Local standard of rest explained

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 .

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). 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]

See also

• Comoving coordinates for an example of another convenient astronomical reference frame.

Notes and References

1. Book: The Physical Universe . Frank H Shu . 261 . registration . 0-935702-05-9 . 1982 . University Science Books.
2. Web site: LOCAL STANDARD OF REST definition and meaning . Collins English Dictionary . November 25, 2023 . November 25, 2023.
3. Book: Galactic Astronomy . James Binney . Michael Merrifield . 536 . 1998 . 0-691-02565-7 . Princeton University Press.
4. Reid, M. . etal . Trigonometric Parallaxes of High Mass Star Forming Regions: The Structure and Kinematics of the Milky Way . 10 March 2014 . The Astrophysical Journal . 10.1088/0004-637X/783/2/130 . 130 (14pp) . 2 . 783 . 2014ApJ...783..130R . 1401.5377. 119186799 .
5. Book: https://books.google.com/books?id=bP9hZqoIfhMC&pg=PA19 . Mapping the Galaxy and Nearby Galaxies . F. Combes . Keiichi Wada . 2008 . Springer . 978-0-387-72767-7 . Mark Reid . etal . Mapping the Milky Way and the Local Group . 19–20.
6. The Sun's peculiar motion relative to the LSR is 13.4 km/s. See, for example, Book: Binney, J. . Merrifield, M. . amp . op. cit. . 0-691-02565-7 . §10.6. 6 September 1998 . Princeton University Press . or On the distance to the Ophiuchus star-forming region . Astron. Nachr. . AN 329 . 10.1002/asna.200710827 . 0709.0505 . 2008 . 12; §2.3 . E.E. Mamajek. 1 . 2008AN....329...10M . 14027548 .
7. Precision Astrometry, Galactic Mergers, Halo Substructure and Local Dark Matter . Steven R. Majewski1 . Proceedings of IAU Symposium 248 . 0801.4927 . 2008. 2008IAUS..248..450M . 10.1017/S1743921308019790 . 3 . 450–457 . 18252986 .
8. Reid, M. . etal . Trigonometric Parallaxes of High Mass Star Forming Regions. VI. Galactic Structure, Fundamental Parameters, and Noncircular Motions . 20 July 2009 . The Astrophysical Journal . 10.1088/0004-637X/700/1/137 . 137–148 . 1 . 700 . 2009ApJ...700..137R . 0902.3913. 11347166 .
9. Dehnen, W. . Binney, J.J. . Local stellar kinematics from HIPPARCOS data . October 1998 . . 10.1046/j.1365-8711.1998.01600.x . 387–394. 2 . 298 . free . 1998MNRAS.298..387D . astro-ph/9710077. 15936627 .
10. Bovy, J. . etal . The Milky Way's Circular-velocity Curve between 4 and 14 kpc from APOGEE data . 10 November 2012 . The Astrophysical Journal . 10.1088/0004-637X/759/2/131 . 131 (20pp) . 2 . 759 . 2012ApJ...759..131B . 1209.0759. 119279938 .