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The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre. It is typically rendered graphically as a plot , and the data observed from each side of a spiral galaxy are generally asymmetric, so that data from ...
Spiral galaxies range from S0, the lenticular galaxies, to Sb, which have a bar across the nucleus, to Sc galaxies which have strong spiral arms. In total count, ellipticals amount to 13%, S0 to 22%, Sa, b, c galaxies to 61%, irregulars to 3.5%, and peculiars to 0.9%. At the center of most galaxies is a high concentration of older stars.
Hence, when we observe a distant background galaxy (or some other celestial body), we may be lucky to see the same image of the galaxy multiple times, albeit more and more distorted. [11] A complete mathematical description for how light bends around the equatorial plane of a Kerr black hole was published in 2021. [12]
This illustration shows the oblate appearance of the star Achernar caused by rapid rotation.. Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface.
Modified Newtonian dynamics (MOND) is a theory that proposes a modification of Newton's second law to account for observed properties of galaxies.Its primary motivation is to explain galaxy rotation curves without invoking dark matter, and is one of the most well-known theories of this class.
In astronomy, the rotation period or spin period [1] of a celestial object (e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the sidereal rotation period (or sidereal day ), i.e., the time that the object takes to complete a full rotation around its axis relative to the background stars ( inertial space ).
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The reciprocal of the rotational shear is the lap time, i.e. the time it takes for the equator to do a full lap more than the poles. The relative differential rotation rate is the ratio of the rotational shear to the rotation rate at the equator: α = Δ Ω Ω 0 {\displaystyle \alpha ={\frac {\Delta \Omega }{\Omega _{0}}}}