HEIC0915: EMBARGOED UNTIL 12:00 (CET)/06:00 am EST 01 Dec, 2009
http://www.spacetelescope.org/news/html/heic0915.html

Photo release: Blushing dusty nebula

01-Dec 2009 A recent NASA/ESA Hubble Space Telescope image of part of NGC 7023, 
or the Iris Nebula, highlights a perfect dust laboratory in the sky.

On Earth, we tend to find dust nothing more than a nuisance that blankets our furniture 
and causes us to sneeze. Cosmic dust can also be a hindrance to astronomers because 
cameras using visible light cannot see through it. However, studying cosmic dust in detail 
helps astronomers to pin down the ingredients of the raw mixture that eventually gives 
birth to stars.

This close-up of an area in the northwest region of the large Iris Nebula seems to be 
clogged with cosmic dust. With bright light from the nearby star HD 200775 [1] 
illuminating it from above, the dust resembles thick mounds of billowing cotton. It is 
actually made up of tiny particles of solid matter, with sizes from ten to a hundred times 
smaller than those of the dust grains we find at home [2]. Both background and 
foreground stars are dotted throughout the image.

NGC 7023 is a reflection nebula, which means it scatters light from a massive nearby star, 
in this case, HD 200775. Reflection nebulae are different from emission nebulae, which 
are clouds of gas that are hot enough to emit light themselves. Reflection nebulae tend to 
appear blue because of the way light scatters, but parts of the Iris Nebula appear 
unusually red.

Researchers studying the object are particularly interested in the region to the left and 
slightly above centre in the image, where they find dusty filaments to be redder than 
expected. An unknown chemical compound, most likely based on hydrocarbons, is 
responsible for the red tinge. The high resolution and sensitivity of Hubble’s instruments 
allow astronomers to study the area in detail. Images and spectra are only part of the 
analysis. On Earth, scientists are performing additional laboratory tests to assess better 
the exact chemical composition of the nebula.

NGC 7023 was discovered by Sir William Herschel in 1794; the nebula is in the 
constellation of Cepheus, the King, in the northern sky. NGC 7023 is approximately 1400 
light–years from Earth and about six light-years across. This aethereal image was taken by 
Hubble's Advanced Camera for Surveys. Astronomers also used Hubble’s Near Infrared 
Camera and Multi-Object Spectrometer (NICMOS) instrument to try to determine which 
chemical elements are present in the nebula.

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Notes for editors

North is down, East is right. The field of view is 3.3 arcminutes. The image is a composite 
of four images obtained through blue, green, near-infrared and H-alpha filters. 

[1] HD 200775 is about ten times the mass of the Sun.

[2] The typical sizes of cosmic dust grains range between a few hundredths of a micron 
and several microns.

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

Image credit: NASA & ESA

These observations were obtained by a team led by Karl Gordon from the Space 
Telescope Science Institute in Baltimore, Maryland, USA.

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For more information, please contact:

Colleen Sharkey
Hubble/ESA, Garching, Germany
Tel: +49-89-3200-6306
Cell: +49-015115373591
E-mail: csharkey@eso.org