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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]
The disk of stars in the Milky Way does not have a sharp edge beyond which there are no stars. Rather, the concentration of stars decreases with distance from the center of the Milky Way. Beyond a radius of roughly 40,000 light years (13 kpc) from the center, the number of stars per cubic parsec drops much faster with radius. [120]
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]
across the Milky Way: 100 000 years: from the Andromeda Galaxy to Earth: 2.5 million years: ... Does Gravity Travel at the Speed of Light? in The Physics FAQ (also here).
Citizen scientists spotted an object zipping through the Milky Way at more than 1 million miles an hour, and a new study shows it could be a rare hypervelocity star.
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]
Intergalactic travel is the hypothetical travel between galaxies. Because the Milky Way and its closest neighbors are separated by millions of light-years, any such venture would also require millions of years based on our current understanding of physics. Thus, intergalactic travel is impossible within the human lifetime.
Escape speed at a distance d from the center of a spherically symmetric primary body (such as a star or a planet) with mass M is given by the formula [2] [3] = = where: G is the universal gravitational constant (G ≈ 6.67 × 10 −11 m 3 ⋅kg −1 ⋅s −2 [4])