Local standard of rest

In astronomy, the local standard of rest or LSR is a reference frame which 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] on average sharing the same velocity around the Milky Way as the Sun.[2] The path of this material is not precisely circular.[3] 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[4] about the center of the galaxy near Sgr A*, and has only a slight motion, towards the solar apex, relative to the LSR.[5][6]

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.[7] 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).[4] There is significant correlation between the circular motion of the solar circle, the solar peculiar motion, and the predicted counterrotation of star-forming regions.[8] Additionally, local estimates of the velocity of the LSR based on stars in the vicinity of the Sun[9] may potentially yield different results than global estimates derived from motions relative to the Galactic Center.[10]

  1. ^ Frank H Shu (1982). The Physical Universe. University Science Books. p. 261. ISBN 0-935702-05-9.
  2. ^ "LOCAL STANDARD OF REST definition and meaning". Collins English Dictionary. November 25, 2023. Retrieved November 25, 2023.
  3. ^ James Binney; Michael Merrifield (1998). Galactic Astronomy. Princeton University Press. p. 536. ISBN 0-691-02565-7.
  4. ^ a b 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.
  5. ^ 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.
  6. ^ 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.
  7. ^ 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.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  8. ^ 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.
  9. ^ 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.
  10. ^ 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.