ESA's ISO provides the first view of monstrous stars being born (Forwarded)

ESA News
http://www.esa.int

20 April 2006

ESA's ISO provides the first view of monstrous stars being born

Scientists have secured their first look at the birth of monstrous stars
that shine 100 000 times more brightly than the Sun, thanks to ESA's
Infrared Space Observatory (ISO).

The discovery allows astronomers to begin investigating why only some
regions of space promote the growth of these massive stars.

Space is littered with giant clouds of gas. Occasionally, regions within
these clouds collapse to form stars. "One of the major questions in the
field of study is why do some clouds produce high- and low-mass stars,
whilst others form only low-mass stars?" asks Oliver Krause,
Max-Planck-Institut für Astronomie, Heidelberg and Steward Observatory,
Arizona.

The conditions necessary to form high-mass stars are difficult to deduce
because such stellar monsters form far away and are shrouded behind
curtains of dust. Only long wavelengths of infrared radiation can escape
from these obscuring cocoons and reveal the low temperature dust cores
that mark the sites of star formation. This radiation is exactly what
ISO's ISOPHOT far-infrared camera has collected.

Stephan Birkmann, Oliver Krause and Dietrich Lemke, all of the
Max-Planck-Institut für Astronomie, Heidelberg, used ISOPHOT's data to
zero-in on two intensely cold and dense cores, each containing enough
matter to form at least one massive star. "This opens up a new era for
the observations of the early details of high-mass star formation," says
Krause.

The data was collected in the ISOPHOT Serendipity Survey (ISOSS), a
clever study pioneered by Lemke. He realised that when ISO was turning
from one celestial object to another, valuable observing time was being
lost. He organised for ISOPHOT's far-infrared camera to continuously
record during such slews and beam this data to Earth.

During the ISO mission, which lasted for two and a half years during
1995-98, the spacecraft made around 10 000 slews, providing a web of
data across the sky for the previously unexplored window of infrared
emission at 170 micrometres. This wavelength is 310 times longer than
optical radiation and reveals cold dust down to just 10K (-263 Celsius).
A catalogue was produced of the cold sites in the survey.

Birkmann and his colleagues investigated this catalogue and found fifty
potential places of high-mass stellar birth. A campaign of follow-up
observations using ground-based telescopes revealed that object ISOSS
J18364-0221 was in fact two cold dense cores that looked suspiciously
like those associated with the birth of low-mass stars, but containing
much more mass.

The first core is at 16.5 Kelvin (-256.5 Celsius). It contains
seventy-five times the mass of the Sun and shows signs of gravitational
collapse. The second one is around 12K (-261 Celsius) and contains 280
solar masses. The team are currently studying the other potential sites.

Note to editors

Although ISO is no longer operational, ESA is currently participating in
the Japanese Aerospace Exploration Agency's infrared mission, Akari
(former ASTRO-F). It will fill in the blanks in the ISOSS data by
surveying the whole sky at six infrared wavebands. Beyond Akari, ESA
will continue to pioneer infrared astronomy with its space telescope,
Herschel, due to launch in 2008. Birkmann says, "With its 3.5 metre
mirror and its far-infrared detectors, Herschel will unveil the earliest
phases of massive star birth in unprecedented detail."

This work could also help make sense of the most distant objects in the
Universe. "When astronomers look billions of light years into space, all
they can see are the bright, high-mass stars in very distant galaxies.
If we can understand how these stars form, we may be able to apply that
knowledge to understand how galaxies evolve," says Krause.

The findings appear on the 20 January 2006 issue of The Astrophysical
Journal (637:380-383). The original article, titled "Very cold and
massive cores near ISOSS J18364-0221: implications for the initial
conditions of high-mass star formation," is by S. M. Birkmann and D.
Lemke (Max-Planck-Institut für Astronomie, Heidelberg, Germany), and O.
Krause (Max-Planck-Institut für Astronomie, Heidelberg, Germany, and
Steward Observatory, University of Arizona, Tucson, AZ, US)

For more information

Stephan Birkmann, Max-Planck-Institut für Astronomie, Heidelberg, Germany
E-mail: birkmann @ mpia-hd.mpg.de

Alberto Salama, ESA ISO and ASTRO-F/Akari Project Scientist
E-mail: Alberto.Salama @ esa.int

Related links

* ISO
http://www.esa.int/science/iso
* ISO major achievements
http://www.iso.vilspa.esa.es/science/SSR/

Related articles

* From galaxy collisions to star birth: ISO finds the missing link
http://www.esa.int/esaCP/SEM7SVRMD6E_index_0.html
* Observations: Seeing in infrared wavelengths
http://www.esa.int/esaSC/SEMS72T1VED_index_0.html

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/esaCP/SEM8MZNFGLE_index_1.html]
Massive star forming region as seen by ISO

The ISOSS J18364-0221 region contains two dense cores, each containing
enough matter to become at least one massive star. The background image
was taken by the Calar Altar 3.5 metre telescope during October 2003 and
June 2004. The white contours show cold dust and were taken by the James
Clerk Maxwell Telescope during May 2003. The diffuse and elongated
emission displayed in green is due to shocked molecular hydrogen (was
also observed at Calar Alto) and this traces the outflow of the obscured
central source.

Credits: Birkmann/Krause/Lemke (Max-Planck-Insitut für Astronomie)

[Image 2:
http://www.esa.int/esaCP/SEM8MZNFGLE...html#subhead1]
Massive star forming region caught in ISO's web of data

The massive star-forming region ISOSS J18364-0221 is in the centre of
the image. The data was collected by the Infrared Space Observatory's
ISOPHOT's far-infrared camera at 170 micrometres. ISO produced a web of
data as it turned from one celestial object to another during its mission.

Credits: ESA/Birkmann/Krause/Lemke (Max-Planck-Insitut für Astronomie)