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An introduction to LISA

The following is a brief guide to introductory materials about LISA physics. If you're just taking up LISA physics, or if you want to catch a glimpse of aspects of LISA physics other than what you're working on yourself, this should be a good place to start. This list, just as the rest of the website, is a community effort - if you know of useful additions, please drop us a line, either using our Contact form or at outreach@lisa-science.org.

The LISA mission

An excellent general introduction LISA physics, from the basic operating principle of LISA as an interferometer to an overview of what we can hope to learn from the mission, is

  • S. L. Larson, "LISA: A modern astrophysical observatory" (2005) [PDF (1.1 MB)]

General information about the LISA mission can be found in the review

  • K. Danzmann and A. RĂ¼diger, "LISA Technology - Concepts, Status, Prospects", Class. Quant. Grav. 20 (2003), S1-S9 [PDF version (200 kB) online courtesy of LIST]

LISA data

Since the armlengths of LISA can differ by few percent, the direct recombination of the two beams at a photo detector will not effectively remove the laser frequency noise. This is because the frequency fluctuations of the laser will be delayed by different amounts within the two unequal length arms. The laser frequency noise is the biggest norse source in the LISA data. In order to cancel the laser frequency noise, the time-varying Doppler data received from the different spacecraft must be recorded and post-processed to allow for arm-length differences. The post processing technique is called time-delay interferometry. More information can be found in these articles:

  • M. Tinto and S. V. Dhurdandhar, "Time-Delay Interferometry", Living Rev. Relativity 8, (2005), 4. URL (cited on June 16, 2006): http://www.livingreviews.org/lrr-2005-4 [also online as 0409034].
  • N. J. Cornish, L. J. Rubbo, "The LISA Response Function", Phys.Rev. D67 (2003) 022001 [online as gr-qc/0209011].

Mock LISA Data Challenges (MLDC)

The Mock LISA Data Challenges are a series of challenges for those engaged in developing methods and tools for LISA data analysis. In each round, data sets modeled after what real LISA data is expected to look like are released; to accept the challenge, you need to find and characterize the one or more gravitational wave signals embedded in the data.

Basic information and data sets can be found on the AstroGravS MLDC web pages.

The MLDC taskforce wiki features the taskforce's working documents and the minutes of MLDC telecons.

See here for MLDC papers and proceedings.

LISA Sources

Here are some informations about the most important gravitational wave sources that LISA will be listening for.

Galactic binaries

The study of galactic binaries by LISA will provide a rich yield of new information on compact binaries including a complete three-dimensional map of the ultra-compact binaries in our and nearby galaxies, and much improved knowledge of the evolutionary pathways of compact binaries. To accomplish this, LISA will aim to detect and characterize over 10 000 individual compact binary systems at frequencies above 1mHz. For lower frequency gravitational waves galactic binaries will create stochastic background which exceeds instrumental noise. If you want to learn more about this aspect of LISA physics, here are some recommended papers:

  • G. Nelemans, "The Galactic Gravitational wave foreground", arXiv:0901.1778 (2009).
  • J. A. Edlund et al., "The White Dwarf -- White Dwarf galactic background in the LISA data", Phys.Rev. D71 (2005) 122003 [online as gr-qc/0504112].
  • S. E. Timpano et al., "Characterizing the Galactic Gravitational Wave Background with LISA", Phys.Rev. D73 (2006) 122001 [online as gr-qc/0504071].
  • N. J. Cornish and S. L. Larson, "LISA data analysis: Source identification and subtraction", Phys.Rev. D67 (2003) 103001 [online as astro-ph/0301548].

Mergers of supermassive black-hole binaries

One of the principal science goals of LISA is the study of the mergers of massive black-hole binaries at high redshift. The aim is to detect all such mergers down to approximately the instrumental noise limit. Post-facto detection of massive black hole binaries in the LISA data should be reasonably straightforward because of the large anticipated signal-to-noise ratio (SNR) for such systems (namely about 1000). An important requirement is the early detection of systems and accurate determination of the parameters, particularly sky position, luminosity distance, and predicted time of merger. To learn more about about detection of, and parameter estimation for supermassive black holes, we recommend that you start with these papers:

  • C. Cutler, "Angular Resolution of the LISA Gravitational Wave Detector", Phys.Rev. D57 (1998) 7089-7102 [online as gr-qc/9703068].
  • A. Vecchio, "LISA observations of rapidly spinning massive black hole binary systems", Phys. Rev. D 70, 042001 (2004) [online as astro-ph/0304051]
  • D. E. Holz and S. A. Hughes, "Using gravitational-wave standard sirens", Ap. J. 629 (2005), 15-22 [online as astro-ph/0504616].

Extreme-mass-ratio inspirals

The detection of the inspirals of compact objects into the supermassive objects at the centers of galaxies (Extreme-mass-ratio inspirals or EMRIs) can provide some of the most exciting scientific payoffs in the LISA mission. From a general-relativistic viewpoint, the waveforms will encode the spacetime geometry induced by the central ob ject, allowing for high-precision measurements of its multipole moments, which could confirm black hole no-hair theorems, or possibly identify the central ob ject as something other than a black hole (e.g., a solitonic star, a boson star, a naked singularity). The waveforms could also be used to measure the response of the central body to the tidal gravity of the orbiting ob ject, again confirming or disproving the predictions of general relativity. From an astrophysical viewpoint, a catalog of detected EMRI events would probe the astrophysics of the dense clusters in galactic nuclei, including the mass demographics of cluster ob jects and the presence of intermediate mass black holes in the nuclei and dense disks around the central object. Here is some literature on EMRIs:

  • Pau Amaro-Seoane et al., "Intermediate and extreme mass-ratio inspirals - astrophysics, science applications and detection using LISA", Class. Quant. Grav. 24 (2007), R113-R170 [online as astro-ph/0703495]
  • J. R. Gair et al., "Event rate estimates for LISA extreme mass ratio capture sources", Class. Quant. Grav. 21 (2004), S1595-S1606 [online as gr-qc/0405137]
  • L. Barack and C. Cutler, "LISA Capture Sources: Approximate Waveforms, Signal-to-Noise Ratios, and Parameter Estimation Accuracy", Phys. Rev. D69 (2004) 082005 [online as gr-qc/0310125]

Cosmology backgrounds and bursts

Another exciting prospect of LISA observations is the detection of gravitational waves from the early universe. Just like the electromagnetic cosmic background radiation, such waves get redshifted as the universe expands. LISA with its superior sensibility at low frequencies will be able to listen much further into the past than ground-based detectors. An introduction to the stochastic gravitational wave background can be found in

  • B. Allen, "The stochastic gravity-wave background: sources and detection", Proceedings of Les Houches School on Astrophysical Sources of Gravitational Waves 1996 [online as gr-qc/9604033]

LISA in the context of astrophysics

LISA is not just about gravitational waves - both the LISA observations and mission plannings have numerous connections to other areas of astrophysics. LISA observations and observations in the electromagnetic spectrum are bound to complement each other. There are important cases in which we should be able to combine, for instance, gravitational wave observations with LISA and X-ray observations of black holes:

  • M. Milosavljevic and E. S. Phinney, "The Afterglow of Massive Black Hole Coalescence", Ap. J. 622 (2005), L93-L96 [online as astro-ph/0410343]

On the other hand, the planning of LISA data analysis relies on results from various areas of astrophysics. For an example, see

  • M. C. Miller et al., "Binary Encounters With Supermassive Black Holes: Zero-Eccentricity LISA Events", Ap. J. 631 (2005), L117-L120 [online as astro-ph/0507133]