241210 - Sh2-284 "Smiling Cat" nebula

Even the Cheshire Cat in Lewis Carroll's classic tale, "Alice's Adventures in Wonderland", noted for his mischievous grin, didn't have a smile as wide as this cosmic "Smiling Cat".  This distant stellar nursery appears as a grinning celestial feline with a head that is appx 150 light-years wide.

The feline-looking cloud is the brightest part of the Sh2–284 nebula and is host to a huge population of infant stars created as overly dense patches of gas and dust collapse under their own gravitational forces. The stellar nursery is located around 26,000 ly from Earth in the constellation of Monoceros.

"Monoceros" (the Unicorn), is one of 12 constellations mapped by Dutch astronomer and cartographer Petrus Plancius.  Of the 12, two (2) are still recognized by the International Astronomical Union ("IAU") today.  (The other is "Camelopardalis", the Giraffe).  Plancius based his star-shapes on observations performed by Dutch maritime navigators.  He published 6 of them, including Monoceros, on a celestial globe in Amsterdam in 1612. Monoceros was created to fill a large gap between the constellations of Orion and Hydra.  There is no known mythology associated with Monoceros today.

Sh2-284 is a vast HII region of star formation.  It is also listed in the catalogue of 'Lynd's Bright Nebulae' as LBN 983.  Located just below the 'nose' of the cat, is a cluster of large, hot, young blue stars, dubbed the "Dolidze 25" (or Do25).  Do25 is packed with a class of stars called OB stars, which are blue in color, massive, and incredibly hot. OB stars live hydrogen-burning lives of between one million and 560 million years, depending on their mass.  Larger examples burn through their fuel more rapidly, while smaller ones burn their reserves more slowly.  This may seem like an unimaginably long time, but compared to the predicted ten billion-year hydrogen-burning lifespan of our own Sun, which has burned roughly halfway through its anticipated life, OB stars live and die in the blink of a cosmic eye.

Yet, despite their short lifetimes, OB stars blast out an incredibly large amount of ultraviolet radiation, which has a significant impact on their environments. In the case of the Sh2–284 nebula, the Do25 star-cluster produces large quantities of radiation and powerful stellar winds.  The radiation is powerful enough to ionize the hydrogen gas in the entire cloud.  It is this ionization of the nebula's elemental clouds that produces the bright red and orange colors we see.  In addition, powerful stellar winds from the cluster act like a plow pushing away gas and dust out the center of the nebula, shaping and evolving it into a distinctive hollow spherical shape.  Because of its orientation to our line of sight, we are able to see inside the sphere through a "blasted-out" wall of the sphere, creating a definite "Christmas ornament" affect that is highly sought-after by amateur astrophotographers.  Then on the flip side of this process, when these stellar winds meet more dense pockets of matter offering more resistance to the erosion effect, and causing the areas around them to be eroded away first, the resulting effect is to create "pillars" of material that can be seen radiating outward from the heart of the Sh2–284 nebula.  The most famous, in-like-kind nebula to this one is M16, the "Eagle" nebula with its "Pillars of Creation" made famous in 1995 by the Hubble Telescope.

The distance of Sh2-284 has been a subject of debate.  In the 1980s, it was thought to be about 17,000 ly away, located between the Perseus Arm and the Swan Arm of the Milky Way.   Then in 2007, through the study of the dynamics of galactic spiral arms, the cloud was assigned a distance of about 26,000 ly away, and therefore located in the outermost regions of the Milky Way, on the Cygnus Arm (also called the Outer Arm).

The stars within this region exhibit low metallicity, a trait common among stars in the Milky Way's outer regions.  Active star formation is supported by over thirty sources of infrared radiation, and there is strong evidence of very young protostars and pre-main sequence stars, including three water (H2O) masers and three carbon monoxide (CO) masers.  The 2007 study suggests that smaller and nearby nebulous regions Sh2-283, 285, and 286 are physically linked to the larger Sh2-284, thereby giving support for labeling the entire region as a cloud complex under the catalogue designation Sh2-284.

IMAGER'S COMMENTS:Sh2-284 is not often photographed, but is a good target for both beginning and experienced astrophotographers.  While challenging due to its relatively low surface brightness and the huge population of stars between us and it within the galaxy, imagers who accept the challenge are often rewarded with a very beautiful assortment of colors and sculptures that rival many similar objects.