Two cosmic butterflies: NGC 6302 and Minkowski 2-9

Image credit: Hubblesite/STScI-2009-25

Both nebulae featured here are bipolar, axisymmetric planetary nebulae and both have been called the Butterfly Nebula, although each has other names. The central star of NGC 6302 is one of the hottest stars known:

NGC 6302 lies within our Milky Way galaxy, roughly 3,800 light-years away in the constellation Scorpius. The glowing gas is the star’s outer layers, expelled over about 2,200 years. The “butterfly” stretches for more than two light-years, which is about half the distance from the Sun to the nearest star, Alpha Centauri. The central star itself cannot be seen, because it is hidden within a doughnut-shaped ring of dust, which appears as a dark band pinching the nebula in the center. The thick dust belt constricts the star’s outflow, creating the classic “bipolar” or hourglass shape displayed by some planetary nebulae. The star’s surface temperature is estimated to be about 400,000 degrees Fahrenheit, making it one of the hottest known stars in our galaxy. Spectroscopic observations made with ground-based telescopes show that the gas is roughly 36,000 degrees Fahrenheit, which is unusually hot compared to a typical planetary nebula.


Minkowski 2-9 is an outstanding example of a highly collimated outflow and is in many respects a quite unique object. All evidence points to the presence of a pair of interacting stars at its centre, the observed jet being produced as the result of mass transfer between the two components, and its rotation around the axis of symmetry of the nebula being a direct consequence of the orbital motion:

The data (right) reveal that the pattern moves around the unseen central star with a period around 90 years, and that it is likely to be produced by a rotating, highly supersonic beam of particles (a tenous jet) which hits and ionizes the gaseous walls of the hollow hourglass nebula. The jet travels at the unsually high speed of 10000-15000 km per second. At the densities of the gas in the nebula, certain atoms like O2+ recombine and their emission switches off as soon as the beam sweeps past, producing the observed effect of a rotating lighthouse (green feature in the figure).

The animated gif at right is courtesy of Wikipedia. A stunning image of the object, which does indeed resemble a ‘space lighthouse’, is available via the IAC, here. The paper is Corradi et al., 2011, A&A, 529, 43, ‘The evolution of M 2-9 from 2000 to 2010’.


One Response to “Two cosmic butterflies: NGC 6302 and Minkowski 2-9”

  1. Ciao! Vorrei solo dire un grazie enorme per le informazioni che avete condiviso in questo blog! Di sicurò diverrò un vostro fa accanito!

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