THE IN­SIDE-OUT NEB­ULA

All About Space - - The Impossible Star -

Noth­ing lasts for­ever. Even our own Sun will die even­tu­ally. It will swell into a red gi­ant be­fore puff­ing its outer lay­ers into space to form a beau­ti­ful plan­e­tary neb­ula. Astronomers are con­fi­dent that this is the fate await­ing our star be­cause they have seen it hap­pen many times be­fore across the uni­verse. Yet one plan­e­tary neb­ula in par­tic­u­lar is caus­ing quite a stir – it ap­pears to be in­side out.

In 2018 astronomers were study­ing the plan­e­tary neb­ula known as HuBi 1, which sits around 17,000 light years from Earth. They soon no­ticed some­thing odd about the way its gas is ionised. Ion­i­sa­tion is the process by which elec­trons are stripped away from atoms to cre­ate charged par­ti­cles known as ‘ions’. Nor­mally the in­ner re­gions of a plan­e­tary neb­ula – where it’s hot­ter – are more ionised than the cooler outer shell, yet with HuBi 1 it’s the other way around. Be­fore this dis­cov­ery such a sce­nario was thought to be im­pos­si­ble.

One po­ten­tial ex­pla­na­tion is that the star briefly came back to life, cre­at­ing a shock­wave that moved out through the sur­round­ing gas. The shock­wave was so en­er­getic that it passed straight through the in­ner gas, only ion­is­ing the outer gas.

The weird neb­ula may re­veal the fu­ture of our sun

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