Astronomers using ESO's Very Large Telescope have discovered a pair of stars orbiting each other at the centre of one of the most remarkable examples of a planetary nebula. The new result confirms a long-debated theory about what controls the spectacular and symmetric appearance of the material flung out into space. The results are published in the 9 November 2012 issue of the journal Science.
Planetary nebulae are glowing shells of gas around white dwarfs -- Sun-like stars in the final stages of their lives. Fleming 1 is a beautiful example that has strikingly symmetric jets that weave into knotty, curved patterns. It is located in the southern constellation of Centaurus (The Centaur) and 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.
Astronomers have long debated how these symmetric jets could be created, but no consensus has been reached. Now, a research team led by Henri Boffin (ESO, Chile) has 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.
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.
"The origin of the beautiful and intricate shapes of Fleming 1 and similar objects has been controversial for many decades," says Henri Boffin. "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."
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. 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. Some of the most spectacular nebulae -- including Fleming 1 -- present point-symmetric structures. For this planetary nebula it means that the material appears to shoot from both poles of the central region in S-shaped flows. This new study shows that these patterns for Fleming 1 are the result of the close interaction between a pair of stars -- the surprising swansong of a stellar couple.
"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. This movement affects the behaviour of any material that has been pushed outwards from the poles of the system, such as outflowing jets. This study now confirms that precessing accretion discs within binary systems cause the stunningly symmetric patterns around planetary nebulae like Fleming 1.
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.
"Our results bring further confirmation of the role played by interaction between pairs of stars to shape, and perhaps even form, planetary nebulae," concludes Boffin.
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
Scientists are puzzled by a new image taken by NASA's Dawn spacecraft, which found two bright spots on the dwarf planet Ceres. The spots are noticeably brighter than other parts of the surface.
Moscow assures it will continue funding the International Space Station until 2024 but will then disconnect its modules to build a national base
The first ever photograph of our planet from space marks the moment when rockets became space exploration vehicles and not just bomb carriers
(Reuters) - An unusual pink cloud that lit up the sky over New Mexico and Arizona early on Wednesday was caused by a NASA research rocket launched to study the outer reaches of Earth's atmosphere, scientists said.
CAPE CANAVERAL, Fla. (Reuters) - Two U.S. astronauts finished a 6-1/2-hour spacewalk on Wednesday to prepare parking spots for new commercial space taxis then discovered water had leaked into a spacesuit helmet, a problem that led to the near-drowning of another astronaut in 2013, officials said.
Astronomers are confounded that an object so big could have formed so soon after the Big Bang
Exceptional sensitivity might one day reveal largest structure of universe
We're getting ready to send a probe to Jupiter's icy moon – but how will we know if anything lives there?
During a spacewalk outside ISS, NASA's Barry "Butch" Wilmore snapped an amazing selfie with Earth in the background
NASA astronauts will exit the space station three times to prepare it for visits from new space ferries carrying new crews