Hydra is already the longest constellation in the sky, its faint length carrying the myth of Corvus and Crater across a wide stretch of stars. Far beyond that length, in the same direction as seen from Earth, lies an entire cluster of galaxies bearing the serpent's name.
The Hydra Cluster, catalogued as Abell 1060, is a rich concentration of galaxies roughly 150 million light years away, its individual members far too faint and far too numerous to have meant anything to any tradition that named the visible water snake overhead. Clusters of this kind are bound together by their own mutual gravity, hundreds of galaxies orbiting a shared centre of mass over timescales of billions of years, and the Hydra Cluster is one of several such structures used by astronomers to study how galaxies behave when crowded together rather than sitting in relative isolation the way the Milky Way mostly does.
The name is a modern astronomer's convenience, borrowed from the constellation the cluster happens to sit within as seen from Earth, exactly as the Hercules Cluster of galaxies borrows its name from the hero rather than from any mythological connection between the two.
A serpent stretched across a quarter of the visible sky turns out, at far greater distance than any star in its outline, to have an entire society of galaxies looking back along the same line of sight.