University of California, Santa Barbara | 2014 Oct 13
Is matter falling into the massive black hole at the center of the Milky Way or being ejected from it? No one knows for sure, but a UC Santa Barbara astrophysicist is searching for an answer.
Carl Gwinn, a professor in UCSB’s Department of Physics, and colleagues have analyzed images collected by the Russian spacecraft RadioAstron. Their findings appear in the current issue of The Astrophysical Journal Letters.
RadioAstron was launched into orbit from Baikonur, Kazakhstan, in July 2011 with several missions, one of which was to investigate the scattering of pulsars — the cores of dead stars — by interstellar gas. What the team found led them to examine additional observations of Sagittarius A-Star (A*), the source that marks the Milky Way’s central black hole. Sagittarius A* is visible at radio, infrared and X-ray wavelengths.
This massive black hole — which contains 4 million solar masses — does not emit radiation but is visible from the gas around it. The gas is being acted upon by the black hole’s very strong gravitational field. The wavelengths that make Sagittarius A* visible are scattered by interstellar gas along the line of sight in the same way that light is scattered by fog on Earth.
Gwinn and his colleagues found that the images taken by RadioAstron contained small spots. “I was quite surprised to find that the effect of scattering produced images with small lumps in the overall smooth image,” explained Gwinn. “We call these substructure. Some previous theories had predicted similar effects in the 1980s, and a quite controversial observation in the 1970s had hinted at their presence.” ...
Discovery of Substructure in the Scatter-Broadened Image of Sgr A* - C.R. Gwinn et al
- Astrophysical Journal Letters 794(1) L14 (2014 Oct 10) DOI: 10.1088/2041-8205/794/1/L14
arXiv.org > astro-ph > arXiv:1409.0530 > 01 Sep 2014 (v1), 11 Sep 2014 (v3)
http://asterisk.apod.com/viewtopic.php?t=32003