Tuesday, 24 July 2018

NGC7008: Evidence of extrasolar planets

Every planetary nebula, the remnant of a small to medium-sized star, is unique. Just browse through all of my sketches and I'm sure that you'll agree. They all tell a different story and even reveal a lot about the nature of the star system that eventually got destroyed when the central star exhaled its dying breath. 

NGC7008, nicknamed the "Fetus Nebula", is one of my all-time favourites. Just look at its highly irregular structure, which is already obvious through a small telescope. After zooming in with the binoscope I had to pick up my jaw from the ground because I'd never seen anything like this before... and believe me, I've seen quite a few planetaries in my 36 years of being an astronomy enthusiast.

On either side of the central star there are bright patches of nebulosity. Remember the FLIERs I told you about when discussing NGC6826? These are exactly the same but much older and more developed. But obviously there's more... much more. Usually planetary nebulae form a spherical or ellipsoid sort of bubble. Here, the bubble's irregular and even appears ruptured. 

Scientists speculated that the big central star was in fact a binary and that the interaction with this companion disrupted the nebula's formation. More recent observations with the Hubble space telescope revealed dual layers of completely different content in them. Moreover, these layers appear near the edge of the nebula, where it meets the interstellar medium. This makes a companion star highly unlikely. A new theory suggests that the expanding nebula's interacting with planetary debris... bits and bobs of planets that were destroyed during the expulsion of the central star's atmosphere. This would account for the inhomogeneities in the nebula and, if massive enough, rings of matter would be formed that generate the sort of structures we see here when stellar gas crashes into them.

In short, it seems that this odd-looking nebula is providing us with key evidence that once a complex planetary system existed around the central star. 


 

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