A cosmic archaeological dig has unfolded within a giant ball of stars some 55,000 light-years away, courtesy of NASA’s Hubble Space Telescope.
The famed orbiting observatory has snapped this amazing portrait of IC 4499, a globular cluster of stars that resides just outside of the disk of our Milky Way galaxy. The star cluster is just one of hundreds suspended in a halo around our galaxy that are thought to contain seem of the oldest stars in the universe. Many of the stars are more than ten billion years old.
Now however, Hubble’s keen eyesight has dug up the details of this particular globular cluster’s stars, which reveal its overall age.
Astronomers had long believed that all the stars that make up a cluster should have formed at the same time, making it easy to determine their age. But actual observations show that the largest globulars are peppered with stars of varying vintages. One possible reason: the giant cluster’s intense gravity would pull in any gas and dust wandering too close by and use it to cook up new stars.
IC 4499 turns out to be kind of a cosmic oddball in terms of its mass, lying somewhere in the middle weights of the more common high and low mass clusters. This unique property of IC 4499 has now allowed astronomers to explore how mass can affect how these cosmic fossils evolve.
Hubble observations show that despite its mid-size mass, all of IC 4499’s stars belong to a single generation of stellar births. This single fact has now led to an accurate age dating of the entire globular cluster, a determination that had eluded astronomers for decades.
The new data suggests that IC 4499 is about the same age as the other globular clusters buzzing around the Milky Way—some 12 billion years old.
See for Yourself
Shining at a lowly tenth magnitude, IC 4499 is a faint target for backyard telescopes using high magnification in the Southern Hemisphere. To track it down it’s best to start off by identifying the constellation Crux, the Southern Cross, halfway up the southern sky late evening in August.
IC 4499 lies in the neighboring tiny, faint constellation Apus, the Bird of Paradise. Draw an imaginary line between the brightest star in Apus and the next star to its left, Delta Octantis. The globular cluster lies just above that imaginary connecting line.
But if you really want to get a sense of the true majesty of what a globular cluster looks like, there are much brighter counterparts in the southern sky. Arguably one of the most beautiful is Omega Centauri, nestled within the bright constellation of Centaurus. Located just 17,000 light-years from Earth, it is the closest and brightest globular cluster in the entire sky. It spans 175 light-years and contains a few million stars.
For those of us in the Northern Hemisphere, there is another famous cousin, the Great Hercules Cluster, which is a favorite target for backyard telescopes. Hanging halfway up in the western sky in evenings at the end of August, it resides in the constellation Hercules, the Strongman, and it will be easy to hunt down, thanks to four stars that make up a keystone pattern there.
Nestled within is the great binocular/telescope showpiece, the Great Hercules Cluster, or M13.
Located about 24,000 light-years from Earth, this globular cluster is made up of a swarm of half a million stars packed into a ball, stretching more than 100 light-years across.
On dark, moonless nights, away from city lights, M13 can be glimpsed with the naked eye, appearing as a faint, small, fuzzy patch.