A Little Gem

Little gemThis is NGC 6818. It’s a planetary nebula also known as the Little Gem Nebula. It about 6,000 light-years away in the constellation Sagittarius. The cloud is a bit more than half a light-year across, huge compared to its central star  but still a little gem as nebulas go.

When stars like the Sun are read to “retire,” they shed their outer layers into space which creates glowing clouds of gas called planetary nebulae. The ejection of mass is uneven, and planetary nebulae often have very complex shapes. NGC 6818 has a bright and enclosed central bubble surrounded by a larger, more diffuse cloud. It appears that the stellar wind from the central star propels the outflowing material, shaping NGC 6818. As the fast stellar wind smashes through the slower-moving cloud, it creates particularly bright blowouts in the bubble’s outer layers.

Image Credit: NASA

The Backward Galaxy

backward galaxyThe Backward Galaxy (aka NGC4622) lies 111 million light years away in the constellation Centaurus. NGC 4622 is an example of a galaxy with leading spiral arms. In most spiral galaxies, the spiral arms trail; that is, the tips of the spiral arms are winding away from the center of the galaxy in the direction of the disk’s orbital rotation. In NGC4622, however, the outer arms are leading spiral arms; the tips of the spiral arms point towards the direction of disk rotation. This may be the result of a gravitational interaction between NGC 4622 and another galaxy or the result of a merger between NGC 4622 and a smaller object.

Image Credit: NASA

Asteroid (6478) Gault

This isn’t a comet. It’s Asteroid (6478) Gault out in the main belt between Mars and Jupiter. So what’s it doing with a pair of tails? The longer tail stretches more than 800,000 km) and is roughly 4,800 km wide. The shorter one is roughly a quarter as long.

One theory suggests that the tiny asteroid, only 2.5 miles wide, is disintegrating as a result of long-term effects of sunlight. Sunlight? Yes, the cumulative force of the Sun’s light can slowly speed up a small body’s spin, and when spinning fast enough, it will throw off material. Pressure from sunlight very slowly began spinning up the diminutive asteroid at an estimated rate of 1 second every 10,000 years, the it may have taken 100 million years or so to get the spin rate up to a destructive level.

Image Credit: NASA