47 Tucanae by Don Goldman

Closer to the Heart – 47 Tucanae

19 May , 2008 by

Those huge, gravitationally bound balls of stars know as globular clusters aren’t without a heart. Containing a thick concentration of 10,000 to more than a million stars in a region spanning just 10 to 30 light-years, globular clusters are more akin to seething masses of suns where the lightweights head for the outer edges while the giants collect in the core. What causes this process? Do globular clusters really have a way of getting some stars closer to the heart?

What you see here is 47 Tucanae, the second largest globular cluster in the Milky Way’s busy galactic halo. As its name “47 Tucanae” implies, its core was first cataloged as a star and numbered the 47th in Tucana the Toucan – but not for long. On September 14, 1751 a French astronomer named Nicholas Louis de Lacaille was the first to discover its true nature with a half inch diameter spy glass and cataloged it as nebulous object. Next to observe and catalog it were James Dunlop in 1826, and John Herschel in 1834 when it became New General Catalog (NGC) 104.

At home some 13,400 to 16,000 light years away from our Earth, this inconceivably dense concentration of at least a million stars spans 120 light years at the outside, yet at its heart is more than 15,000 individual stars that are packed so densely that you couldn’t fit our solar system between them. Believed to have all been born about the same time from the same cloud of gas, globular clusters like 47 Tucanae are a wonderful study of how stars evolve and interact.

With such busy conditions, it only stands to reason that stellar collisions have occurred at one time or another and 47 Tucanae is no exception. In the core, 23 unusually hot and bright stars called blue stragglers have been identified – the double massive result of two stars bumping into one another. Due to the associated gravitational pull, heavier stars slow down and sink to the cluster’s core, while lighter stars pick up speed and head for the outer edges. The more often collisions happen the more dramatic the results – pushing the smaller stars ever faster towards the periphery and creating exotic objects.

What no earthly photo can ever show is that 47 Tucanae contains at least twenty millisecond pulsars – better known as neutron stars. Can you imagine a sun that rotates on its axis a few hundreds to one thousand times a second? Just imagine the power. According to scientists, such peculiar objects are generally thought to have a companion from which they receive matter. Close interacting binaries and bright cataclysmic binaries… dwarf novae and nova-like variable candidates…. They all make their home here closer to the heart.

This incredible image of 47 Tucanae was done by Don Goldman of Macedon Ranges Obervatory


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Brian Ventrudo
Member
May 19, 2008 6:40 PM

Globular clusters are absolutely fascinating. These remnants of the early days of our galaxy are intrinsically beautiful, even in a small telescope.

But aside from aesthetics, globular clusters are a “laboratory” for many important physical processes… gravitation, classical dynamics, statistical mechanics, and stellar evolution.

Once you know a little about globulars, you can never get tired of looking at them!

Jeff
Guest
Jeff
May 19, 2008 11:25 PM

If you would live on a planet in such a cluster, would it be permanently light? (Not taking heat/radiation into account, purely the amount of light). How should I imagine a sky looking living on a planet orbiting one of those stars, at least 20 stars the size of the sun in the sky at any part of the day?

Andrew James
Member
May 20, 2008 3:38 AM
Tammy said; “In the core, 23 unusually hot and bright stars called blue stragglers have been identified – the double massive result of two stars bumping into one another. Due to the associated gravitational pull, heavier stars slow down and sink to the cluster’s core, while lighter stars pick up speed and head for the outer edges. The more often collisions happen the more dramatic the results – pushing the smaller stars ever faster towards the periphery and creating exotic objects.” I truly doubt this scenario. Current theory believed there clusters are controlled by “hard” core binary which contains much of the angular momentum. Scattered through out the cluster are “soft” core binaries acting a localised gravity “sinks.”… Read more »
Andrew James
Member
May 20, 2008 6:42 AM

Tammy,
Thanks very much for the references, but I’ve already read all but one.
Whilst there are so many papers on these two magnificent globular clusters, there often contain very contradictory information that makes interpretations difficult. Certainly, understanding of these objects are coming along, but the weakness is theory of their evolution and interpreting dynamical constraints.
Don’t get me wrong, observations like these are important – especially one you’ve mentioned – “Stellar Exotica in 47 Tucanae”. No doubt the smagasbraod of different stellar objects makes it likely the history of globulars are very complex. If this was the aim of this news item – you’ve focused on the key investigations of astronomers on globular clusters.

Andrew James
Member
May 20, 2008 9:03 AM
Tammy Looked at it the other night. Still takes you breath away! Differences in the structures of globulars is certainly interesting, however they suffer from two issues – the kiloparsecs (kpc) distances of them and the small (relative) numbers of them. Comparing, say, M55 in Sagittarius and 47 Tucanae, at least gives you an idea of their diversity. it also reminds me of the Ivan R. King’s reference that appeared in the now defunct Quarterly Journal of the Royal Astronomical Society) QJRAS (QJRAS., 22, 227-243 (1981), where he says at the very start ; “There is no better way to introduce that the theme than to contemplate a picture of a globular cluster: it smoothness, its regularity, its… Read more »
Astrofiend
Member
Astrofiend
May 21, 2008 6:07 PM

Ha! Cheers guys (Tammy, Andrew) – I enjoyed that little exchange!

Bridh Hancock
Guest
Bridh Hancock
May 22, 2008 7:06 PM

An ab-fab ‘wow!’; and thank you to you two, too.

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