Sunday, April 10, 2022

Speeds in the Universe

Map of the direction of movement of light in microwaves (Image: Reproduction/DMR, COBE, NASA, Four-Year Sky Map)

The colors in the image above are part of a complete map of the sky produced by the COBE satellite (acronym for "Cosmic Background Explorer") in 1993, which shows the direction of motion of microwave radiation. To understand, keep in mind that as the Earth travels around the Sun, our star orbits the center of the Milky Way — and our galaxy, in turn, follows the orbit of the Local Group of Galaxies.

Even together, the speeds of these motions are still quite low relative to the cosmic microwave background (or “CMBR”) composed of radiation between the infrared and radio portions of the electromagnetic spectrum. The CMBR gets its name because it's present everywhere, no matter where you look, and it clearly doesn't come from neighboring stars or galaxies.

In the image, microwave light in the direction of Earth's motion appears blue-shifted, which indicates higher temperature. Microwave light on the opposite side of the sky is redshifted and therefore cooler. In addition to temperatures, the map also indicates that the Local Group moves at a speed of approximately 600 km/s relative to primordial radiation. This high speed was initially met with surprise by astronomers, who don't know why. 

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