Evolved Laser Interferometer Space Antenna

Evolved Laser Interferometer Space Antenna

Artist's conception of LISA spacecraft
Operator ESA
Mission type astrophysics
Launch date 2034 (proposed)[1][2]
Satellite of Sun
Homepage www.elisascience.org
Orbital elements
Semimajor axis 1 AU
Orbital period 1 year

The Evolved Laser Interferometer Space Antenna (eLISA), previously called the Laser Interferometer Space Antenna (LISA), is a proposed European Space Agency mission designed to detect and accurately measure gravitational waves[3] — tiny ripples in the fabric of space-time — from astronomical sources.[4]

A forerunner mission, LISA Pathfinder, was launched by ESA on 3 December 2015; the Pathfinder will not directly search for gravitational waves but will test several new technologies planned for eLISA.[5][6][7]

eLISA would be the first dedicated space-based gravitational wave detector. It aims to measure gravitational waves directly by using laser interferometry. The LISA concept has a constellation of three spacecraft, arranged in an equilateral triangle with million-kilometre arms (5 million km for classic LISA, 1 million km for eLISA) flying along an Earth-like heliocentric orbit. The distance between the satellites is precisely monitored to detect a passing gravitational wave.[3]

The LISA project was previously a joint effort between the United States space agency NASA and the European Space Agency ESA. However, on April 8, 2011, NASA announced that it would be unable to continue its LISA partnership with the European Space Agency[8] due to funding limitations.[9] ESA has therefore revised the mission's concept to fit into a European-only cost envelope. The scaled down design was initially known as the New Gravitational-wave Observatory (NGO) when proposed for ESA's L1 mission selection.[10] Following this unsuccessful application, the name was changed to eLISA.[11] The project was chosen as the L3 mission within the ESA Cosmic Vision Program, with a tentative launch date in 2034.[2]

A LISA-like mission is designed to directly observe gravitational waves, which are distortions of space-time travelling at the speed of light. Passing gravitational waves alternately squeeze and stretch objects by a tiny amount. Gravitational waves are caused by energetic events in the universe and, unlike any other radiation, can pass unhindered by intervening mass. Launching eLISA will add a new sense to scientists' perception of the universe and enable them to listen to a world that is invisible in normal light.[12][13]

Potential sources for signals are merging massive black holes at the centre of galaxies,[14] massive black holes[15] orbited by small compact objects, known as extreme mass ratio inspirals, binaries of compact stars in our Galaxy,[16] and possibly other sources of cosmological origin, such as the very early phase of the Big Bang,[17] and speculative astrophysical objects like cosmic strings and domain boundaries.[18]

Mission description

LISA spacecrafts orbitography and interferometer -yearly-periodic revolution in heliocentric orbit.

The LISA/eLISA Mission’s primary objective is to detect and measure gravitational waves produced by compact binary systems and mergers of supermassive black holes. LISA/eLISA will observe gravitational waves by measuring differential changes in the length of its arms, as sensed by laser interferometry.[19] Each of the LISA spacecraft contains two telescopes, two lasers and two test masses, arranged in two optical assemblies pointed at the other two spacecraft. This forms Michelson-like interferometers, each centred on one of the spacecraft, with the platinum-gold test masses defining the ends of the arms.[20] The entire arrangement, which is ten times larger than the orbit of the Moon, will be placed in solar orbit at the same distance from the Sun as the Earth, but trailing the Earth by 20 degrees, and with the orbital planes of the three sciencecraft inclined relative to the ecliptic by about 0.33 degree, which results in the plane of the triangular sciencecraft formation being tilted 60 degrees from the plane of the ecliptic.[19] The mean linear distance between the constellation and the Earth will be 50 million kilometers.[21]

To eliminate non-gravitational forces such as light pressure and solar wind on the test masses, each spacecraft is constructed as a zero-drag satellite, and effectively floats around the masses, using capacitive sensing to determine their position relative to the spacecraft, and very precise thrusters to keep itself centered around them.[22]

eLISA detection principle

View of amplified effects of a + polarized gravitational wave (stylized) on eLISA laser beams / arms paths.

Like every modern gravitational wave observatory, eLISA is based on laser interferometry technique. Its three satellites form a giant Michelson interferometer in which two "slave" satellites play the role of reflectors and one "master" satellite the one of source and observer. While a gravitational wave is passing through the interferometer, lengths of the two eLISA arms are varying due to space-time distortions resulting from the wave. Practically, it measures a relative phase shift between one local laser and one distant laser by light interference. Comparison between the observed laser beam frequency (in return beam) and the local laser beam frequency (sent beam) encodes the wave parameters.

