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

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

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

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.


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.

(full size JPG 850kB)

Star trails as the United Kingdom Infrared Telescope (UKIRT) watches the
night sky. CREDIT: Nik Szymanek.

(full size JPG 190kB)

(smaller size JPG 47kB)



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.


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).


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

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

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

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

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


Centre for Astrophysics of the University of Porto (CAUP)

More about the United Kingdom Infrared Telescope (UKIRT)

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