Despite their small number, massive stars are the main architects of a
galaxy - the Sun and the multitude of its dwarf analogs are pretty dull in
comparison. However, these monster stars are apparently unable to achieve
one task that the Sun is very good at performing : regenerating endlessly its
An international team of astrophysicists1 conducted
by researchers from CNRS just discovered an atypical magnetic field on a massive
star in the constellation of Orion; this discovery may shake our understanding
of magnetism in massive stars.
are in press in the Monthly Notices of the Royal Astronomical Society.
Massive stars are rare - typically 1 in 1000. However, they largely compensate by
being extreme in many ways - gigantic, extra hot and super luminous.
But they pay their utter oddness the highest price : by living fast, they die young.
During the few million years of their short life, they strip off massive amounts
of gas from their surfaces under their own radiation, and propel it in the interstellar
medium at an incredible speed of almost 100,000 km/s!
Thanks to this, they are the main galactic sources of atoms heavier than oxygen;
rocks, trees and animals all started their life in massive stars.
For this reason, they control the chemical life of a galaxy. They also trigger
star formation, such as
that occuring at the heart of the famous
They end their life as an apocalypse firework - a
- and give birth to the well known
However, the Sun and its cool cousins (as well as some planets including the Earth)
have one property that massive stars do not - the ability to generate their own
a kind of a star-size electromagnet powered by the
giant convection cells
that cool dwarf stars upkeep in their external layers.
Admittedly, some massive stars host magnetic fields as well; these may
even by the progenitors of the intriguing
magnetars, the most
magnetic stars of the Universe.
But they differ from the Sun in a very important aspect: magnetic fields
of massive stars are likely birth imprints - fossil remnants that only degrade
with time - rather than magnetic fields in continuous rebirth like that of the
Sun, which starts afresh every 11 years.
Located in the constellation of Orion, in the immediate neighbourhood of the
and flame nebula,
is a blue supergiant known from astronomers since a long time.
At a distance of about 1200 light years from us, it is a naked-eye star,
actually the brighest of all massive stars in the sky.
Zeta Orionis is 40 times more massive, 25 times larger, 5 times hotter and
500,000 more luminous than the Sun.
An international team of astrophysicists1
just discovered that zeta Orionis apparently hosts a very special magnetic
field. "This field is about 10 times weaker than that detected in all other massive
stars up to now. This peculiarity may suggest that the field of zeta Orionis is
not a fossil", as Jean-Claude Bouret explains. "Could it be of the same nature as
that of the Sun? And if so, how can it be generated - since zeta Orionis is obviously
lacking the necessary ingredients (the outer convection zone) to produce a field
like that of the Sun?"
The magnetic field of zeta Orionis is thus a true mistery, that Jean-Claude Bouret and
his colleagues will try to unravel in the forthcoming years. In this aim, they will
use the new
spectropolarimeter, recently installed at the 2m
Pic du Midi in
the southern Pyrenees (France). NARVAL is the instrument with which the magnetic field
of zeta Orionis was discovered - it is the only instrument worldwide fully dedicated
to the study of stellar magnetic fields, and detects them through the polarisation they generate
in stellar light.
Montpellier: Fabrice Martins, Groupement d'Astronomie et Astrophysique du Languedoc,
Université Montpellier II Tel: +33 467144042,
This team includes
JC Bouret (CNRS/Université de Provence),
JF Donati (CNRS/Université de Toulouse),
F Martins (CNRS/Univesité Montpellier II),
C Escolano (CNRS/Université de Provence),
W Marcolino (CNRS/Université de Provence),
T Lanz (University of Maryland, USA),
I Howarth (University College London, UK)
NARVAL was cofunded by the Région Midi-Pyrénées, the Ministère de la Recherche,
the conseil Général des Hautes Pyrénées, the European Union (FEDER funds) and
CNRS/INSU. First light occured on 2006 Nov 13.
The operation of the 2m Télescope Bernard Lyot (TBL) is funded by the CNRS Institut National des
Sciences de l'Univers (INSU).