Laser Interferometer Space Antenna
LISA is a
space-based
gravitational wave
observatory building on the success of
LISA Pathfinder
and
LIGO.
Led by ESA, the LISA mission is
a collaboration
of ESA,
NASA, and an
international consortium of scientists.
Why LISA? ...Gravitational Waves.
What are Gravitational Waves?
Gravitational waves were first theorized by Albert Einstein. They are created during events such as supermassive black hole mergers, or collisions between two black holes that are billion times bigger than our Sun. These collisions are so powerful that they create distortions in spacetime, known as gravitational waves.
Gravitational waves detectable by the LISA mission could also come from other distant systems including smaller stellar mass black holes orbiting supermassive black holes, known as Extreme Mass Ratio Inspirals (EMRIs).
What do Gravitational Waves tell us?
There are many astrophysical phenomena that are either very dim or completely invisible in any form of light that astronomy has relied on for 400 years. Gravitational waves are a powerful new probe of the Universe that uses gravity instead of light to take measure of dynamical astrophysical phenomena. Studying gravitational waves gives enormous potential for discovering the parts of the universe that are invisible by other means, such as black holes, the Big Bang, and other, as yet unknown, objects. LISA will complement our knowledge about the beginning, evolution and structure of our universe.
Why do we need to go to space?
A space-based configuration allows for an extremely large detector to study regions of the gravitational wave spectrum that are inaccessible from Earth.
A Different Frequency Range from Different Objects
The gravitational wave spectrum covers a broad span of frequencies. LISA operates in the low frequency range, between 0.1 mHz and 1 Hz (compared to LIGO's frequency of 10 Hz to 1000 Hz). The difference means that the waves LISA is looking for have a much longer wavelength, corresponding to objects in much wider orbits and potentially much heavier than those that LIGO is searching for, opening up the detection realm to a wider range of gravitational wave sources.
LISA has three spacecraft that form an equilateral triangle in space where the sides of the triangle, also called LISA's "arms", extend about a million miles. Therefore, from space, LISA can avoid the noise from Earth and access regions of the spectrum that are inaccessible from Earth due to these extremely long arms. The gravitational wave sources that LISA would discover include ultra-compact binaries in our Galaxy, supermassive black hole mergers, and extreme mass ratio inspirals, among other exotic possibilities.
The Entire Spectrum
We aim to study the entire gravitational wave spectrum, covering a range of gravitational wave sources using experiments on
- cosmic microwave background (offsite)
- Pulsar Timing Arrays (offsite)
- International Pulsar Timing Array (IPTA) (offsite)
- More Info at NANOGrav.org (offsite)
- LIGO (offsite)
What is LISA?
LISA is a space-based gravitational wave detector constructed of three spacecraft separated by millions of miles.
LISA's Size and Precision are Out of this World
LISA consists of three spacecraft that are separated by millions of miles and trailing tens of millions of miles, more than one hundred times the distance to the Moon, behind the Earth as we orbit the Sun. These three spacecraft relay laser beams back and forth between the different spacecraft and the signals are combined to search for gravitational wave signatures that come from distortions of spacetime. We need a giant detector bigger than the size of Earth to catch gravitational waves from orbiting black holes millions of times more massive than our sun. NASA is a major collaborator in the European Space Agency (ESA)-led mission, which is scheduled to launch in the early 2030s and we are getting ready for it now!
How does LISA Detect Gravitational Waves?
Gravitational wave events will cause the three LISA spacecraft to shift slightly with respect to each other.
Catching Waves
A bit like the objects moving on the surface of a pond produce ripples and waves, massive objects moving in space distort the fabric of spacetime and produce gravitational waves. Some of these gravitational wave events will cause the three LISA spacecraft to shift slightly with respect to each other, as they "ride the gravitational waves", to produce a characteristic pattern in the combined laser beam signal that depends on the location and physical properties of the source.
LISA is Extremely High Precision
These signals are extremely small and require a very sensitive instrument to detect. For example, LISA aims to measure relative shifts in position that are less than the diameter of a helium nucleus over a distance of a million miles, or in technical terms: a strain of 1 part in 1020 at frequencies of about a millihertz.
