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2.8 Million Stars Sparkle in This Incredible Image of the Milky Way

The Gaia star surveyor captured a densely packed area near the center of the galaxy

(ESA/Gaia/DPAC)
smithsonian.com

This week, the European Space Agency released a series of breathtaking images captured by its Gaia star-surveyor: hi-res slices of the heavens that show an estimated 2.8 million stars, reports Deborah Byrd at Earth & Sky.

The image was taken on February 7, 2017, and depicts a region of the Milky Way galaxy two degrees below the galactic center. This particular view, which was taken the direction of the constellation Sagittarius, has a relatively low amount of interstellar dust, giving Gaia a good line of sight to the inner sanctum of our galaxy.

This region of the Milky Way has a density of 4.6 million stars per square degree, according to a press release. Since the images cover 0.6 square degrees of the sky, there should be roughly 2.8 million points of light in the picture—but no one has counted them.

The Gaia instrument was launched by the ESA in 2013 on a five-year mission to map 1 billion stars, or roughly 1 percent of the Milky Way to help astronomers make a detailed map of our galaxy. Byrd explains that Gaia studies the motions of individual stars using a technique called astrometry. By cataloguing and analyzing the movements of those stars, researchers hope to better understand the evolution of the Milky Way and learn what’s in store over the next few millions of years.

Most of the time Gaia is pretty discriminating, only sending down data on the stars it studies. But according to the press release, Gaia occasionally finds regions of space that are so jam packed that measuring the motion of individual stars is very difficult. Instead, it sends down a data dump-image of the whole area. That’s what it did with the current mega-star image, which researchers plan to analyze over time.

Despite its short stay in space, Gaia is already reshaping our view of the universe. Researchers released its first catalogue of 1 billion stars, collected over 14 months of observations, in September 2016. A second catalogue will be released in 2018 and, if its five-year mission is extended, subsequent sets in 2020 and 2022. 

Research based on that first catalogue appeared in Astronomy & Astrophysics just last week. As Shannon Hall at Sky & Telescope reports, after analyzing some of the Gaia data, researchers have discovered that one star in particular, Gliese 710, will pass through the inner Oort Cloud, a shell of icy debris surrounding the solar system in around 1.3 million years. Gliese 710 will be about 16,000 astronomical units away from the sun. While that’s not close enough to scorch the Earth, a star passing through the Oort cloud is not ideal. Researchers aren’t sure yet if Gliese is massive enough to stir up the rock and ice in the cloud. If it is, it could be catastrophic, sending 100 times more comets than normal into the Solar System, leading to some epic planetary smash-ups.  

“You don't want a Category 4 storm coming close to a population center and then just sitting,” Eric Mamajek of the Jet Propulsion Laboratory, not involved in the study, tells Hall. “And it's the same thing for a massive star passing through the Oort cloud.”

The researchers also found that on average, 87 stars come within 6.5 light-years of the sun every million years, meaning there’s much more “stellar traffic” in our area of space than previously believed.

There are likely many other similar stories locked in the Gaia data waiting to be told. But it may take some time. According to the ESA, the star mapper will send down enough data to fill 1.5 million CD-ROMs over five years, which need to be processed on Earth before it can be fully analyzed.

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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