A cosmic cradle in sight: images of a very young star system contradict the image of the planets as children of the stars. They may already be forming while the radiant center itself is still growing. This can be seen from the structural features of the protostellar disk that surrounds the baby star IRS 63. The results can help understand how planetary systems like ours were formed, say the astronomers.
What happens in the beginning This question is particularly appealing in many areas of science – including astronomy. That is why insights into the nurseries of the stars and planets are particularly popular. You have already made it clear: The celestial bodies are formed from an accumulation of gas and dust, which ultimately takes the form of a protostellar disk. Our sun and its companions were also once lumps that grew in such a structure through the agglomeration of the material. Up until now, it was assumed that the star in the center was largely formed before the planets began to emerge from the protoplanetary disk. But the current observations now call this sequence into question.
500,000 years young
The astronomers headed by Dominique Segura-Cox from the Max Planck Institute for Extraterrestrial Physics in Garching (MPE) focused on the protostar IRS 63. This system is located 470 light years from Earth in the constellation of the Serpent Bearer. As they report, the protostar has an age that corresponds to the blink of an eye on a cosmic scale: At 500,000 years, IRS 63 is a decidedly baby star. Such young protostars are still surrounded by a large amount of matter from which the protostar and its disk are formed. In systems older than a million years, in which the protostars have already accumulated most of their mass, astronomers have already discovered rings and gaps that indicate the formation of planets. The presence of the protoplanets imprints these structures on the disks.
But the observations made by IRS 63 are now moving this mark significantly further into the early phase of development: On the images of the Atacama Large Millimeter / submillimeter Array (ALMA), several gaps or ring structures can already be seen in the protostellar disk of the star, which is still growing strongly. In this, the scientists see evidence that planet formation began at this very early phase of the system’s development. “Up to now we thought that the stars would grow up first and then they would be mothers of the planets that come later. But now it is becoming apparent that protostars and planets are growing and developing together like siblings, ”says Segura-Cox.
But is it perhaps just “structured food” for the further formation of the star? This seems possible, because even if a planet embryo has formed from lumps of dust, the nascent planet could disappear again by drifting on a spiral path towards the center and being swallowed by the protostar. But this may only apply to the protoplanets near the star. If celestial bodies form very early and at a great distance from the center, they could survive and later migrate closer to the star, the scientists say.
Possible clues to the history of our solar system
In this context, the team was able to show that the young disk of IRS 63 still has about 0.5 Jupiter masses of dust at a comparatively great distance from the center: It corresponds to the distance between Uranus and the sun in our solar system. As they explain, at least 0.03 Jupiter masses of solid are required to form a planetary core, which can accumulate more matter and grow into a giant planet. That means: The dust that surrounds IRS 63 has the potential to form planets that will be preserved in the system.
This directs our attention to our own solar system: There are already indications that Jupiter could originally have formed beyond the orbit of Neptune and only later migrated inward to its current location. The system of IRS 63 may thus be similar to our solar system in its baby phase. “The size of the disk is also very similar to our own solar system,” emphasizes Segura-Cox in this context. “Even the mass of the protostar is only a little less than that of our sun”.
The researchers’ conclusions now need to be substantiated by further observations, and so they hope to be able to study other very young systems: “These results show that we need to focus on the most recent systems in order to really understand the formation of planets “Says co-author Jaime Pineda from MPE. His colleague Segura-Cox concludes: Investigating such young disks around protostars, in which planets are formed, can provide us with important information about our own origins, ”says the astronomer.
Source: Max Planck Institute for Extraterrestrial Physics, specialist article: Nature, doi: 10.1038 / s41586-020-2779-6