Astronomers see the awakening of a massive black hole

Image: An artist’s impression of galaxy SDSS1335+0728, which has been steadily getting brighter since 2019. Credit: iso/m. Kornmesser

At the end of 2019, the blurring galaxy SDSS1335+0728 suddenly began to shine brighter than ever before. To understand why, astronomers used data from several space-based and ground-based instruments, including the European Southern Observatory’s (ESO) Very Large Telescope (VLT), to track how the galaxy’s brightness changes. In a paper published today, they conclude that they are witnessing unprecedented changes in the galaxy – likely due to the sudden awakening of the massive black hole at its core.

“Imagine you had been observing a distant galaxy for years, and it always seemed quiet and inactive,” says Paula Sanchez Saez, an astronomer at the European Southern Observatory in Germany and lead author of the 2015 paper. Astronomy and astrophysics. “Then suddenly its core begins to show dramatic changes in brightness — in a way you’ve never seen before.” That’s what happened to SDSS1335+0728, which is now classified as an “active galactic nucleus” — a bright compact region powered by a massive black hole — after its brightness increased sharply in December 2019.

Some phenomena, such as supernova explosions or Tidal disturbance events (An event in which a star comes too close to a black hole and is disintegrated) can suddenly light up the galaxy. But these variations in brightness usually only last a few tens or hundreds of days at most. SDSS1335+0728, on the other hand, is still bright more than four years after astronomers saw it. Moreover, the variations in brightness of the galaxy, located 300 million light-years away in the constellation Virgo, are unprecedented. For this reason, astronomers began looking for another explanation.

Alternative explanations

The team tried to understand the brightness variations using a combination of archived data and new observations from several instruments including the X-shooter on the European Southern Observatory’s VLT in Chile’s Atacama Desert. By comparing data before and after December 2019, they found that SDSS1335+0728 now emits more light at ultraviolet, optical, and infrared wavelengths. In February 2024, the galaxy also began emitting X-rays.

The most plausible explanation for this phenomenon is that the black hole at the heart of the galaxy is starting to become active. If this is indeed the case, this would be the first time astronomers have seen a massive black hole wake up.

To rule out alternative explanations, further observations are necessary. For example, there may also be an unusually slow process Tidal disturbance occurred Or even a completely new phenomenon.