The globular cluster NGC 6440 is a system of very ancient stars, gravitationally bound into a single structure with a diameter of about 100-200 light years.
Clusters contain hundreds of thousands or possibly millions of stars. The large mass in the star-rich center of the cluster pulls the stars inward, forming a stellar ball.
The word globulus, from which these clusters take their name, is Latin for “small sphere”.
Globular clusters are considered to be among the oldest known objects in the universe and are relics from the first eras of galaxy formation.
It is believed that every galaxy has many globular clusters. There are at least 150 such objects in our own galaxy, the Milky Way, and there are probably several more hidden behind the thick disk of the galaxy.
Globular cluster NGC 6440 lies 8,470 parsecs (27,625 light-years) from Earth in the direction of the constellation Sagittarius.
The cluster, also known as C 1746-203 or GCl 77, was discovered by German-born British astronomer William Herschel on May 28, 1786.
Globular cluster NGC 6440 has an apparent magnitude of about 10 and a diameter of about 6 arcminutes.
“Clusters such as NGC 6440 are roughly spherical, densely packed collections of stars that live on the outskirts of galaxies,” the astronomers said in a statement.
They contain hundreds of thousands to millions of stars that are on average about one light year apart, but they can be as close to each other as Mercury is to Pluto.
The Hubble data used to create this image was obtained from five different observing programs, four of which focused on the properties of pulsars.
Pulsars are highly magnetized, rapidly rotating neutron stars that emit a beam of electromagnetic radiation from their magnetic poles.
To us, this beam looks like a short burst or impulse. Pulsars spin very fast. The fastest pulsar spins at 716 revolutions per second, but a pulsar could theoretically spin at 1,500 revolutions per second before it slowly loses energy or breaks apart.