It's a cosmic irony: the biggest things in the universe can also be the hardest to find.
Elizabeth Blanton, a Boston University associate professor of astronomy, started hunting for distant galaxy clusters more than 20 years ago. A single galaxy cluster can be as massive as a quadrillion suns, yet faraway clusters are so faint that they are practically invisible to all but the biggest Earth-bound telescopes. Distant clusters hold pieces of the story of how the web-like structure of the universe first emerged and could help illuminate the true nature of dark energy and dark matter. Now, her team's search is delivering its biggest return yet: a catalog of about 200 candidate galaxy clusters which, if confirmed, may include some of the most distant clusters ever found. The new results, which will be a useful tool for astronomers worldwide, were published in the July 26, 2017, edition of the Astrophysical Journal by a team that includes Rachel Paterno-Mahler (GRS'15), PhD candidate Emmet Golden-Marx (GRS'16,'19), Gagandeep Anand (GRS'17), Joshua Wing (GRS'07,'13), and colleagues at the University of Missouri-Kansas City and the Harvard-Smithsonian Center for Astrophysics.
Galaxy clusters can contain thousands of galaxies and many trillions of stars—and that's just what astronomers can see with ordinary telescopes. Hot gas between the galaxies glows with X-rays, and astronomers suspect that more than 85 percent of every cluster's mass is hidden in the form of dark matter. Mapped in three dimensions, the universe is a web of bright filaments and dark voids, with galaxy clusters occupying the spots where the filaments intersect.
Woven into this cosmic web are clues to two major cosmic mysteries: dark matter, the invisible stuff that permeates galaxies and the spaces between them, and dark energy, which is driving the accelerating expansion of the universe. Together, dark matter and dark energy make up some 95 percent of our universe, scientists suspect, but astrophysicists know of dark matter and dark energy's existence only indirectly, by their influence on the stars and galaxies that light up the sky.
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