X-ray Echoes Reveal the 3D Structure of Molecular Clouds in our Galaxy's Center

This image represents a study using decades of data to learn about the 3D structure of molecular clouds in the center of the Milky Way. The panorama in this graphic contains radio data from the Submillimeter Array (green), and infrared from the Herschel Space Telescope (red), and the Spitzer Space Telescope (blue). The inset shows the X-ray data from a molecular cloud from NASA’s Chandra X-ray Observatory.

Researchers created the first 3D maps of molecular clouds, where stars form, in one of the most extreme environments in our Galaxy. They have studied previous flaring events from our Galaxy’s supermassive black hole, Sagittarius A* (Sgr A*). The center of the Milky Way Galaxy is an extreme environment where gas temperatures, densities, and turbulence are about ten times higher than the rest of the Galaxy. In this central region inflowing gas can sometimes find its way into the supermassive black hole at the very center. When Sgr A* feeds on this material it emits X-ray flares that propagate outwards in all directions. These flares interact with molecular clouds — gas clouds where stars form — in our Galaxy’s Center through the process of fluorescence. As the X-ray light travels, it illuminates slices of the molecular clouds over time, like an Xray scan.

The team developed a new X-ray tomography method to make 3D maps of two Galactic Center molecular clouds dubbed the “Stone” and the “Sticks” clouds. These maps are the first ever renderings of Galactic Center molecular clouds in three spatial dimensions. They used Chandra data spanning two decades to create their 3D models of the Stone and Sticks molecular clouds. While astronomers typically only see two spatial dimensions of objects in space, the X-ray tomography method allows us to measure the third dimension of the cloud because the X-rays illuminate individual slices of the cloud over time.

3D maps of “Sticks” & “Stone” Galactic Center molecular clouds:

The researchers also used data from the Submillimeter Array and Herschel Space Observatory to compare the structures seen in the X-ray echoes to those seen in other wavelengths. Because X-ray data is not collected continuously, there are some structures seen in submillimeter wavelengths that are not seen in X-rays. However, these “missing” structures allowed the researchers to constrain the duration of the X-ray flare event illuminating the Stone Cloud. They determined that the X-ray flare couldn’t have been much longer than four to five months.

These results were presented by Danya Alboslani (University of Connecticut) at the 245th meeting of the American Astronomical Society meeting in National Harbor, MD. A paper describing these results is available at [link]. NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.