Demise in ice and fire (Forwarded)

ESA News
http://www.esa.int

29 April 2004

Demise in ice and fire

The Bug Nebula, NGC 6302, is one of the brightest and most extreme planetary
nebulae known. At its centre lies a superhot dying star smothered in a blanket
of 'hailstones'. A new Hubble image reveals fresh detail in the wings of this
'cosmic butterfly'.

This image of the Bug Nebula, taken with the NASA/ESA Hubble Space Telescope
(HST), shows impressive walls of compressed gas. A torus ('doughnut') shaped
mass of dust surrounds the inner nebula (seen at the upper right).

At the heart of the turmoil is one of the hottest stars known. Despite an
extremely high temperature of at least 250 000 degrees Celsius, the star itself
has never been seen, as it shines most brightly in the ultraviolet and is hidden
by the blanket of dust, making it hard to observe.

Chemically, the composition of the Bug Nebula also makes it one of the more
interesting objects known. Earlier observations with the European Space Agency's
Infrared Space Observatory (ISO) have shown that the dusty torus contains
hydrocarbons, carbonates such as calcite, as well as water ice and iron. The
presence of carbonates is interesting. In the Solar System, their presence is
taken as evidence for liquid water in the past, because carbonates form when
carbon dioxide dissolves in liquid water and forms sediments. But its detection
in nebulae such as the Bug Nebula, where no liquid water has existed, shows that
other formation processes cannot be excluded.

Albert Zijlstra from UMIST in Manchester, UK, who leads a team of astronomers
probing the secrets of this extreme object, says: "What caught our interest in
NGC 6302 was the mixture of minerals and crystalline ice -- hailstones frozen
onto small dust grains. Very few objects have such a mixed composition."

The dense, dark dust torus around the central star contains the bulk of the
measured dust mass and is something of a mystery to astronomers. They believe
the nebula was expelled around 10 000 years ago, but do not understand how it
formed or how long the dust torus can survive evaporation by the very hot
central star.

Notes for editors:

Stars like the Sun end their lives ejecting much of their gas into space. The
gas ejections happen over relatively short timescales, from 1000 to 10 000
years, and form some of the most beautiful objects in the night sky -- the
planetary nebulae. The Bug Nebula lies in the southern constellation of Scorpius
and its distance is estimated to be about 4000 light-years.

This Hubble image is composed of two WFPC2 (Wide Field and Planetary Camera 2)
exposures: a 610 second exposure through an H-alpha filter (shown in blue) and a
470 second exposure through an ionized nitrogen filter (shown in red). The
nitrogen (red colours) is especially abundant in the outer regions where the gas
is coolest.

The study based on the HST image and observations with ESO's Very Large
Telescope and the James Clerk Maxwell Telescope on Hawaii is submitted to the
European journal Astronomy & Astrophysics.

The detection of carbonates in NGC 6302 was made by Ciska Kempers, of the
University of Amsterdam, and was published in 2002 in Nature, 415, 295.

Animations and general Hubble Space Telescope background footage are available from:

http://www.spacetelescope.org/videos...heic0407a.html

Interactive, zoomable images are available at:

http://www.spacetelescope.org/images...heic0407a.html

The Hubble Space Telescope is a project of international cooperation between ESA
and NASA.

Contacts:
Albert Zijlstra
UMIST, Machester, UK
Tel: + 44-161-200-3925
E-mail:

Lars Lindberg Christensen
Hubble European Space Agency Information Centre, Garching, Germany
Tel: +49-(0)89-3200-6306
Cellular (24 hr): +49-(0)173-3872-621
E-mail:

Related Links

* Scientific paper by Matsuura, Zijlstra et al. (pdf)
http://iapetus.phy.umist.ac.uk/NGC63...reparation.pdf
* More on NGC 6302
http://www.seds.org/~spider/ngc/ngc.cgi?6302
* Hubble overview
http://www.esa.int/science/hubble
* Hubble ESA Information Centre
http://www.spacetelescope.org

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/esaCP/SEM2L477ESD...reWeek_1.html]
The Bug Nebula, NGC 6302, is one of the brightest and most extreme planetary
nebulae known. At its centre lies a superhot, dying star smothered in a blanket
of icy 'hailstones'. A new Hubble image reveals fresh detail in the wings of
this 'cosmic butterfly'.

Credits: Credit: ESA/NASA and Albert Zijlstra

[Image 2:
http://www.esa.int/esaCP/SEM2L477ESD...html#subhead2]
The Bug Nebula, NGC 6302, here imaged with the 3.6-metre telescope at ESO's La
Silla Observatory by astronomer Romano L.M. Corradi.

Credits: Credit: ESA/NASA and Romano Corradi (ING)