physics and in space. The meeting started with an opening talk by Roger Bonnet, the Science Programme Director at ESA. This was followed by a number of introductory talks covering the early universe, gravitational physics, and the questions that can be addressed by fundamental physics missions. Talks on expected improvements in accelerometers and clocks needed for gravitational physics tests in space also were included.

Four main missions were discussed in the remaining lectures. Two are approved missions that are scheduled for flight. One is the Alpha Magnetic Spectrometer for the detection of antimatter in space and the search for dark matter. It will fly on the Shuttle and on the International Space Station. The other is the Gravity Probe B mission, that will measure relativistic dragging of inertial frames due to the Earth's rotation, and also geodetic precession caused by the Earth's mass.

The other proposed missions have been the subject of international studies, but are not yet approved. One is the Mini-STEP mission, where STEP stands for Satellite Test of the Equivalence Principle. The differential accelerations of pairs of concentric masses will be compared with great precision to determine if the ratio of gravitational to inertial mass is the same for different elements. The other mission is the Laser Interferometer Space Antenna (LISA) for gravitational wave studies. It will inventory thousands of galactic binaries containing compact stars, and look for signals from sources out to cosmological distances that contain massive black holes.

A unique feature of the School is that the students spent about half their daytime hours in workshops, where they studied and prepared proposals for possible future missions. The students broke up into two teams, "coordinated" by Robin Laurance from the European Space Technology Research Center in The Netherlands and Nicholas Lockerbie from Strathclyde University in Glasgow. Each team worked on its mission proposals during the workshops and often for many hours at night, using ten PCs to search for information and carry out their studies. The proposals were presented on the last day of the School at a session chaired by Hans Balsiger, the current ESA Science Program Committee chair.

One team chose to concentrate their efforts on a mission to study MACHOs - Massive Compact Halo Objects. Intensive ground-based measurement programs have detected nearly 100 temporary brightenings of stars in the galactic bulge or the Large Magellanic Cloud due to dark objects passing between them and us causing gravitational lensing. The objective of the space mission would be to detect small displacements of star images as well as brightenings using a 1 m diameter telescope and advanced microchannel plate detectors similar to those being developed for particle physics experiments. The relative timing of pulses from dozens of stars would be determined as a star field was swept across the roughly 10,000 parallel strip channels of the detector by a rotating mirror.

The other team presented studies of five missions, of which three were developed into specific proposals. One proposal was for adding the capability to the Alpha Magnetic Spectrometer to convert neutralinos into detectable gamma-rays with energies of 30 to 300 Gev. If this can be done without losing sensitivity for antimatter detection, it would permit searches for neutralinos from the galactic center, an important dark matter candidate.

The other two proposals were for missions designed to considerably exceed the sensitivity of the LISA gravitational wave mission at frequencies lower than and higher than LISA is optimized for. The "extra low frequency" mission would improve the sensitivity for sources involving supermassive black holes such as those found in active galactic nuclei, and also would improve observations of non-compact galactic binaries. The "medium frequency" mission would have its best sensitivity at frequencies between the optimum frequencies for LISA and for ground-based detectors. It would use multiple bounces between mirrors in the different spacecraft. The main objectives would be to permit observations of neutron star binary coalescence much earlier than possible on the ground, and to look for possible coalescence of few hundred solar mass black holes in dense galactic nuclei.

The Proceedings of the Alpbach Summer School, including descriptions of the missions studied in the workshops, will be published by ESA.

Jorge Pullin
Wed Sep 10 15:05:58 EDT 1997