A dying star surrounded by gas takes on the appearance of a lionâs face in new images from the James Webb Space Telescope. Behind this spectacular shape, infrared observations of NGC 2392 mainly reveal small clumps of dust, several gas shells, and the effects of radiation produced by the very hot remnant of the central star.
NGC 2392 is a planetary nebula. Despite its name, it has nothing to do with a planet. It consists of material expelled by a star nearing the end of its existence. The star gradually ejected its outer layers, which now form the visible structures around its center.
The James Webb Space Telescope photographed the planetary nebula NGC 2392, known as the Lion Nebula, using the NIRCam and MIRI instruments.
The remains of the central star are responsible for the nebulaâs structure, including a âmaneâ of ionized gas and dust shaped like a lionâs head.
Image: NASA, ESA, CSA, STScI; Image processing: Alyssa Pagan (STScI)
This center now contains a white dwarf, the very dense and hot remnant of the former star. Its radiation supplies energy to the surrounding gas. It alters the material expelled over several thousand years and helps produce the different regions visible in the nebula. James Webb observes this material in infrared light, which is invisible to our eyes.
This capability complements the images captured in visible light by the Hubble Space Telescope. The broad overall shapes remain recognizable, but infrared brings out other details. The NIRCam camera observes mainly in near-infrared light. The MIRI instrument looks at longer wavelengths, which are particularly useful for distinguishing certain dust and gas structures.
The new observations notably show numerous small clumps spread across the region resembling the lionâs mane. The material is therefore not arranged in a simple, regular shell. It forms filaments, denser regions, and several shells created during successive episodes of mass loss from the star.
To understand this appearance, imagine a star that does not lose its entire envelope all at once. Its pulsations and winds eject material at different times and speeds. More recent layers can then encounter material expelled earlier. The white dwarfâs radiation also acts on this gas.
These images therefore make it possible to study the nebulaâs history through its current structure. The different shells preserve traces of the stages the star went through. For astronomers, their shape, composition, and temperature help reconstruct how a star with a mass comparable to that of the Sun gradually reaches the end of its life.
Observations of NGC 2392 must now be compared across their different wavelengths. By comparing NIRCam and MIRI data with earlier Hubble observations, astronomers can more precisely distinguish dust from ionized gasâthat is, gas whose atoms have lost electrons under the effect of the central starâs energetic radiation.