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NGC 6302

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NGC 6302 is a spectacular planetary nebula located in the constellation Scorpius. It is known by several names, including the Butterfly Nebula, the Bug Nebula, and Caldwell 69. This object is classified as a bipolar planetary nebula. This means its structure features two primary lobes that extend from a central point. The shape is remarkably complex, representing some of the most intricate structures ever seen in such nebulae.

NGC 6302 Hubble 2009.full
NGC 6302 Hubble 2009.full

The nebula's unique shape is created by a specific physical mechanism. A dense equatorial disc, made of gas and dust, surrounds the central star. This disc acts as a barrier at the star's equator. When the star releases outflows of material, the disc forces the gas to escape through the poles instead. This process results in a bipolar structure that resembles an hourglass. The lobes contain various features, including ionization walls, knots, and sharp edges.

Gemini South Images the Butterfly Nebula (noirlab2530a)
Gemini South Images the Butterfly Nebula (noirlab2530a)

One specific part of the nebula is the prominent northwest lobe. This lobe extends up to 3.0 arcminutes away from the central star. Scientists estimate this structure formed during an eruptive event roughly 1,900 years ago. The lobe has a circular section with expanding walls. In this area, the speed of the expansion is proportional to the distance from the star. At an angular distance of 1.71 arcminutes, the flow velocity is 263 km/s. At the very edge of the lobe, the outward velocity exceeds 600 km/s. The western edge suggests the outflow collided with existing globules of gas.

Gemini South Images the Butterfly Nebula (noirlab2530a)
Gemini South Images the Butterfly Nebula (noirlab2530a)

The history of observing NGC 6302 spans many decades. It has been part of the New General Catalogue since at least 1888. Many sources credit its discovery to James Dunlop in 1826. However, some researchers argue that Barnard may have mistakenly credited Dunlop. The earliest known detailed study was conducted by Edward Emerson Barnard in 1907. He provided drawings and descriptions of the object. More recently, the Hubble Space Telescope provided groundbreaking images after its final servicing mission in September 2009.

NGC6302map
NGC6302map

At the heart of the nebula lies a central star that was difficult to find. It remained hidden for a long time due to its high temperature and the surrounding dust. The star radiates mostly in the ultraviolet spectrum. Additionally, the dusty torus, or ring, absorbs much of the light from the central region. It was not until 2009 that the Wide Field Camera 3 on the Hubble Space Telescope revealed the star. This central star is a white dwarf. It has a current mass of approximately 0.64 solar masses.

NGC 6302 Hubble 2009.full
NGC 6302 Hubble 2009.full

This white dwarf is one of the hottest known stars in the universe. Its surface temperature is in excess of 250,000 degrees Celsius. This extreme heat implies the original star was very large. In its earlier life, the star was likely a B type main sequence star, specifically a B5-9V. That original star had a mass of around five solar masses. Most of that mass was ejected during the event that created the nebula. Currently, the star has ceased nuclear burning. It is now fading at a predicted rate of 1% per year.

NGC 6302 Hubble 2009.full
NGC 6302 Hubble 2009.full

The chemistry of the dust in the central dark lane is quite unusual. It contains multiple crystalline silicates, crystalline water ice, and quartz. There is also evidence of carbon-bearing polycyclic aromatic hydrocarbons, also known as PAHs. Scientists have also debated the detection of carbonates in this non-aqueous environment. Usually, stars are either oxygen-rich or carbon-rich. This change typically happens late in a star's life due to chemical changes in its atmosphere. NGC 6302 is unique because it contains both oxygen-bearing silicate molecules and carbon-bearing molecules. This makes it a vital subject for studying how stars evolve and change their chemical makeup.

Gemini South Images the Butterfly Nebula (noirlab2530a)
Gemini South Images the Butterfly Nebula (noirlab2530a)
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File:NGC 6302 Hubble 2009.full.jpg
NGC 6302 Hubble 2009.full.jpg
File:NGC6302map.png
NGC6302map.png
Gemini South Images the Butterfly Nebula...
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