Cosmic Scale
Alcyoneus
Giant radio galaxy · 3.5 billion light-years
How big is Alcyoneus?
Alcyoneus is about 16 million light-years across.
See Alcyoneus in 3D, at true scale
Alcyoneus is a giant radio galaxy whose jets have inflated two lobes of plasma stretching 16 million light-years end to end — one of the largest single structures made by one galaxy. The galaxy itself is unremarkable.
At a glance
| Diameter | 16 million light-years |
|---|---|
| Diameter compared with Earth | 1.2 × 10¹⁶ × Earth |
| Distance | 3.5 billion light-years |
| Span | 16.3 million light-years |
| Found | 2022, with LOFAR |
| Source | Jets from its central black hole |
Good to know
- Its lobes are 160 times wider than the Milky Way, yet emptier than the best vacuum we can make.
- Nothing about its host galaxy or black hole looks special, which makes the size a puzzle.
- It is visible only at radio wavelengths; in ordinary light there is nothing to see.
- Next smaller: Virgo Cluster · 14 million light-years
- Next larger: Coma Cluster · 20 million light-years