When stars like the Sun grow old, after burning through their initial supply of hydrogen fuel, nuclear fusion grinds to a halt, their cores shrink and their outer atmospheres balloon outward, a process that turns the a main sequence star into a red giant. Increased pressure in the deep interior can cause hydrogen to begin fusing in a shell around the core, generating intense radiation that illuminates expanding shells of gas that were blown away earlier. Objects such as this one, NGC 2022 in the constellation of Orion, are known as planetary nebulae because their compact appearances made them look a bit like planets in early telescopes. In this view from the Hubble Space Telescope, the compact remnant of the original star is visible at the center of surrounding shells of gas that once formed its outer layers. When fusion completely stops, only a slowly cooling, Earth-size white dwarf will be left to mark the spot where a main sequence star once shined.
Astronomers using observations from the NASA/ESA Hubble Space Telescope and NASA’s Chandra X-ray Observatory have studied how dark matter in clusters of galaxies behaves when the clusters collide. The results show that dark matter interacts with itself even less than previously thought, and narrows down the options for what this mysterious substance might be.
This new NASA/ESA Hubble Space Telescope image, released to celebrate Hubble’s 26th year in orbit, captures in stunning clarity an object known as the Bubble Nebula (NGC 7635) — a cloud of gas and dust illuminated by the brilliant star within it. The vivid new portrait wins the Bubble Nebula a place in the exclusive Hubble hall of fame.
This NASA/ESA Hubble Space Telescope image reveals a delicate blue group of stars — actually an irregular galaxy named IC 3583 — that sits some 30 million light-years away in the constellation of Virgo. This small galaxy is thought to be gravitationally interacting with one of its neighbours, the spiral Messier 90.