A giant cocoon of molecular hydrogen discovered around a massiveyoung star (Forwarded)

[http://outreach.jach.hawaii.edu/pres...hotshockedh2/]

Joint Astronomy Centre
Hilo, Hawaii

Contacts

Dr M. S. Nanda Kumar
Centro de Astrofisica da Universidade do Porto (CAUP)
Tel: (+351) 226 089 841
Fax: (+351) 226 089 831
Email:


Dr Amadeu Fernandes
Centro de Astrofisica da Universidade do Porto (CAUP)
Email:

Dr Chris Davis
Joint Astronomy Centre, Hawaii
Tel: +1 808 969 6520
Email:

Dr Stan Kurtz
Instituto de Astronomia, UNAM-Morelia
Tel: +52 443 322 2757
Email:

Dr Douglas Pierce-Price (for questions about UKIRT)
Joint Astronomy Centre, Hawaii
Tel: +1 808 969 6524
Email:

Monday 8th December 2003

A giant cocoon of molecular hydrogen discovered around a massive young star

Astronomers have discovered a giant envelope or disk of glowing gas more than
half a light year across, illuminated by shockwaves caused by winds travelling
at up to 360,000 km/hour (220,000 miles/hour). The disk is orbiting a massive
star 20,000 light years from Earth. This is the first time such a disk has been
found emitting its own light. The discovery is reported today (8 December 2003)
in the journal "Astronomy and Astrophysics".

The work, led by Dr Nanda Kumar of the Centre for Astrophysics of the University
of Porto (CAUP), Portugal, used the United Kingdom Infrared Telescope (UKIRT) in
Hawaii, and other telescopes. The team used the new UKIRT Imager Spectrometer
(UIST) on UKIRT, to study the young stellar object (YSO) known as IRAS
07427-2400. Their results show that the envelope or disk around the young star
is glowing in the light of molecular hydrogen and ionised iron.

Dr Stan Kurtz of the National Autonomous University of Mexico (UNAM), who is an
expert in studies of solar system sized disks around massive stars, said:
"Protostellar disks are known to exist around Sun-like stars, but they are
usually seen in silhouette against background light from nebulae. In this case,
however, the molecules in the disk are hot enough to shine brightly themselves."

Dr Kumar adds, "This is the first time an envelope like this has been seen in
molecular hydrogen emission. It tells us that massive stars form with very
different conditions and physical aspects when compared to Sun-like stars."

The central star itself is very young, at roughly 100,000 years old. By
comparison, our middle-aged Sun is about 5 billion years old. The surrounding
gas disk is huge -- its diameter is one thousand times larger than Pluto's orbit
in our own Solar System. The young star is rapidly changing as gas and dust
spiral down onto its surface through the disk, a process called "accretion". The
star is already more than one thousand times more luminous than our Sun.

Dr Amadeu Fernandes of CAUP, Porto states "The UKIRT results show that the glow
from the disk is not due to the intense light from the central star, but is
instead caused by powerful shock waves". Dr Chris Davis of the Joint Astronomy
Centre in Hawaii explains, "The disk is possibly being shocked by supersonic
winds driven by the central star. These winds, travelling at hundreds of
thousands of kilometres per hour, crash into the disk and heat the gas to
thousands of degrees."

Dr Kumar adds, "It is also possible that the shocks are powered by large amounts
of gas and dust collapsing through the disk onto the young star. Further
investigation is required to understand their origin."

Disks around young, Sun-like stars are known to be the birth places of planets,
which can condense out of the gas and dust after the star has formed. This disk
has about 150 times the mass of our Sun -- enough gas and dust to make a hundred
Sun-like stars, or many thousands of planets. However, the results suggest that
it will not produce new planets or stars in the future. The intense shock waves
have made the gas far too hot to condense. Dr Davis says, "This tells us that
massive stars like this may not be able to form planets, as their surrounding
gas is too hot."

Instead of forming a cluster of stars, or a family of orbiting planets, the disk
will ultimately be destroyed by the intense ultraviolet radiation from the
central star. The radiation is already at work, gnawing at the inner edges of
the disk and evaporating the gas. Dr Kumar says, "We've seen open rings of gas
around similar stars, also with UKIRT. We think they may be the remnants of
large disks that have been almost completely evaporated."

The complete destruction of the disk will take many thousands of years. Before
this happens, the size and brightness of the disk allow researchers to study it
with powerful ground-based telescopes such as UKIRT, without the need for a
space telescope.

Dr Davis says, "We now have the task of searching for other hot, molecular disks
around massive young stars, and of fitting the existence of this super-disk into
our theories on the birth of massive stars."

The disk was first discovered in January 2001 by UKIRT, but further observations
were needed to confirm its nature. The team used the Caltech Submillimeter
Observatory in Hawaii to provide supporting evidence to prove the rotating
nature of the disk. Stan Kurtz used the Very Large Array radio telescope in New
Mexico to image the central massive star at radio wavelengths. The team returned
to use UKIRT in December 2002.

The work described is published on 8th December 2003 in "Astronomy and
Astrophysics" volume 412.

Notes for editors

UKIRT

The world's largest telescope dedicated solely to infrared astronomy, the
3.8-metre UK Infrared Telescope (UKIRT) is sited near the summit of Mauna Kea,
Hawaii, at an altitude of 4194 meters above sea level. It is operated by the
Joint Astronomy Centre in Hilo, Hawaii, on behalf of the UK Particle Physics and
Astronomy Research Council.

UIST

The UKIRT Imager Spectrometer (UIST) was designed and built at the UK Astronomy
Technology Centre (UK ATC) in Edinburgh. It detects infrared light at
wavelengths between 1 and 5 microns with a 1024 x 1024 pixel Indium Antimonide
detector array. It can be used for imaging, spectroscopy, integral field
spectroscopy, and polarimetry. It cost just under UKP 3M to build and was funded
by the Particle Physics and Astronomy Research Council (PPARC).

Web links

* Centre for Astrophysics of the University of Porto (CAUP)
http://www.astro.up.pt/
* More about the United Kingdom Infrared Telescope (UKIRT)
http://outreach.jach.hawaii.edu/articles/aboutukirt/
* Joint Astronomy Centre public outreach site
http://outreach.jach.hawaii.edu/

Images

[Image 1:
http://outreach.jach.hawaii.edu/pres...2/iras07pp.jpg (850KB)]
Main image: near-infrared (K-band) image of the young stellar object IRAS
07427-2400, made with the UKIRT Fast-Track Imager (UFTI). Inset image: the
central region processed to show only the hot molecular hydrogen gas surrounding
the star. CREDIT: Dr Nanda Kumar (CAUP) et al.

[Image 2:
http://outreach.jach.hawaii.edu/pres...ight-small.jpg
(46KB)
http://outreach.jach.hawaii.edu/pres...ight-large.jpg
(184KB)]
Star trails as the United Kingdom Infrared Telescope (UKIRT) watches the night
sky. CREDIT: Nik Szymanek.