The End of a Carbon Star

U Camelopardalis, aka U Cam, is a star nearing the end of its life. It is running low on fuel and so is becoming increasingly unstable. Every few thousand years it expels a nearly spherical gas shell when a layer of helium around its core starts to fuse. The gas ejected in the star’s latest eruption is visible in this image from the NASA/ESA Hubble Space Telescope, as a faint ‘bubble’ enveloping the star.

U-Cam is a carbon star, which is a rare type of star with an atmosphere that contains more carbon than oxygen. These stars have low surface gravity so they can lose as much as half of their total mass due to powerful stellar winds. Its shell of gas is much larger and much fainter than its parent star, and unlike the irregular and unstable gas ejections that occur at the end of other stars’ lives, this gas shell is almost perfectly spherical.

U-Cam is found within the constellation of Camelopardalis (The Giraffe), near the North Celestial Pole. The star is actually much smaller than it appears in this image; it could fit within a single pixel at the centre of the image. It is the star’s brightness which makes it appear bigger than it is, as it overwhelmed the capability of Hubble’s Advanced Camera for Surveys.