In late 2019, the galaxy SDSS1335+0728 suddenly began shining brighter than ever before, leading astronomers to believe that the massive black hole at its core had awakened. This sudden increase in brightness was unlike any typical events seen in galaxies before, prompting the classification of SDSS1335+0728 as having an ‘active galactic nucleus’. While phenomena like supernova explosions or tidal disruption events can cause galaxies to light up briefly, the continued brightness increase in SDSS1335+0728 is unprecedented, lasting more than four years.
To understand the changes in brightness, astronomers used data from various space and ground-based observatories, such as the European Southern Observatory’s Very Large Telescope (ESO’s VLT). Comparisons of data taken before and after December 2019 revealed that SDSS1335+0728 was emitting significantly more light at ultraviolet, optical, and infrared wavelengths, with X-ray emissions beginning in February 2024. This behavior, coupled with the unprecedented longevity of the brightness variations, suggested that the core of the galaxy was experiencing a new kind of activity, possibly related to the activation of the massive black hole.
The team of astronomers, using a combination of archival data and new observations, concluded that the awakening of the massive black hole at the centre of SDSS1335+0728 was causing the increase in brightness. This awakening process had never been observed before in real-time, with previous studies only reporting inactive galaxies becoming active after a period of time. The team speculated that the massive black hole in the Milky Way, known as Sgr A*, could potentially undergo a similar awakening event in the future, although this remains uncertain.
Further observations are necessary to confirm the explanation for SDSS1335+0728’s brightness variations. While the possibility of an unusually slow tidal disruption event or a new phenomenon cannot be ruled out, the data collected provides valuable insights into how black holes grow and evolve. Instruments like MUSE on the VLT or those on the upcoming Extremely Large Telescope (ELT) are expected to be crucial in further understanding the phenomenon and why the galaxy is brightening.
The unusual brightness variations of the SDSS1335+0728 galaxy were first detected by the Zwicky Transient Facility (ZTF) telescope in the US, leading to its classification as an active galactic nucleus by the Chilean-led Automatic Learning for the Rapid Classification of Events (ALeRCE) broker. Archival data from various observatories, including NASA’s Wide-field Infrared Survey Explorer (WISE) and Galaxy Evolution Explorer (GALEX), were used in the study, along with follow-up observations conducted with several facilities such as the Southern Astrophysical Research Telescope (SOAR) and the W. M. Keck Observatory.
In conclusion, the sudden and ongoing brightness variations of the SDSS1335+0728 galaxy have provided astronomers with a rare opportunity to witness the awakening of a massive black hole in real-time. The unprecedented nature of this event offers valuable information on the growth and evolution of black holes, shedding light on previously unobserved processes. With continued observations and the use of advanced instruments, scientists hope to gain further insights into this phenomenon and uncover the mysteries behind why galaxies suddenly brighten.