Copyright: NASA/ESA/Hubble Heritage Team (STScI/AURA)
Stars of different masses end their lives in different ways. While
truly massive stars go out in a blaze of glory, intermediate-mass stars —
those between roughly one and eight times the mass of the Sun — are
somewhat quieter, forming cosmic objects known as planetary nebulas.
Named
because of their vague resemblance to planets when seen through early,
low-resolution telescopes, planetary nebulas are created when a dying
star flings off its outer layers of gas into space. This cloud forms an
expanding shell around the central star, while the star itself slowly
cools to become a white dwarf. This is what has happened in this
NASA/ESA Hubble Space Telescope image, taken in 2007, which shows a
planetary nebula known as NGC 2371.
NGC 2371 resides 4300
light-years away from us, in the constellation of Gemini. It is one of
the largest planetary nebulas known, measuring roughly three light-years
across. Its progenitor star can be seen here as a pinprick of
orange–-red light, surrounded by a green, blue and aqua-tinged puff of
gas. This shell appears to have a regular, elliptical shape that is
sliced in half by a dark lane running through the nebula, which also
encompasses the central star.
This dark feature misled astronomers
when NGC 2371 was initially catalogued because the two lobes visually
resembled two objects, not one. As a result of this confusion, the
nebula has two names in William Herschel’s New General Catalogue: NGC
2371 and 2372 (often combined as NGC 2371/2 or NGC 2371-2).
Two
prominent pink patches are also visible on either side of the central
star. These features are thought to be knots of gas, most likely jets,
thrown off by the star at some point in the past. Their pink colour
indicates that they are cooler and denser than their surroundings.
The
nebula’s central star was once similar to the Sun, but is now only a
shadow of its former self. It is slowly cooling after energetically
shedding most of its gas, but has a long way to go yet. It currently
boasts a scorching surface temperature of over 130 000ºC – some 25 times
hotter than the surface of the Sun – and glows with the luminosity of
at least 700 Suns.
The hot ultraviolet radiation streaming
outwards into the nebula energises the gas it touches, causing NGC 2371
to glow in the beautiful aquamarine colours seen in this image.
This
picture was taken in November 2007 by Hubble’s Wide Field Planetary
Camera 2. It is a false-colour image created with a combination of
filters to detect light coming from sulphur and nitrogen (shown in red),
hydrogen (green) and oxygen (blue). The observations were gathered as
part of the Hubble Heritage project.
This image was originally published on the Hubble Space Telescope website on 4 March 2008.
Source: ESA/Images
