Watch: Abu Dhabi captures Cat’s Eye Nebula after nine-day imaging effort

Abu Dhabi: An Abu Dhabi observatory has captured a detailed image of the Cat’s Eye Nebula, one of the best-known and most structurally complex planetary nebulae, after nine days of observations and more than 36 hours of combined exposure.

The image was produced by Al Khatim Astronomical Observatory, part of the International Astronomy Centre, using 724 individual exposures taken through four filters. It reveals both the nebula’s bright central “eye” and a much larger, fainter and irregular shell of gas surrounding it.

Known formally as NGC 6543, the Cat’s Eye Nebula lies in the constellation Draco, about 3,000 light-years from Earth. A planetary nebula is not related to planets; it is created during one of the final stages in the life of a star roughly comparable in mass to the Sun.

As such a star exhausts its nuclear fuel, it expands into a red giant and begins shedding its outer layers into space. What remains at the centre eventually becomes a hot, dense white dwarf, whose radiation illuminates the expelled gas.

The Abu Dhabi image took nine days to complete using the observatory’s main 14-inch reflecting telescope equipped with a monochrome camera. Three narrow-band filters captured emissions from hydrogen, oxygen and sulphur, while a fourth recorded infrared light.

The final image represents a total exposure time of 36 hours and 12 minutes. It combines 183 hydrogen-filter images, amounting to nine hours and nine minutes of exposure; 187 oxygen images totalling nine hours and 21 minutes; 178 sulphur images totalling eight hours and 54 minutes; and 176 infrared images totalling eight hours and 48 minutes. Each exposure lasted three minutes.

At the centre is the structure that gives the nebula its name: a small but intensely bright region of overlapping shells, bubbles and arcs of gas surrounding the dying star.

Images from the Hubble Space Telescope have shown the inner Cat’s Eye to be among the most intricate structures seen in a planetary nebula, containing gas shells, high-speed jets and knots of material, some formed by shock waves.

Astronomers believe fast stellar winds from the hot central white dwarf helped sculpt those structures by colliding with gas expelled during earlier stages of the star’s life.

X-ray observations from NASA’s Chandra observatory have also shown that the nebula’s core is surrounded by gas heated to millions of degrees. Some material expelled from the star is travelling at speeds approaching six million kilometres an hour.

The precise reason for the Cat’s Eye’s unusually complicated shape remains under study. One explanation is that the white dwarf may have interacted with a companion star, with the gravitational relationship between the two helping channel expelled material into irregular shapes rather than a simple spherical shell.

Beyond the luminous inner eye lies the second major feature captured in the Abu Dhabi image: a vast, faint outer halo of filaments, edges and scattered clouds of gas.

That outer material was expelled during an earlier phase of the star’s decline and therefore acts as a record of an older stage in its evolution. More recent observations combining data from the Hubble and Euclid space telescopes have helped distinguish those earlier emissions from the younger and brighter structures closer to the centre.

Hubble observations have also identified at least 11 concentric shells or rings around the Cat’s Eye. What appear as rings are thought to be the projected edges of nearly spherical bubbles of gas, suggesting the star experienced repeated episodes of mass loss separated by roughly 1,500 years rather than shedding its outer layers in a single event.

The enormous difference in brightness between the inner nebula and its outer halo makes the latter particularly difficult to photograph, requiring long exposures and image processing capable of bringing out very faint gas spread across a much wider area.

The Cat’s Eye also offers a glimpse of the distant future of the Sun. In several billion years, the Sun is expected to expel its outer layers and leave behind a white dwarf. Its resulting nebula, however, would not necessarily resemble the Cat’s Eye, whose form depends on factors including stellar winds, the way material is lost and possibly the presence of a companion star.