science

‘Mysterious spiral structures’ found extending out of strange star



Mysterious, huge spiral structures, extending out of a young star, have been spotted by astronomers.

The “complex set of spiral arms” reaches out 1,000 times the distance between the Earth and the Sun, and could shed new light on how planets are born.

The unexplained spirals were seen coming out of a young variable star, known as RU Lupi, which is thought to be producing new worlds, and has become known as a “planet factory” as a result.


Most images of those planet-forming discs have shown them as a neat collection of gas and dust, with rings and gaps that suggest new planets are being born there. When astronomers first looked at RU Lupi’s collection of dust, it looked the same, with a relatively neat organisation that appeared to be forming new worlds.

But studies of the gas rather than the dust in the disc that surrounds it appears to show that the process of forming those planets is much more complex, and less neatly arranged, than previously thought. The complicated web of gas looks something like a miniature galaxy, researchers said.

Astronomers were encouraged to look at the gas rather than the dust after they noticed hints of carbon monoxide, or CO, extending beyond the disc. When they re-examined it, they spotted the spiralling structures of gas – which makes up much more of such a protoplanetary disc than dust does.

“We discovered a complex set of spiral arms in carbon monoxide (CO) emission extending to nearly 1,000 astronomical units from the young star RU Lup, which has previously been found to exhibit signs of ongoing planet formation via concentric dust gaps in its protoplanetary disk,” said Jane Huang, who led the research, in a statement.

“CO emission reveals complex structures in the planet-formation environment that are invisible in dust observations alone.”

Usually, the discs that surround a star and give rise to new worlds are shown in neat, swirling circles around their sun. But the new study suggests there are other kinds of planet-forming environments that could be much messier than those images might suggest, the authors said.

“The planet-forming environment can be much more complex and chaotic than implied by the numerous, well-known images of concentric ringed protoplanetary disks mapped in millimeter continuum emission,” said Huang.

“The fact that we observed this spiral structure in the gas after a deep observation suggests that we have likely not seen the full diversity and complexity of planet-forming environments. We may have missed much of the gas structures in other disks.”

Researchers have proposed a range of possibilities to explain both the unusual structures and the strange behaviour of the star: that the disc is so massive it is collapsing under its own gravity, that it is interacting with another star, or that interstellar material is being pulled along the arms. But those explanations are incomplete and scientists now hope to find more of the unusual “planet factories” to understand the processes behind the formation better.

“None of these scenarios completely explain what we have observed,” said Sean Andrews, who worked on the study alongside Huang at the Center for Astrophysics, Harvard & Smithsonian.

“There might be unknown processes happening during planet formation that we have not yet accounted for in our models. We will only learn what they are if we find other disks out there that look like RU Lup.”



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