Largest radio galaxy ever discovered, with jets extending 100 times larger than the Milky Way

Astronomers have discovered the largest known radio galaxy ever, stretching at least 16 million light-years in space, and in front of it, the Milky Way, which is about 200,000 light-years in diameter, suddenly becomes tiny.

Radio galaxies are galaxies that are very bright at radio wavelengths and contain supermassive black holes in their cores. When matter falls into the black hole, it releases energy from the center of the galaxy in two jets of ionized plasma, possibly active galactic nuclei or quasi-active galaxies. Stars, blazars, and jets spread far and wide, and the tail ends will spread into huge lobes of radio waves. The Milky Way also has radio lobes, and what scientists have not yet been able to clearly explain is why some galactic jets can grow to surprising sizes, leading them to be called giant radio galaxies.

Leiden University in the Netherlands used the Low-Frequency Array (LOFAR) distributed in 52 locations in Europe to detect the Alcyoneus galaxy at a distance of about 3 billion light-years from the earth through interference technology. The central supermassive black hole ejected two huge jets, The tail end also spreads into radio lobes, which together extend the Alcyoneus galaxy an astonishing 16.3 million light-years, four times larger than the previous record holder: IC 1101, which stretched 3.9 million light-years.

But the Alcyoneus galaxy is a normal elliptical galaxy with half the total mass of the Milky Way (240 billion times the mass of the sun), and the central black hole is about 400 million times the mass of the sun. Compared with most radio galaxies, the proportion of the center of Alcyoneus is generally small. How it produces such a huge jet is still a mystery to scientists.

One possibility is that the environment around the Alcyoneus galaxy is less dense than normal, allowing the jets to expand on an unprecedented scale. Another explanation is that Alcyoneus galaxies reside on filaments of the cosmic web (the vast structures of gas and dark matter that connect vast numbers of galaxies in the universe), allowing jets to extend along the structures and unseen dark matter on the way.

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