Lifting the veil on the black hole at the heart of our Galaxy: Results from GMVA+ALMA observations of Sgr A*

January 21, 2019
Baselines of the GMVA+ALMA array for Sgr A* observations
The Global Millimeter VLBI Array (GMVA), joined by ALMA. Credit: S. Issaoun, Radboud University / D. Pesce, Harvard-Smithsonian Center for Astrophysics

Including the powerful ALMA into an array of telescopes for the first time, astronomers have found that the emission from the supermassive black hole Sagittarius A* (Sgr A*) at the center of our Galaxy comes from a smaller region than previously thought. This may indicate that a radio jet from Sgr A* is pointed almost toward us. The paper, led by the Nijmegen PhD student Sara Issaoun, is published in The Astrophysical Journal.

Observing at a frequency of 86 GHz with the technique of Very Long Baseline Interferometry (VLBI), which combines many telescopes to form a virtual telescope the size of the Earth, the team succeeded in mapping out the exact properties of the light scattering blocking our view of Sgr A*. The removal of most of the scattering effects has produced a first image of the surroundings of the black hole. The new images show that the radiation from Sgr A* has a symmetrical morphology and is smaller than expected – it spans a mere 300 millionth of a degree.

Results from GMVA+ALMA observations of Sgr A*
Top left: simulation of Sgr A* at 86 GHz. Top right: simulation with added effects of scattering. Bottom right: scattered image from the observations, this is how we see Sgr A* on the sky. Bottom left: the unscattered image, after removing the effects of scattering in our line of sight, this is how Sgr A* really looks like. Credit: S. Issaoun, M. Mościbrodzka, Radboud University/ M. D. Johnson, CfA

Find more about these new results based on Sgr A* observations with a global VLBI array at the frequency of 86 GHz in these press releases from:


See also: 2017