New Method For Tracing Dark Matter Reveals Its Location, Abundance As Never Before
“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.”
If you want to know where the dark matter is located in the Universe, you had to infer its presence and abundance by measuring the gravitational effects it had on space. When it comes to large-scale structures, like galaxy clusters, this often involved exceedingly difficult reconstructions involving gravitational lensing, and relied on serendipitous alignments of observable background structures. But a new study has concocted an alternative method that works extremely well: just measure the intracluster light from stars that have been ejected from the component galaxies.