Universiteit Leiden

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Planet formation starts before a star is fully grown

A team of European astronomers under Leiden leadership has discovered that dust particles around a star already coagulate before the star is fully grown. These agglomerated dust particles are the first step in the formation of planets. The research publish their discovery in the journal of Nature Astronomy.

Other planetary systems

In recent years, astronomers have discovered many planetary systems around stars other than the sun. The suspicion is that almost every star is surrounded by one or more planets. Scientists now wonder how and when these planets are formed and why there are so many differences in number and size. The results of the recently completed European research suggest that planet formation starts very early in the process of star formation.

66 telescopes

The scientists used the Atacama Large Millimetre Array (ALMA) for their research. ALMA is a collection of no less than 66 coupled telescopes on a stretch of 16 kilometers in the Atacama desert in Chile. The researchers set the telescope on TMC1A, an still developing star in the constellation Taurus.

Lack of radiation

The astronomers studied the protoplanetary  disk of TMCC1A. This is a flattened cloud of matter that revolves around a star-in-progress. In these disks of gas and dust, planets are created. In the disk-shaped area, the researchers noticed a striking lack of radiation from carbon monoxide. They suspected that the radiation was stopped by large dust particles. With numerical computer models, the astronomers indeed showed that the dust particles in the young protoplanetary disk have grown from a thousandth of a millimeter to a full millimeter.

Early particle growth

Lead researcher Daniel Harsono (Leiden Observatory) explains why the results are so surprising: ‘The results indicate that planets form early in the development of a star. The young star is yet only half to three quarters of its final mass. This is new.’ In addition, early particle growth may be an explanation for the formation of large planets such as Jupiter and Saturn. Only young protoplanetary discs contain enough mass to form giant planets.

One or all?

Co-researcher Matthijs van der Wiel (ASTRON, Netherlands Institute for Radio Astronomy) is pleased with the clear and unambiguous observations. ‘Although it could of course be that this particle growth  so far only takes place in this one planetary disk. Perhaps this young disc is very special.’

In the future, the researchers want to look for tell-tale signs of planet formation around other young stars in similar matter. Ultimately, they want to learn more about when and how planets are formed.

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