Cosmic Alligator Eats its Way Through the Sky
April 18, 2012
Many people enjoy the summer pastime of imagining pictures in clouds in the sky. The same can be done with clouds in the universe. Seen here by NASA's Wide-field Infrared Survey Explorer, or WISE, the cloud CG4 might be imagined as a cosmic alligator eating its way across the sky. Others might see a giant red-nosed slug. The open jaws of the alligator appear poised to chomp down on a red star. This red source is the young stellar object, called Spitzer 073425.3-465409. Young stellar objects are exactly what they sound like: stars that are in their early stages of formation. The reddish color of this star is due to its surrounding dust that glows in infrared light. A little further towards the left lies a galaxy that will make a nice dessert for the alligator (or slug). The galaxy is ESO 257-19, a spiral galaxy that appears elongated because it is inclined to our field of view. At approximately 118,000,000 light-years distant, ESO 257-19 is extremely far away. By comparison, CG4 and Spitzer 073425.3-465409 are 1,300 light-years distant, placing them both well within the bounds of the Milky Way Galaxy. The letters CG in CG4 stand for cometary globule. Despite its name, a cometary globule is not a comet. Comets are icy chunks of frozen gases with embedded rock and dust that orbit around the sun. Cometary globules resemble comets in shape in that they appear to have an opaque "head" and a luminous "tail," but have a vastly different scale than comets. Rather than being a densely packed "snowball" with a tail millions of miles long, CG4 is actually a cloud of gas and dust trillions of miles across. The gas in this cloud is heated by nearby young, hot massive stars, causing it to glow in infrared light. Color in this image represents specific wavelengths of infrared light. Blue and cyan represent light emitted at 3.4 and 4.6 microns, primarily from hot stars. Green and red represent light emitted at 12 and 22 microns, primarily from clouds of dust.