M22 is a bright globular cluster in Sagittarius, among the closest of its kind to the Sun, seen against the rich star fields toward the centre of the Galaxy.
At a glance
| type | globular cluster |
|---|---|
| distance from the Sun | 10,400 light-years (3.2 kpc) |
| its light left it | 10,400 years ago |
| size in the piece | about 120 light-years acrossmodel |
Read off the piece’s own catalogue, the same values it draws with. Model marks a property of the piece’s galaxy model rather than a measurement.
About M22
M22 is a globular cluster, a dense, ancient swarm of stars on an orbit that carries it through the Galaxy’s inner regions. It lies near the bulge on the sky, close to the Teapot of Sagittarius, and is bright enough to see without optical aid from a dark site. It was one of the first globular clusters to be discovered.
It is one of very few globulars known to contain a planetary nebula, the shell cast off by a dying star of modest mass. Radio observations have also found candidate stellar-mass black holes inside it, a surprise, because such black holes had been expected to be ejected from clusters by encounters with other stars.
Its stars show a spread in heavy-element content that is unusual for a globular, a sign that its history may be more complex than a single burst of star formation.
What you see in the piece
It lies close to the Galactic plane in the direction of the bulge, so dust along the way dims and reddens it a little; from close by its old stars show a warm yellow.
Measured or modelled
The size drawn is a modelled extent. The black-hole candidates and the spread in composition are measured but their interpretation is still debated.
Questions
How far away is M22?
M22 is about 10,400 light-years (3.2 kpc) from the Sun, which makes it one of the nearer globular clusters.
Can you see M22 with the naked eye?
Under dark skies, yes: it appears as a faint fuzzy star just above the lid of the Teapot in Sagittarius, and binoculars show it clearly.