At the hearts of galaxies like the Milky Way are supermassive black holes weighing in the millions.
Some of these supermassive black holesare active galactic nuclei (AGN). They emit large amounts of radiation - x-rays and radio waves. AGNs are responsible for the twin jets of ionized gas seen in images of many galaxies.
Scientists don't fully understand how AGNs fade, but a new study of the galaxy Arp 187 brings them closer to the answer.
AGN usually produces a large number of X-rays. However, data from the NuSTAR telescope showed that the galactic core Arp 187 has darkened over the past several thousand years.
This composite image shows Arp 187 at radio wavelengths. Image credit: ALMA (ESO/NAOJ/NRAO), Ichikawa et al.
Arp 187 spans 3,000 light years.This means that the trail of leaving matter is visible for millennia after the "death" of the galactic nucleus. Astronomers call this trail a "light echo" and compare it to smoke from a freshly extinguished fire.
The researchers called their discovery "accidental." Arp 187 could be a stepping stone to learning more about what happens at the end of AGN's life, scientists say.
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