spaceSpace and Physics

This Weird Inside-Out Nebula May Reveal The Future Of Our Sun


Jonathan O'Callaghan

Senior Staff Writer

The planetary nebula in question (left) and a more "normal" such nebula. Guerrero, Fang, Miller Bertolami, et al/WIYN, NOAO, NSF

Astronomers have spotted a nebula that, in a way, appears to be inside out. And it may help us work out what’s going to happen to the Sun in the distant future.

Published in Nature Astronomy, scientists led by Martín Guerrero from the Astrophysics Institute of Andalucía in Granada, Spain describe how they discovered a nebula that looks like it was “born again”. In other words, the outer regions looked like the inner regions should, and vice versa.


This particular nebula is known as a planetary nebula, which is a misnomer from their discovery – they have nothing to do with planets. Instead, they’re the final nebula given off when a star moves from being a red giant to a white dwarf, and ejects its outer layers.

When this happens, the star becomes hotter and ionizes material nearby. That is, it strips electrons from atoms near the star, with the effect lessening as you get further from the star.

In this nebula however, called HuBi 1 and located 17,000 light-years from Earth, the reverse is true. The atoms further from the star are more ionized than those closer.

“Everyone thought it was impossible,” Guerrero told Gizmodo.

Planetary nebulae like NGC 2818 snapped by Hubble here can end up looking pretty spectacular. NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

So, how did this happen? Well, the researchers think that the star basically came back to life briefly at an unusually late time, ejecting matter again. This produced a wave of carbon that caused “shock-heating” in the atoms in the outer regions of the nebula, notes

Because the star has dimmed so rapidly, it has been unable to ionize the material closer to it to such a great extent. Thus, we get this inverse nebula.

“We then came to realize that we had caught HuBi 1 at the exact moment when its central star underwent a brief 'born-again' process to become a hydrogen-poor and metal-rich star, which is very rare in white dwarf stars evolution,” Dr Xuan Fang, a co-author on the paper from the University of Hong Kong, said in a statement.

What’s more, the researchers think this star was originally about 1.1 times the mass of our Sun, and it’s about 5 billion years further along in its life. This means that, when our Sun is expected to become a red giant in 5 billion years, it may undergo a similar process.


"Our findings suggest that the Sun may also experience a 'born-again' process while it is dying out in about 5 billion years from now,” said Dr Fang, adding cheerily: “but way before that event, our Earth will be engulfed by the Sun when it turns into a superhot red giant and nothing living will survive."

Hopefully at least some nearby aliens will get a chance to watch our Sun undergo this unusual process.


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