Free Astronomy Magazine September-October 2024

21 SEPTEMBER-OCTOBER 2024 ASTRO PUBLISHING after it was first seen to ‘switch on’. Moreover, the variations detected in the galaxy, which is located 300 million light-years away in the con- stellation Virgo, are unlike any seen before, pointing astronomers to- wards a different explanation. The team tried to understand these brightness variations using a combi- nation of archival data and new ob- servations from several facilities, in- cluding the X-shooter instrument on ESO’s VLT in Chile’s Atacama Desert. Comparing the data taken before and after December 2019, they found that SDSS1335+0728 is now radiating much more light at ultra- violet, optical, and infrared wave- lengths. The galaxy also started emitting X-rays in February 2024. “This behaviour is unprecedented,” says Sánchez Sáez, who is also affili- ated with the Millennium Institute of Astrophysics (MAS) in Chile. “The most tangible option to ex- plain this phenomenon is that we are seeing how the [core] of the I n late 2019, the galaxy SDSS1335 +0728 suddenly started shining brighter than ever before and was classified as having an active galactic nucleus, powered by a massive black hole in the galaxy’s core. This is the first time the awakening of a mas- sive black hole has been observed in real time. This artist’s impression shows the growing disc of material being pulled in by the black hole as it feeds on the gas available in its surroundings, making the galaxy light up. [ESO/M. Kornmesser]