"Super-planets" and Neptune-sized planets can form around young stars in much larger quantities than scientists believe, according to new research by an international team of astronomers.
Observing the sampling of young stars in a star forming region in the Taurus constellation, scientists have discovered that many of them are surrounded by structures that best can be explained as traces created by invisible young planets in the process of creation. The research, published in the Astrophysical Journal, helps scientists better understand how our own solar system has become.
About 4.6 billion years ago, our solar system was a swirling, undulating swing of gas and dust around our newborn sun. In the early stages this pp. The "protoplanetary disk" had no visible traits, but soon parts of it began to merge into masses of matter – the future planets. As they picked up new material during their journey around the sun, they grew and began to rip patterns of gaps and rings into the disk they were forming. Over time, the dust disk gave way to the relatively ordered arrangement we now know, consisting of planets, moons, asteroids, and occasional comets.
Scientists base this scenario on the way our solar system has become a sight of protoplanetary discs around other stars that are young enough to be in the process of giving birth to planets. Using the Atacama Large Millimeter Array or ALMA, consisting of 45 radio antennas in the Atacama Desert in Chile, the team conducted a study of the young stars in the area forming the Tower's stars, a huge cloud of gas and dust located at a modest 450 light-years from Earth. When explorers depict 32 stars surrounded by protoplanetary discs, they find that 12 of them – 40% – have rings and gaps, structures that according to measurements and team calculations can best be explained by the presence of nascent planets.
"This is fascinating because, for the first time, exoplanet statistics suggesting that super-earth and neptune are the most common types of planets coincide with the observations of protoplanetary disks," says lead author Feng Long, a PhD student at the Institute of Astronomy and astrophysics at the University of Beijing, Beijing, China.
While some protoplanar discs look like identical, pancake-like objects that have no traits or patterns, there are concentric bright rings separated by gaps, but since previous research has turned their attention to the brightest of these objects because they are easier to find, how common discs with ring structures and gaps are really in the universe. This study presents the results of the first impartial study that the target disks were selected irrespective of their brightness – in other words, the researchers did not know if any of their targets had ring structures when they were chosen for the study.
"Most previous observations have been aimed at detecting the existence of many massive planets that we know are rare, which have pulled out large internal holes or gaps in bright discs," says Paola Pinilla, the second author of the book, Arizona Steward's University Observatory . "While massive planets were found in some of these bright disks, little was known about weaker drives."
The team, which includes Nathan Handler and Illarya Pascuchi in the Lunar and Planetary Laboratory of the American University, measures the properties of the rings and gaps seen in ALMA and analyzes the data to assess the possible mechanisms that can cause the observed rings and omissions. Although these structures can be carved out of planets, previous studies have shown that they can be created by other effects. In a commonly predicted scenario, the so-called ice lines caused by changes in particle chemistry in the disk in response to the distance to the receiving star and its magnetic field create changes in the pressure in the disk. These effects can create disc variations that appear as rings and omissions.
Researchers carried out analyzes to test these alternative explanations and could not establish any correlation between the star properties and the patterns of the gaps and rings they were watching.
"Therefore, we can rule out the commonly proposed idea of ice lines that cause rings and gaps," said Pinilla. "Our discoveries leave nascent planets the most likely cause of the patterns we have observed, although some other processes can also be at work."
Since the detection of individual planets is directly impossible due to the brightness of the receiving star, the team made calculations to get an idea of the types of planets that could be formed in the area that forms the stars of Taurus. According to the findings, large-scale Neptune gas planets or so-called super-terrestrial planets with up to 20 terrestrial masses should be the most common. Only two of the monitored discs could accommodate con artists rivaling Jupiter, the largest planet in the solar system.
"As most of the current exoplanet studies can not penetrate the dust of protoplanetary discs, all exoplanets, with one exception, are found in more developed systems where the disk is no longer available," Pinilla said.
In the future, the research group plans to move the ALMA antennas further, which has to increase the array resolution to about five astronomical units (one AU is equal to the average distance between the Earth and the Sun) and make the antennas sensitive to other frequencies are sensitive to other types of dust.
"Our results are an exciting step in understanding this key phase of the formation of the planet," says Long, "and by making these adjustments, we hope to better understand the origin of the rings and the gaps."
Reference: "Gaps and Rings in ALMA Discovery in the Taurus Constellation Area," Feng Long et al., 2018 to appear in the Astrophysical Journal [http://apj.aas.org, preprint: https://arxiv.org/abs/1810.06044],
This work has been accomplished through international collaboration, including astronomers from the Steward Observatory of UA and LPL. Funding for this project was provided by the Beijing University, the China National Science Foundation, the Hubble Stimulus Program, the National Science Foundation, and the Nexus Earth for Other Solar Systems program for research on exoplanetary systems.
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