A jumble of exotic stars: New vista snap of star cluster 47 Tucanae

January 10, 2013
This new infrared image from ESO’s VISTA telescope shows the globular cluster 47 Tucanae in striking detail. This cluster contains millions of stars, and there are many nestled at its core that are exotic and display unusual properties. Studying objects within clusters like 47 Tucanae may help us to understand how these oddballs form and interact. This image is very sharp and deep due to the size, sensitivity, and location of VISTA, which is sited at ESO's Paranal Observatory in Chile.

(Phys.org)—Globular clusters are vast, spherical clouds of old stars bound together by gravity. They are found circling the cores of galaxies, as satellites orbit the Earth. These star clumps contain very little dust and gas—it is thought that most of it has been either blown from the cluster by winds and explosions from the stars within, or stripped away by interstellar gas interacting with the cluster. Any remaining material coalesced to form stars billions of years ago.

These spark a considerable amount of interest for astronomers—47 Tucanae, otherwise known as NGC 104, is a huge, ancient globular cluster about 15 000 light-years away from us, and is known to contain many bizarre and interesting stars and systems.

Located in the southern constellation of Tucana (The Toucan), 47 Tucanae orbits our Milky Way. At about 120 light-years across it is so large that, despite its distance, it looks about as big as the full Moon. Hosting millions of stars, it is one of the brightest and most massive globular clusters known and is visible to the naked eye. In amongst the swirling mass of stars at its heart lie many intriguing systems, including X-ray sources, variable stars, vampire stars, unexpectedly bright "normal" stars known as , and tiny objects known as millisecond pulsars, small that rotate astonishingly quickly.

The Visible and Infrared Survey Telescope--VISTA.

, stars that have exhausted the fuel in their cores and swollen in size, are scattered across this VISTA image and are easy to pick out, glowing a deep amber against the bright white-yellow background stars. The densely packed core is contrasted against the more sparse outer regions of the cluster, and in the background huge numbers of stars in the are visible.

The top image was taken using ESO's VISTA (Visible and Infrared Survey Telescope for Astronomy) as part of a survey of the region of the Magellanic Clouds, two of the closest known galaxies to us. 47 Tucanae, although much closer than the Clouds, by chance lies in the the foreground of the Small Magellanic Cloud, and was snapped during the survey.

VISTA is the world's largest telescope dedicated to mapping the sky. Located at ESO's Paranal Observatory in Chile, this infrared telescope, with its large mirror, wide field of view and sensitive detectors, is revealing a new view of the southern sky. Using a combination of sharp infrared images—such as the VISTA image above—and visible-light observations allows astronomers to probe the contents and history of objects like 47 Tucanae in great detail.

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Jan 10, 2013
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3.4 / 5 (5) Jan 10, 2013
That's because they don't "rotate" like a solid object. They're made up of stars in individual orbits, more like a swarm of bees than a beach ball.

Also, stars do "evaporate" from globular clusters. Interactions between passing stars can transfer enough energy that one star escapes from the cluster while the other moves closer to the center.
Jan 10, 2013
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1 / 5 (1) Jan 10, 2013
What I have yet to see is an explanation as to what keeps the stars at the very center from merging into a black hole.

The closest explanation I've inferred is their mutual attraction to each other is balanced out in that the pull from nearby stars on on side is balanced out by the pull of stars on the other side so to speak, preventing them from merging.
3.7 / 5 (3) Jan 11, 2013
Mostly it's because stars won't merge unless they make physical contact, and just like comets, most don't quite hit. They just make a very close pass, fly back into space, and try again.

In a normal double star, one will eventually become a red giant, and then they will merge. In a globular cluster, unless they form as a binary, they're moving to fast to be captured by each others gravity, and even if they are, another star is likely to pass by within an orbit or two, separating them again.

As for the stars being flung away, who's to say that many haven't been? The ones we see now may be those that were in more distant, or more stable, orbits, and survived any interactions. There could have been several times as many lost already.
1 / 5 (4) Jan 16, 2013
What I have yet to see is an explanation as to what keeps the stars at the very center from merging into a black hole.

The closest explanation I've inferred is their mutual attraction to each other is balanced out in that the pull from nearby stars on on side is balanced out by the pull of stars on the other side so to speak....

What you have inferred is one of the reasons a gravity based model requires DM. There is more baryonic matter/energy at the center of the cluster. Regardless of orbital velocity, over billions of years it should've eventually all come together, it hasn't. Magnetic repulsion is the logical answer, the stars at the center of the cluster are a solar system width apart. These clusters are not located within the plane of the ecliptic, but instead orbit in the upper or lower halo. (although some do border the plane). If this model of the field is correct, the answers are there.

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