Alcyoneus a sixteen million light year long radio galaxy

4 December 2022

Image courtesy of A Owen.

Alcyoneus, a galaxy located some three and a half billion light years from Earth, at over sixteen million light years in length, is — without putting too finer a point on it — staggeringly huge. Our home galaxy, the Milky Way, at a mere one hundred thousand light years long, is positively minuscule in comparison.

But Alcyoneus isn’t a sixteen million light year long container of stars and whatever else fills a galaxy. Alcyoneus is what’s known as a radio galaxy, and the bulk of its length comes from radio lobes, which are a little like jets of radio energy, that fire out from opposite sides, into the surrounding space.

At its starry core Alcyoneus, which is likely an elliptical galaxy (unlike the image of the spiral type galaxy I’ve featured above), may not be all that much larger than the Milky Way. And that’s probably a relief for members of Alcyoneus’ galactic council, who only have to travel several hundred thousand light years to visit their constituents, rather than multiple millions.

If radio galaxies intrigue you though, Universe Guide has put together this explainer.