Messier 4

It is one of the easiest globular clusters to find, being located only 1.3 degrees west of the bright star Antares, with both objects being visible in a wide-field telescope.

Modestly sized telescopes will begin to resolve individual stars, of which the brightest in M4 are of apparent magnitude 10.8.

It features a characteristic "bar" structure across its core, visible to moderate sized telescopes.

This strongly suggests this cluster hosts two distinct stellar populations, differing by age.

One has been found to be a binary star with a pulsar companion, PSR B1620−26 and a planet orbiting it with a mass of 2.5 times that of Jupiter (MJ).

[14] The view of Messier 4 through a good telescope was likened by Robert Burnham Jr. to that of hyperkinetic luminous alpha particles seen in a spinthariscope.

Simulation of stellar motions in Messier 4
Simulation of stellar motions in Messier 4, where astronomers suspect that an intermediate-mass black hole could be present. [ 5 ] [ 16 ] If confirmed, the black hole would be in the center of the cluster, and would have a sphere of influence (black hole) limited by the red circle.