Observations made with the Atacama Large Millimeter/Submillimeter Array (ALMA) in northern Chile, which is scheduled for completion this year, have solved a longstanding mystery in solar system formation. They showed how protoplanets forming around a young star can use their own gravitational pull to slingshot matter in the direction of their host star, fueling its growth.

When a new star is formed, the surrounding clouds of gas and dust, which amount to a very large mass, slowly begin to orbit it creating a flat disk. The disk is not entirely homogeneous and so, over hundreds of millions of years, the material starts sticking together, creating a stronger and stronger gravitational pull as the materials becomes more concentrated in places. Some of these clumps of material will eventually grow to become full-fledged planets orbiting the star.

In capturing all the nearby material, however, the planets end up creating a large gap between themselves and the star, splitting the dust and gas disk into an inner disk that lies next to the star and a very massive outer ring. The gap is large enough that, in theory, it should prevent the young star from gaining any more mass and significantly reduce its lifetime. However, astronomers have observed that this is not the case: despite the seemingly insurmountable gap between the star and the material that would feed its growth, the stars still manage to reach it. But how?

By closely watching HD 142527, a solar system in its infancy only about 450 light-years away from Earth, an international group of astronomers led by Simon Casassus at the University of Chile believe they've finally found the answer to this long-standing question.

In this still-forming solar system, dense streams of gas obscure the planets from direct observation. The gas, the scientists say, is being gathered from the outer ring, pulled in by the planets' gravitational field. Interestingly, though, the vast majority of the gas and dust that is being pulled in doesn't contribute to growing the planets themselves but, rather, is propelled toward the inner ring, from which the host star can grow.

In the system they were observing, Casassus and colleagues calculated that, without the streams of gas being fed by the protoplanets, the inner portion of the disk would be depleted in less than a year. Instead, the large quantity of gas delivered by the streamers is able to both maintain the inner disk and fuel the star's growth.

This discovery was possible thanks to the capabilities of the ALMA telescope, a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. Once construction reaches completion later this year, the telescope will be put to use capturing details about the first stars and galaxies in our universe, investigating the center of our galaxy, and directly imaging the formation of planets.

The findings were reported on the latest issue of the journal Nature.

Source: NRAO