Skip to content


LCO Graduate Student Assists in the Discovery of a Gas Bubble Orbiting Black Hole Sgr A*

Dec 9, 2022

Artist’s rendering of a hot gas bubble orbiting Sgr A*, the black hole at the center of our galaxy. Image Credit: Joseph Farah, LCO

In September of this year, a team of scientists led by Maciek Wielgus at the Nicolaus Copernicus Astronomical Centre in Poland announced the discovery of a hot gas bubble orbiting the supermassive black hole at the center of the Milky Way galaxy. The existence of the black hole — known as Sagittarius A* (Sgr A*, pronounced "sadge-ay-star") — was confirmed in May when the images of the object were published. Further observations of the black hole and its characteristics are pushing the boundaries of astronomy and physics.

The European Southern Observatory published the exciting discovery of a hot gas bubble orbiting Sgr A* with an orbital velocity of 30% the speed of light. The observations were made at the Atacama Large Millimeter/submillimeter Array (ALMA) and the story was published by the ESO in this press release.

“What is really new and interesting is that such flares were so far only clearly present in X-ray and infrared observations of Sagittarius A*. Here we see for the first time a very strong indication that orbiting hot spots are also present in radio observations,” said lead scientist Dr. Wielgus.

LCO and UCSB graduate student Joseph Farah was part of the original team of the Event Horizon Telescope that imaged Sgr A*. As part of the science team that continues to observe the black hole, he played a role, along with the principal investigators, in the discovery of the hot gas bubble.

Joseph explained why this discovery is exciting. The scientists used ALMA to observe Sgr A* before the imaging work with EHT had ended and noticed interesting behavior while processing the data for the imaging. The ALMA array was specifically looking at the light being emitted from the black hole. The magnetic field generated by Sgr A* moves dust in such a way that the light coming out of the region is polarized into a particular orientation. With the ALMA data, scientists generated a map of the polarization of the light and realized that something is brightening and dimming, causing changes in the light’s polarization. They calculated that the relatively bright object that is orbiting SagA* has a period of 70 minutes.

The scientists were able to reconstruct the motion of the object orbiting Sgr A* and concluded that it is a hot clump of electrons and that hot spot’s direction of motion is aligned with the spin of the black hole.

Joseph Farah was a member of the EHT team that studied the ALMA data and helped with discussions and data analysis. This discovery of the orbiting gas bubble is an advancement in understanding the physics of black holes, as he explains, “This is a really exciting analysis, and gives a spectacular glimpse into the real time dynamics of our nearest supermassive black hole neighbor.”

Mr. Farah is grateful to the National Science Foundation for supporting his work through a Graduate Research Fellowship.

LCO graduate student Joseph Farah.