Image Credit & Copyright: Star Shadows Remote Observatory (SSRO), Rick Gilbert.
For those of you that live in the southern hemisphere, this is clearly on of your favorite objects. 47 Tucanae (47 Tuc) is a massive globular star cluster nearly 17,000 light years away in the conetallation Tucana (The Toucan). With a diameter of roughly 120 light years and an apparent size matching that of the full moon, its millions of stars are easily naked eye visible from a dark southern hemisphere location.
It’s seen here as a diffuse bright white ball in the line of sight with the much larger and more distant 7,000 light year diameter Small Magellanic Cloud (SMC) roughly 200,000 light years away. Go ahead and expand this Image and zoom in as much as you can. You can make out a few, more distant globular star clusters looming in the background. Fabulous image by Star Shadows Remote Observatory (SSRO) in New Mexico.
Image Credit & Copyright: NASA/ESA Hubble Space Telescope H. Richer and J. Heyl (University of British Columbia), and J. Anderson and J. Kalirai (STScI).
Let’s take a closer look at this incredible object. It’s a known fact that stars within globular clusters are distributed by mass with the more massive stars near the nucleus and less massive taking up positions on the outskirts. We see this everywhere we look. But what about stars that lose mass which we know happens on a relatively frequent basis. Well, that’s also a known but until now, unobserved process; they relocate!
Astronomers have been studying 3000 white dwarf stars which according to ESA is roughly a third of all the white dwarfs in the cluster and they have witnessed first-hand the migration of these now low mass stars moving to their new positions in more distant orbits. They do however seem to be beginning their journey later than previously thought which may reveal that stars lose much of their mass later in the process than once believed.
47 Tuc was also the hunting grounds for Hubble to search for extrasolar planets though none ever turned up. This was confirmed when a ground based survey looked along the clusters outskirts as well, also finding nothing. In both instances, it was expected that they would find some. The knowledge gleaned through this research shows that planet formation in globular star clusters may be more-rare than previously thought.
47 Tuc boasts roughly 23 millisecond pulsars, hundreds of X-ray sources throughout and more than 20 mysterious blue straggler stars at its core, making this object a favorite for astronomers, amateur and professional alike.
NAME: 47 Tucanae, 47 Tuc, NGC 104.
WHAT IS IT?: Globular star cluster. 2nd brightest globular cluster of the approximately 150 in the Milky Way after Omega Centaury.
HOW BIG IS IT?: Roughly 120 light years in diameter and about the same apparent size as the full moon on the night sky.
HOW FAR AWAY IS IT?: Approximately 16,700 light years.
APPARENT MAGNITUDE: A naked eye visible 4.9.
DISCOVERERY?: French astronomer Nicolas Louis de Lacille in 1751.
HOW OLD IS IT?: About 10.5 billion years old.
WHERE IS IT? (General): Southern constellation Tucana (The Toucan).
WHERE IS IT? (Exact RA/DEC J2000): RA 00h 24m 05.67s / DEC –72° 04′ 52.6″.
Star Shadows Remote Observatory (SSRO) page for this image: http://www.starshadows.com/gallery/display.cfm?imgID=242
ESA science page for the Hubble 47 Tuc image: http://sci.esa.int/hubble/55902-hubble-traces-the-migration-of-white-dwarfs-in-cluster-47-tucanae-heic1510/