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 tale of two pulsars' tails: Plumes offer geometry lessons to astronomers
18.01.2017 | Penn State

nachricht Studying fundamental particles in materials
17.01.2017 | Max-Planck-Institut für Struktur und Dynamik der Materie

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: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Explaining how 2-D materials break at the atomic level

18.01.2017 | Materials Sciences

Data analysis optimizes cyber-physical systems in telecommunications and building automation

18.01.2017 | Information Technology

Reducing household waste with less energy

18.01.2017 | Ecology, The Environment and Conservation

VideoLinks
B2B-VideoLinks
More VideoLinks >>>