LISA Pathfinder

Main article: LISA Pathfinder

An ESA test mission called LISA Pathfinder (LPF) is currently testing LISA/eLISA's key technologies in space.[23] LPF consists of a single spacecraft with one of the LISA/eLISA interferometer arms shortened to about 38 cm (15 in), so that it fits inside a single spacecraft. LPF was launched on December 3, 2015.[24] The spacecraft reached its operational location in heliocentric orbit at the Lagrange point L1 on 22 January 2016, where it underwent payload commissioning.[25] Scientific research started on March 8, 2016 and will last 6 months.[26]

Science

Detector noise curves for LISA and eLISA as a function of frequency. They lie in between the bands for ground-based detectors like Advanced LIGO (aLIGO) and pulsar timing arrays such as the European Pulsar Timing Array (EPTA). The characteristic strain of potential astrophysical sources are also shown. To be detectable the characteristic strain of a signal must be above the noise curve.[27]

Gravitational-wave astronomy seeks to use direct measurements of gravitational waves to study astrophysical systems and to test Einstein's theory of gravity. Indirect evidence of gravitational waves was derived from observations of the decreasing orbital periods of several binary pulsars, such as the Hulse–Taylor binary pulsar.[28] In February 2016, the Advanced LIGO project announced that it had directly detected gravitational waves from a black hole merger.[29][30][31]

Observing gravitational waves requires two things: a strong source of gravitational waves—such as the merger of two black holes—and extremely high detection sensitivity. A LISA-like instrument should be able to measure relative displacements with a resolution of 20 picometers—less than the diameter of a helium atom—over a distance of a million kilometres, yielding a strain sensitivity of better than 1 part in 1020 in the low-frequency band about a millihertz.

A LISA-like detector is sensitive to the low-frequency band of the gravitational-wave spectrum, which contains many astrophysically interesting sources.[32] Such a detector would observe signals from binary stars within our galaxy (the Milky Way);[33][34] signals from binary supermassive black holes in other galaxies;[35] and extreme-mass-ratio inspirals and bursts produced by a stellar-mass compact object orbiting a supermassive black hole.[36][37] There are also more speculative signals such as signals from cosmic strings and primordial gravitational waves generated during cosmological inflation.[38]

Other gravitational-wave experiments

Simplified operation of a gravitational wave observatory
Figure 1: A beamsplitter (green line) splits coherent light (from the white box) into two beams which reflect off the mirrors (cyan oblongs); only one outgoing and reflected beam in each arm is shown, and separated for clarity. The reflected beams recombine and an interference pattern is detected (purple circle).
Figure 2: A gravitational wave passing over the left arm (yellow) changes its length and thus the interference pattern.

Previous searches for gravitational waves in space were conducted for short periods by planetary missions that had other primary science objectives (such as Cassini–Huygens), using microwave Doppler tracking to monitor fluctuations in the Earth-spacecraft distance. By contrast, LISA is a dedicated mission that will use laser interferometry to achieve a much higher sensitivity. Other gravitational wave antennas, such as LIGO, VIRGO, and GEO 600, are already in operation on Earth, but their sensitivity at low frequencies is limited by the largest practical arm lengths, by seismic noise, and by interference from nearby moving masses. Thus, LISA and ground detectors are complementary rather than competitive, much like astronomical observatories in different electromagnetic bands (e.g., ultraviolet and infrared).

History

The first design studies for gravitational wave detector to be flown in space were performed in the 1980s under the name LAGOS (Laser Antena for Gravitational radiation Observation in Space). LISA was first proposed as a mission to ESA in the early 1990s. First as a candidate for the M3-cycle, and later as 'cornerstone mission' for the 'Horizon 2000 plus' program. As the decade progressed, the design was refined to a triangular configuration of three spacecraft with three 5-million kilometer arms. This mission was pitched as a joint mission between ESA and NASA in 1997.[39]

In the 2000s the joint ESA/NASA LISA mission was identified as a candidate for the 'L1' slot in ESA's Cosmic Vision 2015-2025 programme. However, due to budget cuts, NASA announced in early 2011 that it would not be contributing to any of ESA's L-class missions. ESA nonetheless decided to push the program forward, and instructed the L1 candidate missions to present reduced cost versions that could be flown within ESA's budget. A reduced version of LISA was designed with only two 1-million kilometer arms under the name NGO (New/Next Gravitational wave Observatory). Despite NGO being ranked highest in terms of scientific potential, ESA decided to fly Jupiter Icy Moon Explorer (JUICE) as its L1 mission. One of the main concerns was that the LISA Pathfinder mission had been experiencing technical delays, making it uncertain if the technology would be ready for the projected L1 launch date.[39]

Soon afterwards, ESA announced it would be selecting themes for its L2 and L3 mission slots. A theme called "the Gravitational Universe" was formulated with the reduced NGO rechristened eLISA as a straw-man mission.[40] In November 2013, ESA announced that it selected "the Gravitational Universe" for its L3 mission slot (expected launch in 2034).[41]

See also

Wikimedia Commons has media related to Laser Interferometer Space Antenna.

