#planet formation disk substructures

[skycrorg]

Hasta la fecha, se han realizado numerosas observaciones de discos protoplanetarios (o discos circunestelares) con ALMA.

[spacetimewithstuartgary]

Protoplanetary disks are much smaller than previously thought, new study finds

Many protoplanetary disks in which new planets are formed are much smaller than thought. Using the Atacama Large Millimeter/submillimeter Array (ALMA) scientists of the Leiden Observatory (the Netherlands) looked at 73 protoplanetary disks in the Lupus region. They found that many young stars host modest disks of gas and dust, some as small as 1.2 astronomical units. The research, accepted for publication in Astronomy & Astrophysics, establishes an important link between observed protoplanetary disks and exoplanets.

In the past decade, astronomers have imaged hundreds of protoplanetary disks around young stars using powerful radio telescopes on Earth, like ALMA. When compared to the size of our own solar system, many of these disks extend far beyond the orbit of Neptune, our outermost planet. Furthermore, most of the disks show gaps where giant planets are thought to be formed. Research of Ph.D. candidate Osmar M. Guerra-Alvarado, postdoc Mariana B. Sanchez and assistant professor Nienke van der Marel of the Leiden Observatory now show that these disks might not be typical.

Using ALMA, the researchers imaged all known protoplanetary disks around young stars in Lupus, a star-forming region located about 400 light years from Earth in the southern constellation Lupus. The survey reveals that two-thirds of the 73 disks are small, with an average radius of six astronomical units. This is about the orbit of Jupiter. The smallest disk found was only 0.6 astronomical units in radius, smaller than the orbit of Earth.

"These results completely change our view of what a 'typical' protoplanetary disk looks like," Guerra-Alvarado says. "Only the brightest disks which are the easiest to observe show large-scale gaps, whereas compact disks without such substructures are actually much more common."

Optimal conditions for super-Earths

The small disks were primarily found around low-mass stars, with a mass between 10 and 50% of the mass of our sun. This is the most common type of star found in the universe.

"The observations also show that these compact disks could have optimal conditions for the formation of so-called super-Earths, as most of the dust is close to the star, where super-Earths are typically found," Sanchez says. She is a postdoc at Leiden Observatory and a contributor to this research. Super-Earths are rocky planets like Earth but with masses up to ten times that of our planet. This could also explain why super-Earths are often found around low-mass stars.

Furthermore, the research suggests that our solar system was formed from a large protoplanetary disk that produced large gas planets like Jupiter and Saturn, but no super-Earth. Super-Earths are thought to be the most common planet types in the universe.

The missing link

The research establishes a "missing link" between observations of protoplanetary disks and observations of exoplanets. "The discovery that the majority of the small disks do not show gaps, implies that the majority of stars do not host giant planets," Van der Marel says. "This is consistent with what we see in exoplanet populations around full-grown stars. These observations link the disk population directly to the exoplanet population."

Previous high-resolution observations of ALMA mainly focused on bright disks which are often much larger. For the smaller disks only the brightness was measured and not the size. High-resolution observations can be more complicated to take, and it was not clear if ALMA would be able to image the relatively faint disks.

For their research, the scientists used ALMA observations, taken in 2023 and 2024, with the highest possible resolution of 0.030 arcseconds. They also used archival data to create a complete high-resolution disk survey of an entire star-forming region for the first time.

Van der Marel says, "The research shows that we've been wrong for a long time about what a typical disk looks like. Clearly, we've been biased towards the brightest and largest disks. Now we finally have a full overview of disks of all sizes."

IMAGE: Images of 73 protoplanetary discs in the Lupus star forming region (two of the images contain binary stars). Only a fraction of the discs extend beyond the orbit of Neptune, when compared to our own Solar System. Most of the observed discs are small and show no structures like gaps and rings. Credit: Guerra-Alvarado et al.

[wayti-blog]

"The Hidden Universe of Protoplanetary Disks: New Insights on Planet Formation"

"For decades, astronomers have peered into the depths of space, searching for answers to one of the most fundamental questions: how do planets form? Until recently, the prevailing view was that protoplanetary disks—the swirling clouds of gas and dust that birth planets—were often large, extending far beyond the orbit of Neptune. However, new research from Leiden Observatory, using the powerful Atacama Large Millimeter/submillimeter Array (ALMA), is rewriting that narrative. Their findings reveal that many protoplanetary disks are significantly smaller than previously believed, fundamentally changing our understanding of planetary formation.

