February 5, 2013
New Observations Help Understand Massive Solar Winds
Lee Rannals for redOrbit.com — Your Universe Online
These massive stellar winds derive from rare, giant stars which burn their nuclear fuel more rapidly than stars like the Sun, and that live for millions of years before exploding into a supernova.
Massive stars lose a significant fraction of their mass through fierce winds of gas driven from the surface by the intense light given off by the star. These winds are at least a hundred million times stronger than the solar wind emitted by our Sun.
Solar winds could trigger the collapse of surrounding clouds of gas and dust to form new stars, or blast the clouds away before they have the chance to get started. The structure of the winds from massive stars can still be considered a bit of a mystery.
The ESA astronomers have gained a detailed glimpse into this wind structure by taking observations with XMM-Newton spread over a decade to study variability in the X-ray emission from Zeta Puppis.
X-rays can be derived from collisions seen between slow- and fast-moving clumps in the wind, which heats them to a few million degrees. As colliding clumps in the wind are heated and cooled, the strength and energy of the emitted X-rays vary.
If a small number of large fragments are present, variations in the combined emission could be large. As the number of fragments grow, a change in the X-ray emission from any fragment becomes less important.
The X-ray emission was found to be stable over short timescales of just a few hours, which points to a large number of fragments. There could still be clumps in the wind to make X-rays in the first place, but there could be many of them to yield this low variability.
An unexpected variation in the emission was seen over several days which implied the presence of a few very large structures in the wind superimposed on the highly fragmented wind co-rotating within the star.
“Studies at other wavelengths had already hinted that the winds from massive stars are not simply a uniform breeze, and the new XMM-Newton data confirm this, but also reveal hundreds of thousands of individual hot and cool pieces,” YaÃ«l NazÃ©, UniversitÃ© de LiÃ¨ge, Belgium, who led the study´s analysis, said in a statement.
“This is the first time constraints have been placed on the number of fragments in a stellar wind of an adult massive star, a number which far exceeds theoretical predictions.”
In order to fully understand these observations, improved models of stellar winds will be needed.
“Zeta Puppis also goes by the name Naos, which in antiquity was the name given to the innermost sanctuary of a temple, accessible to only a few people; thanks to XMM-Newton, scientists have been able to unlock the secrets of this mysterious stellar object,” Dr NazÃ© explained.
Norbert Schartel, ESA´s XMM-Newton project scientist, said this study has provided the first constraints of the number of fragments in a stellar wind from a massive star. "There is no dataset with comparable sensitivity or time and or spectral coverage currently available for any other massive star."