Washington, March 11 : Astronomers at the University of Rochester, US, have determined that low-mass stars and possibly even super-Jupiter-sized planets may indeed be responsible for creating the planetary nebula.
A planetary nebula is an astronmical object consisting of a glowing shell of gas and plasma formed by certain types of stars at the end of their lives.
When this object was discovered 300 years ago, astronomers couldn't tell what it was and named it for its resemblance to the planet Uranus. But as early as the mid-19th century, astronomers realized these objects are really great clouds of dust emitted by dying stars.
Now, Rochester researchers have found that planets or low-mass stars orbiting these aged stars may indeed be pivotal to the creation of the nebulae's fantastic appearance.
For the research, the team of astronomers studied the consequences of a dying star that possesses an orbiting companion.
"Few researchers have explored how something as small as a very low-mass star, a brown dwarf, or even a massive planet can produce several flavors of nebulae and even change the chemical composition of the dust around these evolved stars," said Eric Blackman, professor of physics and astronomy at the University of Rochester.
According to Blackman, most medium-sized stars, such as our Sun, will end their lives as planetary nebulae. The stage lasts only several tens of thousands of years, so it is a relatively rare sight.
As the star begins to deplete its fuel near the end of its life, its core contracts and its envelope expands, eventually throwing off its outermost layers millions of miles into space.
"One time in five, this envelope keeps its roughly spherical shape as it expands, but much more often this envelope contorts and elongates into new and fantastic shapes," said Blackman.
The Rochester team showed that in the case when the planet or companion star is in a very wide orbit, the planet's gravity begins to drag some of the envelope material around with it.
"The envelope material-essentially a thin mixture of gas and dust-becomes compressed in spiral waves radiating out from the central star like a twisted wagon wheel," said Blackman.
The dust and gas compresses more and more in these spiral waves until they crest, much like waves breaking on a beach. Eventually, a torus of dust forms around the star's mid-section, likely blocking much of the expanding envelope like a belt around an inflating balloon.
Over time, such constrained expansion can lead to striking shapes, such as seen in the appropriately named Dumbbell Nebula.