Free Astronomy Magazine September-October 2024

22 SEPTEMBER-OCTOBER 2024 ASTRO PUBLISHING galaxy is beginning to show [...] activ- ity,” says co-author Lorena Hernández García, from MAS and the University of Valparaíso in Chile. “If so, this would be the first time that we see the activation of a massive black hole in real time.” Massive black holes — with masses over one hundred thou- sand times that of our Sun — exist at the centre of most galaxies, including the Milky Way. “These giant mon- sters usually are sleeping and not directly visible,” ex- plains co-author Claudio Ricci, from the Diego Portales University, also in Chile. “In the case of SDSS1335+0728, we were able to observe the awakening of the mas- sive black hole, [which] suddenly T his artist’s im- pression shows two stages in the formation of a disc of gas and dust around the massive black hole at the centre of the galaxy SDSS1335+0728. The core of this galaxy lit up in 2019 and keeps brightening today — the first time we observe a massive black hole become active in real time. [ESO/M. Kornmesser] started to feast on gas available in its surroundings, becoming very bright.” “[This] process (...) has never been observed before,” Hernán- dez García says. Previous studies reported inac- tive galaxies be- coming active after several years, but this is the first time the process it- self — the awakening of the black hole — has been ob- served in real time. T his animation shows the growing disc of material around the massive black hole at the centre of the galaxy SDSS1335+0728. In late 2019 this galaxy suddenly started shining brighter than ever before and was classified as having an active galactic nucleus, powered by the central black hole feeding off the surrounding material. [ESO/M. Kornmesser] Ricci, who is also af- filiated with the Kavli Institute for Astronomy and As- trophysics at Peking University, China, adds: “This is some- thing that could happen also to our own Sgr A*, the massive black hole (...) located at the centre of our galaxy,” but it is unclear how likely this is to happen. Follow-up observations are still needed to rule out alternative ex- planations. Another possibility is that we are seeing an unusually slow tidal disruption event, or even a new phenomenon. If it is in fact a tidal disruption event, this would be the longest and faintest such event ever observed. “Regardless of the nature of the variations, [this galaxy] provides valuable information on how black holes grow and evolve,” Sánchez Sáez says. “We expect that instru- ments like [MUSE on the VLT or those on the upcoming Extremely Large Telescope (ELT)] will be key in understanding [why the galaxy is brightening].” !