It took more than 200 years to find out, but a globular cluster discovered in 1778 by comet-hunter Charles Messier turned out to be the first such star swarm located outside the Milky Way. As astronomers discovered in 1994, the cluster, known as M54 in Messier’s famous catalogue, is actually located some 90,000 light years away in the Sagittarius Dwarf Elliptical Galaxy, about three times farther than Earth is from the center of the Milky Way. But if you wait a while – a very long while – M54 will become part of Earth’s galaxy as the Sagittarius dwarf slowly merges with the larger body. This photograph of M54 was taken in 2011 by the Hubble Space Telescope’s Advanced Camera for Surveys.
This NASA/ESA Hubble Space Telescope image reveals the vibrant core of the galaxy NGC 3125, approximately 50 million light-years away. Discovered by John Herschel in 1835, NGC 3125 is a great example of a starburst galaxy — a galaxy in which unusually high numbers of new stars are forming, springing to life within intensely hot clouds of gas.
The eerie glow of a dead star, which exploded long ago as a supernova, reveals itself in this NASA Hubble Space Telescope image of the Crab Nebula in the constellation of Taurus. But don’t be fooled. The ghoulish-looking object still has a pulse. Buried at its centre is the star’s telltale heart — a neutron star which beats with rhythmic precision.