NGC 660

Lore & Background

NGC 660 likely formed when two galaxies collided about a billion years ago, though it may have begun as a disk galaxy that captured matter from a passing galaxy, which later became strung out into a rotating ring. The ring is not truly polar but inclined roughly 45 degrees from the host disk. It is much broader than the disk itself, spanning 50,000 light-years, and contains a greater amount of gas and star formation, suggesting a violent origin. Hundreds of objects populate the ring, including many red and blue supergiant stars; the youngest stars there are about 7 million years old, indicating ongoing star formation over a long period. The host disk emits radio waves from a core region only 21 light-years across, possibly a super-cluster of stars within a gas cloud, and the central area is so luminous in star formation that the galaxy is considered a starburst galaxy. In late 2012, NGC 660 produced an enormous outburst about ten times brighter than a supernova, possibly from a jet emitted by the central black hole.

Reader's Guide

NGC 660 is significant as a rare polar-ring galaxy, and uniquely among such objects, its host is a late-type lenticular galaxy. Its structure provides a natural laboratory for studying galaxy collisions and the accumulation of material into rings. The extreme star formation along the ring, including hundreds of red and blue supergiants, offers insights into how gravitational interactions trigger starbursts. The 2012 outburst, ten times brighter than a supernova, underscores the dynamic activity at its core, possibly linked to a supermassive black hole. Observations of the disk and ring rotation allow astronomers to infer properties of the dark matter halo. As a member of the M74 Group, NGC 660 contributes to understanding galaxy evolution in a group environment. Its ongoing star formation and violent history make it a key object for studying the aftermath of galactic mergers.

Did You Know?

• The ring is inclined about 45 degrees from the plane of the host disk, not truly polar.
• In late 2012, the galaxy produced an outburst roughly ten times brighter than a supernova.
• The youngest stars in the ring are approximately 7 million years old.