At the center of galaxies are supermassive black holes (SMBHs), with a mass of 1 million to 10 billion solar masses, some of which are in a bright phase called active galactic nuclei (AGN).
Active galactic nuclei eventually burn up because there is an upper limit to the mass of supermassive black holes, and scientists have long thought about when this might happen.
Kohei Ichikawa of Tohoku University and his research group may have discovered a dying galactic nucleus by chance after picking up an AGN signal from Arb 187.
Discovery of a Dying Supermassive Black Hole Via a 3000-year-long Light Echohttps://t.co/LMV4MW6wWM
By combining data from ALMA, VLA and NuSTAR, astronomers succeeded in capturing the moment when an active galactic nuclei is ending its activity. pic.twitter.com/CwuRATBEqb
– NAOJ ALMA project (@NAOJ_ALMA_en) June 8, 2021
By observing radio images in the galaxy using two astronomy observatories, the Atacama Large Millimeter Array (ALMA) and the Carl Gee Very Large Array (VLA), they found a jet lobe, a hallmark of active galactic nuclei.
However, they did not notice any signal from the nucleus, which indicates that the activity of the galactic nuclei may indeed be muted.
After further analysis of the multi-wavelength data, they found that all the indices of the small-sized AGNs were silent, while the broad-band indices were bright. This is because active galactic cores have recently been quenched within the last 3,000 years.
Once the AGN dies, the properties of the SMNs become dulled because more photon supply is also cut off. But the large-scale ionized gas region is still visible because the photons take about 3,000 years to reach the edge of the region. Previously, observing the activity of galactic nuclei was known as light echo.
“We used NASA’s Neustar X-ray Telescope, which is the best tool for monitoring current galactic nuclei activity. It allows for undetected, so we were able to detect that the nucleus is completely dead,” Ichikawa said.
The results indicate a break in AGNs over a 3,000-year timescale, with the cores becoming 1,000 times fainter over the last 3,000 years.
They will continue to investigate moribund AGNs, Ishikawa says. “We will look for more moribund AGNs using a method similar to this study. We will also obtain high-resolution spatial-resolution follow-up observations to investigate inflows and outflows of gas, which may explain how to stop activity of the galactic nuclei”.
Source: Science Daily