Local standard of rest
Astronomical reference frame defined by motion of near-Sun stars around Galactic Centre / From Wikipedia, the free encyclopedia
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]
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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]