Messier 70

Messier 70 or M70, also known as NGC 6681, is a globular cluster of stars to be found in the south of Sagittarius.^[a] It was discovered by Charles Messier in 1780.^[b][6] The famous comet Hale–Bopp was discovered near this cluster in 1995.^[10][c]

Messier 70
Globular cluster Messier 70 by Hubble Space Telescope; 3.3′ view
Observation data (J2000 epoch)
Class	V[1]
Constellation	Sagittarius
Right ascension	18h 43m 12.76s[2]
Declination	–32° 17′ 31.6″[3]
Distance	29.4 kly (9.0 kpc)[4]
Apparent magnitude (V)	7.9[5]
Apparent dimensions (V)	8.0′[6]
Physical characteristics
Mass	1.79×105[4] M☉
Radius	34 ly[7]
Tidal radius	11.2′[8]
Metallicity	${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = –1.35[9] dex
Estimated age	12.80 Gyr[9]
Other designations	GCl 101, M70, NGC 6681[3]
See also: Globular cluster, List of globular clusters

It is about 29,400^[4] light years away from Earth and around 6,500 light-years^[11] from the Galactic Center. It is roughly the same size and luminosity as its neighbour in space, M69.^[12] M70 has a very small core radius of 0.22 ly (0.068 pc)^[13] and a half-light radius of 182.0 ly (55.80 pc).^[14] This cluster has undergone core collapse, leaving it centrally concentrated^[15] with the luminosity distribution following a power law.^[11]

There are two distinct stellar populations in the cluster, with each displaying unique abundances. These likely represent different generations of stars.^[16] Five known variable stars lie within its broadest radius, the tidal radius, all of which are RR Lyrae variables.^[8][17] The cluster may have two blue stragglers near the core.^[11]

Gallery

• 
  Image by Hubble Space Telescope
• 
  Map showing M70, against a conventional (southern) horizon

See also

• List of Messier objects