The striking resemblance of the planet-forming disc
With the help of ALMA, the mass distribution of more than 870 planet-forming disks in the Orion A cloud can be investigated. It turned out that away from hostile environments such as hot stars, the drop in disk mass depends only on its age. This could mean that the planet-forming disk and planetary system evolved in a similar way.
This artist’s rendering shows what the planet-forming disks around young stars often look like. These initially consist of dust and gas that condense into rings of condensed material. Over time, the solid components develop into boulders that can eventually develop into planets.
visual: MPIA Graphics Department [Großansicht]
Some of the most exciting questions of today’s astronomical research are: What do other planetary systems look like and how comparable is the Solar System with other systems? A team of astronomers has now discovered important clues to solve this mystery. “Until now, we did not know which properties dominated the development of planet-forming discs around young stars,” says scientist Sirk van Terwisga of the Max Planck Institute for Astronomy in Heidelberg. “Our new results now show that in an atmosphere without relevant external influences, the disk mass available for new planetary formation depends only on the age of the star-disc system.”
Disc mass is the key property when studying the evolution of planet-forming discs. This size determines how much material is available for implementation in the planets. Depending on the age of the disc, it could also provide clues to planets already there. External influences such as radiation and winds from nearby massive stars clearly affect the disk’s firmness. However, such environments are rare, and these processes don’t reveal much about the disks themselves.
Instead, experts are more interested in internal disc properties such as the age, chemical composition or dynamics of the parent cloud from which young stars and their discs emerged. To explore the various contributions, the team selected a large and well-known region of the Orion A cloud, a disk containing young stars. It is about 1350 light years away from Earth. Team member lvaro explains, “Orion A provided us with an unprecedentedly large sample of more than 870 discs around young stars. Discs with age and even with the local atmosphere within the cloud It was important to be able to discover small changes in mass.” Hacker, scientist at the University of Vienna.
The sample is based on earlier observations with the Herschel Space Telescope, which were able to identify the disk. The combination of several wavelengths provided a criterion for estimating their age. Since they all belong to the same cloud, the researchers expected only minor effects from chemical and temporal changes in the cloud. They avoided any impact of massive stars except for a disk less than 13 light-years away in the nearby Orion Nebula star cluster.
To measure disk mass, the team used Atacama Large Millimeter/submillimeter Array (ALMA) is located on the Chajnantor Plateau in the Atacama Desert of Chile. ALMA consists of 66 parabolic antennas that act like a single telescope with an adjustable angular resolution. The scientists used an observation mode that allowed them to efficiently target each disk at a wavelength of about 1.2 millimeters. The cold disk is very bright in this spectral range. On the other hand, the contribution of the central stars is negligible.
With this approach, astronomers were able to determine the disk’s dust mass. However, observations are insensitive to objects much larger than a few millimeters, e.g. B. boulders and planets. So the team actually measured the mass of the disk material from which the planets could have formed. Before calculating the disk mass, the researchers combined and calibrated data from several dozen ALMA telescopes.
This task is quite challenging with large datasets. Using standard procedures, it would have taken months to process the collected data. Instead, the team developed a new method that relies on parallel computers: “Our new approach increased processing speeds by a factor of 900,” emphasized Raymond Oink from collaborative IT services provider SURF. 3000 CPU hours required to complete the task and prepare the data for subsequent analysis in less than a day.
Altogether Orion A has planet-forming disks, each containing a few hundred Earth masses of dust. However, only 20 of the 870 disks contain dust of at least 100 Earth masses. In general, the number of disks decreases rapidly towards higher masses, with most containing less than 2.2 Earth masses of dust. “To look for anomalies, we segmented the Orion A cloud and examined these regions separately. Thanks to the hundreds of slices, the subsets were still large enough to provide statistically meaningful results,” explains van Terwisga. Huh.
Indeed, within Orion A, the team found small changes in the distribution of disc mass on the scale of tens of light-years, but these can all be explained by age effects, i.e. disc masses diminish within a few million years. old population. However, within error tolerances, clusters of planet-forming discs of the same age have similar mass distributions.
Not surprisingly, the mass of dust in the planet-forming disk tends to decrease over time. After all, dust is one of the raw materials for planets. Therefore, due to the formation of planets, the amount of available dust undoubtedly decreases. Other well-known processes are the migration of dust towards the center of the disk and the evaporation of dust from the central star’s radiation. Still, it is surprising that there is such a strong correlation between disc mass and age.
All of these disks formed from the same environment that makes up the Orion A cloud today. How does it compare to other young star-disk populations? Astronomers investigated this question by comparing their results with planet-forming disks from several nearby star-forming regions. All but two fit well with the mass-age relationship found in Orion A. “Overall, we believe that our study shows that at least within the next 1000 or so light-years, all clusters of planet-forming discs have the same mass distribution at a given age. And they will be more or less the same.” appear to be evolving,” he concluded van Terwisga. The result could also be a clue to the formation of surprisingly similar planetary systems.
In the next step, the team will investigate possible impacts from nearby stars at short distances of a few light years. While they have avoided the powerful radiation field caused by massive stars in the Orion Nebula, there may be other, less powerful fields stars that can affect dust in neighboring disks and alter the disk’s mass figures. Such contributions may explain some of the discrepancies found in the relationship between disc mass and age. The results may help strengthen the overall picture of the age-dominated evolution of the planet-forming disk.
The team reports on the results in an expert article published in the journal astronomy and astrophysics has appeared.
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