Using the ALMA observatory in Chile, a group of astronomers captured an image of distinct spiral arms in the large disk of gas and dust surrounding Elias 2-27, a young star that lies in the constellation Ophiuchus located 450 light-years away from Earth.

It is not the first time that such feature has been spotted on the surface of a protoplanetary disk. Spiral arms are also found in the Milky Way of the solar system. What makes the newly spotted spiral structure unique is its location. It is the first time that spiral ams were found at the circumstellar disk midplane where planet formation takes place.

The structure may indicate either the presence of a newly formed planet or may create the conditions necessary for planetary formation. The findings, which were published in the journal Science AAAS on Sept. 30, may shed light on how planets form and how some planets become so large, which could eventually pave way for a better understanding on how planetary systems such as the solar system came into being.

How do giant spiral structures influence planet information?

A step by step process is involved in planet formation. Dust particles present in the gas of the disk occasionally collide into each other and clump together. With successive collisions, larger particles, grains and then solid bodies eventually form.

Scientists, however, are still uncertain as to how the colliding particles form large planets since once colliding bodies measure about 1 meter in width (39 inches), the drag produced by the surrounding gas makes the bodies migrate toward the young star. The migration can take around a thousand years but larger timescales are needed for the formation of considerably bigger objects such as planets.

The answer may be on structures such as the spiral arm. Planets may not be able to form without the spiral disks. With gravitational pull and confined space, these structures accelerate the normal rate of planet formation in regions with high density of particles by increasing the odds of collision, which would allow the bodies to go beyond 1 meter to 10 meters (39 to 394 inches).

"These results provide a distinct benchmark for numerical simulations of spiral structure in protoplanetary disks, particularly because fragmentation of such spirals remains the only plausible formation mechanism for planets and companions at large disk radii, where core-accretion becomes inefficient," wrote study researcher Laura Pérez, from Max Planck Institute for Radio Astronomy, and colleagues.

"The detection of spiral features in Elias 2-27 is a first step to determine what is the dominant mechanism of planet formation at different locations in the disk."

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