Gravity is talking. LISA will listen.
The Cosmos sings with many strong gravitational voices, causing ripples
in the fabric of space and time that carry the message
of tremendous astronomical events:
the rapid dances of closely orbiting stellar remnants,
the mergers of massive black holes
millions of times heavier than the Sun,
the aftermath of the Big Bang.
These ripples are the gravitational waves predicted
by Albert Einstein's 1915 general relativity; nearly one century
later, it is now possible to detect them.
Gravitational waves will give us an entirely new way
to observe and understand the Universe, enhancing and complementing
the insights of conventional astronomy.
LISA, the Laser Interferometer Space Antenna, is a joint NASA–ESA
mission to observe astrophysical and cosmological sources of gravitational
waves of low frequencies (0.03 mHz to 0.1 Hz, corresponding to oscillation periods
of about 10 hours to 10 seconds). This frequency band contains the
emission from massive black-hole binaries that form after galactic mergers;
the song of compact stellar remnants as they slowly spiral to their final fate in the
black holes at the centers of galaxies; the chorus of millions of
compact binaries in our own Galaxy; and possibly the
faint whispers of waves generated shortly after the Big Bang.
LISA consists of three identical spacecraft flying in a triangular
constellation, with equal arms of 5 million kilometers each.
As gravitational waves from distant sources reach LISA,
they warp space-time, stretching and compressing the triangle.
Thus, by precisely monitoring the separation
between the spacecraft, we can measure the waves;
and by studying the shape and timing of the waves
we can learn about the nature and evolution
of the systems that emitted them.
“LISA is an extraordinarily original and technically bold mission concept.
LISA will open up an entirely new way of observing the Universe,
with immense potential to enlarge our understanding of physics and astronomy
in unforeseen ways.”
(National Academy of Sciences, NASA's Beyond Einstein Program:
an Architecture for implementation, 2007.)
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