JWST observations detect dusty disk around the central star of Ring Nebula

Using the James Webb Space Telescope (JWST), an international team of astronomers has observed a planetary nebula designated Messier 57 (also known as NGC 6720), dubbed the Ring Nebula. As a result, they found that the central star of this nebula is surrounded by a dusty ring. The finding was detailed in a paper published April 1 on the arXiv preprint server.

Planetary nebulae are expanding shells of gas and dust that have been ejected from a star during the process of its evolution from a main sequence star into a red giant or white dwarf. They are relatively rare, but are important for astronomers studying the chemical evolution of stars and galaxies.

Discovered in 1779, the Ring Nebula is a well-known planetary nebula in the constellation of Lyra, at a distance of about 2,570 light years away from Earth. It is a slightly elliptical ring of gas with a radius of about 1.3 light years and is often regarded as an archetypal planetary nebula.

The central star of the Ring Nebula, which is becoming a white dwarf, has a mass of about 0.61 solar masses and its effective temperature is estimated to be around 135,000 K. The star consists primarily of carbon and oxygen with a thin outer envelope composed of lighter elements.

A group of astronomers led by Raghvendra Sahai of NASA’s Jet Propulsion Laboratory (JPL) recently performed new imaging of the Ring Nebula and its central star in the near- to mid-infrared wavelength range. For this purpose, they employed JWST’s Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI).

The observations detected excess emission in the spectral energy distribution at wavelengths above 5.0 µm as well as radially-extended emission in the 7.7, 10 and 11.3 µm images. These findings suggest the presence of a compact dust cloud disk around the central star.

According to the paper, the dust cloud has a size of approximately 2,600 AU and consists of relatively small amorphous silicate dust grains. The total mass of this dust was estimated to be around 0.00000186 Earth masses.

Furthermore, the observations found that the central star of the Ring Nebula has a luminosity at a level of 310 solar luminosities and line-of-sight interstellar extinction of 0.15 mag. The study also found that the central star showcases significant photometric variability. Such variability may be caused by the presence of a close main-sequence dwarf companion star with a mass below 0.1 solar masses.

Based on the results, the authors of the paper noted that the dust cloud surrounding the central star of the Ring Nebula may be a remnant of the disk resulting from binary interaction during an earlier evolutionary phase of this star, which has now been almost completely dissipated.

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