Is our solar system comparable to other solar systems? What are other systems like? We know from exoplanet studies that many other systems have hot Jupiters, massive gas giants orbiting their stars extremely closely. Is this normal and our solar system is the outlier?
One way to answer these questions is to study the planet-forming disks around young stars to see how they are evolving.
But studying a large sample of these systems is the only way to get an answer.
That’s what a group of astronomers did when they studied 873 protoplanetary disks.
Mass is the key element in a new study of planet-forming disks. The mass of the disk determines how much matter is available to form planets.
By measuring the mass of the disks around young stars, astronomers can constrain the total masses of the planets that could form there and get a step closer to understanding the Solar System’s architecture.
The new study is “Survey of Orion Disks with ALMA (SODA): I. Cloud-level demographics of 873 protoplanetary disks.” It is published in the magazine 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 did not know exactly which properties dominate the evolution of planet-forming disks around young stars,” said van Terwisga in a press release.
“Our new results now indicate that in environments without relevant external influence, the observed disk mass available for the formation of new planets depends only on the age of the star-disk system.”
The dust mass not only tells astronomers the mass of planets that could form from a disk. Depending on the age of the disk, 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 winds and radiation from nearby stars outside the disk can also affect mass.
How were the researchers able to isolate these effects in such a large sample?
They focused on a known region of protoplanetary disks called the Orion A cloud, which is part of the Orion Molecular Cloud Complex (OMCC).
About 1,350 light-years away, OMCC is 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 as observed by the SPIRE (Spectral and Photometric Imaging Receiver) instrument on board the Herschel Space Telescope. It traces the large-scale distribution of cold dust. Orion A is about 1350 light-years away and is made up of individual star-forming regions, as indicated by their label. The positions of planet-forming disks (+) observed by ALMA are indicated, while disks with dust masses over 100 Earth masses equivalent appear as blue dots.
Álvaro Hacar is a co-author of the study and a researcher at the University of Vienna, Austria. “Orion A gave us an unprecedentedly large sample size of more than 870 disks around young stars,” Hacar said. “Being able to look for small variations in disk mass by age and even by on-premises environments within the cloud was critical.”
This is a good example as all disks belong to the same cloud. This means their chemistry is consistent and they all share the same story.
The nearby Orion Nebular Cluster (ONC) hosts some massive stars that could affect other disks, so the team rejected any disks in Orion A that are closer than 13 light-years to the ONC.
Measuring the mass of all these discs was difficult. 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 disks at a wavelength of 1.2 mm.
At this wavelength, the dust is bright but the star is faint, helping to eliminate the effect of the star in each disk. Since the observation at 1.2 millimeters makes the observations insensitive to objects larger than a few millimeters – for example planets that have already formed – the team’s measurements only measured dust available for new planets to form .
Measuring dust free from stellar interference was one hurdle, but the researchers faced another: data.
A detailed study of nearly 900 protoplanetary disks produces a lot of data, and all of that data must be processed before it can have any collective meaning. If the team had relied on existing methods, it would have taken about six months to process all of this data.
Instead, they developed their own method to process the data in parallel. What would have taken months took less than a day. “Our new approach improved processing speed by a factor of 900,” said co-author Raymond Oonk.
When they processed the data, the researchers found that most disks contained only 2.2 Earth masses of dust. Only 20 of the nearly 900 disks contained enough dust for 100 or more Earths.
“To look for variations, we dissected the Orion A cloud and analyzed these regions separately. Thanks to the hundreds of slices, the sub-samples were still large enough to provide statistically meaningful results,” explains van Terwisga.
The researchers found some variability in disk dust mass in different regions of Orion A, but the variations were minimal. According to the authors, the age effect may be responsible for the variations. As plates age, plate mass decreases, and clusters of plates of the same age have the same mass distribution.
“We must emphasize that the differences between these widely separated clusters in the sky are small and, even in the most extreme cases, are not very significant relative to each other and to the field,” the authors write in their paper.
Above: This figure shows the six low-mass, low-density YSO clusters in the study. Despite their wide distribution in Orion A, the disks show the same mass-age correlation.
It is expected that as the discs age, their dust mass will decrease. Planet formation is responsible for most of this decline: what was once dust becomes planets.
But other effects also contribute to dust loss. Dust can migrate to the center of the disk, and radiation from the host star can vaporize the dust.
But this study reinforces the correlation between age and dust loss.
Can the results of this study be applied to other populations of young star discs? The authors compared their results from Orion A to several neighboring star-forming regions with young disks.
Most of them, but not all, match the age-related mass loss observed at Orion A.
“Overall, we believe our study proves that at least within the next 1000 light-years, all populations of planet-forming disks of a given age have the same mass distribution. And they seem to be developing in more or less the same way,” van Terwisga said.
The researchers have more work they’d like to get done. 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 stars in the ONC can have on neighboring 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 combine with the mass to provide a clearer picture of the solar system emerging from the disk. Astronomers are unable to take such data and predict what type of planets might form in any given solar system.
But it is noteworthy that the correlation between plate age and plate mass is strong, even for large structures like Orion A.
“The remarkably homogeneous properties of disk samples of the same age are a surprising finding,” the authors conclude, and their results confirm what previous studies and surveys have suggested.
“Now, however, we can show that this is true for a larger number of YSOs 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 magnify the effects of age gradients and clustering in a single star-forming region.
This article was originally published by Universe Today. Read the original article.
https://www.sciencealert.com/survey-of-more-than-800-planet-forming-disks-reveals-an-evolutionary-surprise Examination of more than 800 planet-forming disks reveals a surprise in planetary evolution