Finding “Missing” Matter: New Light on Baryonic Matter and Gravity on Cosmic Scales

The presence of ionized gas around galaxies with moves with them leaves a trace in the microwave background radiation (left panel) which can be detected knowing the pattern of velocities of the galaxies provided by the map of fluctuations in their redshift (right panel).
Credit: Carlos Hernández-Monteagudo (IAC)

Scientists estimate that dark matter and dark energy together are some 95% of the gravitational material in the universe while the remaining 5% is baryonic matter, which is the “normal” matter composing stars, planets, and living beings. However, for decades almost one half of this matter has not been found either.

Now, using a new technique, a team in which the Instituto de Astrofísica de Canarias (IAC) has participated, has shown that this “missing” baryonic matter is found filling the space between the galaxies as hot, low density gas. The same technique also gives a new tool that shows that the gravitational attraction experienced by galaxies is compatible with the theory of General Relativity. This research is published in three articles in the journal Monthly Notices of the Royal Astronomical Society (MNRAS).

In designing this new technique they have analyzed the changes in the electromagnetic spectrum, its shift to the red, caused by the reddening of the light from the galaxies as they speed away from us. In the Universe, the sources which move away show a redder spectrum, and those which approach us show a bluer spectrum. This effect has given essential data for the development of modern cosmology.

Almost a century ago, Edwin Hubble discovered that the redshifts of galaxies are bigger the further away from us they are, and this was the initial evidence that eventually led to the Big Bang model of the universe. Since then these redshifts have been used to find the distances to the galaxies and to build three dimensional maps of their distribution in the Universe.

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