In late 2019, the previously unremarkable galaxy SDSS1335+0728 suddenly began to shine brighter than ever. To understand why, a team of astronomers has used data from several space and ground-based observatories, including ESO’s Very Large Telescope (VLT), to study how the galaxy’s brightness has changed. In a paper published today, they conclude that they are witnessing never-before-seen changes in a galaxy, likely the result of the sudden awakening of the massive black hole at its core.
“Imagine that you have been observing a distant galaxy for years and it always seems calm and inactive,” declares Paula Sánchez Sáez, an astronomer at ESO in Germany and lead author of the study accepted for publication in the journal Astronomy & Astrophysics. Suddenly, your [núcleo] “It begins to show drastic changes in brightness, in a totally different way than what had been observed before.” This is what happened to SDSS1335+0728 when, in December 2019 [1] It increased its brightness shockingly. That’s why it is now classified as an “active galactic nucleus” (AGN, a compact, bright region fed by a massive black hole).
Some phenomena, such as supernova explosions or tidal disruption events (when a star gets too close to a black hole and breaks apart), can cause galaxies to suddenly light up. But these brightness variations typically last a few dozen or, at most, a few hundred days. Today, more than four years after it was first seen “igniting,” SDSS1335+0728 continues to increase in brightness. Furthermore, the variations detected in the galaxy, which is located 300 million light years away in the constellation Virgo, are unlike anything that has been observed before, pointing towards a different explanation.
The team sought to understand these brightness variations using a combination of archival data and new observations from several facilities, including the X-shooter instrument, installed on ESO’s VLT in the Atacama Desert. [2]. By comparing data taken before and after December 2019, they found that SDSS1335+0728 now radiates much more light in ultraviolet, optical, and infrared wavelengths. The galaxy also began emitting X-rays in February 2024. “This behavior is unprecedented,” says Sánchez Sáez, who is also affiliated with the Millennium Institute of Astrophysics (MAS), in Chile.
«The most tangible option to explain this phenomenon is that we are seeing how the [núcleo] of the galaxy is beginning to show (…) activity,” declares co-author Lorena Hernández García, postdoctoral researcher at the TITANS Millennium Nucleus and the Institute of Physics and Astronomy of the University of Valparaíso, in Chile. “If so, this would be the first time we see the activation of a massive black hole in real time.”
Most galaxies, including the Milky Way, have a massive black hole at their center (with masses more than one hundred thousand times that of our Sun). “These giant monsters are usually sleeping and are not directly visible,” explains 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 massive black hole, [que] Suddenly, it began to feast on the gas available in its surroundings, becoming very bright.”
[Este] process (…) had never been observed before,” confirms Hernández García. Previous studies have noted that dormant galaxies become active after several years, but this is the first time that the process itself, the awakening of the black hole, has been observed in real time. Ricci, who is also affiliated with the Kavli Institute of Astronomy and Astrophysics at Peking University (China), adds: “This is something that could also happen to our own Sgr A*, the massive black hole (…) located at the center of our galaxy”, but it is not clear with what probability this could happen.
Follow-up observations are still needed to rule out alternative explanations. Another possibility is that we are seeing an unusually slow tidal disruption event, or even a new phenomenon. If this is indeed a tidal disruption event, this would be the longest and weakest event ever observed. «Regardless of the nature of the variations, [esta galaxia] “It provides valuable information about how black holes grow and evolve,” says Sánchez Sáez. “We hope that instruments like MUSE on the VLT or those on the upcoming Extremely Large Telescope (ELT) will be key to understanding [por qué la galaxia está brillando]».
Source: IFA/ Photo: ESO.
