Planet-forming disks evolve in remarkably similar ways

(ORDO NEWS) — A team of astronomers led by Serk van Terwiesg of the Max Planck Institute for Astronomy analyzed the mass distribution of more than 870 planet-forming disks in the Orion A cloud.

Using the statistical properties of this unprecedented sample of hot stars, for example, they found that far from harsh conditions like hot stars, the mass of disks only decreases.

Using the statistical properties of this unprecedentedly large sample of disks and developing an innovative data processing scheme, they found that away from harsh environments such as hot stars, the reduction in mass of disks depends only on their age.

The results show that, at least within 1000 light-years of Earth, planet-forming disks and planetary systems evolve in a similar fashion.

One of the most interesting questions of modern astronomical research is “What do other planetary systems look like?” and “How comparable is the solar system to other planetary systems?”. A group of astronomers have made a decisive contribution to solving this riddle.

“Until now, we didn’t know for sure which properties dominate the evolution of planet-forming disks around young stars,” says Serk van Terwisga, a scientist at the Max Planck Institute for Astronomy in Heidelberg, Germany.

He is the lead author of a major scientific paper published today in the journal Astronomy & Astrophysics.

“Our new results show that in an environment without any relevant external influence, the observed disk mass available for the formation of new planets depends only on the age of the star-disk system,” adds van Terwisga.

The disk mass is a key property in studying the evolution of planet-forming disks. This value determines how much material is available to be converted into planets. Depending on the age of the disk, it can also provide clues about planets already existing there.

External effects such as radiation and winds from nearby massive stars obviously affect the disk’s survival. However, such environments are rare, and these processes say little about the drives themselves.

Instead, astronomers are more interested in the internal properties of the disk, such as the age, chemical composition, or dynamics of the parent cloud from which the young stars and their disks emerged.

To separate the various contributions, the team of astronomers chose a large and well-known region of young stars with disks – the Orion A cloud. It is located at a distance of about 1350 light-years from Earth.

“The Orion A cloud provided us with an unprecedentedly large sample of more than 870 disks around young stars. It was very important to find small changes in disk mass depending on age and even on the local environment within the cloud,” explains Alvaro Jacar, co-author of the study and a scientist from University of Vienna (Austria).

The sample is based on earlier observations with the Herschel Space Telescope that identified the disks. The combination of several wavelengths provided a criterion for estimating their age.

Since they all belong to the same cloud, astronomers expected little influence from the chemical composition and variations in the cloud’s history. They also avoided the influence of massive stars in the nearby Orion Nebula Cluster (ONC) by rejecting disks closer than 13 light-years away.

To measure the disk’s mass, the team used the Atacama Large Millimeter/Submillimeter Array (ALMA) located on the Chajnantor Plateau in Chile’s Atacama Desert. ALMA consists of 66 parabolic antennas that function as a single telescope with adjustable angular resolution.

The scientists applied an observation mode that allowed them to effectively target each disk at a wavelength of about 1.2 millimeters. Cold disks are bright in this spectral range. On the other hand, the contribution of the central stars is insignificant.

Using this approach, astronomers have determined the mass of dust in the disks. However, the observations are insensitive to objects much larger than a few millimeters, such as rocks and planets. So the team effectively measured the mass of disk material capable of forming planets.

Before calculating the mass of the disk, astronomers combined and calibrated data from several dozen ALMA telescopes. This task becomes quite difficult when dealing with large data arrays.

Using standard methods, it would take months to process the collected data. Instead, the team developed a new method using parallel computers.

“Our new approach has increased data processing speed by 900 times,” says co-author Raymond Oonk of collaborating IT service provider SURF. The 3,000 processor hours required to complete the task and prepare the data for subsequent analysis were completed in less than a day.”

In general, Orion A contains planet-forming disks, each of which contains dust weighing up to several hundred Earth masses. However, out of 870 discs, only 20 contain dust equivalent to 100 Earth masses or more.

In general, the number of disks decreases rapidly with increasing mass, and most contain less than 2.2 Earth masses of dust. “In order to find variations, we cut through the Orion A cloud and analyzed these regions separately. With hundreds of disks, the subsamples were large enough to give statistically significant results,” explains van Terwisga.

Indeed, scientists have found minor changes in the distribution of disk masses on scales of tens of light years within Orion A. However, all of them can be explained as an age effect, that is, within a few million years, disk masses tend to decrease towards older populations.

Within the margin of error, clusters of planet-forming disks of the same age exhibit the same mass distribution. There is nothing surprising in the fact that the mass of dust in planet-forming disks decreases with time.

After all, dust is one of the raw materials for planets. Therefore, the formation of planets certainly reduces the amount of free dust. Other well-known processes are the migration of dust towards the center of the disk and the evaporation of dust when irradiated from the host star. However,

All of these disks originated from the same environment that is now the Orion A cloud. How does this compare to other populations of young stellar disks? Astronomers answered this question by comparing their results to several nearby star-forming regions with planet-forming disks.

With the exception of two, they all agree well with the mass-age relationship found in Orion A. “Overall, we believe our study proves that, for at least the next 1,000 light-years or so, all populations of planet-forming disks show the same distribution of mass at a certain age.

And they seem to evolve more or less the same way,” concludes van Terwisga. The result could even hint at the formation of stunningly similar planetary systems.”

As a next step, scientists will study possible collisions with nearby stars on smaller scales of a few light years. Although they have avoided the strong radiation field caused by massive stars in ONC, there are potentially fainter stars that could influence dust in nearby disks and change disk mass statistics.

Such a contribution may explain some of the deviations found in the dependence of disk mass on age. The results obtained may help to strengthen the overall picture of the evolution of the planet-forming disk, which is dominated by age.

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