Stars and Planets Grow Up Together as Siblings

Astronomers have found compelling evidence that planets start to form while infant stars are still growing. The high-resolution image obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) shows a young protostellar disk with multiple gaps and rings of dust. This new result, just published in Nature, shows the youngest and most detailed example of dust rings acting as cosmic cradles where the seeds of planets form and take hold.

An international team of scientists lead by Dominique Segura-Cox at the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany targeted the protostar, IRS 63, which is 470 light years from Earth and located deep within the dense L1709 interstellar cloud in the Ophiuchus constellation. Protostars as young as IRS 63 are still swaddled in a large and massive blanket of gas and dust called an envelope, and the protostar and disk feed from this reservoir of material.

Rings of dust have been previously detected in great numbers in systems older than 1,000,000 years, after the protostars have finished gathering most of their mass. IRS 63 is different: at under 500,000 years old, it is less than half the age of other young stars with dust rings, and the protostar will still grow significantly in mass. "The rings in the disk around IRS 63 are so young," emphasizes Segura-Cox. "We used to have this idea that stars entered adulthood first and were the mothers of planets that came afterwards, but now we see that protostars and planets grow and evolve together from early times like siblings."

Planets face some serious obstacles during their earliest stages of formation. Planets have to grow from tiny dust grains, smaller than the particles of dust found in a house here on Earth. "The rings in the IRS 63 disk are vast pile-ups of dust, ready to stick together on the way to forming planets," notes co-author Anika Schmiedeke at MPE. Even once the dust clumps together to form a larger planet embryo, the still-forming planet could spiral inwards and be consumed by the central protostar. If planets start to form very early and at large distances from the protostar, this problem can start to be overcome.

The team of researchers found that there is about 150 Earth masses of dust in the young disk of IRS 63 outside of 20 au (close to Uranus’s orbit in our own Solar System). It takes at least 10 Earth masses of solid material to form a planet core that will efficiently accrete gas and form a gas giant planet. Team member Jaime Pineda at MPE adds, "These results show that we must focus on the youngest systems to truly understand planet formation." There is growing evidence that Jupiter may have actually formed much farther out in the Solar System, beyond Neptune’s orbit, and then migrated inwards to its present location. The dust surrounding IRS 63 shows that there is enough material far from the protostar and at an early enough time that there is a chance for this Solar System analogue to form planets in the way that Jupiter was formed.

"The size of the disk is very similar to our own Solar System," Segura-Cox explains. "Even the mass of the protostar is just a little smaller than the mass of our Sun. Studying such young planetforming disks around protostars can give us important insights into our own origins."

This research is presented in a paper titled "Four annular structures in a protostellar disk less than 500,000 years old", by D. M. Segura-Cox et al., in Nature .

The team is composed of Dominique M. Segura-Cox (Max Planck Institute for Extraterrestrial Physics/University of Illinois), Anika Schmiedeke (Max Planck Institute for Extraterrestrial Physics), Jaime E. Pineda (Max Planck Institute for Extraterrestrial Physics), Ian W Stephens (Center for Astrophysics Harvard & Smithsonian), Manuel Fernández-López (Instituto Argentino de Radioastronomía), Leslie W. Looney (University of Illinois), Paola Caselli (Max Planck Institute for Extraterrestrial Physics), Zhi-Yun Li (University of Virginia), Lee G. Mundy (University of Maryland), Woojin Kwon (Korea Astronomy and Space Science Institute) and Robert J. Harris (University of Illinois).

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

About Center for Astrophysics

Harvard & Smithsonian (CfA) is a collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

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