A Colorful Bubble

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 ready 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

Panning Across the Starburst Arc

This Hubble image shows a massive galaxy about 4.6 billion light years away. Around that galaxy’s border are four bright arcs. They are images the same distant galaxy nicknamed the Sunburst Arc. The Sunburst Arc galaxy is almost 11 billion light-years away. Its light is lensed into multiple images by gravitational lensing of the nearer galaxy. The Sunburst Arc is one of the brightest lensed galaxies known, and its image is visible at least 12 times within the four arcs.

Video Credit: ESA / NASA / Rivera-Thorsen et al.

Hercules A

Hercules A is the brightest radio source in the constellation of Hercules. Astronomers found that the double-peaked radio emission was centered on a giant elliptical galaxy known as 3C 348. This galaxy is not found within a large cluster of hundreds of galaxies, but rather within a comparatively small group of dozens of galaxies. The active part of the galaxy is the supermassive black hole in its core, sending out strong jets of energetic particles that produce enormous lobes of radio emission. It’s been suggested that Hercules A may be the result of two galaxies merging together.

This video imagines a three-dimensional look at the combined visible light (Hubble Space Telescope) and radio emission (Very Large Array) from Hercules A. The radio lobes dwarf the large galaxy and extends throughout the volume of the surrounding galaxy group. This visualization is only a scientifically reasonable guess of the three-dimensional structures. For example, the galaxy distances within the group are based on a statistical model, and not measured values.

Video Credit: NASA