By comparing archived images over twenty years, astronomers observed an unusual phenomenon.
Thanks to data from the Sloan Digital Sky Survey and the Subaru telescope, they noted a dramatic dimming of the galaxy named J0218−0036, located about 10 billion light-years away. It went from an intense glow to an almost imperceptible gleam.
The reason? A black hole.
On the left, a distant supermassive black hole during its bright feeding phase.
On the right, the same black hole after its supply stopped, with diminished brightness.
Credit: Chiba Institute of Technology
When a supermassive black hole absorbs matter, it forms an accretion disk that shines intensely, sometimes outshining all the starlight of its galaxy. This is called an active galactic nucleus. In this case, the matter supply to the disk was reduced by 98% in seven years, causing its marked dimming.
We are thus dealing with a galaxy that had a luminosity super-amplified by its active nucleus and returned to a resting state in just a few years. The central regions of galaxies can thus change rapidly, unlike models that assumed much longer timescales.
To identify the cause of the dimming, the team used several observatories, from the Gran Telescopio Canarias to the Keck Observatory. They ruled out the hypothesis of a gas cloud masking the light. Observations covering from X-rays to infrared allowed tracking changes across different wavelengths, providing a complete view of the process, thus confirming a reduction in matter supply to its central black hole.
Visible light images of galaxy J0218−0036, indicated by yellow arrows. On the left, taken by the Sloan Digital Sky Survey in 2002; on the right, by Hyper Suprime-Cam on the Subaru telescope in 2018, showing notable dimming.
Credit: SDSS, HSC-SSP/NAOJ
This discovery challenges current models that predict changes over thousands of years. As a team member indicated, this provides a test case for developing new theories. The rapidity of the phenomenon shows that black hole activity can fluctuate on a scale comparable to a human lifetime, paving the way for "real-time" studies.
Researchers hope to discover other similar objects to understand how black hole activity stops and restarts. Their work has been published in
Publications of the Astronomical Society of Japan. This advance could help better predict the behavior of galactic nuclei across the Universe by incorporating shorter timescales into simulations.