Endings and Beginnings – Magnetic Jets Shape Stellar Transformation

The incredible visual appearance of planetary nebulae are some of the most studied and observed of deep space objects. However, these enigmatic clouds of gas have defied explanation as to their shapes and astronomers are seeking answers. Thanks to a new discovery made by an international team of scientists from Sweden, Germany and Austria, we have now observed a jet of high-energy particles in the process of being ejected from an expiring star.

When a sun-like star reaches the end of its life, it begins to shed itself of its outer layers. These layers blossom into space at speeds of a few kilometers per second, forming a variety of shapes and sizes – yet we know little about what causes their ultimate appearance. Now astronomers are taking a close look at a rather normal star that has reached the end of its life and is beginning to form a planetary nebula. Cataloged as IRAS 15445-5449, this stellar study resides 230,000 light years away in the constellation of Triangulum Australe (the Southern Triangle). Through the use of the CSIRO Australia Telescope Compact Array, a compliment of six 22-meter radio telescopes in New South Wales, Australia, researchers have found what may be the answer to this mystery… high-speed magnetic jets.

“In our data we found the clear signature of a narrow and extremely energetic jet of a type which has never been seen before in an old, Sun-like star,” says Andrés Pérez Sánchez, graduate student in astronomy at Bonn University, who led the study.

How does a radio telescope aid researchers in an optical study? In this case the radio waves emitted by the dying star are compatible with the trademark high-energy particles they are expected to produce. These “spouts” of particles travel at nearly the speed of light and coincident jets are also known to emanate from other astronomical objects that range from newborn stars to supermassive black holes.

“What we’re seeing is a powerful jet of particles spiraling through a strong magnetic field,” says Wouter Vlemmings, astronomer at Onsala Space Observatory, Chalmers. “Its brightness indicates that it’s in the process of creating a symmetric nebula around the star.”

Will these high-energy particles contained within the jet eventually craft the planetary nebula into an ethereal beauty? According to the astronomers, the current state of IRAS 15445-5449 is probably a short-lived phenomenon and nothing more than an intense and dramatic phase in its life… One we’re lucky to have observed.

“The radio signal from the jet varies in a way that means that it may only last a few decades. Over the course of just a few hundred years the jet can determine how the nebula will look when it finally gets lit up by the star,” says team member Jessica Chapman, astronomer at CSIRO in Sydney, Australia.

Will our Sun also follow suit? Right now the answer is unclear. There may be more to this radio picture than meets the ear. However, rest assured that this new information is being heard and might well become the target of additional radio studies. Considering the life of a planetary nebula is generally expected to last few tens of thousands of years, this is a unique opportunity for astronomers to observe what might be a transient occurrence.

“The star may have an unseen companion – another star or large planet — that helps create the jet. With the help of other front-line radio telescopes, like ALMA, and future facilities like the Square Kilometre Array (SKA), we’ll be able to find out just which stars create jets like this one, and how they do it,” says Andrés Pérez Sánchez.

Original Story Source: Royal Astronomical Society News Release.

Hubble Movies “Star” Supersonic Jets

[/caption]Don’t you know that you are a shooting star… Thanks to the NASA/ESA Hubble Space Telescope, an international team of scientists led by astronomer Patrick Hartigan of Rice University in Houston, USA, has done something pretty incredible. Using photos and information gathered from the last 14 years of observations, they’ve sewn together an unprecedented look at young jets ejected from three stars. Be prepared to be “blown” away…

The time-lapse sequence of “moving pictures” offers us an opportunity to witness activity that takes place over several years in just a few seconds. Active jets can remain volatile for periods of up to 100,000 years and these movies reveal details never seen – like knots of gas brightening and dimming – and collisions between fast-moving and slow-moving material. These insights allow scientists to form a clearer picture of stellar birth.

“For the first time we can actually observe how these jets interact with their surroundings by watching these time-lapse movies,” said Hartigan. “Those interactions tell us how young stars influence the environments out of which they form. With movies like these, we can now compare observations of jets with those produced by computer simulations and laboratory experiments to see which aspects of the interactions we understand and which we don’t understand.”

As a star forms in its collapsing cloud of cold gas, it gushes out streams of material in short bursts, pushing out from its poles at speeds of up to about 600,000 miles an hour. As the star ages, it spins material and its gravity attracts even more, creating a disc which may eventually become protoplanetary. The fast moving jets may be restricted by the neophyte star’s magnetic fields and could cease when the material runs out. However, by looking at this supposition in action, new questions arise. It would appear that the dust and gas move at different speeds.

“The bulk motion of the jet is about 300 kilometers per second,” Hartigan said. “That’s really fast, but it’s kind of like watching a stock car race; if all the cars are going the same speed, it’s fairly boring. The interesting stuff happens when things are jumbling around, blowing past one another or slamming into slower moving parts and causing shockwaves.”

But the “action” doesn’t stop there. In viewing these sequential shockwaves, the team was at a loss to understand the dynamics behind the collisions. By enlisting the aid of colleagues familiar with the physics of nuclear explosions, they quickly discovered a recognizable pattern.

“The fluid dynamicists immediately picked up on an aspect of the physics that astronomers typically overlook, and that led to a different interpretation for some of the features we were seeing,” Hartigan explained. “The scientists from each discipline bring their own unique perspectives to the project, and having that range of expertise has proved invaluable for learning about this critical phase of stellar evolution.”

Hartigan began using Hubble to collect still frames of stellar jets in 1994 and his findings are so complex he has employed the aid of experts in fluid dynamics from Los Alamos National Laboratory in New Mexico, the UK Atomic Weapons Establishment, and General Atomics in San Diego, California, as well as computer specialists from the University of Rochester in New York. The Hubble sequence movies have been such a scientific success that Hartigan’s team is now conducting laboratory experiments at the Omega Laser facility in New York to understand how supersonic jets interact with their environment.

“Our collaboration has exploited not just large laser facilities such as Omega, but also computer simulations that were developed for research into nuclear fusion,” explains Paula Rosen of the UK Atomic Weapons Establishment, a co-author of the research. “Using these experimental methods has enabled us to identify aspects of the physics that the astronomers overlooked — it is exciting to know that what we do in the laboratory here on Earth can shed light on complex phenomena in stellar jets over a thousand light-years away. In future, even larger lasers, like the National Ignition Facility at the Lawrence Livermore National Laboratory in California, will be able explore the nuclear processes that take place within stars.”

And all the world will love you just as long… as long as you are… a shooting star!

Original Story Source and Video Presentation: Hubble News. For further reading, Rice University News.