Peter L. Bender, for the LISA Science Study Team and the LISA Mission Definition Team
JILA, University of Colorado and National Institute of Standards and Technology Boulder, Colorado, USA

The Laser Interferometer Space Antenna (LISA) has been proposed to make detailed studies of gravitational wave signals at low frequencies.  The results will be complementary to those of ground-based detectors.  The frequency range will extend from below 0.01 millihertz to at least 1 Hz, and possibly to 5 Hz.  The antenna consists of 3 spacecraft forming an equilateral triangle with 5 million km sides, located 50 million km from the Earth.  Laser heterodyne measurements between freely floating test masses in each spacecraft are used to determine gravitational wave signals and correct for laser phase noise.  Although up to 50,000 km changes in the side lengths occur due to celestial mechanics, the changes in the measurement frequency range will be mainly those due to spurious accelerations of the test masses.

From an astrophysical point of view, the potential LISA sources of most interest are those involving massive black holes (MBHs). Coalescence of even two 500 solar mass black  holes at a redshift of 5 could be observed clearly. Information hopefully will be obtained about the following: the formation, growth, and abundance of MBHs;  coalescence of compact objects with MBHs in galactic nuclei;  and coalescence of central MBHs after galaxy mergers.