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Galaxy rotation curve for the Milky Way – vertical axis is speed of rotation about the galactic center; horizontal axis is distance from the galactic center in kpcs; the sun is marked with a yellow ball; the observed curve of speed of rotation is blue; the predicted curve based upon stellar mass and gas in the Milky Way is red; scatter in ...
The galactic year, also known as a cosmic year, is the duration of time required for the Sun to orbit once around the center of the Milky Way Galaxy. [1] One galactic year is approximately 225 million Earth years. [2]
However, the time it takes for the Sun to go around the Milky Way (a galactic year) may be longer because (in a simple model) it is circulating around a point further from the centre of the galaxy where Ω is smaller (see Sun#Orbit in Milky Way). The values in km s −1 kpc −1 can be converted into milliarcseconds per year by dividing by 4.740.
Attempts to model of galaxy rotation based on a general relativity metric, showing that the rotation curves for the Milky Way, NGC 3031, NGC 3198 and NGC 7331 are consistent with the mass density distributions of the visible matter [44] and other similar work [45] have been disputed. [46]
Most of these fast-moving stars are thought to be produced near the center of the Milky Way, where there is a larger population of these objects than further out. One of the fastest known stars in our Galaxy is the O-class sub-dwarf US 708, which is moving away from the Milky Way with a total velocity of around 1200 km/s.
The nature of the Milky Way's bar, which extends across the Galactic Center, is also actively debated, with estimates for its half-length and orientation spanning between 1–5 kpc (short or a long bar) and 10–50°. [23] [25] [27] Certain authors advocate that the Milky Way features two distinct bars, one nestled within the other. [28]
Astronomers using the Gaia space telescope have located two ancient streams of stars that helped the Milky Way galaxy grow and evolve more than 12 billion years ago.
Figure 1.The observed structure of the Milky Way's spiral arms [1]. The Orion Arm, also known as the Orion–Cygnus Arm, is a minor spiral arm within the Milky Way Galaxy spanning 3,500 light-years (1,100 parsecs) in width and extending roughly 20,000 light-years (6,100 parsecs) in length. [2]