The LISA Pathfinder Mission was a proof-of-concept mission to test and prove the technology needed for LISA's success.
What is LISA Pathfinder?
LISA Pathfinder Mission was a proof-of-concept mission for LISA.
LISA Pathfinder Exceeded Expectations
LISA Pathfinder was launched on December 3, 2015 as a proof-of-concept that tests that the noise characteristics of free-floating test masses within the spacecraft are small enough compared to an expected gravitational wave signal. Completing its mission in July, 2017, LISA Pathfinder has shown that the residual noise levels surpassed the original requirements by a factor of ∼100. The LISA Pathfinder mission even outperformed the requirements for the full LISA mission, demonstrating that key technology for LISA is well underway.
This plot shows the primary result from LISA Pathfinder's year and a half of science operations. The plot shows the measured level of imperfection from pure free-fall of the two gold-platinum test masses. The solid and hatched shaded areas show the designed level of performance for LISA Pathfinder and LISA respectively. The blue trace shows the preliminary result from Pathfinder, which was obtained just two months after science operations began. The red trace shows the final result, obtained in February 2017 after the instrument was tuned to improve performance. These measurements demonstrate that the technology developed for Pathfinder can be used as the basis for LISA's detection of gravitational waves.
Credit: ESA/LISA Pathfinder Collaboration.
Related Articles
What is LIGO?
LIGO is a ground-based observatory that first detected gravitational waves.
Opening the Gravitational Wave Window
On September 14, 2015, the Laser Interferometer Gravitational-wave Observatory (LIGO), a ground-based gravitational wave observatory, made history by detecting the first gravitational waves from the merger of two stellar mass black holes. Since then, LIGO and its European counterpart VIRGO, have announced the detection of several additional black hole systems as well as a neutron star merger which also produced light detected by dozens of telescopes on ground and in space. This represents nothing less than the birth of an entirely new field of astronomy.
Ground Based vs Space Based
As LIGO, VIRGO, and other ground-based detectors increase their sensitivity, the number of observed black hole and neutron star merger events will increase, and the signals will be clearer. New kinds of events, such as nearby supernovae, may be detected as well. However, there are some gravitational wave sources that are not detectable by even the most advanced ground-based detectors. Gravitational Waves at very low frequencies have wavelengths larger than the Earth itself. Deploying an antenna large enough to efficiently detect them requires going to space. LISA's three spacecraft will create an equilateral triangle in space and the paths between each pair of spacecraft, referred to as LISA's arms, will extend millions of miles. By measuring distance changes in these arms caused by passing gravitational waves, LISA will be able to measure their amplitude, direction and polarization. Astronomers will use this information to learn about the sources in this previously-unexplored region of the gravitational wave spectrum.
Who's Involved?
Led by ESA, the project is a collaboration of ESA, NASA, and the global scientific community.
The European Space Agency (ESA) is leading the LISA mission. Together with NASA and an international consortium of scientists, the project brings together global expertise in gravitational wave detection.
What is NASA's Role?
NASA supports both ESA and the LISA Consortium as a collaborative partner providing science and engineering expertise, technology development, and interface with the U.S. research community. This includes development of enabling technologies, systems engineering support, prototyping of ground segment and data analysis infrastructure, and research in LISA-related astrophysics.
NASA is directly supporting the development of five key technologies for possible contribution to the ESA-led LISA mission. LISA Telescope and laser systems are being developed at the Goddard Space Flight Center; a phase measurement system and precision micropropulsion system are being developed at the Jet Propulsion Laboratory; and a Charge Management System is being developed by the University of Florida under an award from NASA. The NASA LISA Study Office is coordinating this suite of development activities and managing interfaces with European partners.
How to Get Involved
For Scientists
- NASA LISA Study Team
- LISA Consortium (offsite)
- Gravitational Wave Science Interest Group (GWSIG) (offsite)
- The LISA Data Challenges (offsite)
Education and Outreach Resources
Links to gravitational wave education resources for teachers and students.
- LISA Ambassadors (offsite)
- NASA Space Place (offsite)
- LIGO detection educator's guide [ PDF ]
Citizen Science Projects
- Einstein at Home (offsite)
- Gravity Spy (offsite)