Consequently, tey are said to belong to different stellar population. Te mass of a star also translates to its life span; teir weight is usually measured in terms of solar mass. Te lighter the solar mass the longer the stars life span. Te Milky Way is just one galaxy in a collection of a group of galaxies called the Local group. Te Milky Way moves at 300 km/sec in the direction of the constellation Virgo. Te Milky Way is in constant movement with the other galaxies in the Te galaxies found within the local group include the Milky Way Galaxy, te Andromeda Galaxy, Tiangulum Galaxy and others, ech containing their satellite system.
Te stars and the gasses of the Milky Way rotate about its center differently meaning that there is a variation in the period of rotation depending on location. Hwever, te orbital speed of the stars in a spiral galaxy is not entirely dependent on the distance from the center. Te typical stellar orbital velocity of a star away from the central bulge is between 210 km/s.
Hnce, w can deduce that the orbital period of a typical star in the Milky Way is directly corresponds to the distance it travels. Te other fact is that, twards the center of the Milky Way, te orbital speeds are too low but as one goes further away, te orbital speeds increase. I reaches the point that it defies the universal law of gravity. Tere are many models that try to explain the formation of the Milky Way, bt we will put our focus on one particular that popularly accepted.
Te ELS model was conceived in the early 1960’s by three astronomers, nmely Donald Lynden-Bell, Alan Sandage and Olin Eggen. Tis model was based on the relative velocities and chemical compositions of stars in population I (metal-rich) and II (metal-poor). Te population I stars follow orbits in the plane of the galactic disk whereas the population II stars found in the halo follow elliptical orbits that cut across the plane of the Milky Way. Acording to the ELS, te Milky Way began as a spherical of gas was collapsing towards the center.
Te original gas had minimal levels of metal, ad this consequently resulted in the stars being formed having low levels of metal. Tese stars that were formed maintained the kinematic properties of the gas from the collapsing cloud, tus making them follow eccentric orbits around the central part of the galaxy. Cnsequently, tis led to the formation of population. ..
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