When stars get ejected from galaxies within massive clusters, they go where the dark matter is.
Dark matter is one of the greatest mysteries in the Universe, displaying its effects in every massive, large-scale cosmic structure.
It neither emits nor absorbs light like normal matter does, but its gravitational impact is undeniable.
Forming large halos around individual galaxies, it hold galaxy clusters and the great cosmic web together.
By measuring the distorted light from distant galaxies behind a galaxy cluster, scientists can reconstruct the total cluster mass.
In every galaxy cluster, the majority of the mass is outside of the galaxies: there is a huge dark matter halo.
The intracluster gas, however, may be distributed differently, as normal matter can collide and heat up, emitting X-rays.
But individual stars, ejected from galaxies, should trace the same path as the dark matter.
In a cosmic first, scientists measured this intracluster light, and found it traces out the dark matter perfectly.
Their locations are identical because both “are free-floating on the gravitational potential of the cluster itself,” elucidates co-author Mireia Montes.
Because both the stars and the dark matter follow the same gravitational paths, this diffuse starlight matches the reconstructed cluster lensing profiles.
This is the fastest, most accurate visual signature ever used to successfully identify dark matter.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.