November 8, 2012
What Controls The Spectacular And Symmetric Appearance Of Material Flung Into Space
Lee Rannals for redOrbit.com - Your Universe Online
Astronomers have discovered a pair of stars orbiting each other at the center of a remarkable example of a planetary nebula.
The latest find confirms a theory about what controls the spectacular and symmetric appearance of the material flung out into space.
Planetary nebulae are glowing shells of gas around white dwarfs, and Fleming 1 is considered a great example that has strikingly symmetric jets that weave into curved patterns.
The nebula is located in the southern constellation of Centaurus and was discovered just over a century ago by Williamina Fleming.
Astronomers have debated about how these symmetric jets could be created, but no conclusion has been reached so far. Now, researchers have combined observations of Fleming 1 with existing computer modeling to explain in detail how these shapes occur.
They found that Fleming 1 is likely to have not one, but two white dwarfs at its center, orbiting each other every 1.2 days. Although binary stars have been found in the center of planetary nebulae before, systems with two white dwarfs are a rare sighting.
“The origin of the beautiful and intricate shapes of Fleming 1 and similar objects has been controversial for many decades,” said lead author Henri Boffin of ESO. “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."
He said their models and observations enabled them to examine the unusual system in greater detail, and look right into the heart of the nebula.
When a star with a mass up to eight times that of the Sun reaches the end of its life, it blows off its outer shell and begins to lose mass. This allows the inner core of the star to radiate, and cause the gas to glow brightly as a planetary nebulae.
Many planetary nebulae are strikingly complex, and have intense jets of material that form intricate patterns.
The new study shows that these patterns for Fleming 1 are a result of the close interaction between a pair of stars.
“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,” according to co-author Brent Miszalski from SAAO and SALT.
The two stars in the middle of the nebula is vital to help astronomers explain the observed structure. As the stars aged, they expanded, and one acted as a stellar vampire, sucking material from its companion. This material then flowed out towards the vampire, encircling it with a disc known as an accretion disc.
As the stars orbited one another, they both interacted with this disc and caused it to behave like a wobbling spinning top. This movement affects the behavior of any material that has been pushed outwards from the poles of the system.
The study confirms that processing accretion discs within binary systems cause the symmetric patterns around planetary nebulae.
The images from the VLT have also led to the discovery of a knotted ring of material within the inner nebula. This material is 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,” Boffin said.