Astronomers have released a giant view of the Milky Way’s galactic plane. The new dataset contains a whopping 3.32 billion celestial objects – perhaps the largest catalog to date. The data for this unprecedented study was taken with the Dark Energy Camera, built by the US Department of Energy, at the NSF’s Cerro Tololo Inter-American Observatory in Chile, a program of NOIRLab.
The Milky Way galaxy contains hundreds of billions of stars, glittering star-forming regions, and towering dark clouds of dust and gas. Imaging and cataloging these objects for study is a mammoth task, but a recently released astronomical dataset known as the second data release of the Dark Energy Camera Plane Survey (DECaPS2) reveals a staggering number of these objects in unprecedented detail. The DECaPS2 survey, which took two years to complete and produced more than 10 terabytes of data from 21,400 individual exposures, identified approximately 3.32 billion objects – perhaps the largest such catalog compiled to date. Astronomers and the public can explore the dataset here.
This unprecedented collection was captured by the Dark Energy Camera (DECam) instrument on the Víctor M. Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory (CTIO), a program of NSF’s NOIRLab. CTIO is a constellation of international astronomical telescopes atop Cerro Tololo in Chile at an elevation of 2,200 meters (7,200 ft). CTIO’s high vantage point gives astronomers an unparalleled view of the southern hemisphere, allowing DECam to capture the southern galactic plane in such detail.
DECaPS2 is an overview of the plane of the Milky Way as seen from the southern sky, taken at optical and near-infrared wavelengths. The first treasure trove of data from DECaPS was released in 2017, and with the addition of the new data release, the survey now covers 6.5% of the night sky and spans a whopping 130 degrees in longitude. While it may sound modest, this equates to 13,000 times the angular area of the full moon.
The DECaPS2 dataset is available to the entire scientific community and hosted by NOIRLab’s Astro Data Lab, which is part of the Community Science and Data Center. Interactive access to the imaging with pan/zoom in a web browser is available through the Legacy Survey Viewer, the World Wide Telescope and Aladin.
Most of the stars and dust in the Milky Way are in the disk — the bright band that spans this image — in which the spiral arms lie. While this abundance of stars and dust makes for beautiful images, it also makes the galactic plane challenging to observe. The dark wisps of dust snaking through this image absorb starlight and completely obscure fainter stars, and the light from diffuse nebulae interferes with any attempt to measure the brightness of individual objects. Another challenge comes from the sheer number of stars, which can overlap in the image and make it difficult to distinguish individual stars from their neighbors.
Despite the challenges, astronomers delved into the galactic plane to better understand our Milky Way. By observing at near-infrared wavelengths, they were able to peer past much of the light-absorbing dust. The researchers also used an innovative approach to data processing, which allowed them to better predict the background behind each star. This helped to reduce the effects of nebulae and dense starfields on such large astronomical images, making the final catalog of processed data more accurate.
“One of the main reasons for DECaPS2’s success is that we simply pointed to a region with an extraordinarily high density of stars and were careful to identify sources that appear almost on top of each other,” said Andrew Saydjari, a graduate student at Harvard University, researcher at the Center for Astrophysics| Harvard & Smithsonian and lead author of the paper. “This allowed us to produce the largest such catalog ever with a single camera, in terms of the number of objects observed.”
“Combined with images from Pan-STARRS 1, DECaPS2 completes a 360-degree panoramic view of the Milky Way’s disk and also reaches much fainter stars,” said Edward Schlafly, a researcher at the AURA-run Space Telescope Science Institute and a co-author of the paper describing DECaPS2, published in the Astrophysical Journal Supplement. “With this new research, we can map the three-dimensional structure of the stars and dust in the Milky Way in unprecedented detail.”
“Since my work on the Sloan Digital Sky Survey two decades ago, I’ve been looking for a way to get better measurements on top of complex backgrounds,” said Douglas Finkbeiner, a professor at the Center for Astrophysics, co-author of the paper and principal investigator behind the project. “This work accomplished that and more!”
“This is quite a technical feat. Imagine a group shot of over three billion people and every individual is recognizable!” says Debra Fischer, divisional director of Astronomical Sciences at NSF. “Astronomers will be delving into this detailed portrait of more than three billion stars in the Milky Way for decades to come. This is a fantastic example of what federal agency partnerships can achieve.”
DECam was originally built to conduct the Dark Energy Survey, which was conducted between 2013 and 2019 by the Department of Energy and the US National Science Foundation.
- AK Saydjari, EF Schlafly, D. Lang, AM Meisner, GM Green, C. Zucker, I. Zelko, JS Speagle, T. Daylan, A. Lee, F. Valdes, D. Schlegel, DP Finkbeiner. The Dark Energy Camera Plane Survey 2 (DECaPS2): More Sky, Less Bias, and Better Uncertainties” appears in the Astrophysical Journal Supplement. DOI: 10.3847/1538-4365/aca594