The Milky Way, the galaxy that surrounds the Earth’s sun, is a spiral galaxy, with a tightly-packed group of stars at its center and other stellar bodies spinning away from it. It was once assumed that the center, also known as a “bulge,” was made up of very old stars. More recently, scientists have learned that the galactic bulge is a rich and complex environment, containing star clusters, infalling objects captured by the Milky Way’s gravity, metal-rich stars, as well as some of the oldest stars in the galaxy. Various factors, like the complex geometry of lines-of-sight toward the inner galaxy, along with extreme crowding and light-obscuring regions of dust and gas, have made this part of the galaxy difficult to study and understand.
The Blanco DECam Bulge Survey (BDBS), a three-year NSF-funded project, alleviates these difficulties by creating images of approximately 200 square degrees of the Milky Way galaxy’s bulge region. To do so, the project uses the Dark Energy Camera (DECam) attached to the Blanco 4m Telescope at the Cerro Tololo Inter-American Observatory in Chile.
Due to the difficulty of studying the bulge, researchers tend to have the most success understanding its formation history through high-quality multi-band imaging that is sensitive to stars’ chemical composition and allows corrections for extinction and reddening along a line-of-sight. Christian Johnson, a graduate of Indiana University (Ph.D., 2010) and a research scientist at the Harvard-Smithsonian Center for Astrophysics, leads the project with Professor R. Michael Rich, Research Astronomer at UCLA. In addition to IU, Harvard, and UCLA, the BDBS project also includes collaborators from the Shanghai Astronomical Observatory, University of Michigan-Dearborn, and Saint Martin’s University.
Johnson notes that the BDBS produces near-ultraviolet, optical, and near-infrared images for roughly 250 million stars in the bulge to accomplish this task. “The near-UV data will permit the first comprehensive investigations of the oldest stars in the bulge and will help find new star clusters and streams of infalling material; the optical and near-IR data will be used to investigate the chemical composition of stars, large scale structures, and age distributions within the inner Galaxy, and combinations of all three sets will allow us to quantify the effects of dust in gas on our observations.”
Dr. Johnson worked with Dr. Michael Young of Indiana University’s Scalable Compute Archive (IU SCA) to process and analyze the thousands of DECam images using Indiana University’s Karst and Carbonate computing clusters and Data Capacitor II shared storage system, extracting and correlating billions of astronomical measurements of the bulge stars. Dr. Young then developed a system to enable researchers to search through this large dataset, including a portal (https://bdbs.sca.iu.edu) and big data processing pipeline. He started with the service stack and codebase of the One Degree Imager - Portal, Pipeline, and Archive (ODI-PPA: https://portal.odi.iu.edu), which he refactored and adapted to the BDBS project’s requirements. Dr. Young then built a pipeline execution environment that takes advantage of the Karst “data intensive” nodes configured in a Hadoop cluster to comb through nearly 250 million rows and 4 billion distinct astronomical measurements when researchers submit a query through the portal’s search interface.
According to Caty Pilachowski, Distinguished Professor and Daniel Kirkwood Chair of the Indiana University Department of Astronomy, “the photometric data from the survey allows astronomers to study the origin, evolution, and structure of the interior of the Galaxy. From the photometric data, we can determine the ages and compositions of the various populations of stars that make up the Bulge, and trace their origins. The survey region also includes more than a dozen globular star clusters, which are fossil relics of early episodes of star formation as the galaxy formed.”