Terzan 5 is a heavily obscured globular cluster belonging to the bulge (the central star concentration) of the Milky Way galaxy.

[5] In 2009 it was discovered that Terzan 5 consists of at least two generations of stars with ages of 12 and 4.5 billion years and slightly different metallicities, possibly indicating that it is the core of a disrupted dwarf galaxy, not a true globular cluster.

[10] Terzan 5 is known to contain 49 millisecond radio pulsars as of December 2023,[12] the largest MSP population among all globular clusters in the Galaxy; their true number may be as high as 200.

[16] The large number of X-ray sources and millisecond pulsars may be a direct consequence of the high density of the cluster's core, which leads to a high rate of star collisions, and to formation of close binaries, including binary systems which contain a neutron star.

The high energy gamma rays probably originate in the magnetosphere of abundant millisecond pulsars, while ultra-high energy gamma rays likely result from the inverse Compton scattering by the relativistic electron emitted by the pulsars off the cosmic microwave background radiation.