U Camelopardalis (aka U Cam) is a star nearing the end of its life. When stars run low on fuel for their normal fusion reactions, they become unstable. Every few thousand years, U Cam coughs out an almost spherical shell of gas as helium from its core begins to fuse. The gas ejected in the star’s latest eruption can be seen in this picture as a faint bubble around the star.
U Cam is a carbon star,a rare type with an atmosphere that contains more carbon than oxygen. Because of relatively low surface gravity, as much as half of the total mass of a carbon star may we swept away by powerful stellar winds. U Cam is much smaller than it appears in this image taken by the Hubble Space Telescope. The star would easily fit within a single pixel in the image. However, it is bright enough to saturate the camera’s photosensors which causes the star look much larger.
The shell of gas, both much larger and much fainter than its parent star, is visible in the picture. Gas clouds from expolsions are often quite irregular and unstable, but the shell of gas ejected from U Cam is almost perfectly spherical.
Image Credit: NASA