Tuesday, 20 June 2017

The Famous ‘Ring Nebula’ in the Summer constellation of Lyrae

M 57 | Magnitude: 9.40 | Name: NGC 6720  | Surface brightness: 9.30 | Dimension: 86.0 x 62.0 seconds of arc | Position angle: 90o Class: 4(3)  |The Central Star is variable Mag 14 to 16 | RA 18h54m16.2s Dec +33°03' 26”

Hubble image of the Ring Nebula (Messier 57)Messier 57 lies midway between the two bright stars Gamma and Beta Lyra

This nebula was discovered by the French astronomer Charles Messier while searching for comets in late January 1779. Messier's report of his independent discovery of Comet Bode reached fellow French astronomer Antoine Darquier de Pellepoix two weeks later, who then independently rediscovered the nebula while following the comet. Darquier later reported that it was "...as large as Jupiter and resembles a planet which is fading" (which may have contributed to the use of the "planetary nebula" terminology). It would be entered into Messier's catalogue as the 57th object. Messier and German-born astronomer William Herschel speculated that the nebula was formed by multiple faint stars that were unresolvable with his telescope.

In 1800, German Count Friedrich von Hahn announced that he had discovered the faint central star at the heart of the nebula a few years earlier. He also noted that the interior of the ring had undergone changes, and said he could no longer find the central star. In 1864, English amateur astronomer William Huggins examined the spectra of multiple nebulae, discovering that some of these objects, including M57, displayed the spectra of bright emission lines characteristic of fluorescing glowing gases. Huggins concluded that most planetary nebulae were not composed of unresolved stars, as had been previously suspected, but were nebulosities. The nebula was first photographed by the Hungarian astronomer Eugene von Gothard in 1886 [Wikipedia].

Above: From Earth’s perspective, the nebula looks like a simple elliptical shape with a shaggy boundary. However, new observations combining existing ground-based data with new NASA/ESA Hubble Space Telescope data show that the nebula is shaped like a distorted doughnut. This doughnut has a rugby-ball-shaped region of lower-density material slotted into in its central “gap”, stretching towards and away from us.

Credit: NASA, ESA, and C. Robert O’Dell (Vanderbilt University).

The geometry and structure of the Ring Nebula (Messier 57)This schematic shows the geometry and structure of the Ring Nebula (Messier 57) as viewed side-on. This shows the nebula’s wide halo, inner region, lower-density lobes of material stretching towards and away from us, and the prominent, glowing disc.

We are gazing almost directly down one of the poles of this structure, and view the brightest part of this nebula as the colourful main “ring”. This is composed of gas thrown off by a dying star at the centre of the nebula.

Credit: NASA, ESA, and A. Field (STScI)

Formed by a star throwing off its outer layers as it runs out of fuel, the Ring Nebula is an archetypal planetary nebula. It is both relatively close to Earth and fairly bright, and so was first recorded in the late 18th century. As is common with astronomical objects, its precise distance is not known, but it is thought to lie just over 2000 light-years from Earth.

From Earth’s perspective, the nebula looks roughly elliptical. However, astronomers have combined ground-based data with new observations using the NASA/ESA Hubble Space Telescope to observe the nebula again, hunting for clues about its structure, evolution, physical conditions and motion.

Wide-field image of the Ring Nebula (ground-based image)It turns out that the nebula is shaped like a distorted doughnut. We are gazing almost directly down one of the poles of this structure, with a brightly coloured barrel of material stretching away from us. Although the centre of this doughnut may look empty, it is actually full of lower density material that stretches both towards and away from us, creating a shape similar to a rugby ball slotted into the doughnut’s central gap.

The brightest part of this nebula is what we see as the colourful main ring. This is composed of gas thrown off by a dying star at the centre of the nebula. This star is on its way to becoming a white dwarf — a very small, dense, and hot body that is the final evolutionary stage for a star like the Sun.


This image from the Digitized Sky Survey shows the Ring Nebula (Messier 57) midway between the two bright stars Gamma and Beta Lyra, and its surroundings.

Credit: NASA, ESA, Digitized Sky Survey 2

Post a Comment