Large Magellanic Cloud Cluster Member
May be a Planetary Nebula
In a "Where's Waldo" montage of stellar proportions, the Hubble Space Telescope image of the globular cluster NGC 1846 holds some non-typical treasures. The spherical collection of hundreds of thousands of stars resides in the outer halo of the Large Magellanic Cloud (LMC), our dwarf galaxy neighbor.
Bright stars in the cluster glow in intense shades of red and blue, indicative of their temperatures. The majority of fainter stars are bluish-white in color. Hidden deep between the stars of NGC 1846 are some optical gems. Slightly up and to the right of the center of the cluster, a bright edge-on galaxy can be found. Further out at the lower left is a background face-on spiral galaxy, shaped like a "Bull's Eye." More and more galaxies can be found with a keen eye - some with elongated shapes, others reddish in color.
But the most intriguing object, and the one that just doesn't seem to belong, is a faint, round, green bubble near the bottom center of the image. This is the aftermath of a stellar explosion of a star, known as a planetary nebula. The remnant central star can be seen neatly confined inside the bubble.
The bubble's color comes from the fact that Hubble's broad filters were used to examine the starlight from the cluster. Planetary nebulae, like this one, emit bright oxygen gas, which is being picked up by the green filter. It is uncertain whether the star that is now a planetary nebula is a member of NGC 1846. Measurements of the motion of the cluster stars and the planetary nebula's central star are close enough to rule in favor of the dying star being a cluster member.
This Hubble image was taken with the Advanced Camera for Surveys in January of 2006. The cluster was observed in filters that isolate blue, green, and infrared starlight. As a member of the LMC, NGC 1846 is located roughly 160,000 light-years away in the direction of the constellation Doradus.
Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Acknowledgment: P. Goudfrooij (STScI)