It’s now a full 25 years since the Gemini South telescope in Chile achieved first light, and they've marked their anniversary by releasing this stunning new image of the Butterfly Nebula (NGC 6302).
Along with Gemini North, which is located in Hawaii, Gemini South is one of two twin 8.1-metre (26.6 ft) telescopes that make up the Gemini Observatory – a prime example of the kind of international co-operation that makes big-picture astronomy possible.
Around 70% of the Gemini Observatory’s funding comes from the USA’s National Science Foundation, but the other 30% comes from similar government agencies in Canada, Chile, Brazil, Argentina and South Korea.
To celebrate the scopes’ 25th anniversary, NOIRLab – the division of NSF that’s responsible for operating the Gemini Observatory – asked students in Hawaii and Chile to nominate objects for the scopes to image, with the Butterfly Nebula winning out in the Planetary Nebulas category for the southern hemisphere.
The throes of a dying star
Planetary nebulae are so-called thanks to their round shape, which led early telescopic observers to assume they were planetary bodies several centuries ago.
We know now that they don’t actually have anything to do with planets, but the name has stuck.
Instead, planetary nebulae form when a massive star reaches the end of its life.
The dying star gives off material that billows outward in huge, swelling clouds, which are then heated (and hence illuminated) by the powerful radiation still emanating from the nebula’s centre.
It's predicted that our Sun will become a planetary nebula when it finally exhausts all its fuel in about 5 billion years.
That means images of planetary nebulae like this could give us an insight into how the Sun will end its life.
How the Butterfly gets its shape
Even the least observant among us has probably already noticed that despite being classed as a planetary nebula, the Butterfly Nebula very much ISN’T round, but is instead shaped like a butterfly or moth.
The nebula’s distinctive structure is believed to be the result of its central star evolving from a red giant to a white dwarf several thousand years ago.
The dying red giant would have given off vast clouds of hydrogen and oxygen (seen here in red and blue, respectively).
Later on, when the star became a white dwarf, further material was emitted along a different axis, perpendicular to the first, that ‘carved’ what would have been a typical, spherical planetary nebula into the complex shape we see today.
Gases in the cloud are being heated to incredible temperatures by radiation from this central white dwarf, which has a surface temperature of 250,000°C (450,000°F) – making it one of the hottest stars known.
Accordingly, the reason the energized hydrogen atoms are glowing red, and the oxygen ones blue, is that they’re currently heated to a positively toasty 20,000°C (35,000°F)!
The Butterfly Nebula was first described in a 1907 paper by Edward E. Barnard, though some believe it may have been spotted by other astronomers up to 90 years earlier.
Also known as NGC 6302 or Caldwell 69, it is located between 2,500 and 3,800 lightyears from Earth in the constellation of Scorpius.
