Science1 publisher2 min readPublished
Astronomers untangle three overlapping X-ray sources to map the supernova remnant nearest Sgr A*
Mayura Balakrishnan and colleagues separated three overlapping X-ray sources in Chandra data to make the first uncontaminated maps of Sgr A East. The cleaner signal gives a baseline for testing whether the remnant has heated the gas around the Milky Way's central black hole.
The Scientist · Science desk
What happened
- Besides the remnant, the field's main X-ray sources are colliding winds from a cluster of hot, massive stars and a diffuse glow from many faint binaries, mostly sun-like stars orbiting white dwarfs.
- Separating those sources let the team map iron, sulfur, argon and calcium inside Sgr A East.
- The authors find the remnant expanded into, compressed and heated the gas around it, giving it an asymmetric three-dimensional structure.
- The authors say their work supports the idea that Sgr A East kept the gas around Sgr A* hot and turbulent over a lifetime of about 10,000 years.
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Why it matters
- capability With the remnant's own light isolated, the X-ray data can start to address what kind of star exploded, according to the report.
- precedent Any claim that Sgr A East set off past outbursts from Sgr A* can now be checked against a remnant signal with no stellar-wind or binary emission mixed in.
- constraint The remnant's age is still uncertain, so any estimate of how much energy it has fed into the black hole's surroundings over time is uncertain by the same amount.
The contaminants in this field were already known [13]. Taking their light out was the hard part [16]. Sgr A* is a black hole of about 4 million solar masses, surrounded by gas, dust, strong magnetic fields and stars at every stage of life [1], and Sgr A East is the closest supernova remnant to it that astronomers know of [2]. A remnant glows in X-rays because shock waves run outward after the explosion and heat the stellar debris to millions of degrees [12]. Here it shares Chandra's field with other X-ray emitters. According to the phys.org report, this is the first time Chandra's X-rays of the remnant have been free of their light [4].
The thing this report doesn't tell you is how the separation was done. It calls the method a special technique for pulling apart the three main X-ray sources [4]. The details are in the paper by Balakrishnan and colleagues in The Astrophysical Journal, titled "Isolating Sgr A East: The First Uncontaminated X-Ray Maps of a Galactic Center Supernova Remnant" [11]. The team also removed point-like X-ray sources to study the diffuse emission in more detail [6]. Before leaning on the iron or calcium maps, I'd want to see how each contaminant was modelled and how much of it is left behind.
The published picture layers the Chandra X-rays with radio data from the NSF's Very Large Array and submillimeter data from the James Clerk Maxwell Telescope [7]. Bright radio emission surrounds both the remnant's X-rays and the region around Sgr A* [14].
The massive-star cluster is both a contaminant and a subject. Its colliding winds had to be subtracted from the X-ray signal [3]. The cleaned image is meant to let researchers examine how those same winds shaped the remnant's evolution [10].
Astronomers have long wondered whether Sgr A East and Sgr A* influence one another [15]. The authors word their heating result as support for that idea [8]. Support is a weaker standard than a measured transfer of energy from remnant to gas. I think the cleaned maps are the lasting result of this paper, and the heating story is a hypothesis they make easier to test.
What to watch
- Whether an independent group, working from the same Chandra data, gets the same three-way separation and the same element maps.
- A tighter age for Sgr A East than the rough 10,000 years now quoted; the heating result cannot be turned into an energy budget without one.
- Follow-up papers that use the clean maps to identify the progenitor star or to test a link to past Sgr A* outbursts.