Survey of more than 800 planet formation disks reveals a surprise in planetary evolution

Is our solar system similar to other solar systems? What do other systems look like? We know from studies of exoplanets that many other systems have hot exoplanets, huge gas giants that orbit near their stars. Is this normal and our solar system is outside?

One way to address these questions is to study the 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.

That’s what a group of astronomers did when they surveyed 873 protoplanetary disks.

Mass is the crucial piece in a new study of the planet’s constituent disks. The mass of the disk determines how much matter is available for planetary formation.

By measuring the mass of disks around young stars, astronomers can constrain the total mass of planets that might form there and get one step closer to understanding the structure of the solar system.

The new study is “Survey of Orion Disks with ALMA (SODA): I. Cloud-level demographics of 873 protoplanetary disks.” It was published in the magazine Astronomy and astrophysicsand lead author is Cirque van Teroosga, a scientist at the Max Planck Institute for Astronomy in Heidelberg, Germany.

“Until now, we haven’t known for sure which characteristics dominate the evolution of planet-forming disks around young stars,” Van Teroosga said in a press release.

“Our new results now indicate that in environments without any relevant external forcing, the observed disk mass available for the formation of new planets depends solely on the age of the stellar disk system.”

The mass of dust doesn’t just tell astronomers what mass of planets a disk might consist of. Depending on the age of the disk, it can also tell astronomers which planets actually formed.

But there are other factors that affect disk mass as well, 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 could researchers isolate these effects in such a large sample?

They focused on a well-known region of protoplanetary disks called the Orion A cloud, which is part of the Orion Molecular Cloud Complex (OMCC).

OMCC is located about 1,350 light-years away and is home to the well-studied Orion Nebula, a feature that even backyard astronomers can see.

(SE van Terwisga et al./MPIA)

above: This image depicts the giant star-forming cloud Orion A as observed by the SPIRE (Spectral and Optical Imaging Receiver) instrument aboard the Herschel Space Telescope. It tracks the widespread distribution of cold dust. Orion A is about 1,350 light-years away and consists of individual star-forming regions as indicated by their nomenclature. The locations of planet-forming disks (+) observed with ALMA are indicated, while disks with dust masses greater than the equivalent of 100 Earth masses are shown as blue dots.

Alvaro Hacar is a co-author of the study and a scientist at the University of Vienna, Austria. “Orion A has provided us with an unprecedentedly large sample size of more than 870 disks around young stars,” Hakkar said. “It was necessary to be able to look for small differences in disk mass depending on age and even on local environments within the cloud.”

This is a good sample because all disks belong to the same cloud. This means that their chemistry is uniform, and they all have the same history.

The nearby Orion Nebular Cluster (ONC) hosts some massive stars that could affect other disks, so the team rejected any disks in Orion A closer than 13 light-years to the ONC.

Measuring the mass of all these disks was difficult. The team used the Atacama Large Millimeter/ Submillimeter Array (ALMA) to monitor the dust. ALMA can be tuned to different wavelengths, so the team noted the small disks with a wavelength of 1.2 mm.

At this wavelength, the dust is bright, but the star is dim, which helps eliminate the star’s influence in each disk. Because observations at 1.2 millimeters render observations insensitive to objects larger than a few millimeters—for example, planets that have already formed—the team’s measurements only measured available dust to form new planets.

Measuring dust without interference from stars was one hurdle, but the researchers encountered another: the data.

A detailed survey of nearly 900 protoplanetary disks yields a lot of data, and all of this data must be processed before it can have any collective meaning. If the team relied on existing methods, it would take about six months to process all that data.

Instead, they developed their own way of handling data using parallel processing. What would have taken months took less than a day. “We developed our new approach to processing speed by a factor of 900,” co-author Raymond Onk said.

When they processed the data, the researchers found that most of the disks contained only 2.2 Earth masses of dust. Only 20 of the 900 disks carried enough dust for 100 or more planet Earths.

“In order to look for differences, we dissected the Orion A cloud and analyzed these regions separately. With hundreds of discs, the subsamples were still large enough to produce statistically significant results,” Van Teroosga explained.

The researchers found some discrepancy in the mass of disk dust in different regions of Orion A, but the differences were negligible. According to the authors, the effect of age could explain the differences. As disks age, disk mass decreases, and groups of disks of the same age have the same mass distribution.

“We must emphasize that the differences between these groups, which are located far from each other in the sky, are small and not very significant in relation to each other and in the field, even in extreme cases,” the authors wrote in a paper.

diffusion point(Van Teroisga et al., Astronomy and Astrophysics, 2022)

above: This figure shows the six low-mass, low-density groups of YSOs in the study. Despite their wide distribution in Orion A, the discs show the same association between mass and age.

Its dust mass is expected to decrease as the discs age. Planetary composition accounts for most of this decline: what was once dust turns into planets.

But there are other effects that contribute to dust loss as well. Dust can move toward the center of the disk, and radiation from the host star can vaporize the dust.

But this study strengthens the link between age and dust loss.

Could the results of this study apply to other young star disk clusters? The authors compared their results from Orion A with several neighboring star-forming regions with small disks.

Most, but not all, of them fit the age-related mass loss seen in Orion A.

“Altogether, we think our study proves that for at least the next thousand light years or so, all the constellations of disks that make up the planet show the same mass distribution at a given age. They appear to evolve around the same time,” Van Teroosga said.

The researchers have more work they’d like to do. They will examine the effect that young 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 could have on neighboring disks. But smaller background stars may still influence the disks, and may explain some of the small differences in the relationship between age and mass.

The age of the star and its disk, chemical properties, and the dynamics of the original cloud combine with mass to paint a clearer picture of the solar system emerging from the disk. Astronomers are unable to take such data and predict what kind of planets might form in any given solar system.

Remarkably, however, the relationship between disk age and disk mass is strong, even across structures as large as Orion A.

The authors conclude that “remarkably homogeneous characteristics of disc samples of the same age are a surprising finding,” and their results confirm what previous studies and surveys have indicated.

“Now, however, we can show that this applies to a larger number of YSO and YSO clusters, which form in well-separated parts of the same giant cloud. For the first time, the unprecedented size of SODA (Scan Orion disks with Alma) allows us to sample The disc magnifies 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.