Carnegie Science | Spring 2019 7 Studying the supernovae using the near-infrared light was crucial to this finding. The light from these explosions travels through cosmic dust to reach our telescopes, and interstellar particles obscure light on the blue end of the spectrum more than they do on the red end of the spectrum, like smoke from a forest fire making everything appear redder. This can trick astronomers into thinking that a supernova is farther away than it is. Observing in the infrared allows them to penetrate this dust. “One of the Carnegie Supernova Project’s primary goals has been to provide a reliable, high-quality sample of supernovae and dependable methods for inferring their distances,” said lead author Burns. “The quality of this data allows us to better correct our measurements to account for the dimming effect of cosmic dust,” added Phillips, a coauthor. The calibration of these mile markers is important, because there are disagreements between different methods for determining the universe’s expansion rate. The Hubble Constant can independently be estimated using the glow of background radiation left over from the Big Bang. This cosmic microwave background radiation has been measured with exquisite detail by the Planck satellite, and it gives astronomers a more slowly expanding universe than when measured using Type la supernovae. “This discrepancy could herald new physics, but only if it’s real,” Burns explained. “So, we need our Type la supernova measurements to be as accurate as possible, but also to identify and quantify all sources of error.”  This artwork shows two white dwarf stars, which will slowly move closer. The eventual explosion is a Type Ia supernova. Image courtesy ESO/L. Calçada COAUTHORS AND SUPPORT: Other Carnegie coauthors on the paper include Carlos Contreras, Jorge Anais, Luis Boldt, Luis Busta, Abdo Campillay, Sergio Castellon, Gaston Folatelli, Barry Madore, Consuelo Gonzalez, Wojtek Krzeminski, Nidia Morrell, Eric Persson, Miguel Roth, Francisco Salgado, Jacqueline Serón, and Simon Torres. The other coauthors are Emilie Parent of McGill University, Maximilian Stritzinger of Arhus University, Kevin Krisciunas and Nicholas B. Suntzeff of Texas A&M University, Wendy Freedman of the University of Chicago, Eric Y. Hsiao and Peter Hoeflich of Florida State University, and Mario Hamuy of Universidad de Chile. The U.S. National Science Foundation supports the Carnegie Supernova Project. Computing resources for this work were made possible by the Ahmanson Foundation. The Cynthia and George Mitchell Foundation and Sheridan Lorenz supported several CSP workshops. The Carnegie Supernova Project group poses for a picture at one of their meetings. Lead author Chris Burns is second from left in the first row. Mark Phillips is first in that row. Image courtesy Mark Phillips Carnegie Science | Spring 2019 7