September 27, 2013
Magnetic Field May Give Shape To Blooming Stars
[ Watch The Video: CSIRO’s Australia Telescope Compact Array ]
John P. Millis, PhD for redOrbit.com - Your Universe Online
Many objects in the Universe contain jets – intense magnetic fields twisted around their axes, ejecting plasma into the Cosmos. In general, however, these objects tend to be powerful, exotic entities such as black holes and neutron stars. Or, at the other end of the spectrum, forming stars – called proto-stars – can form such jet structures as well, but on smaller scales.
But scientists have also observed jets in some very odd places, such as in a small number of old stars. One of these peculiar cases, known as IRAS 15445-5449, has now been observed to be in the early stages of creating a collimated outflow of particles. The benefit of observing this star in such an early stage of jet formation is that scientists can probe the structure of the jet: is it similar to those in dense objects, like black holes, or does it persist by a different physical process?
The key, according to Jessica Chapman of CSIRO Astronomy and Space Science, is that the team has observed a significant radio signature from the base of the jet, noting that “this is the first one where the radio waves tell us the jet is held together by a strong magnetic field. That’s a clue to what makes these jets switch on.”
This particular object, located some 23,000 light-years away in the constellation Triangulum Australe, is in the early stages of its death cycle. Soon, the star will cease being a star altogether and will transition into a new object, known as a planetary nebula. The outer layers of the star will drift off into the surrounding space, creating a beautiful cocoon around the stellar core, the only remaining structure of its previous existence. Eventually, the core - a burning ember known as a white dwarf - will fade into darkness.
In general, planetary nebulae – so named because early astronomers thought they looked like giant gas planets – have one of two structures. Either they are round blobs, or, as in this case, a long symmetrical tube resembling an a hourglass. The question this research hopes to answer is what creates this symmetrical shape?
Chapman and her team propose that it is this early emerging jet structure that drives the tube formation, rather than allowing the outer layers of the star to drift off in all directions. The reason this has been so difficult to determine is that compared to the lifetime of a star, the jet is just a "blink of an eye in a star's life," says Dr Chapman, "probably lasting only about a hundred years."
To be able to observe a star in such early stages of this transition is important. Of course, future work is needed, and astronomers hope to be able to find other stars at similar life stages to confirm their findings.