NGC 6302 by Don Goldman

NGC 6302 by Don Goldman

23 Jun , 2008 by

Over the weeks we’ve looked at a lot of curious objects and today is no exception. NGC 6302 is often called the “Bug Nebula”, but its resemblance to an insect isn’t what makes it unique – it’s the complex structure. Deep inside this bipolar planetary nebula lay an unseen star… One of the hottest objects in the galaxy.

Residing about 4,000 light years away in the constellation of Scorpius, NGC 6302 is the end remains of an enormous dying star. With a surface temperature of an estimated 200,000 K, its central star exceeds our own Sun’s mean temperature output by nearly 35 times – yet has never been observed. Why? Because it is shielded from view at all wavelengths by an impossibly dense equatorial disc composed of gas and dust… One that may have restricted the star’s outflow into the unusual bipolar structure we can see.

But the hidden central star isn’t what’s bugging scientists, it’s the chemical composition!

Filled with ionization walls, edges and lobes, this dust is both oxygen and carbon-rich – a dual chemistry which means it has undergone recent changes and alternate formation processes in its 10,000 year life. Studies done by the European Space Agency’s Infrared Space Observatory (ISO) have shown that the dusty torus contains hydrocarbons, carbonates such as calcite, as well as water ice and iron. If the word carbonates made you raise an eyebrow, it should because carbonates form when carbon dioxide dissolves in liquid water and forms sediments.

Says Albert Zijlstra from UMIST: “What caught our interest in NGC 6302 was the mixture of minerals and crystalline ice – hailstones frozen onto small dust grains. Very few objects have such a mixed composition.”

Yet NGC 6302 is even more complex, displaying evidence that a second pair of lobes may have formed during a previous phase of the star’s mass loss. The visible northwest lobe is believed to have been created some 1,900 years ago and shows some signs that it may have once collided with pre-existing globules of gas which changed its outflow. According to studies done by Groves, Doptia, Williams and Hua; “We find that for NGC 6302, the visible to IR extinction law is indistinguishable from `standard’ interstellar reddening, but that the UV extinction curve is much steeper than normal, suggesting that more small dust grains had been ejected into the nebula by the PN central star.”

Kinematical studies done by Minkowski and Johnson suggest that NGC 6302 originated in some type of explosive event. It exhibits a rich spectrum of lines, indicating rich deposits of helium and nitrogen – far more than an ordinary planetary nebula. What the Bug Nebula seems to lack in its diet, however, is iron and calcium – two elements which may very well be tied up as solid grains.

So what’s next for this extreme, high-excitation planetary nebula? According to Wright, Barlow, Ercolano and Rauch; “We use the 3D photoionisation code to model the emission from the gas and dust. We have produced a good fit to the optical emission-line spectrum, from which we derived a density distribution for the nebula. A fit to the infrared coronal lines places strong constraints on the properties of the unseen ionising source. We find the best fit comes from using a 220,000 K hydrogen-deficient central star model atmosphere, indicating that the central star of this PN may have undergone a late thermal pulse.”

ngc 6302 mapBut don’t you be late observing the Bug Nebula yourself! NGC 6302 is located in Scorpius (RA 17 13 44 Dec -37 06 15). At around magnitude 9, this surprisingly bright planetary is well within the reach of a mid-size telescope and a treat to larger aperture. NGC 6302 was discovered by James Dunlop in 1826 with a handmade reflecting telescope he had constructed himself and the earliest known study of NGC 6302 is Edward Emerson Barnard who, in 1907, drew and described it.

Seek it out… And enjoy!

This week’s awesome image was taken by Don Goldman from Macedon Ranges Observatory.


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IKE:) the Alien lifeform
Guest
IKE:) the Alien lifeform
June 23, 2008 10:48 AM

An extremely intriguing nebula, and just around the block. smile

RL
Member
RL
June 23, 2008 12:16 PM

My first reaction (and made verbally) when I saw this photo was “Whoa!”

How do they know that this is the results of an explosion? Can you tell by the spectral lines (indicating what elements are possessed) that it was an explosion or is it something else?

Aodhhan
Member
Aodhhan
June 23, 2008 3:06 PM

Do the reports state the approximate total volume of all the material? Is it possible some of the material came from 1 or 2 large “earth” type planets (or planets with a lot of water with vegitation) which were caught up in the raveges of the dying star?

Stuart Watson
Member
Stuart Watson
June 23, 2008 5:55 PM

I can almost imagine this image being viewed from the bridge of the original Starship Enterprise, while Spock raises an eyebrow and remarks “fascinating”.

Great photo Don!

Neutron-Glitch
Member
Neutron-Glitch
June 24, 2008 1:45 AM

sounds interesting

Aodhhan
Member
Aodhhan
June 24, 2008 5:04 AM

Actually it helps a lot. Although, it doesn’t give a lot of information, the fact the torus is made of interesting material compared to the core gives some hope there was something containing all these elements in the area before all heck broke loose. I like hearing there are two distinct compositions of dust as well.
What a great time to be alive!

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