At Last, the Milky Way Gets a Better Close Up

After two years of data collection and number crunching, a team of astronomers has dropped a snapshot of literally cosmic proportions. It’s brimming with stellar goodness: the image shows the reddish-brown dust clouds clustered along our Milky Way’s centerline, teeming with over 3 billion pinpricks of light — nearly all stars, with a faint neighboring galaxy here and there.

The project, based at the Harvard-Smithsonian Center for Astrophysics, is called the Dark Energy Camera Plane Survey and aims to index celestial objects that are in our galactic plane. In January, the researchers published their second data publication in The Astrophysical Journal Supplement Series, making it the largest catalog or index of stars ever collected by a single instrument, and one of the few instances where we have pointed a camera at the center of our own galaxy. It’s a space selfie, if you will.

But while the stars are the showstoppers, the other point of this poll is to capture the elusive substance floating between them: dust. Because dust masks light, it distorts our view of the cosmos. Knowing how much there is out there can help astronomers filter its effects out of their data and more accurately estimate the chemistry and position of stars. Over the next decade, scientists will use this catalog to map out galactic dust maps, trace ancient star systems, and study the formation and structure of our Milky Way.

For the survey, the research team repurposed the Dark Energy Camera, or DECam, an optical instrument at the Cerro Tololo Inter-American Observatory in Chile that was originally built to study faint objects far from the galactic plane. “We took this instrument that was made for cosmology,” says Eddie Schlafly, an astronomer at the Space Telescope Science Institute, “and we pointed it right at the center of the galactic plane, where there are tons and tons of stars, dust and gas there and fog.” The aim is to resolve as many individual light sources as possible.

That’s quite a lot to ask: most astronomers deviate from observing the galactic plane because it’s notoriously difficult to image. “The Milky Way is a spiral galaxy. So most of its stars are in a flat pancake,” says Andrew Saydjari, a physics graduate student at Harvard University who led the survey. Unfortunately for observers on Earth, we’re sitting right in the middle of this pancake. It’s easy to see in this disk above or below our plane where the stellar haze is sparse. But looking into the center of the galaxy or backwards to the outer rim is difficult because the view is crowded. “Many of the stars can appear as if they are on top of each other,” says Saydjari.

Other things hanging around the galactic center don’t help. For example, some gases are hot enough to emit their own photons in a color similar to that of starlight. And dust can make celestial objects appear fainter and redder than they actually are. Both can skew astronomers’ measurements of the brightness and position of stars.