Using the NASA / ESA Hubble Space Telescope, a team of astronomers has discovered that the brightest galaxies within galaxy clusters “wobble” relative to the cluster’s center of mass. This unexpected result is inconsistent with the predictions made by the current standard model of dark matter. Does it indicate the presence of a new physics?
Dark matter makes up about 27% of all matter and energy in the universe, but it cannot be observed directly, making it one of the greatest mysteries in modern astronomy. The invisible halos of elusive dark matter enclose galaxies and galaxy clusters alike. Clusters are massive groupings of up to 1,000 galaxies immersed in hot intergalactic gas, whose clusters have very dense nuclei, each containing a massive galaxy called “the brightest galaxy.”
Current dark matter models predict that galaxy clusters have very dense nuclei, and those nuclei contain a very massive galaxy that never moves from the center of the cluster, but is held in place by the enormous gravitational influence of matter. dark.
However, the international team made up of Swiss, French and English astronomers has analyzed 10 clusters of galaxies observed with Hubble, discovering that these galaxies were not in a fixed position in the center as expected and that their density is much lower than expected. predicted: the galaxy in the center is actually moving.
The researchers compared their observations with the predictions of the BAHAMAS series of cosmological hydrodynamic simulations and found that they did not match. According to the Standard Model of dark matter (called “cold dark matter”), this wobble does not exist because the sheer density of dark matter holds it firmly attached to the center of the galaxy cluster. Therefore, this clear mismatch suggests the existence of still unknown physics.
These galaxy clusters also act as huge gravitational lenses that warp spacetime enough to distort the light that passes through them. Hence, we can use them to make a map of dark matter, determine where the center is, and then observe how the brightest galaxy wobbles or oscillates around this center.
“We found that they ‘spilled over’ at the bottom of the halos. This indicates that instead of a dense region in the center of the galaxy cluster, there is a much shallower central density – a surprising signal from exotic forms of dark matter. right in the heart of galaxy clusters “, explains David Harvey, co-author of the work published in the magazine Monthly Notices of the Royal Astronomical Society.
The wobble also shows that these galaxies cannot exactly match the cluster’s halo, which means that certain models of galaxy clusters must also be modified.
The scientists will expand their research with larger studies of galaxy clusters and hope this will allow them to confirm their findings:
“We look forward to broader surveys, such as the Euclid survey, that will expand our data set. Then we can determine whether the wobbling of these galaxies is the result of a new astrophysical phenomenon or a new fundamental physics. Both would be exciting!” says Frederic Courbin, co – author of the study.
Referencia: David Harvey et al. A detection of wobbling brightest cluster galaxies within massive galaxy clusters, Monthly Notices of the Royal Astronomical Society (2017). DOI: 10.1093/mnras/stx2084
Image credit: NASA
