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Astronomers have measured for the first times on "failed stars"

Astronomers have measured for the first times the mass of a
series of brown dwarfs. These "failed stars" are massive and
very little light. Researchers have discovered that their
theoretical models do not stuck entirely consistent with the
observations. Although small, this disagreement will force them
to review their copy ...

Since the work of pioneers such as Edington, Milne and
Chandrasekhar, the theory of stellar structure is a fairly well
understood field of astrophysics. It allows linking the mass of
a star in its temperature and its brightness. There is however a
class of objects rather individuals who are intermediaries
between stars and planets, brown dwarfs.

The latter are too massive to be really described as giant
gaseous, like Jupiter, but they are not enough to make them
ignite thermonuclear reactions, except that fusion of deuterium,
which occurs perhaps during a short period for the most massive
of them.

This does not mean that these stars are inert and does not
radiate. Just as proto-stars or Jupiter itself, they contract
and slowly released gravitational energy is converted into heat.
Called Kelvin-Helmoltz, named researchers from the nineteenth
century, which had originally proposed to explain the luminosity
of the Sun, this process heats despite all the latter which
radiate therefore, although marginally.

Again, astrophysicists have predicted a relationship between the
mass of brown dwarfs, their brightness and surface temperature.
Measuring these last two is relatively easy to measure remained
grounded.

As for normal stars, this can only happen if one has a binary
system. By measuring the size and frequency of the orbit of this
system to two body, it becomes possible to determine the mass of
two stars and this is as astrophysicists have been able to test
their theory of stellar structure, 'Backbone of astrophysics.




2MASS 1534-2952AB observed infrared, orbiting around a
solar-type star on the right. Credit: Dr. Michael Liu (Institute
for Astronomy, University of Hawaii)

The determination of the masses of two systems binary brown
dwarfs, 4 stars at all, therefore, has been achieved through
several years of patient and careful observations with the
telescope Keck II adaptive optics on Mauna Kea in Hawaii.

Limit instrumental

Indeed, brown dwarfs are themselves small objects, their orbits
are not very big either and it requires a telescope gifted with
a good resolution to form two distinct images of these stars.
Without the use of adaptive optics techniques to escape the
turbulence of the atmosphere, it would be impossible.

By creating an artificial star in the sky with a laser beam,
astronomers measured in some way the turbulence of the
atmosphere and a system of jacks controlled by computer
constantly alters the structure mirrors of the Keck telescopes
to correct the image deteriorated by turbulence.



In the upper left HD 130948BC infrared. Credit: Mr. Trent Dupuy,
Dr. Michael Liu (Institute for Astronomy, University of Hawaii)


The two binary observed are colder than we know. In the first
case, stars with methane in their atmospheres and known as 2MASS
1534-2952AB. Its total mass is about 30 times that of Jupiter,
divided by half for each star of the binary, making only 6% of
that of the Sun.

In the second case, the measures have provided a total mass of
11% of that of the Sun, is also shared evenly, and as expected,
these stars are a little warmer than in the case of the first
binary . This system is it known as HD 130948BC stars and the
grantor are richer in dust.

MaisMASS 1534-2952AB seems too cold in relation to its mass and
its luminosity, while HD 130948BC is hotter than is the theory
of stellar structure.

However, many astrophysicists found the right order of magnitude
but their predictions are sufficiently precise so that
disagreements observed imply a mistake somewhere, but where? In
theory or in the chain of measures that provided the parameters
of these stars? More likely in the theory and that is why, even
though astronomers will refine their measures in the coming
years, astrophysicists, they will revise their theoretical
models.