Astronomers have discovered a mysterious object, which they believe is a giant hot bubble of gas around the Milky Way’s black hole every seventy minutes.

The orbit of the newly discovered rapid hot spot around Sagittarius A* superimposed on top of the first image of the supermassive black hole captured by the Event Horizon Telescope (EHT) collaboration. (Image credit: EHT Collaboration, ESO/L. Calçada (Acknowledgment: M. Wielgus))

This means that the object is moving at a mind-boggling 30% of the speed of light.

Observations by the Atacama Large Millimeter/submillimeter Array (ALMA) have revealed something unusual near the Milky Way’s supermassive black hole. Astronomers believe there is a mystery object, a hot spot that circles around Sagittarius A*. According to the researchers, the discovery will aid in our comprehension of the bizarre yet dynamic ecosystem.

The object that circles the black hole is most likely a hot bubble of gas that swirled around Sagittarius A* in an orbit comparable to that of the planet Mercury, according to the experts. The only difference is that it completes one orbit in around seventy minutes.

Orbits of the G objects at the center of our galaxy, with the supermassive black hole indicated with a white cross. Stars, gas and dust are in the background. (Credit: Anna Ciurlo, Tuan Do/UCLA Galactic Center Group)

In other words, according to Maciek Wielgus of the Max Planck Institute for Radio Astronomy in Bonn, Germany, this puzzling object requires a mind-boggling velocity of nearly 30% of the speed of light to complete its orbit in seventy minutes. Wielgus conducted the study that described the hot gas bubble orbiting the black hole, which was published in the journal Astronomy & Astrophysics.

ALMA, a radio telescope co-owned by the European Southern Observatory (ESO), was utilised to perform observations during the Event Horizon Telescope (EHT) Collaboration’s attempt to picture black holes. In April 2017, the EHT joined eight existing radio telescopes across the world, including ALMA, and photographed Sagittarius A*, the black hole at the heart of the Milky Way galaxy, for the first time. To calibrate the EHT data, a team of EHT Collaboration members, including Wielgus, used ALMA data taken concurrently with the EHT observations of Sagittarius A. The scientists discovered further information about the black hole’s nature using solely ALMA observations.

The observations were made just after NASA’s Chandra Space Telescope detected an X-ray flare produced from our galaxy’s centre. There is a suggestion that these flares are caused by hot spots, which are hot gas bubbles that orbit exceedingly quickly and near to black holes. Previously, they were observed using X-ray and infrared telescopes.

This is particularly intriguing because flares of this type were previously recorded solely in X-rays and infrared. “For the first time, we detect a very strong hint that orbiting hot spots are also present in radio data,” Wielgus explains.

According to Jesse Vos, a Radboud University Ph.D. student who was also involved in this study, these hot spots detected at infrared wavelengths are most likely manifestations of the same physical phenomenon: as hot spots emitting infrared cool, they become visible at longer wavelengths, similar to those observed by ALMA and the EHT.

Recent discoveries lend credence to the notion that flares are created by magnetic interactions in the highly hot plasma circling the black hole. These flares appear to have a magnetic origin, and scientific findings shed light on their geometry. We now have the possibility to build a theoretical interpretation of these events as a result of the additional data,” explains Radboud University co-author Monika Mocibrodzka.

Scientists can use ALMA to analyse polarized radio emissions from Sagittarius A* and thereby establish the magnetic field of the black hole. In addition to these findings, the scientists investigated the hot spot’s genesis and environment, particularly the magnetic field encircling Sagittarius A*, using theoretical models. Their finding places more limitations on the form of this magnetic field than prior observations in the process of discovering the nature of our black hole and its environs.

The GRAVITY instrument on ESO’s Very Large Telescope (VLT), which looks into the cosmos in infrared, has validated some of the prior discoveries. Both GRAVITY and ALMA data indicate that the flare originates in a cluster of gas revolving clockwise around the black hole at around 30% the speed of light. The hot spot’s orbit is also practically face-on, according to scientists.

To be able to track hot spots at multiple wavelengths using GRAVITY and ALMA coordinated multiwavelength observations in the future would be a true milestone for our understanding of the physics of flares in the Galactic centre,” says Ivan Marti-Vidal of the University of Valencia, a study co-author.

Furthermore, the EHT team wants to directly examine the gas clumps around the black hole, allowing them to delve closer and obtain a better knowledge of the object.

What happens near Sagittarius Acosmic *’s environment is a mystery to researchers. Wielgus, on the other hand, thinks that one day we may ultimately learn more about it and be able to construct a clearer picture of what happens at the centre of our galaxy.