Short-lived sources of radio radiation in the sky, known as radio transients, can originate in the vicinity of black holes. They are the result of processes that take place under extreme physical conditions. While most radio transients last from only days to weeks or months, the supermassive black hole at the centre of the galaxy SDSS J110546.07+145202.4 has been shining very brightly in the radio for several years — the first source of its kind. The spiral galaxy SDSS J110546.07+145202.4 is located at a redshift of 0.12, about 1.8 billion light-years from Earth.  It was not detected in NVSS (the NRAO VLA Sky Survey) in the early 1990s, implying that it was fainter than 2 milli-jansky, but has been around 40 mJy for the past 8 years and shows no signs of weakening. The team have dubbed this a “radio changing-look galaxy” as its behaviour is analogous to galaxies that undergo rapid, dramatic transitions in their optical spectra.

The source of the radiation is located near the black hole at the galaxy’s centre. This black hole has a comparatively low mass, which is increasing exceptionally fast, however, through the accretion of matter. Komossa et al. report observations with numerous telescopes, including the 100-metre radio telescope in Effelsberg, the Australia Telescope Compact Array, and satellites in space, confirm the source’s unique properties.  The team suspects that more matter has been falling into the black hole for several years, which in turn has triggered a jet — a concentrated beam of particles traveling at nearly the speed of light that emits radiation.  The relative closeness of SDSS J110546.07+145202.4 allows for detailed observations and insights into the physical processes surrounding the evolution of black holes and the formation of jets. The image above is a composite visible and near-infrared light image of SDSS J110546.07+145202.4. (Image credit: DESI Legacy Survey)