Equal-mass black holes have just
merged into a single object in this image from a supercomputer
simulation. The merged black hole has settled into its "ringdown" phase
and is emitting the last gravitational waves (purple) produced by the
event. Credit: NASA/Goddard/UMBC/Bernard J. Kelly, NASA/Ames/Chris Henze, CSC Government Solutions LLC/Tim Sandstrom
This illustration shows ESA's (the European Space
Agency's) LISA observatory, a multi-spacecraft mission to study
gravitational waves expected to launch in 2034. In the mission concept,
LISA consists of three spacecraft in a triangular formation spanning
millions of kilometers. Test masses in spacecraft on each arm of the
formation will be linked together by lasers to detect passing
gravitational waves.Credits: AEI/Milde Marketing/Exozet
ESA (the European Space Agency) has selected the Laser Interferometer
Space Antenna (LISA) for its third large-class mission in the agency's
Cosmic Vision science program. The three-spacecraft constellation is
designed to study gravitational waves in space and is a concept long
studied by both ESA and NASA.
ESA’s Science Program Committee announced
the selection at a meeting on June 20. The mission will now be
designed, budgeted and proposed for adoption before construction begins.
LISA is expected to launch in 2034. NASA will be a partner with ESA in
the design, development, operations and data analysis of the mission.
Gravitational radiation was predicted a century ago by Albert
Einstein's general theory of relativity. Massive accelerating objects
such as merging black holes produce waves of energy that ripple through
the fabric of space and time. Indirect proof of the existence of these
waves came in 1978, when subtle changes observed in the motion of a pair of orbiting neutron stars showed energy was leaving the system in an amount matching predictions of energy carried away by gravitational waves.
In September 2015, these waves were first directly detected by the National Science Foundation’s ground-based Laser Interferometer Gravitational-Wave Observatory (LIGO). The signal arose from the merger of two stellar-mass black holes located some 1.3 billion light-years away. Similar signals from other black hole mergers have since been detected.
Seismic, thermal and other noise sources limit LIGO to
higher-frequency gravitational waves around 100 cycles per second
(hertz). But finding signals from more powerful events, such as mergers
of supermassive black holes in colliding galaxies, requires the ability
to detect frequencies much lower than 1 hertz, a sensitivity level only
possible from space.
LISA consists of three spacecraft separated by 1.6 million miles (2.5
million kilometers) in a triangular formation that follows Earth in its
orbit around the sun. Each spacecraft carries test masses that are
shielded in such a way that the only force they respond to is gravity.
Lasers measure the distances to test masses in all three spacecraft.
Tiny changes in the lengths of each two-spacecraft arm signals the
passage of gravitational waves through the formation.
For example, LISA will be sensitive to gravitational waves produced
by mergers of supermassive black holes, each with millions or more times
the mass of the sun. It will also be able to detect gravitational waves
emanating from binary systems containing neutron stars or black holes,
causing their orbits to shrink. And LISA may detect a background of
gravitational waves produced during the universe's earliest moments.
For decades, NASA has worked to develop many technologies needed for
LISA, including measurement, micropropulsion and control systems, as
well as support for the development of data analysis techniques.
For instance, the GRACE Follow-On mission, a U.S. and German collaboration to replace the aging GRACE
satellites scheduled for launch late this year, will carry a laser
measuring system that inherits some of the technologies originally
developed for LISA. The mission's Laser Ranging Interferometer will
track distance changes between the two satellites with unprecedented
precision, providing the first demonstration of the technology in space.
In 2016, ESA's LISA Pathfinder successfully demonstrated key
technologies needed to build LISA. Each of LISA's three spacecraft must
gently fly around its test masses without disturbing them, a process
called drag-free flight. In its first two months of operations, LISA Pathfinder demonstrated this process with a precision some five times better than its mission requirements
and later reached the sensitivity needed for the full multi-spacecraft
observatory. U.S. researchers collaborated on aspects of LISA Pathfinder
for years, and the mission carries a NASA-supplied experiment called
the ST7 Disturbance Reduction System, which is managed by NASA’s Jet Propulsion Laboratory in Pasadena, California.
For more information about the LISA project, visit: https://lisa.nasa.gov
Editor: Rob Garner
Source: ESA/Solar System and Beyond
