‘Inside-Out’ Planetary Nebula Found Around Born-Again Star Is The First Of Its Kind

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Planetary nebulae are common in the cosmos. Around 90 percent of the major stars end their lives in a planetary nebula, as they flare up into red giants and then collapse into white dwarfs.

According to a recent study, our sun will endure the same fate some 10 billion years from now, ending up as a planetary nebula — a ring-shaped shell of gas surrounding a dim relic of its former self, the Inquisitr previously reported.

But a new study published yesterday in the journal Nature Astronomy documents the finding of a planetary nebula unlike any other.

Described as an “inside-out” nebula, this strange astronomical object boasts an unusual cloud of gas and dust, in which the layers of charged material are arranged in an abnormal order — the exact opposite of how they’re supposed to be, notes Phys.org.

In your run-of-the-mill planetary nebula, the enveloping cloud has a stratified structure that keeps the heavily ionized material closer to the dear star.

“The closest layer is generally made up of heavily ionized helium; the next closest contains less-ionized oxygen, and the outermost region is usually made up of a mix of barely ionized oxygen and nitrogen,” explains the media outlet.

Yet, in this particular case, the nebula’s cloud has more ionized material on the outside than on the inside, and is made up of a shell of nitrogen and oxygen, followed by an outer shell of ionized helium. This is the first time ever that astronomers have spotted a planetary nebula of this kind, which was previously thought impossible to occur.


The bizarre nebula has been named HuBi 1 and was discovered by an international team of researchers led by Martin Guerrero of the Instituto de Astrofisica de Andalucia in Spain, reports Gizmodo.

Trying to find out what could cause such an exotic occurrence, the scientists scoured the nebula with the help of a telescope in the Canary Islands and made a surprising discovery.

As it turns out, the central star in HuBi 1 is unexpectedly cool. Moreover, after looking at older observations of this star, the team uncovered that it has gone through a rapid process of dimming, decreasing in brightness 10,000 times over the past 46 years.

Models of star evolution suggest that HuBi 1’s star “is the descendant of a low-mass star that has experienced a ‘born-again’ event,” the authors write in their paper, referring to the process in which a star gets reignited when the heavily ionized helium in the nebula’s inner layer catches on fire.

This process ended up sending a shock-wave through the ionized material in the nebula’s cloud, spewing out ejecta from the star and exciting the inner shell. This is what made HuBi 1 appear “inside-out,” notes Gizmodo.


By all accounts, the ionized helium that would have been in the inner layer got pushed outward by the shockwave, making room for ejecta that eventually cooled down into dust and surrounded the star, explains Nature Asia.

“Everyone thought it was impossible,” Guerrero said in a statement. “But at the end, we have learned that there is a lot of physics on stellar evolution… in studying these funny things.”

Considering that the original star was 1.1 the mass of our sun, these new findings could be a window into the future and might show how our solar system will end up after the death of the sun.