References

  1. ↑ "Selected: The gravitational universe; ESA decides on next large mission concepts". eLISA Consortium. Retrieved 29 November 2013.
  2. 1 2 "ESA's new vision to study the invisible universe". ESA. Retrieved 29 November 2013.
  3. 1 2 "eLISA, The First Gravitational Wave Observatory in Space". eLISA Consortium. Retrieved 12 November 2013.
  4. ↑ "eLISA, Partners and Contacts". eLISA Consortium. Retrieved 12 November 2013.
  5. ↑ "ESA Lisa Pathfinder overview". ESA. 6 June 2013. Retrieved 12 November 2013.
  6. ↑ "eLISA: LPF". eLISA Consortium. Retrieved 12 November 2013.
  7. ↑ "N° 45–2015: VV06 Launch Postponed". ESA press releases. ESA. 1 December 2015. Retrieved 1 December 2015.
  8. ↑ "LISA on the NASA website". NASA. Retrieved 12 November 2013.
  9. ↑ "President's FY12 Budget Request". NASA/US Federal Government. Retrieved 4 Mar 2011.
  10. ↑ Amaro-Seoane, Pau; Aoudia, Sofiane; Babak, Stanislav; Binétruy, Pierre; Berti, Emanuele; Bohé, Alejandro; Caprini, Chiara; Colpi, Monica; Cornish, Neil J; Danzmann, Karsten; Dufaux, Jean-François; Gair, Jonathan; Jennrich, Oliver; Jetzer, Philippe; Klein, Antoine; Lang, Ryan N; Lobo, Alberto; Littenberg, Tyson; McWilliams, Sean T; Nelemans, Gijs; Petiteau, Antoine; Porter, Edward K; Schutz, Bernard F; Sesana, Alberto; Stebbins, Robin; Sumner, Tim; Vallisneri, Michele; Vitale, Stefano; Volonteri, Marta; Ward, Henry (21 June 2012). "Low-frequency gravitational-wave science with eLISA/NGO". Classical and Quantum Gravity 29 (12): 124016. arXiv:1202.0839. Bibcode:2012CQGra..29l4016A. doi:10.1088/0264-9381/29/12/124016.
  11. ↑ Selected: The Gravitational Universe ESA decides on next Large Mission Concepts.
  12. ↑ "eLISA: Science Context 2028". eLISA Consortium. Retrieved 15 November 2013.
  13. ↑ "Gravitational-Wave Detetectors Get Ready to Hunt for the Big Bang". Scientific American. 17 September 2013.
  14. ↑ "eLISA whitepaper, sec. 5.2 p 40, arXiV:1201.3621v1". eLISA consortium. 17 Jan 2012.
  15. ↑ "eLISA whitepaper, sec. 4.3, p. 25, arXiV:1201.3621v1". eLISA consortium. 17 Jan 2012.
  16. ↑ "eLISA whitepaper, sec 3.3, p 11, arXiV:1201.3621v1". eLISA consortium. 17 Jan 2012.
  17. ↑ "eLISA whitepaper, sec 7.2, p 59, arXiV:1201.3621v1". eLISA consortium. 17 Jan 2012.
  18. ↑ "eLISA whitepaper, sec 1.1, p 5, arXiV:1201.3621v1". eLISA consortium. 17 Jan 2012.
  19. 1 2 "eLISA: the mission concept". eLISA Consortium. Retrieved 12 November 2013.
  20. ↑ "eLISA: distance measurement". eLISA Consortium. Retrieved 12 November 2013.
  21. ↑ "eLISA: key features". eLISA Consortium. Retrieved 12 November 2013.
  22. ↑ "eLISA: dragfree operation". eLISA Consortium. Retrieved 12 November 2013.
  23. ↑ "ESA: Lisa Pathfinder overview". European Space Agency. Retrieved 12 November 2013.
  24. ↑ "LISA Pathfinder enroute to gravitational wave demonstration". European Space Agency. Retrieved 3 December 2015.
  25. ↑ "First locks released from LISA Pathfinder's cubes". ESA (ESA Press Release). February 3, 2016. Retrieved 2016-02-12.
  26. ↑ "LISA Pathfinder begins its science mission". Max Planck Institute for Gravitational Physics (eLISA Science.org). March 8, 2016. Retrieved 2016-04-06.
  27. ↑ Moore, Christopher; Cole, Robert; Berry, Christopher (19 July 2013). "Gravitational Wave Detectors and Sources". Retrieved 14 April 2014.
  28. ↑ Stairs, Ingrid H. "Testing General Relativity with Pulsar Timing". Living Reviews in Relativity 6. arXiv:astro-ph/0307536. Bibcode:2003LRR.....6....5S. doi:10.12942/lrr-2003-5.
