Here's a holiday card from 27,000 light-years away, offering a little yuletide cheer and astronomical intrigue from the mysterious central zone of the Milky Way. The composite image above shows an enormous swath of the galactic center, spanning about 750 light-years across, where a giant "cosmic candy cane" stands out among colorful molecular clouds.
This festive scene was captured by a NASA camera, the Goddard-IRAM Superconducting 2-Millimeter Observer (GISMO). It's the subject of two scientific studies — one led by Johannes Staguhn of Johns Hopkins University, and one led by Richard Arendt at the University of Maryland — both recently published in The Astrophysical Journal.
The image offers a rare glimpse into the bustling downtown Milky Way, home to the largest and densest collection of molecular clouds in our galaxy. These cold, colossal structures can give birth to new stars, and the molecular clouds in this image hold enough dense gas and dust to form tens of millions of stars like our sun, according to NASA.
"The galactic center is an enigmatic region with extreme conditions where velocities are higher and objects frequently collide with one another," says Staguhn, a research scientist at Johns Hopkins who also leads the GISMO team at NASA's Goddard Space Flight Center, in a statement. "GISMO gives us the opportunity to observe microwaves with a wavelength of 2 millimeters at a large scale, combined with an angular resolution that perfectly matches the size of galactic center features we are interested in. Such detailed, large-scale observations have never been done before."
That "candy cane" in the center of the image is made of ionized gas and measures 190 light-years from end to end, NASA explains in a news release. It includes a prominent radio filament known as the Radio Arc, which forms the straight part of the candy cane, as well as filaments known as the Sickle and the Arches, which form the cane's handle.
This labeled version of the GISMO image highlights the Arches, Sickle and Radio Arc that form a 'cosmic candy cane,' as well as other key features like Sagittarius A, home to a supermassive black hole at the center of our galaxy. (Image: NASA’s Goddard Space Flight Center)
GISMO gathered enough data to detect the Radio Arc after gazing into the sky for eight hours, making this the shortest wavelength where these strange structures have been observed by humans. These radio filaments mark the edges of a large bubble, researchers say, which was produced by some kind of energetic event at the galactic center.
"We're very intrigued by the beauty of this image; it's exotic. When you look at it, you feel like you're looking at some really special forces of nature in the universe," Staguhn says.
In addition to GISMO, the researchers used data from the European Space Agency's Herschel satellite and from telescopes in Hawaii and New Mexico to create the composite image, with various colors representing different emission mechanisms.
The new microwave observations from GISMO are portrayed in green, for example, while blue and cyan reveal cold dust in molecular clouds where "star formation is still in its infancy," NASA explains. In yellow regions like the Arches or the Sagittarius B1 molecular cloud, we're looking at ionized gas in well-developed "star factories," courtesy of light from electrons that are slowed but not captured by the gas ions. Red and orange represent "synchrotron emission" in features like the Radio Arc and Sagittarius A, a bright region inhabited by a supermassive black hole.
This image shows another view of the galactic center, thanks to infrared cameras on the Spitzer Space Telescope. (Image: Susan Stolovy (SSC/Caltech) et al./NASA, JPL-Caltech)
The center of our galaxy is largely obscured by clouds of dust and gas, preventing us from directly observing scenes like this with optical telescopes. We can still peek in other formats, though, such as infrared light — used by NASA's Spitzer Space Telescope, for instance, and the upcoming James Webb Space Telescope — or radio waves, including the microwaves detected by GISMO.
In future missions, GISMO may help us see even deeper in space. Staguhn hopes to take GISMO to the Greenland Telescope, where it could produce vast sky surveys in search of the first galaxies where stars formed.
"There's a good chance that a significant part of star formation that occurred during the universe's infancy is obscured and can't be detected by tools we've been using," Staguhn says, "and GISMO will be able to help detect what was previously unobservable."