Messier 28

This globular cluster holds a dense neutron star that rotates once every three milliseconds.

Distance

17,900 light-years

Apparent Magnitude

7.7

constellation

Sagittarius

object type

Globular Cluster

M28
This globular cluster, M28, is most notable for being the first of its kind known to contain a millisecond pulsar: PSR B1821–24. This dense neutron star rotates rapidly (about once every three milliseconds) and emits radiation from its poles, which sweeps past Earth as the star spins, much like a beam of light from a lighthouse.
NASA, ESA, STScI, R. Buonanno (Universita di Roma Tor Vergata), K. Gebhardt (University of Texas at Austin), J. Grindlay (Harvard University), and F. Ferraro (Universita di Bologna)

M28 is a globular cluster located 17,900 light-years away from Earth in the constellation Sagittarius. It was discovered by Charles Messier in 1764. With an apparent magnitude of 7.7, the cluster appears as a faint patch of light through a pair of binoculars. Large telescopes can resolve its individual stars more effectively. The month of August is the best time to view M28.

The cluster is most notable for being the first of its kind known to contain a millisecond pulsar: PSR B1821–24. This dense neutron star rotates rapidly (about once every three milliseconds) and emits radiation from its poles, which sweeps past Earth as the star spins, much like a beam of light from a lighthouse. This makes it appear to be pulsing to observers on Earth. PSR B1821–24 was discovered in 1986 using a radio telescope in England called the Lovell Telescope.

This Hubble image of M28’s center was assembled from observations taken at visible, infrared and ultraviolet wavelengths.

For more information about Hubble’s observations of M28, see:

locator star chart for M28
This star chart for M28 represents the view from mid-northern latitudes for the given month and time.
Image courtesy of Stellarium

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