The Ring Nebula Has an “Iron Bar”

A composite image of the Ring Nebula (also known as Messier 57 and NGC 6720) constructed from four WEAVE/LIFU emission-line images. The bright outer ring is made up of light emitted by three different ions of oxygen, while the bar across the middle is seen in light emitted by ionized iron atoms, each stripped of four electrons. North is up and east is to the left in the image. Credit: University College London / CC BY 4.0

The Ring Nebula in Lyra, also known as Messier 57, is the most famous planetary nebula in the sky. It’s also one of the most imaged and studied objects of its class. But when Roger Wesson (Cardiff University, UK) and his colleagues analyzed a series of spectra taken between May and June 2023, they found something completely new: An oddly shaped “bar” of ionized iron gas that crosses the nebula roughly from west to east along the elliptical ring’s major axis.

The bar is 500 times wider than Pluto’s orbit around the Sun, and it contains enough iron to form a planet the size of Mars. Why has it been overlooked for so long? And where did it come from?

Key to their discovery, Wesson explains, was the newly installed WHT Enhanced Area Velocity Explorer (WEAVE) at the 4.2-meter William Herschel Telescope on La Palma, Spain. WEAVE is a fiber-fed multi-object spectrograph, which means it can obtain hundreds of spectra all at the same time. In its Large Integral-Field Unit (LIFU) mode, this means that in just one observing session, 547 fibers record spectra of 2.6 arcsecond-wide “pixels” across a hexagonal field that measures 90 by 78 arcseconds. To cover Messier 57, the researchers combined three such fields.

After two nights of taking data, they analyzed these spectra to identify different chemical elements such as hydrogen, oxygen, carbon, neon, and iron.

(Source: skyandtelescope.org)