Mysteries of the Milky Way Are Revealed in Spectacular Detail

This color-composite shows a main part of the new Blanco DECam Bulge Survey of 250 million stars in our galaxy’s bulge. The 4 x 2 degrees excerpt can be explored in all its whopping 50,000 x 25,000 pixels in the zoomable version. In the image interstellar dust and gas seemingly acts like a red “filter” in front of the background stars, scattering the blue light away. Since we are surrounded by dust and gas in the Milky Way, this scattering effect is important to many parts of astronomy and is known as interstellar reddening.
Credit: CTIO/NOIRLab/DOE/NSF/AURA, Acknowledgment: Image processing: W. Clarkson (UM-Dearborn), C. Johnson (STScI), and M. Rich (UCLA), Travis Rector (University of Alaska Anchorage), Mahdi Zamani & Davide de Martin.

Astronomers are Bulging with Data

Star-studded image shows the glittering central parts of the Milky Way

For the first time, over 250 million stars in our galaxy’s bulge have been surveyed in near-ultraviolet, optical, and near-infrared light, opening the door for astronomers to reexamine key questions about the Milky Way’s formation and history. Using ultraviolet data, and with 450,000 individual images, the team was able to measure the chemical composition of tens of thousands of stars spanning a large area of the bulge. The vast dataset can be explored in spectacular detail in this image.

The mysteries of the Milky Way are revealed in spectacular detail, thanks to the efforts of a team of astronomers who have observed 250 million stars in the bulge at the heart of the Milky Way using the Dark Energy Camera (DECam). DECam, primarily funded by the U.S. Department of Energy, is mounted on the Víctor M.Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile, a program of NSF’s NOIRLab. By detecting the ultraviolet light from stars in the bulge known as Red Clump stars, they were able to analyze the chemical composition of over 70,000 stars over an area of sky 1,000 times as large as the full Moon (an area larger than 20 x 10 degrees stretching over the constellations Sagittarius and Scorpius).

The data are hosted and served to the community by NOIRLab’s Community Science and Data Center (CSDC), also a program of NSF’s NOIRLab, which handled the more than 7,000 DECam exposures, comprising more than 3.5 trillion pixels. A color-composite showing a main part of these data is shown in this image, and can be explored in all its whopping 50,000 x 25,000 pixels in this zoomable version.

The newly published study has shown that the stars near the very center of the Milky Way have a very similar composition, which suggests that they formed at around the same time. Normally composition is measured with a spectrograph, targeting a relatively small number of stars at a time (although the revolutionary DESI instrument at Kitt Peak National Observatory, a program of NSF’s NOIRLab, will soon be able to do thousands). However, the Blanco DECam Bulge Survey took a different approach and instead precisely measured the stars’ brightness differences from ultraviolet to infrared wavelengths. These differences in brightness at different wavelengths are called photometric colors by astronomers, and can reveal the composition of stars when the dataset is calibrated with stars measured spectroscopically.

The team used DECam’s three square degree field of view to take over 450,000 individual images, before focusing on the subsample of 70,000 stars, which is substantially larger than previous spectroscopic bulge surveys. Future work with the full DECam data set will yield millions of composition measurements, a sample size more than 200 times that of even the largest spectroscopic surveys.

Kathy Vivas, co-author and NOIRLab astronomer said, “This is exactly the strength of the Dark Energy Camera — to undertake these kinds of studies. While it was originally aimed at the study of the distant Universe to measure its expansion, DECam has proven to be a powerful instrument to study our Milky Way as well.”

MORE of the story and 4 more associated images plus another VIDEO / click image