  29. ↑ Castelvecchi, Davide; Witze, Witze (February 11, 2016). "Einstein's gravitational waves found at last". Nature News. doi:10.1038/nature.2016.19361. Retrieved 2016-02-11.
  30. ↑ B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration) (2016). "Observation of Gravitational Waves from a Binary Black Hole Merger". Physical Review Letters 116 (6). arXiv:1602.03837. Bibcode:2016PhRvL.116f1102A. doi:10.1103/PhysRevLett.116.061102.
  31. ↑ "Gravitational waves detected 100 years after Einstein's prediction | NSF - National Science Foundation". www.nsf.gov. Retrieved 2016-02-11.
  32. ↑ Amaro-Seoane, Pau; Aoudia, Sofiane; Babak, Stanislav; Binétruy, Pierre; Berti, Emanuele; Bohé, Alejandro; Caprini, Chiara; Colpi, Monica; Cornish, Neil J; Danzmann, Karsten; Dufaux, Jean-François; Gair, Jonathan; Jennrich, Oliver; Jetzer, Philippe; Klein, Antoine; Lang, Ryan N; Lobo, Alberto; Littenberg, Tyson; McWilliams, Sean T; Nelemans, Gijs; Petiteau, Antoine; Porter, Edward K; Schutz, Bernard F; Sesana, Alberto; Stebbins, Robin; Sumner, Tim; Vallisneri, Michele; Vitale, Stefano; Volonteri, Marta; Ward, Henry (21 June 2012). "Low-frequency gravitational-wave science with eLISA/NGO". Classical and Quantum Gravity 29 (12): 124016. arXiv:1202.0839. Bibcode:2012CQGra..29l4016A. doi:10.1088/0264-9381/29/12/124016.
  33. ↑ Nelemans, Gijs (7 May 2009). "The Galactic gravitational wave foreground". Classical and Quantum Gravity 26 (9): 094030. arXiv:0901.1778. Bibcode:2009CQGra..26i4030N. doi:10.1088/0264-9381/26/9/094030.
  34. ↑ Stroeer, A; Vecchio, A (7 October 2006). "The LISA verification binaries". Classical and Quantum Gravity 23 (19): S809–S817. arXiv:astro-ph/0605227. Bibcode:2006CQGra..23S.809S. doi:10.1088/0264-9381/23/19/S19.
  35. ↑ Flanagan, Éanna É. "Measuring gravitational waves from binary black hole coalescences. I. Signal to noise for inspiral, merger, and ringdown". Physical Review D 57 (8): 4535–4565. arXiv:gr-qc/9701039. Bibcode:1998PhRvD..57.4535F. doi:10.1103/PhysRevD.57.4535.
  36. ↑ Amaro-Seoane, Pau; Gair, Jonathan R; Freitag, Marc; Miller, M Coleman; Mandel, Ilya; Cutler, Curt J; Babak, Stanislav (7 September 2007). "Intermediate and extreme mass-ratio inspirals—astrophysics, science applications and detection using LISA". Classical and Quantum Gravity 24 (17): R113–R169. arXiv:astro-ph/0703495. Bibcode:2007CQGra..24R.113A. doi:10.1088/0264-9381/24/17/R01.
  37. ↑ Berry, C. P. L.; Gair, J. R. (12 September 2013). "Expectations for extreme-mass-ratio bursts from the Galactic Centre". Monthly Notices of the Royal Astronomical Society 435 (4): 3521–3540. arXiv:1307.7276. Bibcode:2013MNRAS.435.3521B. doi:10.1093/mnras/stt1543.
  38. ↑ Binétruy, Pierre; Bohé, Alejandro; Caprini, Chiara; Dufaux, Jean-François (13 June 2012). "Cosmological backgrounds of gravitational waves and eLISA/NGO: phase transitions, cosmic strings and other sources". Journal of Cosmology and Astroparticle Physics 2012 (06): 027–027. arXiv:1201.0983. Bibcode:2012JCAP...06..027B. doi:10.1088/1475-7516/2012/06/027.
  39. 1 2 and
  40. ↑ Danzmann, Karsten; The eLISA Consortium (2013). "The Gravitational Universe" (PDF). Retrieved 15 April 2014.
  41. ↑ "Selected: The Gravitational Universe ESA decides on next Large Mission Concepts". Max Planck Institute for Gravitational Physics.

External links

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