Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

RAS PN06/32: The Magnetic Nature of a Mysterious Cosmic X-ray Emitter

07.06.2006


Our Sun has its explosive flares and spots and high speed wind, but it is a placid star compared to some. Stars that are much more massive live fast and die young, with blue-white, intensely hot surfaces that emit energy at a rate millions of times greater than that of the Sun. These stars are so bright that their light alone propels outflowing stellar winds - up to a billion times stronger than the solar wind - at speeds of up to 30,000 km/s, or one per cent of the speed of light.



An international team of astronomers [1] has discovered that one such star, the naked-eye tau Scorpii, unexpectedly hosts a complex network of magnetic field lines over its surface. Tau Scorpii has been known for some time to emit X-rays at an unusually high rate and to rotate slower than most otherwise similar stars. The newly discovered magnetic field, presumably a relic from the star’s formation stage, goes some way to explaining both characteristics, although the mechanism by which the magnetic field slowed down tau Scorpii’s rotation so strongly remains mysterious.

These results will be published in the Monthly Notices of the Royal Astronomical Society.


The processes by which hot, massive stars expel their surface layers through their strong outflowing winds have a major impact on a star’s long-term fate. The cast-off material can also interact with other nearby stars, contribute matter and energy to the surrounding interstellar medium, and even induce bursts of new star formation. Hot massive stars are thus key actors in the life of a galaxy.

One such hot star is tau Scorpii, whose intrinsic brightness is so great that it is easily visible with the naked eye, despite its distance of over 400 light-years. Weighing as much as 15 Suns, tau Scorpii is 5 to 6 times bigger and hotter than our own star. Such massive stars are relatively few in number compared to stars like the Sun, and tau Scorpii is actually one of our closest massive neighbours.

Massive stars are thought to emit X-rays because of supersonic shocks occurring within their outflowing winds. However, tau Scorpii is an unusually strong X-ray source compared to stars which are otherwise similar.

The reason for this enhanced activity was a puzzle until the present discovery, which revealed that the star hosts a complex network of magnetic field lines over its surface (see image). According to the discovery team, this field is most probably a relic from the star’s formation stage.

The most interesting aspect, though, is how the field interacts with the wind, forcing it to flow along magnetic field lines, like beads along wires. Wind streams along ’open’ magnetic field lines (shown in blue) freely escape the star, something that wind streams in magnetic ’arcades’ (shown in white) cannot achieve. The result is that, within each magnetic arcade, wind flows from both footprints collide with each other at the loop summits, producing tremendously energetic shocks and turning the wind material into blobs of million-degree, X-ray emitting plasma tied to the magnetic loops.

This model provides a natural explanation of why tau Scorpii is such an intense X-ray emitter. However, it is not yet clear how the magnetic field succeeded in slowing down the rotation rate of the star to less than one-tenth that of otherwise similar, non-magnetic, massive stars.

Sun-like stars can be slowed down through their magnetic wind, just as ice-skaters are spun down when outstretching their arms. Tau Scorpii does not, however, lose material fast enough to have its rotation modified within its very short lifetime of a few million years.

The researchers discovered and examined the magnetic field of the star by looking at the tiny, very specific polarisation signals that magnetic fields induce in the light of magnetic stars. To do this, they used ESPaDOnS [2], by far the most powerful instrument in the world for carrying out this kind of research. This new instrument, currently attached to the Canada-France-Hawaii Telescope [3] on Hawaii, was specially designed at the Observatoire Midi-Pyrénées in France for observing and studying magnetic fields in stars other than the Sun.

[1] The team includes J. F. Donati (Observatoire Midi-Pyrenees/LATT, CNRS/UPS, France), I. D. Howarth (University College London, UK), M. M. Jardine (University of StAndrews, UK), P. Petit (Observatoire Midi-Pyrenees/LATT, CNRS/UPS, France), C. Catala (Observatoire Paris-Meudon/LESIA, CNRS/UP7, France), J. D. Lanstreet (University of Western Ontario, Canada), J. C. Bouret (Observatoire de Marseille/LAM, CNRS/UdP, France), E. Alecian (Observatoire Paris-Meudon/LESIA, CNRS/UP7, France), J. R. Barnes (University of St Andrews, UK), T. Forveille (Canada-France-Hawaii Telescope Corporation, USA), F. Paletou (Observatoire Midi-Pyrenees/LATT, CNRS/UPS, France) and N. Manset (Canada-France-Hawaii Telescope Corporation, USA).

[2] ESPaDOnS was co-funded by France (CNRS/INSU, Ministère de la Recherche, LATT, Observatoire Midi-Pyrénées, Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique, Observatoire de Paris-Meudon), Canada (NSERC), CFHT and ESA (ESTEC/RSSD). First light occurred at CFHT on 2 September 2004.

[3] CFHT operation is funded by Canada (NSERC), France (CNRS/INSU) and the University of Hawaii.

Prof. Ian Howarth | alfa
Further information:
http://www.star.ucl.ac.uk
http://www.ras.org.uk/

More articles from Physics and Astronomy:

nachricht A better way to weigh millions of solitary stars
15.12.2017 | Vanderbilt University

nachricht A chip for environmental and health monitoring
15.12.2017 | Friedrich-Alexander-Universität Erlangen-Nürnberg

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First-of-its-kind chemical oscillator offers new level of molecular control

DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.

Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Engineers program tiny robots to move, think like insects

15.12.2017 | Power and Electrical Engineering

One in 5 materials chemistry papers may be wrong, study suggests

15.12.2017 | Materials Sciences

New antbird species discovered in Peru by LSU ornithologists

15.12.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>