Researchers always wanted to take a direct image of a black hole. Thanks to the APEX radio telescope in Chile, they are getting closer to having one. Data from the Atacama Pathfinder Experiment (APEX) combined with Event Horizon Telescope (EHT) could create the final image of the black hole shadow and reveal new details about the structure of Sagittarius A *, a supermassive black hole at the center of the galaxy Milky Way . Other instruments have been able to observe the effects of a black hole on visible matter such as stars and planets. But until now, nobody has really seen the supermassive black hole of the Milky Way.
The researchers used a method called VLBI (Very Long Basal Interferometry) to join a group of radio telescopes distributed throughout the world. VLBI measures the time difference between the arrival of the radio signal to different telescopes. The participating telescopes are at high altitude. Therefore, they can pick up the desired radio waves between a barrage of background noise. The Sgr A * radio source was detected with all the stations, but the APEX participation significantly improved its image quality.
"We have worked hard at more than 5000 meters of altitude to install the equipment to prepare the APEX telescope for VLBI observations at 1.3 mm wavelength," said Alan Roy, who leads the VLBI team at APEX . "We are proud of the good performance of APEX in this experiment."
The black hole at the center of our galaxy is embedded in a dense interstellar medium that may have affected the activity of electromagnetic waves along the line of sight. The researchers believe that future observations with more telescopes could be used to eliminate any ambiguity.
The new effort focused on the study of supermassive black holes with sufficient resolution to directly observe the event horizon. Event Horizon is a region of space around a black hole from which nothing (not even light) can escape.
"We began to discover what the structure would look like at the horizon, instead of just drawing generic conclusions from the visibilities we tested," said lead author Ru-Sen Lu of the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany. "It is very encouraging to see that the installation of a ring-shaped structure matches very well with the data, although we can not exclude other models, for example, a composition of bright spots."