An artist’s impression of ULAS J222711-004547. This newly discovered
brown dwarf is characterized by an unusually thick layer of clouds, made
of mineral dust. These thick clouds give ULAS J222711-004547 its
extremely red colour, distinguishing it from “normal” brown dwarfs.
Credit: Neil J Cook, Centre for Astrophysics Research, University of
Hertfordshire
A peculiar example of a celestial body, known as a brown dwarf, with
unusually red skies has been discovered by a team of astronomers from
the University of Hertfordshire’s Centre for Astrophysics Research. The
scientists publish their results in the journal Monthly Notices of the Royal Astronomical Society.
Brown dwarfs straddle the line between stars and planets. They are
too big to be considered as planets; yet they do not have sufficient
material to fuse hydrogen in their cores to fully develop into stars.
They are midway in mass between stars, like our Sun, and giant planets,
like Jupiter and Saturn. Sometimes described as failed stars, they do
not have an internal source of energy – so they are cold and very faint,
and keep on cooling over time.
The brown dwarf, named ULAS J222711-004547, caught the researchers’
attention for its extremely red appearance compared to “normal” brown
dwarfs. Further observations with the Very Large Telescope (VLT) in
Chile and the use of an innovative data analysis technique have shown
that the reason for its peculiarity is the presence of a very thick
layer of clouds in its upper atmosphere.
Federico Marocco, who led the research team from the University of
Hertfordshire, said: “These are not the type of clouds that we are used
to seeing on Earth. The thick clouds on this particular brown dwarf are
mostly made of mineral dust, like enstatite and corundum.
“Not only have we been able to infer their presence, but we have also
been able to estimate the size of the dust grains in the clouds.”
The size of the dust grains influences the colour of the sky. In a
similar way that the old saying of “Red sky at night, shepherd's
delight. Red sky in the morning, shepherd's warning” is used at sunrise
and sunset to indicate the changing weather, a red sky on the brown
dwarf suggests an atmosphere loaded with dust and moisture particles. If
our morning skies are red, it is because clear skies to the east permit
the sun to light the undersides of moisture-bearing clouds coming in
from the west. Conversely, in order to see red clouds in the evening,
sunlight must have a clear path from the west in order to illuminate
moisture-bearing clouds moving off to the east. However, the recently
discovered brown dwarf ULAS J222711-004547 has a very different
atmosphere where the sky is always red.
The giant planets of the Solar System, like Jupiter and Saturn, show
various cloud layers including ammonia and hydrogen sulphide as well as
water vapour. The atmosphere observed in this particular brown dwarf is
hotter - with water vapour, methane and probably some ammonia but,
unusually, it is dominated by clay-sized mineral particles.
Getting a good understanding of how such an extreme atmosphere works
will help us to better understand the range of atmospheres that can
exist.
Dr Avril Day-Jones, from the University of Hertfordshire’s Centre for
Astrophysics Research, who contributed to the discovery and analysis
said: “Being one of the reddest brown dwarfs ever observed, ULAS
J222711-004547 makes an ideal target for multiple observations to
understand how the weather is in such an extreme atmosphere.”
“By studying the composition and variability in luminosity and
colours of objects like this, we can understand how the weather works on
brown dwarfs and how it links to other giant planets.”
Part of this work was carried out under the Marie Curie 7th European
Community Framework Programme grant no. 247593, Interpretation and
Parameterization of Extremely Red COOL dwarfs (IPERCOOL) International
Research Staff Exchange Scheme.
Media contact (for interviews with Federico Marocco)
Julie Cooper
University of Hertfordshire Press Office
Tel: +44 (0)1707 284095
j.cooper5@herts.ac.uk
Further information:
The new work appears in “The extremely red L dwarf ULAS J222711−004547 - dominated by dust”,
F. Marocco, A. C. Day-Jones, P. W. Lucas, H. R. A. Jones, R. L. Smart,
Z. H. Zhang, J. I. Gomes, B. Burningham, D. J. Pinfield, R. Raddi and
L. Smith, Monthly Notices of the Royal Astronomical Society. A preprint of the paper is also available.
Image and caption:
An image is available from http://www.ras.org.uk/images/stories/press/Red%20brown%20dwarf.jpg
Full resolution versions are available from https://www.ras.org.uk/images/stories/press/Red%20brown%20dwarf%20large.jpg and http://star.herts.ac.uk/~fmarocco/redskies/
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