This image was taken by the European Space Agency’s Infrared Space Observatory,
ISO, which operated until May 1998 and which is, so far, the best infrared
space telescope astronomers have ever had. As an infrared telescope ISO had
the ability to see objects and material that other telescopes cannot see, for
example, cold dust[*]. The dust in the Eagle, seen in the picture as a ‘bluish
fog’, is at about minus 100 C. Although perhaps difficult to believe, it is
inside freezing dust like this that new, hot stars are born. In this image
ISO has captured a view of the ice enshrouding the fire.
The Eagle nebula is an active ‘star nursery’ located 7000 light-years away,
in the constellation Serpens. It is a huge cloud composed mainly of gas
with microscopic particles of dust. Surprising as it may seem, its cold
temperature is a key requirement for star-birth to actually occur.
Stars are huge balls of hot gas that emit energy because a non-stop nuclear
fusion reaction is taking place in their cores, a reaction that can only
happen if the atoms in the gas become highly compressed. The cause of this
compression is gravity, and in fact the formation of a new star begins when
the inward force of gravity pulls together the gas and dust in the nebula.
At that very moment a ‘battle’ between forces begins: when the gas and dust
condense they also become warmer, and they start to radiate thermal (heat)
energy. An outward pressure, opposed to the inward force of gravity, is
therefore created. If the gas becomes too hot this outward force ‘wins’,
and the star-birth process is interrupted because the atoms in the gas will
never be compressed enough to trigger a nuclear reaction. That is why the
cold environment of the nebula plays such a key role: only if the nebula is
cold enough and allows the heat created in the gravitational collapse to be
radiated away, can a new star be born. The whole birth process can take
anything from a few thousand to tens of thousands of years for the most
massive stars, and up to many millions of years for the least massive stars.
A star like the Sun takes a few tens of millions of years to form.
ESA astronomer Göran Pilbratt, who made ISO observations of the Eagle nebula,
explains: “in the ISO images we can see the emission of the dust itself. The
cold dust is very important if we want to unveil what is actually happening
in the nebula. The process of star-formation is still not well understood,
and infrared observations are adding vital pieces to the puzzle.”
ISO was ‘tuned’ to detect dust in a certain range of temperatures. For these
observations the tuning (temperature) corresponded to emissions arising under
very particular conditions. Specifically, ISO was searching for evidence of
organic molecules associated with very small dust grains on the outskirts of
the clouds of gas and dust, and heated by a star outside of the cloud. The
interior of such clouds — where the actual star-formation takes place —
is much colder than these outer regions and to see this astronomers need
extremely far infrared and submillimetre space telescopes ( telescopes
sensitive to light with wavelengths in the millimetre range). In 2007 ESA
will launch the first space telescope able to detect radiation in this range;
it is called the Herschel Space Observatory and is the largest imaging space
telescope ever designed.
[*]Cold objects emit most of their energy in the infrared, and hence only
infrared telescopes can see them. ISO could detect a 1 cm thick ice cube at
a distance of 1000 km, solely by its heat emission.
About this image
This ISO picture of M16, the Eagle nebula, has been produced by combining
images that were originally obtained as part of the ISOGAL program. The
images were retrieved from the ISO Archive at the ISO Data Centre in
Villafranca, Spain, and reprocessed with the most recent calibration files.
The color image was constructed from a 7.7 micron infrared exposure (shown
as blue), and a 14.5 micron infrared exposure (shown as red).
Further analysis of these data is being carried out by Andrea Moneti
(Institute d’Astrophysique de Paris, IAP) in collaboration with other
members of ISOGAL.
The original observations by Pilbratt et al. were reported on in the
scientific journal Astronomy and Astrophysics 333, L9-L12, (1998).
About ISO
The European Space Agency’s infrared space telescope, ISO, operated from
November 1995 till May 1998. As an unprecedented observatory for infrared
astronomy, able to examine cool and hidden places in the Universe, ISO
successfully made nearly 30,000 scientific observations.
USEFUL LINKS FOR THIS STORY
* More about ISO
* The ISO archive
IMAGE CAPTION:
[http://sci.esa.int/content/searchimage/searchresult.cfm?aid=18&cid=12&oid=28114&ooid=27994]
Cold comfort for newborn stars — ISO unmasks the icy veil around the Eagle’s
fiery heart. Credit: ESA & the ISOGAL team.
Göran Pilbratt, Herschel Project Scientist
ESA, European Space Research and Technology Centre, The Netherlands
Tel: +31 71 565 3621
Email:gpilbratt@astro.estec.esa.nl
Leo Metcalfe, ISO Project Scientist
ESA, Villafranca Satellite Tracking Station, Spain
Tel: +34 91 8131372
Email:lmetcalf@iso.vilspa.esa.es
ESA Science Communication Service
Tel: +31 71 565 3223
