Pre-Phase A Report - Lisa - Nasa

Chapter 1
Scientific Objectives
By applying Einstein’s theory of general relativity to the most up-to-date information
from modern astronomy, physicists have come to two fundamental conclusions about
gravitational waves:
• Both the most predictable and the most powerful sources of gravitational waves emit
their radiation predominantly at very low frequencies, below about 10 mHz.
• The terrestrial Newtonian gravitational field is so noisy at these frequencies that
gravitational radiation from astronomical objects can only be detected by spacebased
instruments.
The most predictable sources are binary star systems in our galaxy; there should be
thousands of resolvable systems, including some already identified from optical and Xray
observations. The most powerful sources are the mergers of supermassive black holes
in distant galaxies; if they occur their signal power can be more than 107 times the
expected noise power in a space-based detector. Observations of signals involving massive
black holes (MBHs) would test general relativity and particularly black-hole theory to
unprecedented accuracy, and they would provide new information about astronomy that
can be obtained in no other way.
This is the motivation for the LISA Cornerstone Mission project. The experimental and
mission plans for LISA are described in Chapters 3 – 10 below. The technology is an outgrowth
of that developed for ground-based gravitational wave detectors, which will observe
at higher frequencies; these and other existing gravitational wave detection methods are
reviewed in Chapter 2 . In the present Chapter, we begin with a non-mathematical introduction
to general relativity and the theory of gravitational waves. We highlight places
where LISA’s observations can test the fundamentals of gravitation theory. Then we survey
the different expected sources of low-frequency gravitational radiation and detail what
astronomical information and other fundamental physics can be expected from observing
them.
Corrected version 2.08 7 3-3-1999 9:33