Space telescopes are giving astronomers unprecedented views of the Universe, including stars at the end of their lives.
The image above is a spectacular look at an object known as the Eskimo Nebula, or NGC 2392 to give it its catalogue name. It is the remnant of an explosive event where a dying star threw off a shell of gas.
This type of nebula is called a planetary nebula though it has nothing to do with planets. The term refers to the spherical shape that many of the gas shells display, which looked like planets to early observers.
The Eskimo Nebula lies 4,200 light-years from Earth. It doesn’t look quite like this through an amateur telescope. This image is a composite made up from images taken in different regions of the spectrum beyond visible light.
It contains X-ray data from NASA’s Chandra X-ray Observatory, shown in purple, which reveals the location of million-degree gas near the nebula’s centre. It also includes data from the Hubble Space Telescope – shown in red, green, and blue – which displays the intricate pattern of outer layers of the star that have been ejected. The comet-shaped filaments form when the faster wind and radiation from the central star interact with cooler shells of dust and gas that were already ejected by the star.
Planetary nebulae form when a star uses up all of the hydrogen in its core. The Sun is expected to go through this process in about five billion years. When this happens, the star begins to cool and expand, growing to as much as hundreds of times its original size.
Eventually, the outer layers of the star are carried away by a thick 50,000 km per hour wind, leaving behind a hot core. This hot core has a surface temperature of about 50,000 degrees Celsius, and is ejecting its outer layers in a much faster wind traveling six million km per hour.
The radiation from the hot star and the interaction of its fast wind with the slower wind creates the complex and filamentary shell of a planetary nebula. Eventually the remnant star will collapse to form a white dwarf star.
Chandra’s observations reveal that NGC 2392 has unusually high levels of X-ray emission compared to two other planetary nebulae that it observed. Scientists think this might be caused by an invisible companion to the hot star at the centre of NGC 2392.