- Find described as 'one of the most remarkable examples of a planetary nebula'
By Mark Prigg
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Astronomers using ESO’s Very Large Telescope have discovered a pair of stars orbiting each other at the centre of one of a unique 'cosmic sprinkler.
Astronomers say the discovery is one the most remarkable examples of a planetary nebula ever seen.
It also proves a long-debated theory about what controls the spectacular and symmetric appearance of the material flung out into space.
The 'cosmic sprinkler' planetary nebula Fleming 1 in the constellation of Centaurus. It is a glowing cloud of gas around a dying star.
FLEMING 1
Fleming 1 is located in the southern constellation of Centaurus (The Centaur).
It was discovered just over a century ago by Williamina Fleming, a former maid who was hired by Harvard College Observatory after showing an aptitude for astronomy.
During her time she discovered — and was credited for — numerous astronomical objects, including 59 gaseous nebulae, over 310 variable stars, and 10 novae
When a star with a mass up to eight times that of the Sun approaches the end of its life, it blows off its outer shells and begins to lose mass, the researchers say.
This allows the hot, inner core of the star to radiate strongly, causing this outward-moving cocoon of gas to glow brightly as a planetary nebula.
While stars are spherical, many of these planetary nebulae are strikingly complex, with knots, filaments, and intense jets of material forming intricate patterns.
Astronomers have long debated how these symmetric jets could be created, but until now no consensus has been reached.
'The origin of the beautiful and intricate shapes of Fleming 1 and similar objects has been controversial for many decades,' says Henri Boffin, who led the team.
'Astronomers have suggested a binary star before, but it was always thought that in this case the pair would be well separated, with an orbital period of tens of years or longer.
'Thanks to our models and observations, which let us examine this unusual system in great detail and peer right into the heart of the nebula, we found the pair to be several thousand times closer.'
The new research combined new Very Large Telescope (VLT) observations of Fleming 1 with existing computer modelling to explain in detail for the first time how these bizarre shapes came about.
This map shows most of the stars visible to the unaided eye under good conditions, and the location of the nebula is highlighted with a red circle on the image. It can only be seen with larger amateur telescopes.
The team used ESO’s VLT to study the light coming from the central star.
They found that Fleming 1 is likely to have not one but two white dwarfs at its centre, circling each other every 1.2 days.
Although binary stars have been found at the hearts of planetary nebulae before, systems with two white dwarfs orbiting each other are very rare.
'This is the most comprehensive case yet of a binary central star for which simulations have correctly predicted how it shaped the surrounding nebula — and in a truly spectacular fashion,' explains co-author Brent Miszalski, from SAAO and SALT (South Africa).
The pair of stars in the middle of this nebula is vital to explain its observed structure.
As the stars aged, they expanded, and for part of this time, one acted as a stellar vampire, sucking material from its companion.
This material then flowed in towards the vampire, encircling it with a disc known as an accretion disc.
As the two stars orbited one another, they both interacted with this disc and caused it to behave like a wobbling spinning top — a type of motion called precession
The deep images from the VLT have also led to the discovery of a knotted ring of material within the inner nebula.
Such a ring of material is also known to exist in other families of binary systems, and appears to be a telltale signature of the presence of a stellar couple.
This artist's impression shows how the two stars at the heart of a planetary nebula like Fleming 1 can control the creation of the spectacular jets of material ejected from the object.
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