Local standard of rest

In astronomy, the local standard of rest or LSR follows the mean motion of material in the Milky Way in the neighborhood of the Sun (stars in radius 100 pc from the Sun).[1] The path of this material is not precisely circular.[2] The Sun follows the solar circle (eccentricity e < 0.1) at a speed of about 255 km/s in a clockwise direction when viewed from the galactic north pole at a radius of ≈ 8.34 kpc[3] about the center of the galaxy near Sgr A*, and has only a slight motion, towards the solar apex, relative to the LSR.[4][5]

LSR could be understood by analogy to a group of cars traveling at similar speed on a highway i.e. at LSR. If a faster car passes by or they pass a slower car then the faster and slower cars could be considered at not traveling at LSR. Typically a large variation of speed in astronomical bodies could be considered as indicator of their extraterrestrial nature. This analogy was used by theoretical physicist Avi Loeb in his 2021 book Extraterrestrial: The First Sign of Intelligent Life Beyond Earth.

The LSR velocity is anywhere from 202–241 km/s.[6] In 2014, very-long-baseline interferometry observations of maser emission in high-mass star-forming regions (HMSFR) placed tight constraints on combinations of kinematic parameters such as the circular orbit speed of the Sun (Θ0 + V☉ = 255.2 ± 5.1 km/s).[3] There is significant correlation between the circular motion of the solar circle, the solar peculiar motion, and the predicted counterrotation of star-forming regions.[7] Additionally, local estimates of the velocity of the LSR based on stars in the vicinity of the Sun[8] may potentially yield different results than global estimates derived from motions relative to the Galactic Center.[9]

See also

References
  1. Frank H Shu (1982). The Physical Universe. University Science Books. p. 261. ISBN 0-935702-05-9.
  2. James Binney; Michael Merrifield (1998). Galactic Astronomy. Princeton University Press. p. 536. ISBN 0-691-02565-7.
  3. Reid, M.; et al. (10 March 2014). "Trigonometric Parallaxes of High Mass Star Forming Regions: The Structure and Kinematics of the Milky Way". The Astrophysical Journal. 783 (2): 130 (14pp). arXiv:1401.5377. Bibcode:2014ApJ...783..130R. doi:10.1088/0004-637X/783/2/130. S2CID 119186799.
  4. Mark Reid; et al. (2008). "Mapping the Milky Way and the Local Group". In F. Combes; Keiichi Wada (eds.). Mapping the Galaxy and Nearby Galaxies. Springer. pp. 19–20. ISBN 978-0-387-72767-7.
  5. The Sun's peculiar motion relative to the LSR is 13.4 km/s. See, for example, Binney, J. & Merrifield, M. (6 September 1998). "§10.6". op. cit. Princeton University Press. ISBN 0-691-02565-7. or E.E. Mamajek (2008). "On the distance to the Ophiuchus star-forming region". Astron. Nachr. AN 329 (1): 12; §2.3. arXiv:0709.0505. Bibcode:2008AN....329...10M. doi:10.1002/asna.200710827. S2CID 14027548.
  6. Steven R. Majewski1 (2008). "Precision Astrometry, Galactic Mergers, Halo Substructure and Local Dark Matter". Proceedings of IAU Symposium 248. 3: 450–457. arXiv:0801.4927. Bibcode:2008IAUS..248..450M. doi:10.1017/S1743921308019790. S2CID 18252986.
  7. Reid, M.; et al. (20 July 2009). "Trigonometric Parallaxes of High Mass Star Forming Regions. VI. Galactic Structure, Fundamental Parameters, and Noncircular Motions". The Astrophysical Journal. 700 (1): 137–148. arXiv:0902.3913. Bibcode:2009ApJ...700..137R. doi:10.1088/0004-637X/700/1/137. S2CID 11347166.
  8. Dehnen, W.; Binney, J.J. (October 1998). "Local stellar kinematics from HIPPARCOS data". Monthly Notices of the Royal Astronomical Society. 298 (2): 387–394. arXiv:astro-ph/9710077. Bibcode:1998MNRAS.298..387D. doi:10.1046/j.1365-8711.1998.01600.x. S2CID 15936627.
  9. Bovy, J.; et al. (10 November 2012). "The Milky Way's Circular-velocity Curve between 4 and 14 kpc from APOGEE data". The Astrophysical Journal. 759 (2): 131 (20pp). arXiv:1209.0759. Bibcode:2012ApJ...759..131B. doi:10.1088/0004-637X/759/2/131. S2CID 119279938.
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