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This strange mist looks from the inside out and born again

Planetary nebulae have rounded, shell-like shapes. An example is NGC 6818, also known as the Little Gem Nebula, seen in this image.

(ESA/Hubble and NASA)

The nebula of a dying star has an “inside-out” appearance, scientists announced in a new study — and this may be our sun’s ultimate fate.

Four years ago, astronomer Martin Guerrero of the Institute for Astrophysics of Andalusia in Granada, Spain, discovered something puzzling: The shell-shaped remains of a stellar explosion known as a planetary nebula — it looked like it was inside out and seemingly re-born in a rare cosmic event.

“I was on a telescope on La Palma is a beautiful island here in Spain, and I was repeatedly images of planetary nebulae,” said Guerrero Space.com. [Glowing Mist Decorates the Space in the Hubble image]

When Guerrero first looked at the planetary nebula HuBi1, everything seemed normal.

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“I have the image in the high-ionization filter; I saw a number of structures, nothing very impressive,” he said. But that was surprising. “The image in the low-ionization stage was something completely crazy. So my first idea was that I was sleepy and I used the wrong filter!”

Ionization occurs in all planetary nebulae; it is a phenomenon that the radiation of an energetic central star strips electrons from the atoms in the clouds of dust and gas. “In almost all cases, the atoms closer to the intense light source is probably more of their electrons stripped than atoms further away,” Bruce Balick, an astronomer at the University of Washington and a close collaborator on other projects with Guerrero, told Space.com in an e-mail.

But HuBi1 showed unusually high ionization of the outside of the shell shape and low ionization in the vicinity of the centre.

After more scientists came on board to run other tests, such as stellar evolutionary modelling, Guerrero and his team put the pieces of the HuBi1 puzzle together.

And to explain, Guerrero used a fruit.

“Imagine that the center of a star of a planetary nebula is like an apple. So you’ve got most of the apple is the flesh, and there is a very thin skin. Imagine that the star, this apple is mostly carbon and oxygen,” he said.

“This inner material is never going to get to the pressure and the temperature at which the carbon and oxygen is going to melt … so this is very stable.” [Spirit of a Dying Star, Tips on Sun’s Future.

Then, Guerrero discusses the skin of this astronomical apple.

“The skin is hydrogen and helium. In 80 to 90 percent of the cases, there is nothing going to happen: The star in this stage is getting its energy from the burning of hydrogen on the surface of the star into helium. But, about 10 or 15 percent of the cases, this helium layer is going to get to a critical mass.

“At this critical mass,” Guerrero said: “the helium is going to burn, it is going to produce carbon and oxygen atoms by the fusion of three or four helium atoms. The funny thing here is that this happens on the surface of the star, this is a very explosive event. Thus, once the helium begins with the production of carbon, the temperature and the pressure will increase, and these tensions are going to explode in the space.”

It is this wave of carbon material, now is emitted in the space, that is shock-heating of the atoms in the nebula of the outer edge, making it is a born-again look, with fresh recombining atoms.

The middle of the apple not realize of the skin is coming apart, in the state of Guerrero ‘ s example. And the team suggests that, in fact, the central star is less quickly: the “optical brightness turned down constantly by 10 magnitudes in a period of 46 years,” the study authors said. Balick called it “great!!”

The researchers determined that the star was ever to 1.1 solar masses, and inferred that HuBi1 can be an example of what will happen when the sun dies in 5 billion years.

The new work was published on Aug. 6 in the journal Nature Astronomy.

Original article on Space.com.

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