Chinese astronomers have investigated quasar candidates from the DESI Legacy Surveys (DESI-LS) photometry catalog. As a result, they detected 19 strongly-lensed, dual and projected quasars. The finding was reported in a paper published Jan. 15 on the arXiv pre-print server.

Quasars, or quasi-stellar objects (QSOs), are active galactic nuclei (AGN) of very high luminosity powered by supermassive black holes (SMBHs), emitting electromagnetic radiation observable in radio, infrared, visible, ultraviolet and X-ray wavelengths. They are among the brightest and most distant objects in the known universe, and serve as fundamental tools for numerous studies in astrophysics as well as cosmology.

Two quasars observed with a small separation can be, in some cases, lensed quasars—where the light from a single quasar is bent, resulting in two images of the same quasar. More often, such objects are dual quasars, which means that they are at similar redshift and physically interacting. However, the most common scenario is projected quasars—coincidentally appearing very close to each other along the line of sight, but actually at different redshifts.

In some cases, the black hole will even spew jets of plasma, millions of light-years across intergalactic space. The plasma gas is so hot that it’s essentially a soup of electrons moving close to the speed of light. These plasma jets glow at radio frequencies, so they can be seen with a radio telescope and are, aptly, named radio galaxies. In a recent episode of the astronomy podcast The Cosmic Savannah, I likened their appearance to two glow sticks (the plasma jets) poking out of a ball of sticky tack (the galaxy). Astronomers hypothesise that the plasma jets keep expanding outwards as time passes, eventually growing so large that they become giant radio galaxies.

Millions of normally sized radio galaxies are known to science. But by 2020 only about 800 giant radio galaxies had been found, nearly 50 years since they had been initially discovered. They were considered rare. However, a new generation of radio telescopes, including South Africa’s MeerKAT, have turned this idea on its head: in the past five years about 11,000 giants have been discovered.

MeerKAT’s newest giant radio galaxy find is extraordinary. The plasma jets of this cosmic giant span 3.3 million light-years from end to end – over 32 times the size of the Milky Way. I’m one of the lead researchers who made the discovery. We’ve nicknamed it Inkathazo, meaning “trouble” in South Africa’s isiXhosa and isiZulu languages. That’s because it’s been a bit troublesome to understand the physics behind what’s going on with Inkathazo.