Free Astronomy Magazine September-October 2021

46 SEPTEMBER-OCTOBER 2021 ASTRO PUBLISHING ices, and development initiatives to connect and support the scientific missions of NOIRLab’s telescopes, in- cluding the Blanco telescope at CTIO. Since DES studied nearby galaxies as well as those billions of light-years away, its maps provide both a snap- shot of the current large-scale struc- ture of the Universe and a view of how that structure has evolved over the past 7 billion years. Ordinary matter makes up only about 5% of the Universe. Dark energy, which cosmologists hy- pothesize drives the accelerat- ing expansion of the Universe by counteracting the force of gravity, accounts for about 70%. The last 25% is dark mat- ter, whose gravitational influ- ence binds galaxies together. Both dark matter and dark en- ergy remain invisible. DES seeks to illuminate their nature by studying how the competition between them shapes the large-scale structure of the Uni- verse over cosmic time. To quantify the distribution of dark matter and the effect of dark energy, DES relied mainly on two phenomena. First, on large scales galaxies are not dis- tributed randomly throughout space but rather form a weblike structure that is due to the gravity of dark matter. DES measured how this cosmic web has evolved over the history of the Universe. The galaxy cluster- ing that forms the cosmic web in turn revealed regions with a higher density of dark matter. Second, DES detected the signa- ture of dark matter through weak gravitational lensing. As light from a distant galaxy trav- T his image shows an immer- sive view from inside the dome of the Víctor M. Blanco 4- meter Telescope at the Cerro Tololo Inter-American Observa- tory (CTIO), a Program of NSF’s NOIRLab. The Dark Energy Sur- vey photographed the night sky using the 570-megapixel Dark Energy Camera on the Blanco. [DOE/FNAL/DECam/R. Hahn/ CTIO/NOIRLab/NSF/AURA]