ALMA | National Astronomical Observatory of Japan | 22 May 2020
Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) found quasi-periodic flickers in millimeter-waves from the center of the Milky Way, Sagittarius (Sgr) A*. The team interpreted these blinks to be due to the rotation of radio spots circling the supermassive black hole with an orbit radius smaller than that of Mercury. This is an interesting clue to investigate space-time with extreme gravity.
“It has been known that Sgr A* sometimes flares up in millimeter wavelength,” tells Yuhei Iwata ... “This time, using ALMA, we obtained high-quality data of radio-wave intensity variation of Sgr A* for 10 days, 70 minutes per day. Then we found two trends: quasi-periodic variations with a typical time scale of 30 minutes and hour-long slow variations.”
Astronomers presume that a supermassive black hole with a mass of 4 million suns is located at the center of Sgr A*. Flares of Sgr A* have been observed not only in millimeter wavelength, but also in infrared light and X-ray. However, the variations detected with ALMA are much smaller than the ones previously detected, and it is possible that these levels of small variations always occur in Sgr A*.
The black hole itself does not produce any kind of emission. The source of the emission is the scorching gaseous disk around the black hole. The gas around the black hole does not go straight to the gravitational well, but it rotates around the black hole to form an accretion disk. ...
Time Variations in the Flux Density of Sgr A* at 230 GHz Detected with ALMA ~ Yuhei Iwata et al
- Astrophysical Journal Letters 892(2):L30 (2020 Apr 01) DOI: 10.3847/2041-8213/ab800d
- arXiv.org > astro-ph > arXiv:2003.08601 > 19 Mar 2020
