"The surface of the Earth is the shore of the cosmic ocean... Recently, we've managed to wade a little way out, and the water seems inviting." - Carl Sagan
Galactic wheels within wheels
How many rings do you see in this striking new image of the galaxy Messier 94 (NGC 4736) as seen by the infrared eyes of NASA’s Spitzer Space Telescope? While at first glance one might see a number of them, astronomers believe there is just one.
Historically, Messier 94 was considered to have two strikingly different rings: a brilliant, compact band encircling the galaxy’s core, and a faint, broad, swath of stars falling outside its main disk.
Astronomers have recently discovered that the outer ring, seen here in the deep blue glow of starlight, may actually be more of an optical illusion. This more complete picture of Messier 94 indicates that we are really seeing two separate spiral arms that, from our perspective, take on the appearance of a single, unbroken ring.
The bright inner ring of Messier 94 is very real, however. This area is sometimes identified as a “starburst ring” because of the frenetic pace of star formation in this confined area. Starbursts like this can often be triggered by gravitational encounters with other galaxies, but in this case may instead be caused by the galaxy’s oval shape.
Tucked in between the inner starburst ring and the outer ring-like arms we find the galaxy’s disk, striated with greenish filaments of dust. While, at first glance, these dusty arcs look like a collection of rings, they actually follow tightly wound spiral arcs.
Image credit: NASA/JPL-Caltech/SINGS Team