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“The Milky Way, our galaxy, is a cluster of stars among
which is the sun. We believe that the Milky Way counts about
150 billion stars, all of them turning around the centre of
the Milky Way. There are several tens of billion galaxies in
our universe. Our planet Earth turns around a star among 150
billion stars in a galaxy which is among a hundred billion galaxies.
To understand the Milky Way, I'm working on the preparation of
the Gaia mission, of the the European Space Agency. That mission
consists in launching a satellite into orbit around the Earth.
Over five years it will observe one billion stars in the Milky
Way and it will measure their distances very precisely, their
positions and their motions. It will provide a great deal of
data that will help us to understand the history and structure
of our Milky Way.
Brown
dwarfs
are “failed stars”: less massive (than magnitude
one stars such as the sun) and less hot in their cores, they
cannot initiate any nuclear fusion reactions essential to make
stars shine. Brown dwarfs become less and less luminous over
time and they slowly fade away until they become extinct. Not
very bright, it's difficult to detect them since their light
is mainly in the near infrared range. We have detected about
one thousand of them, whereas we believe several tens of billion
may exist in our Milky Way.
Paradoxically, we mainly use a computer to study stars and we
are behind our computer screens. We sometimes go to observe stars
directly at big observatories like the one in Mauna Kea - at
the summit of an extinct volcano in Hawaï, at an altitude
of 4200 metres, in a moon-like landscape and under a very clear
sky where the Canada-France-Hawaï telescope is located.” |
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