Viewed through telescopes on Earth, the planetary nebula NGC 2440 appears as little more than an amorphous mass. The Hubble Space Telescope reveals it to be an intricately detailed shell of gas. Look closely and you will see numerous filaments of gas, blobs, and streamers. Nebulae like NGC 2440 are expelled from stars when they begin to contract late in their development. The white dot at the center of this image is the star that ejected the cloud of gas. It is one of the hottest stars in our galaxy, with a surface temperature of 200,000 degrees Kelvin. The heat results from inner regions of the stars, which, having been exposed, are closer to the thermonuclear reactions at the core.