Since gravitational waves are the stretching of spacetime itself, they have the interesting property that the measured displacement between two reference objects scales with the original separation between those objects. In other words, if there is more spacetime to stretch, the total stretch is larger. LISA’s arms are roughly a million times longer than LIGO’s, which means that a gravitational wave of the same amplitude will produce displacements that are roughly a million times larger in LISA. The total displacement is still small, on the order of picometers (one picometer = one trillionth of a meter) but is well within […]
The gravitational waves that LISA is designed to observe have typical timescales of hours. So long as the distance between the satellites is smoothly changing over these time scales, the gravitational waves can be observed as an additional modulation on top of this smooth change. Each satellite is in an independent Keplerian orbit around the Sun with the plane of the triangle inclined at 60 degrees to the plane of the ecliptic. Over the course of the mission, the nominal 2.5 million kilometer distance between each satellite will vary by hundreds of thousands of kilometers. LISA will be able to […]
Gravitational wave science is about much more than just verifying the existence of the waves themselves. Long before LIGO made its first detection in 2015, the consensus amongst most physicists was that gravitational waves were real. The real power of gravitational waves is as a new tool for understanding our Universe. The early results from LIGO have already demonstrated this potential by uncovering what appears to be a new population of heavy black holes as well as determining the origin of heavy elements in the Universe through observations of a neutron star merger that was also observed by a large […]
LISA is an all-sky instrument, with the sensitivity to gravitational waves only weakly depending on the location of the source in the sky. Localization of individual sources comes from two main effects. The first is the motion of the LISA constellation around the Sun, which introduces shifts in both frequency (Doppler effect) and amplitude (sweeping the LISA sensitivity pattern across the sky). These shifts encode information about the sky position of the source in the waveform that LISA observes. Since most LISA sources are observed for months or years, there is sufficient modulation to provide localization. The second effect is […]
At any one moment, LISA will be sensing gravitational waves from millions of individual sources. The vast majority of these will be binary systems of compact objects in the Milky Way, but signals will also be received from extragalactic sources such as the mergers of massive black holes. Each of these signals has a distinct waveform that depends on the astrophysical properties of the source (masses, spins, orientations, positions, etc.). Thanks to extensive work in theory and modeling, we have very good templates for these sources which we can compare to the LISA data and extract individual signals using a […]
Gravitational wave interferometers all operate on the same physical principle that gravitational waves can be observed by measuring the proper distance between freely-falling objects using beams of light. However LISA will operate in a very different regime to ground-based observatories. LISA’s million-kilometer-scale arm lengths are optimized to observe gravitational waves with milliHertz frequencies. These low-frequency gravitational waves don’t influence detector like LIGO very much since they are optimized to detect frequencies in the tens to hundreds of Hertz. In general, LISA will observe systems with larger masses and increased separations in comparison to those observed by LIGO, Virgo, and KAGRA. […]
The Gravitational Universe is a new window in astronomy. Powerful sources of gravitational waves are being used to probe a universe that cannot be explored by other means. Significant advances in astronomy have been made by looking at the Universe using electromagnetic radiation as a probe. But with gravitational waves, we can also study the dark universe, analogous to listening for objects that do not produce light. LISA will enable us to explore the dark universe through gravitational […]
The gravitational waves that LISA will discover include ultra-compact binaries in our Galaxy, supermassive black hole mergers, and extreme mass ratio inspirals, among other possibilities. LISA will be the first to explore gravitational waves in the frequency range of 0.1 milliHertz to 0.1 […]
Since gravitational waves are the stretching of spacetime itself, they have the interesting property that the measured displacement between two reference objects scales with the original separation between those objects. In other words, if there is more spacetime to stretch, the total stretch is larger. LISA’s arms are roughly a million times longer than LIGO’s, which means that a gravitational wave of the same amplitude will produce displacements that are roughly a million times larger in LISA. The total displacement is still small, on the order of picometers (one picometer = one trillionth of a meter) but is well within […]
Key features of LISA are interferometric measurement of distances, million-km long baselines, drag free spacecraft based on inertial sensors, and the familiar “cartwheel”-orbits. Unique are the free-falling test masses inside each spacecraft. The test masses will be undisturbed by forces other than gravitation. A new technology, the so-called “drag-free” operation, allows the spacecraft to follow the test masses, all the while shielding the test masses from spurious […]