Stellar Snow Globe Mystery Solved With Hubble’s Help

This new NASA/ESA Hubble Space Telescope image shows the globular cluster IC 4499.

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.

Cosmic Oddball

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.

This  sky chart shows the southern evening sky as seen from the Southern Hemisphere late August. Using a telescope and a low power eyepiece scan the region in the constellation Apus, to the lower left of its lead star Alpha Apodis. Credit: SkySafari
This sky chart shows the southern evening sky as seen from the Southern Hemisphere in late August. Using a telescope and a low-power eyepiece, scan the region in the constellation Apus, to the lower left of its lead star Alpha Apodis. Courtesy   SkySafari

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.

This wide-angle sky chart shows the sky as seen from Australia. Looking towards the SW in the early evening Omega Centauri globular cluster is an easy binocular target.  Credit: SkySafari
This wide-angle sky chart shows the sky as seen from Australia. Looking toward the southwest in the early evening, the Omega Centauri globular cluster is an easy binocular target. Courtesy SkySafari

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.

This wide scale sky chart shows the view towards the western horizon late night on August 24, and the Hercules constellation between the bright stars Arcturus and Vega. The Great Hercules Cluster, M13 can be found within the chest of the mythical hero. Credit: SkySafari
This wide-scale sky chart shows the view toward the western horizon late night on August 24, and the Hercules constellation between the bright stars Arcturus and Vega. The Great Hercules Cluster, M13, can be found within the chest of the mythical hero. Courtesy SkySafari

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.

This sky chart shows the location of M13 within Hercules' keystone stellar pattern. The insert is an image that shows the hi-power view through a telescope. Credit: Starry Night Software
This sky chart shows the location of M13 within Hercules’s keystone stellar pattern. The insert is an image that shows the high-power view through a telescope. Courtesy Starry Night Software/A.Fazekas

 

On dark, moonless nights, away from city lights, M13 can be glimpsed with the naked eye, appearing as a faint, small, fuzzy patch.

Clear skies!
Follow Andrew Fazekas, the Night Sky Guy, on Twitter and Facebook.

Changing Planet

Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.