Globular clusters are densely packed, spherical collections of hundreds of thousands or even millions of stars. They are among the oldest known objects in the Universe and are relics of the first epochs of galaxy formation.

About 150-180 such clusters are known to exist around our Milky Way Galaxy.

NGC 2419 was discovered on December 31, 1788 by the British astronomer William Herschel and is located in the constellation Lynx.

Also known as GCl 12 and C 0734+390, the cluster is at a distance of about 300,000 light-years from the Solar System and at the same distance from the Milky Way’s center.

It is sometimes called the ‘Intergalactic Wanderer,’ an appropriate title considering that the distance to the Milky Way’s satellite galaxy, the Large Magellanic Cloud, is only about 160,000 light-years.

The stars populating globular clusters are very similar to one another, with similar properties such as metallicity.

The similarity of these stellar doppelgängers is due to their formation early in the history of the galaxy.

As the stars in a globular cluster all formed at around the same time, they tend to display reasonably homogeneous properties.

It was believed that this similarity also extended to the stellar helium content; that is, it was thought that all stars in a globular cluster would contain comparable amounts of helium.

However, Hubble’s observations of NGC 2419 show that this is not always the case.

This surprising globular cluster turns out to be made up of two separate populations of red giant stars, one of which is unusually helium-rich.

Other elements within the different stars in NGC 2419 vary too — nitrogen in particular.

According to a study led by Radboud University astronomer Søren Larsen, these helium-rich stars reside predominantly in the center of the globular cluster.

The researchers also found evidence of rotation for this stellar population.

“The new Hubble observations raise questions about the formation of globular clusters,” Dr. Larsen and colleagues said.

“Did these two drastically different groups of stars form together? Or did this globular cluster come into being by a different route entirely?”