Sweeping Milky Way Portrait Captures More Than 3 Billion Stars

A cropped portion of the new Dark Energy Camera Plane Survey (DECaPS2) from NOIRLab still shows thousands upon thousands of celestial objects.
DECaPS2/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA/M. Zamani & D. de Martin (NSF’s NOIRLab)

How many stars can you count when you look up into the clear night sky? Not nearly as many as the Dark Energy Camera in Chile. Scientists released a survey of a portion of our home Milky Way galaxy that contains 3.32 billion celestial objects, including billions of stars. 

The National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab) operates DECam as part of an observatory project in Chile. The new astronomical dataset is the second release from the Dark Energy Camera Plane Survey (DECaPS2). NOIRLab called it “arguably the largest such catalog compiled to date” in a statement on Wednesday.

Casual viewers can enjoy NOIRLab’s smaller-resolution version of the survey that gives a sweeping overview. For those who like to dive into the details, this web viewer lets you go deeper on the data.  

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This wide strip of the Milky Way contains billions of celestial objects as part of the  Dark Energy Camera Plane Survey.

DECaPS2/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA/M. Zamani & D. de Martin (NSF’s NOIRLab)

The camera used optical and near-infrared wavelengths of light to spot stars, star-forming regions and clouds of gas and dust. “Imagine a group photo of over 3 billion people and every single individual is recognizable,” said Debra Fischer of the NSF. “Astronomers will be poring over this detailed portrait of more than 3 billion stars in the Milky Way for decades to come.” 

The survey looks at the Milky Way’s disk, which appears as a bright band running along the image. It’s packed with stars and dust. There’s so much of both it can be hard to pick out what’s happening. Stars overlap. Dust hides stars. It took careful data processing to sort it all out.

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“One of the main reasons for the success of DECaPS2 is that we simply pointed at a region with an extraordinarily high density of stars and were careful about identifying sources that appear nearly on top of each other,” said Harvard University graduate researcher Andrew Saydjari, lead author of a paper on the survey published in The Astrophysical Journal this week.

Several billion stars may sound like a bonkers number, but it’s just a small drop in the galactic bucket. NASA estimates there are at least 100 billion stars in the Milky Way. The new survey covers just 6.5% of the night sky as seen from the Southern Hemisphere. 

DECaPS2 was an epic, multi-year project consisting of 21,400 individual exposures and 10 terabytes of data. NOIRLab’s description of the survey as a “gargantuan astronomical data tapestry” is fitting. We’ve never seen the Milky Way quite like this before. It’s beautiful and it’s humbling.