Don’t peek at the answer until you’ve given this a good try! Then, scroll down a bit and the truth will be revealed to you.
(Image Credit: NASA, ESA, Y. Nazé (University of Liège, Belgium) and Y.-H. Chu (University of Illinois, Urbana))
A modern artist’s painting of a tulip? An electron microscope view of a nose polyp? Give up?
Well, this unusual image, taken by the NASA’s Hubble Space Telescope, captures a rare view of the celestial equivalent of a geode — a gas cavity carved by the stellar wind and intense ultraviolet radiation from a hot young star.
Real geodes are baseball-sized, hollow rocks that start out as bubbles in volcanic or sedimentary rock. Only when these inconspicuous round rocks are split in half by a geologist, do we get a chance to appreciate the inside of the rock cavity that is lined with crystals. In the case of Hubble’s 35 light-year diameter "celestial geode" the transparency of its bubble-like cavity of interstellar gas and dust reveals the treasures of its interior.
The object, called N44F, is one of a handful of known interstellar bubbles. It is being inflated by a torrent of fast-moving particles (called a "stellar wind") from an exceptionally hot star once buried inside a cold dense cloud. Compared with our Sun (which is losing mass through the so-called “solar wind”), the central star in N44F is ejecting more than a 100 million times more mass per second. Because this star is surrounded by an envelope of gas, the stellar wind collides with this gas, pushing it out, like a snowplow. This forms a bubble, whose striking structure is clearly visible in the crisp Hubble image.