![]() It is heading toward us and will merge with the Milky Way in about 4 billion years. Most of these are Local Group dwarf galaxies however, the Andromeda Galaxy (M31) has a blueshift of about 186 miles per second (300 km/s). Something like 100 nearby galaxies have blueshifts. In the nearby universe, light travel times and cosmological redshifts are relatively small, so sometimes the peculiar motion “wins” and we observe some galaxies with blueshifts. When we measure the redshift or blueshift of light from distant galaxies, it is the sum of the cosmological redshift and the Doppler shift (either red or blue) from their peculiar motion relative to us. For example, our own galaxy is known to be moving through the universe with a velocity of 1.3 million mph (600km/s). Galaxies are large, and the distances between them are large so they have what sound like very large velocities - generally a few hundreds of kilometers per second. These motions cause additional redshifts or blueshifts in the light from the galaxies (red if they are moving away from us, and blue if they are moving toward us). We also find that groups of galaxies on scales of millions of light-years across move together in bulk flows toward the most massive clusters and superclusters. Meanwhile, galaxies in clusters are orbiting the center of mass of their cluster. Gravity causes smaller galaxies to move toward larger ones. ![]() Gravity works on all scales, and it is always attractive. However, galaxies are also moving around in the universe. The farther away a galaxy is, the more time its light has to travel to reach us, and so the redder its light becomes. The universe is expanding, and this “cosmological redshift” causes the light from distant galaxies to be stretched (made redder) during the time it travels from the galaxy to our telescopes. In fact, almost all galaxies are observed to have redshifts. The simple answer to this is no, they do not.
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