Stars and planets grow up together as siblings
ALMA shows rings around the still-growing protostar IRS 63
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 led by Dominique Segura-Cox at the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany targeted the protostar IRS 63 with the ALMA radio observatory. This system 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.
In systems older than 1,000,000 years, after the protostars have finished gathering most of their mass, rings of dust have been previously detected in great numbers. 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 very young,” emphasizes Segura-Cox. “We used to think that stars entered adulthood first and then were the mothers of planets that came later. 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. They have to grow from tiny dust particles, smaller than household dust here on Earth. “The rings in the disk of IRS 63 are vast pile-ups of dust, ready to develop into planets,” notes co-author Anika Schmiedeke at MPE. However, even after the dust clumps together to create a planet embryo, the still-forming planet could disappear by spiraling inwards, and be consumed by the central protostar. If planets start forming at very early stages and at large distances from the protostar, they may better survive this process.
The team of researchers found that there are about 0.5 Jupiter masses of dust in the young disk of IRS 63 further than 20 au from its center (at a distance similar to the Uranus orbit in our solar system). That is not counting the amount of gas, which could add up to 100 times more material. It takes at least 0.03 Jupiter masses of solid material to form a planet core that will efficiently accrete gas and grow to form a giant gas planet. Team member Jaime Pineda at MPE adds, “These results show that we must focus on the youngest systems to truly understand planet formation.” For example, there is growing evidence that Jupiter may have actually formed much further out in the Solar System, beyond the Neptune orbit, and then migrated inwards to its present location. Similarly, the dust surrounding IRS 63 shows that there is enough material far from the protostar and at a stage young enough that there is a chance for this Solar System to form planets in the way that Jupiter is suspected to have 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 less than our Sun's. Studying such young planet-forming disks around protostars can give us important insights into our own origins.”
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 (Seoul National University/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.