Shift towards blue

The shift towards blue or blueshift is the contrary effect of the redshift, occurring when the distance separating a source of light from the observer becomes increasingly weak. The Fréquence of the Rayonnement emitted by the source is then shifted towards blue, contrary to the redshift. The blueshift can also be produced by the gravitational attraction. It is very frequent in the Univers within the Galaxy cluster, in which the redshift does not act.

History

It was in 1912 that the American astronomer Vesto Slipher discovers that the Galaxie of Andromède (then known as Nébuleuse) approaches our Galaxy with 200 km/s. But he will discover thereafter that the majority of the galaxies out of the local Groupe moved away from us. It is the first to raise a manifestation of the blueshift.

Example

Our neighbor the galaxy of Andromède will enter in collision with our own galaxy hundreds of million years under the effect of gravitational attraction, it thus appears to us turned blue overall by her speed of approchement. One estimates his speed at 300 km/s. Donc z = -0.001 for the galaxy of Andromède. But for so low speeds, the blueshift is visible only thanks to the absorption lines.

Applications

In the Universe, the objects can cover Couleur S and very varied Température S. Thus to be able to measure the blueshift/redshift of an object, it is obviously necessary to know its original spectrum. However, the spectra are often more complex. To be able to measure the redshift, the astronomers use fixed reference marks in the spectra, they are the absorption lines. The light emitted by an object partly or is completely absorbed by the element more cold surrounding the object in question. These absorption lines are perfectly everywhere defined in the Universe with wavelengths precise. As we can deduce the elements surrounding the stars, we can identify the difference in position of these lines between the ideal model and the spectrum observed, and thus deduce the shift from it.

Today, one directly uses the blueshift of an object, noted Z, to speak his speed of approach. Z = v/c

In the case of the blueshift, Z is negative.

See too

Internal bond

Bonds external

  • Cosmogony-2

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