Friday, February 19, 2010

Astrophoto Friday: Globular Star Cluster M3 in Infrared

Note: See the update to this post added at the end.


The image above shows the globular star cluster known as M3. The cluster is made up of several hundred thousand stars. It is a member of our Milky Way Galaxy, located nearly 34,000 light years from our solar system.

This star cluster is located within the constellation of Canes Venatici, the hunting dogs. In 1764 the French comet hunter Charles Messier made it the third object, M3, of his now famous catalog.

M3 is thought to be about 180 light-years across, although half of the cluster's stars are located within its innermost 22 light years. M3 contains a relatively large number of "Blue Straggler" stars. These are stars that are bluer than most other stars within the cluster. They are thought to have had their outer layers stripped away by close encounters with other stars in the dense inner regions of the cluster.

This infrared image was taken by Tom Jarrett (Infrared Processing and Analysis Center / Spitzer Science Center / Caltech) using the Palomar Observatory's 200-inch Hale Telescope with its Wide-field Infrared Camera.


UPDATE to post: Thanks to Palomar Skies reader jg for keeping me on my toes about blue straggler stars. Please note that my comments in the post as it was first worded did not reflect any of the science being done by Tom Jarrett.

jg was correct in his comments about how blue straggler stars are thought to be created. Here is a graphic from a HST press release that illustrates the leading two ideas:


Something else that I should have noted the first time around was that blue straggler stars were first discovered by astronomer Allan Sandage who was studying globular cluster M3 with the 200-inch Hale Telescope.

5 comments:

jg said...

Scott,
I was just reading a paper on blue stragglers in a recent issue of Nature. I'll check my notes, but from memory, I thought the blue stragglers were being created in either collisions (the case for globular clusters) and by stellar predation in binary systems where one star goes into red giant phase allowing the other to grab a lot of its matter. In both cases, the remixing rejuvenates the stars, giving the bluer quality.

I guess, near collisions in globulars may suffice, but I thought the blue straggler was the one that got the additional mass rather than lost it.

jg

Scott Kardel said...

Thanks, jg. I may have a source that is out of date. I'll have to take a closer look at this.

- Scott

jg said...

Hi Scott,
So I reread my source. It is pretty clear that the reviewer writing in Nature, 24/31 Dec. 2010 accredits the creation of blue stragglers strictly to two processes: 1) collision and merger of two small mass stars (didn't say what size constitues small mass), and 2) a binary system where the blue straggler results from the star that captured the mass of a red giant campanion star.

Two articles were published in the same issue: 1) by Ferrao et al, "Two distinct sequences of blue straggler stars in the globular cluster M30 -- this article reports evidence of blue stragglers in M30 that result from both mechanisms of blue straggler formation.
And 2) Mathieu and Geller, "A binary star fraction of 76 per cent and unusual orbit parameters of the blue stragglers of NGC 188. I haven't read this one, but I think it's about identifying the orbital signature of binary sytems that created a blue straggler; e.g., an intial orbit had to be of a certain maximum distance to allow mass transfer, then after mass transfer you'd get a small campanion in a farther orbit. I didn't read this article, but I think I will.

jg

Scott Kardel said...

Thanks for keeping me on my toes jg! After I wiped the egg off my face, I revised my post to reflect the correct thinking about blue stragglers.

jg said...

Scott,
There never was any egg on your face. I enjoy this blog immensely, and it's rare that I can have anything to add.
That's a great chart you found. Thanks for sharing it.
jg