NGC 7027

This beautiful image was taken by the NICMOS instrument onboard the Hubble Space Telescope in 1998. It shows an object named NGC 7027 - a planetary nebula - which is about 15 arcseconds in diameter (about a 120th of the angular diameter of the Moon) that can be found in the direction of Cygnus the Swan.

Despite the name, planetary nebulae are not actually planets. They occur during the death throes of a star as it expels gas and dust outwards. Objects like this acquired the name planetary nebula because they looked a bit like planets when viewed through early telescopes. Although it appears to be very small, the nebula is actually about 14,000 times larger than the distance from the Sun to the Earth, so the entire Solar System could easily be swallowed up inside it.

This image isn't quite what you would see through an optical telescope as it is actually an image made from looking at specific parts of the infrared spectrum (1.10, 2.12, and 2.15 microns wavelength). This is a pseudo-colour image with the shorter wavelength represented as blue and the longest as red. The result is that the different colours tell us about different elements in the nebula. Red shows up regions where molecular hydrogen is being split into individual atoms by UV radiation from the central star. The whiter region in the centre is gas at a temperature of tens of thousands of degrees.

NGC 7027 doesn't just give off light in the optical and infrared parts of the spectrum; it also gives off radio wavesas well. At frequencies around 30 GHz, it turns out to be quite bright (5.45 Jy) and also very stable. This means that it gets used to calibrate measurements at radio frequencies.

Posted in astro blog by Stuart on Saturday 19th Mar 2005 (18:35 UTC) | Permalink
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