(DECaPS2/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA/E. Slawik Image processing: M. Zamani & D. de Martin (NSF’s NOIRLab)) | SkyNews
Close-up view of survey section. (DECaPS2/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA/E. Slawik) Image processing: M. Zamani & D. de Martin (NSF’s NOIRLab)

Why the Milky Way survey matters

Observing the galactic plane is the best way for astronomers to understand the Milky Way.

A survey of the Milky Way Galaxy has produced an astronomical tapestry of 3.32 billion celestial objects. The result of the Dark Energy Camera Plane Survey, or DECaPS2, could help astronomers create three-dimensional models of our own galaxy. The data will also contribute to research work for decades, especially as more surveys are completed.

“It’s very striking. The level of resolution you see in those pictures makes it very hard to imagine distinguishing each solar object in those pictures,” said Ioana Zelko, an astrophysicist at the University of Toronto’s Canadian Institute of Theoretical Astrophysics (CITA), in an interview with SkyNews.

“It’s almost as if you can’t even tell when I look at the picture, if it’s a painting or a rendering of something. But no, that’s an actual measurement. Those objects are actually there.”

The Milky Way. | SkyNews
The Milky Way. (DECaPS2/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA. Image processing: M. Zamani & D. de Martin (NSF’s NOIRLab)

Zelko is one of three Canadians who participated in the international project. She was joined by Joshua Speagle, an assistant professor of astrostatistics at the University of Toronto, Ontario; and Dustin Lang of the Perimeter Institute for Theoretical Physics and the University of Waterloo — also in Ontario. 

The three scientists were part of an international team of astronomers in the United States and Germany. Together, they took two years to complete the survey. The data was collected by the Dark Energy Camera at the NSF’s Cerro Tololo Inter-American Observatory in Chile.

Zelko spent eight nights with the telescope, one of the longest runs that was part of the survey.

“When these pictures come back they are separated in wavelengths. As an observer you get a black and white picture for each wavelength, but you can tell there are objects there,” she said. “There are also galaxies you can see through the stars and towards the galactic plane, and that’s unbelievable.”

DECaPS2 is the ultimate long exposure photograph. It builds from an earlier dataset, called DECaPS, that was released in 2017. The combined datasets covers 6.5 per cent of the night sky. 

The project is made up of 21,400 individual exposures taking up more than 10 terabytes of data. The optical and near-infrared survey of the Milky Way spans 130-degrees in length, or 13,000 times the angular area of the full Moon. NOIRLab states it is the largest dataset of its kind ever collected.

Observing the galactic plane is the best way for astronomers to understand the Milky Way, and this region of space at near-infrared wavelengths cuts through much of the light-absorbing dust. 

New "pinprick" dataset of the MilkyWay. | SkyNews
New “pinprick” dataset of the MilkyWay. (DECaPS2/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA.) Image processing: M. Zamani & D. de Martin (NSF’s NOIRLab)

The image is also important for understanding our own galaxy and will provide decades of research for astronomers. In the short-term, it will help researchers model the three-dimensional structure of the Milky Way’s stars and dust in unprecedented detail.

“A dataset like this gives us a huge amount of data that we would want to use to model things like stars, global dust structures, spiral arms and everything else,” said Speagle. “It’s the starting point for all the types of things we want to do to construct 3D maps of our own galaxy. We have a hard time doing that because we’re stuck inside it.”

Sorting through the data collected was a lengthy challenge. Most stars and dust in the Milky Way are at its disk where the spiral arms lie. The dark tendrils of dust and light from diffuse nebulae makes observing the galactic plane hard to observe for astronomers. The number of stars can also overlap in images, making it difficult to distinguish individual stars from their neighbours.

The effects of nebulae and crowded star clusters was mitigated, thanks to advancements in algorithms and data processing. Astronomers used this approach to predict the backgrounds behind each star, making the final processed data more accurate.

“When things are this crowded and there’s so many stars that are close together, it’s like if you try and do image recognition on people in a crowd,” said Speagle. “It’s very different than when you do it in a small setting. There’s just so many more people, you have to figure out what they’re doing.”

There are similar datasets that are being planned or are underway that will look at larger pieces of the night sky. The Legacy Survey of Space and Time (LSST) at the Vera C. Rubin Observatory in Chile will collect more data than DECaPS2. The goal is to collect more data on our own galaxy, other galaxies and on how galaxies change over time.

“This is going to be a survey that’s going to be on the same size and scope of DECaPS2. It’s going to have a huge team and is going to be incredibly exciting to be involved with,” said Speagle. “The legacy value of these surveys and collecting lots of data is having people make really exciting, unplanned discoveries. As we collect better data and more data, I think that’s just going to keep growing.”