Chandra Gives Cleanest X-Ray Map Yet of the Supernova Remnant Next to Sgr A*
By separating three overlapping sources of X-rays, astronomers isolated Sagittarius A East for the first time and mapped its iron, sulfur, argon and calcium.
The center of the Milky Way is a chaotic place. Besides the 4-million-solar-mass black hole known as Sagittarius A*, or Sgr A*, the region is packed with gas, dust, strong magnetic fields and stars at every stage of life. Now astronomers have released the clearest view yet of the remains of an exploded star in that clutter.
The supernova remnant is called Sagittarius A East, or Sgr A East, and it is the closest one to Sgr A* that astronomers know about. It emits light at many wavelengths, including X-rays that NASA's Chandra X-ray Observatory can detect. Remnants like it glow in X-rays because shock waves rumble outward after the explosion and superheat the stellar debris to millions of degrees.
The difficulty has been telling which light comes from the remnant and which comes from everything around it. Astronomers had already identified the two other main sources of X-rays in the field. One is colliding winds from a cluster of hot, massive stars. The other is a diffuse glow from many fainter, overlapping sources, made up mainly of double-star systems in which a star like our sun orbits a white dwarf.
A team led by Mayura Balakrishnan used a special technique to separate those three sources. The result is a composite image of Sgr A East containing Chandra X-rays that, for the first time, are not contaminated by X-rays from other objects. The analysis also let the authors map the elements inside the remnant, including iron, sulfur, argon and calcium. They removed the pointlike sources of X-rays so they could study the diffuse emission in more detail.
In the image, lower-energy X-rays are shown in green and high-energy ones in light blue, which appear purple in the middle of the remnant. The X-ray data are combined with radio data from the NSF's Very Large Array in red and submillimeter data from the James Clerk Maxwell Telescope in dark blue. The bright radio emission surrounds the X-rays from Sgr A East and from the region around Sgr A*. The black hole sits at the center of the yellow spiral structure to the right of the purple X-rays.
The maps show that the iron core of the remnant and the plasma around Sgr A* have different characteristic energies. Plasma tied to Sgr A* sits at median energies of roughly 6 to 6.2 keV, while the remnant's iron core is closer to 6.7 keV.
The cleaner view has two uses. It lets scientists examine how winds from the nearby star cluster have shaped the remnant over time, which could help identify the star that exploded and whether the blast triggered outbursts from Sgr A* in the past.
Because the remnant is so close to the black hole, astronomers have long wondered whether the two influence each other. The new work supports the idea that Sgr A East has played an active role. The authors conclude that it has injected energy into the region and kept the gas around Sgr A* hot and turbulent over the remnant's lifetime of about 10,000 years, although its exact age remains uncertain. They also show that it has expanded into, compressed and heated the surrounding gas, giving it a three-dimensional, asymmetrical shape. The study appears in The Astrophysical Journal.
