How Do Planets Form? New Images Of Baby Star Provide Insight

A team of international researchers have captured an image of a baby star from the ALMA observatory in Chile that sheds some valuable insight on planet formation. Specifically, spiral arms spotted in a large disk of gas and dust surrounding the new star—called Elias 2-27—may explain how some planets become so large. The researchers published their findings in Science AAAS.

The spiral arms surrounding Elias 2-27, located 450 light-years from Earth in the constellation Ophiuchus, extend 6 billion miles from the center of the system. What makes these spiral structure unique, reports Gizmodo, is not their existence—spiral arms are also present in the Milky Way in our solar system—but their location: they are at the circumstellar disk midplane where planets form.

“The observed spirals in Elias 2-27 are the first direct evidence for the shocks of spiral density waves in a protoplanetary disk,” says lead author Laura M. Pérez, an Alexander von Humboldt Research Fellow from the Max Planck Institute for Radio Astronomy (MPIfR), in a statement. “They show that density instabilities are possible within the disk, which can eventually lead to strong disk inhomogeneities and further planet formation.”

The trajectory of how planets form is something like this: particles collide and join together to create larger particles in the disks of gas and dust near a newborn star. But the question that still remains murky for scientists is how these colliding particles configure large planets since the compounds start to make their way towards the young star once they measure a few feet in width. While this migration can take around a thousand years, it still does not explain how planets the size of Saturn and Jupiter can form.

The answer may lie in the spiral arms—according to Pérez, planets may not be able to form without spiral disks. These structures can speed up the normal rate of planet formation in areas with a high density of particles by increasing the odds of collision courtesy of their gravitational pull and confined space.

A release from MPIfR explains:

“In a smooth disk, planets can only grow step by step,” reads a university rele. “Dust particles within the gas of the disk occasionally collide and clump together, and by successive collisions, ever larger particles, grains, and eventually solid bodies form. But as soon as such bodies reach a size of about one meter, drag by the surrounding gas of the disk will make them migrate inwards, towards the star, on a time scale of 1000 years or shorter. The time needed for such bodies to collect sufficient mass by successive collisions, eventually reaching a size where gas drag becomes a negligible influence, is much larger than that.”

Scientists have ways to go to understand how the arms in circumstellar disks work and where they come from.

“Similar observations with ALMA will become increasingly common, and more and more detailed images showing inhomogeneous structures in disk density become available,” says Karl Menten, director at MPIfR and a co-author of the paper, in a statement. “Astronomers should increasingly be able to investigate the properties of such features, and to eventually define their role in the planetary formation process.”