Is our solar system comparable to other solar systems? What are the other systems like? We know from studies of exoplanets that many other systems have hot Jupiters, massive gas giants that orbit extremely close to their stars. Is this normal, and our solar system is the outlier?
One way to address these questions is to study planet-forming disks around young stars to see how they evolve.
But studying a large sample of these systems is the only way to get an answer.
So that’s what a group of astronomers did when they probed 873 protoplanetary disks.
Mass is the critical element of a new study of planet-forming disks. The mass of the disk determines the amount of material available to form the planets.
By measuring the mass of disks around young stars, astronomers can constrain the total mass of planets that might form there and come closer to understanding the architecture of the solar system.
The new study is “Survey of Orion’s Disks with ALMA (SODA): I. Cloud-level demography of 873 protoplanetary disks.“It’s published in the journal Astronomy and astrophysicsand the lead author is Sierk van Terwisga, a scientist at the Max Planck Institute for Astronomy in Heidelberg, Germany.
“Until now, we didn’t know for sure which properties dominate the evolution of planet-forming disks around young stars,” van Terwisga said. mentioned in a press release.
“Our new results now indicate that in environments without any relevant external influences, the observed disk mass available to form new planets depends only on the age of the star-disk system.”
The mass of dust not only tells astronomers the mass of planets that could form from a disk. Depending on the age of the disc, it could also tell astronomers which planets have already formed.
But other factors also affect disk mass, and these factors vary from disk to disk. Things like stellar wind and irradiation from nearby stars outside the disk can also affect mass.
So how were the researchers able to isolate these effects in such a large sample?
They focused on a well-known region of protoplanetary disks called Orion A cloudwhich is part of the Orion Molecular Cloud Complex (OMCC).
The OMCC is about 1350 light-years away and home to the well-studied Orion Nebula, a feature even backyard astronomers can see.
Above: This image shows the giant star-forming cloud Orion A observed by the Spectral and Photometric Imaging Receiver (SPIRE) instrument aboard the Herschel Space Telescope. It traces the large-scale distribution of cold dust. Orion A is about 1350 light-years away and consists of individual star-forming regions as indicated by their labels. The locations of (+) planet-forming disks observed with ALMA are shown, while disks with dust masses greater than an equivalent of 100 Earth masses appear as blue dots.
Álvaro Hacar is a co-author of the study and a scientist at the University of Vienna, Austria. “Orion A provided us with an unprecedented sample size of more than 870 disks around young stars,” Hacar said. mentioned. “It was crucial to be able to search for small variations in disk mass based on age and even local environments inside the cloud.”
This is a good example because all disks belong to the same cloud. This means their chemistry is consistent and they all have the same story.
The nearby Orion Nebular Cluster (ONC) hosts massive stars that could affect other disks, so the team rejected all Orion A disks within 13 light-years of the ONC .
Measuring the mass of all these disks was tricky. The team used the Atacama Large Millimeter/Submillimeter Array (ALMA) to observe the dust. ALMA can be tuned to different wavelengths, so the team observed the young discs at a wavelength of 1.2 mm.
At this wavelength, the dust is bright, but the star is dim, which helps eliminate the effect of the star in each disk. Since observing at 1.2 millimeters renders observations insensitive to objects larger than a few millimeters – for example, already formed planets – the team’s measurements only measure dust available to form new planets.
Measuring dust without star interference was one hurdle, but the researchers encountered another: data.
A detailed study of nearly 900 protoplanetary disks creates a lot of data, and all of this data needs to be processed before it has any collective meaning. If the team had relied on existing methods, it would have taken about six months to process all this data.
Instead, they developed their own method to handle the data using parallel processing. What would have taken months took less than a day. “Our new approach improved processing speed by a factor of 900,” co-author Raymond Oonk mentioned.
When they processed the data, the researchers found that most of the disks contained only 2.2 land masses of dust. Only 20 of the approximately 900 discs contained enough dust for 100 Earths or more.
“In order to look for variations, we dissected the Orion A cloud and analyzed these regions separately. Thanks to the hundreds of disks, the subsamples were still large enough to yield statistically significant results,” van Terwisga said. Explain.
The researchers found some variability in the mass of disk dust in different regions of Orion A, but the variations were minimal. The age effect may explain the variations, according to the authors. As disks age, disk mass decreases and disk clusters of the same age have the same mass distribution.
“It should be emphasized that the differences between these clusters, far apart in the sky, are small and insignificant with respect to each other and to the terrain, even in the most extreme cases”, explain the authors. write in their paper.
Above: This figure shows the six low-mass, low-density groups of YSO in the study. Despite their wide distribution in Orion A, the discs show the same mass-age correlation.
It is expected that as discs age, their dust mass will decrease. Planetary formation explains most of this decrease: what was once dust becomes planets.
But other effects also contribute to dust loss. Dust can migrate to the center of the disc, and irradiation from the host star can evaporate the dust.
But this study reinforces the correlation between age and dust loss.
Can the results of this study be applied to other young populations of stellar disks? The authors compared their results from Orion A with several nearby star-forming regions with young disks.
Most, but not all, of these match the age-related mass loss seen in Orion A.
“Overall, we think our study proves that at least in the next 1000 light-years, all populations of planet-forming disks show the same mass distribution at a given age. And they seem to evolve more or less in the same way”, van Terwisga mentioned.
Researchers have more work than they would like to do. They will examine the effect that smaller stars can have on a smaller scale of a few light-years.
In this study, they avoided the effect that massive ONC stars can have on nearby disks. But smaller background stars could still affect the disks, and they could explain some of the small variations in the age-mass correlation.
The age of the star and its disk, the chemical properties, and the dynamics of the parent cloud all combine with the mass to paint a clearer picture of the solar system that stems from the disk. Astronomers aren’t able to take data like this and predict what kind of planets might form in a given solar system.
But it is remarkable that the correlation between disk age and disk mass is strong, even on large structures like Orion A.
“The remarkably homogeneous properties of disc samples of the same age are a surprising finding,” explain the authors. concludeand their results confirm what previous studies and surveys have suggested.
“Now, however, we can show that this applies to a larger number of YSO and YSO clusters, forming in well-separated parts of the same giant cloud. For the first time, the unprecedented size of the SODA (Survey of Orion Disks with Alma) disk sample allows us to zoom in on the effects of age gradients and clustering in a single star forming region.”
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