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Ring Around a Galaxy, A Pocket Full of Stars...

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Zoom from a Digitized Sky Survey color image of the field around the ring galaxy AM 0644-741 and dissolve into the Hubble Advanced Camera for Surveys image. A pan along the star-forming regions of the bright ring is also included.
Full HST ACS Image of AM 0644-741
Image Credits:
NASA, ESA, and The Hubble Heritage Team (STScI/AURA)
Animation Credit:
NASA, Z. Levay and G. Bacon (STScI)

Getting to know the Lindsay-Shapley Ring
by Jim Higdon (Cornell University) and Ian Jordan (STScI)

Cataloged as "AM0644-741" in the Catalog of "Southern Peculiar Galaxies and Associations" by Halton Arp and Barry Madore, this beautiful system is also known as the "Lindsay-Shapley Ring" after its discoverers. Eric Lindsay, a student under Harlow Shapley, was the first to publish on the existence of the eccentric elliptical ring in 1960. AM 0644-741 is situated in the southern sky close to the Large Magellanic Cloud (LMC), a close companion galaxy of the Milky Way. As a result, it was at first unclear if AM0644-741 was a distant background object. Because of its proximity to the LMC and the lack of confirming radial velocity data, Lindsay and Shapley suggested it might be some sort of stellar remnant. Astronomer John A. Graham first positively identified it as "a peculiar southern ring galaxy" in 1974 by observing the object spectroscopically. Later known as "Graham's Ring Galaxy," AM 0644-741 resides nearly 300 million light-years away, and is over 150,000 light years in diameter, making it larger than our home galaxy.

Cartwheel Galaxy from 1995 HST photo release
Image Credit: Kirk Borne (STScI), and NASA
Digitized Sky Survey image of the field
around AM 0644-741.

This is not the first time that Hubble has captured a ring galaxy. In 1995, Hubble's Wide Field Planetary Camera 2 imaged The Cartwheel ring galaxy. They have several conspicuous differences which can be attributed to differences in the pre-interaction "target" galaxies and details in the collisions. For example, AM0644-741's nucleus is displaced far from the ring's center, whereas the Cartwheel's nucleus is very nearly at the center. This is from the "intruder" galaxies impacting the "target" disks at slightly different radii. In the Cartwheel, the "intruder" scored a nearly perfect hit on the center of the "target". In AM 0644-741, the "intruder" passed through the disk roughly half-way out. Note that unlike AM0644-741 the Cartwheel has a small second ring close to its nucleus. But unlike the Cartwheel, AM0644-741's large outer ring resembles a coiled rope wrapped around the nucleus.

A collection of imaging data shows the environment around AM 0644-741 in ground-based radio, IR, and optical wavelengths. Just as color photographs provide much more information about a scene than does a black-and-white photo, by examining a region of the sky in more than one wavelength, much can be gleaned about what is going on. A brief tour of the region around AM0644-741 is given by successively stepping through multi-wavelength data collected from various astronomical facilities starting at very long wavelengths (radio), and proceed on up through the optical.

See other groundbased images of AM 0644-74