Extended hard-X-ray emission in the inner few parsecs of the Galaxy
Nature 520, 7549 (2015). doi:10.1038/nature14353
Authors: Kerstin Perez, Charles J. Hailey, Franz E. Bauer, Roman A. Krivonos, Kaya Mori, Frederick K. Baganoff, Nicolas M. Barrière, Steven E. Boggs, Finn E. Christensen, William W. Craig, Brian W. Grefenstette, Jonathan E. Grindlay, Fiona A. Harrison, Jaesub Hong, Kristin K. Madsen, Melania Nynka, Daniel Stern, John A. Tomsick, Daniel R. Wik, Shuo Zhang, William W. Zhang & Andreas Zoglauer
The Galactic Centre hosts a puzzling stellar population in its inner few parsecs, with a high abundance of surprisingly young, relatively massive stars bound within the deep potential well of the central supermassive black hole, Sagittarius A* (ref. 1). Previous studies suggest that the population of objects emitting soft X-rays (less than 10 kiloelectronvolts) within the surrounding hundreds of parsecs, as well as the population responsible for unresolved X-ray emission extending along the Galactic plane, is dominated by accreting white dwarf systems. Observations of diffuse hard-X-ray (more than 10 kiloelectronvolts) emission in the inner 10 parsecs, however, have been hampered by the limited spatial resolution of previous instruments. Here we report the presence of a distinct hard-X-ray component within the central 4 × 8 parsecs, as revealed by subarcminute-resolution images in the 20–40 kiloelectronvolt range. This emission is more sharply peaked towards the Galactic Centre than is the surface brightness of the soft-X-ray population. This could indicate a significantly more massive population of accreting white dwarfs, large populations of low-mass X-ray binaries or millisecond pulsars, or particle outflows interacting with the surrounding radiation field, dense molecular material or magnetic fields. However, all these interpretations pose significant challenges to our understanding of stellar evolution, binary formation, and cosmic-ray production in the Galactic Centre.
Astronomy: Light direct from an alien world
Nature 520, 7549 (2015). doi:10.1038/520588b
Astronomers have spotted light reflected off a planet orbiting a distant sun, by teasing it out from the background starlight. The discovery allows direct calculations of the mass and other properties of the exoplanet, rather than inferring them using other methods.Jorge Martins of the
NASA and ESA are celebrating the Hubble Space Telescope's silver anniversary of 25 years in space by unveiling some of nature's own fireworks a giant cluster of about 3,000 stars called Westerlund 2. The cluster resides inside a vibrant stellar breeding ground known as Gum 29, located 20,000 light-years away in the constellation Carina. The comparatively young, 2-million-year-old star cluster contains some of our galaxy's hottest, brightest, and most massive stars. The largest stars are unleashing a torrent of ultraviolet light and hurricane-force winds that etch away the enveloping hydrogen gas cloud. This creates a fantasy celestial landscape of pillars, ridges, and valleys.