Recent Starbursts in the Milky Way Galaxy's Center

WASHINGTON -- Researchers using the Stratospheric Observatory for Infrared Astronomy (SOFIA) have captured new images of a seven light-year-diameter ring of gas and dust surrounding the supermassive black hole at the center of the galaxy, and of a neighboring cluster of extremely luminous young stars embedded in dust cocoons.

These images are the subjects of two posters presented this week during the American Astronomical Society’s meeting in Long Beach, Calif. Ryan Lau of Cornell University (Ithaca, NY) and his collaborators studied the Milky Way’s circumnuclear ring, or CNR (Figure 1a). Matt Hankins of the University of Central Arkansas (Conway, Ark.) is lead author of the other paper, regarding the Quintuplet Cluster, or QC (Figure 2a).

SOFIA is a highly modified Boeing 747SP aircraft carrying a telescope with an effective diameter of 100 inches (2.5 meters) to altitudes as high as 45,000 feet (14 km). The images were obtained during SOFIA flights in 2011 with the FORCAST (Faint Object infraRed Camera for the SOFIA Telescope) instrument built by a team with Principal Investigator Terry Herter of Cornell. Each image is a combination of multiple exposures at wavelengths of 20, 32, and 37 microns that are partially or completely blocked by water vapor in Earth’s atmosphere and thus inaccessible to ground-based observatories even on high mountain peaks. 

Our Galaxy’s nucleus lies behind interstellar dust clouds in the mid-plane of the Milky Way which are mostly or completely opaque to visible and near-infrared light but more transparent at longer infrared wavelengths. Figures 1b and 2b show comparison images of the CNR and QC regions made with a near-infrared camera on the Hubble Space Telescope. The CNR and other exotic features revealed by the FORCAST camera on SOFIA are invisible in the Hubble images. Figure 3 shows the two fields studied in these papers as square insets on a large-scale image of the galactic center made by the Spitzer Space Telescope at a wavelength of 8 microns.

The nucleus of the Milky Way is inhabited by a black hole with 4 million times the mass of the Sun that is orbited by a large disk of gas and dust. The ring seen in Figure 1a is the inner edge of that disk. The galactic center also hosts several exceptionally large star clusters containing some of the most luminous young stars in the Galaxy, one of which is the Quintuplet Cluster seen in Figure 2. The combination of SOFIA’s airborne telescope with the FORCAST camera produced the sharpest images of those regions ever obtained at mid-infrared wavelengths, allowing discernment of new clues about what is happening near the central black hole.

“The focus of our study has been to determine the structure of the circumnuclear ring with the unprecedented precision possible with SOFIA” said Mr. Lau. “Using these data we can learn about the processes that accelerate and heat the ring.” Mr. Hankins, lead author of the QC paper, noted that, “Something big happened in the Milky Way’s center within the past 4 to 6 million years which resulted in several bursts of star formation, creating the Quintuplet Cluster, the Central Cluster, and one other massive star cluster.” Hankins added, “Many other galaxies also have so-called ‘starbursts’ in their central regions, some associated with central black holes, some not. The Milky Way’s center is much nearer than other galaxies, making it easier for us to explore possible connections between the starbursts and the black hole.”

SOFIA Chief Scientific Advisor Eric Becklin, who is working with the CNR group, determined the location of the galaxy’s nucleus as a graduate student in the 1960s by laboriously scanning a single-pixel infrared detector to map the central region. Becklin said, “The resolution and spatial coverage of these images is astounding, showing what modern infrared detector arrays can do when flown on SOFIA. We hope to use these data to substantially advance our understanding of the environment near a supermassive black hole.”

SOFIA is a joint project of NASA and the German Aerospace Center (DLR) that is based and managed at NASA’s Dryden Aircraft Operations Facility in Palmdale, Calif. NASA’s Ames Research Center at Moffett Field, Calif., manages the SOFIA science and mission operations in cooperation with the Universities Space Research Association (USRA) headquartered in Columbia, Md., and the German SOFIA Institute (DSI) at the University of Stuttgart.

The SETI Institute and the Astronomical Society of the Pacific are partners in leading the SOFIA Education and Public Outreach programs. 

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