(Images of 73 protoplanetary discs in the Lupus star forming region (two of the images contain binary stars). Only a fraction of the discs extend beyond the orbit of Neptune, when compared to our own Solar System. Most of the observed discs are small and show no structures like gaps and rings. Credit: Guerra-Alvarado et al.)

A team of scientists from Leiden Observatory in the Netherlands, led by Ph.D. candidate Osmar M. Guerra-Alvarado, postdoctoral researcher Mariana B. Sanchez, and assistant professor Nienke van der Marel, has conducted the most comprehensive high-resolution survey of protoplanetary disks in the Lupus star-forming region. Located about 400 light-years from Earth in the southern constellation Lupus, this region is a cradle of young stars and planetary systems in the making.

By imaging 73 protoplanetary disks with ALMA, the researchers discovered a striking fact: two-thirds of the disks were remarkably small, with an average radius of just six astronomical units (AU)—approximately the distance from the Sun to Jupiter. The smallest disk observed measured a mere 0.6 AU in radius, smaller than Earth’s orbit.

“These results completely change our view of what a ‘typical’ protoplanetary disk looks like,” Guerra-Alvarado states. “Only the brightest disks, which are the easiest to observe, show large-scale gaps where giant planets are thought to form. In contrast, compact disks without such substructures are actually far more common.”"

continue reading article

[spacenutspod]

The ESO’s Atacama Large Millimeter/submillimeter Array (ALMA) is perched high in the Chilean Andes. ALMA is made of 66 high-precision antennae that all work together to observe light just between radio and infrared. Its specialty is cold objects, and in recent years, it has taken some stunning and scientifically illuminating images of protoplanetary disks and the planets forming in them. But its newest image supersedes them all. The formation of solar systems and planets and how they evolve is one of ALMA’s primary subjects. It’s gained a reputation for imaging young T Tauri stars and their protoplanetary disks. These images show the tell-gale gaps created, astronomers think, by young, still-forming planets. ALMA’s high-resolution images of nearby protoplanetary disks are from the Disk Substructures at High Angular Resolution Project (DSHARP). The observatory is often used to look for disks like these. Credit: ALMA (ESO/NAOJ/NRAO), S. Andrews et al.; NRAO/AUI/NSF, S. Dagnello In new research, a team of astronomers took a deeper look at one protoplanetary disk. They measure the polarity of the light coming from the dust grains in the disk. This isn’t the first time ALMA has studied a disk’s polarity. But this image is based on 10x more polarization measurements than any other disk and 100x more measurements than most disks. The research article is “Aligned grains and scattered light found in gaps of planet-forming disk.” It’s published in Nature, and the lead author is Ian Stephens. Stephens is an assistant professor at the Department of Earth, Environment and Physics, Worcester State University, Worcester, MA, USA. What’s so useful about measuring the polarity of dust in a protoplanetary disk? It can reveal things like the size and shape of dust grains. These are their basic characteristics, and somehow, they affect how the dust behaves and eventually forms planets. There’s a lot going on in protoplanetary disks, though it takes millions of years for it all to play out. Eventually, scientists think, young disks like this one around HL Tauri will mature and stabilize. Planets may enter into resonance with one another, some planets may migrate, and eventually, things will likely stabilize like our Solar System has. And it all starts with dust. HL Tau is about 450 light-years away in the Taurus Molecular Cloud, a star-forming region that may be the closest one to Earth. All of the stars in the TMC, including HL Tau, are only about one or two million years old. At that age, the disks around the stars should just be starting to form planets, and that’s why ALMA is studying it. And this isn’t the first time. In fact, the sharpest image ALMA ever captured was of HL Tau. This is the sharpest image ever taken by ALMA — sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope. It shows the protoplanetary disc surrounding the young star HL Tauri. With young stars like this one, observations reveal substructures within the disc that were never been seen before. They may show the possible positions of planets forming in the dark patches within the system. Credit: ALMA (ESO/NAOJ/NRAO) In the new study, Stephens and his colleagues wanted to probe HL Tau even deeper. They focused on the polarity of the dust because there’s so much we don’t know about how planets form. Polarity may provide clues to the process that other observations can’t. Dust polarity could reveal things about the underlying structure of HL Tau’s disk that can’t be revealed in any other way. Over time, the dust grains in the disk begin to stick together. This process goes on and on until planetesimals form, then eventually, planets. HL Tau and its disk have their own magnetic field, and scientists think that the field may affect how the dust grains align and how they accrete into larger structures. However, polarity measurements show that the dust isn’t aligned with the magnetic fields. This figure from the research shows HL Tau’s polarization morphology. The polarity of the grains doesn’t line up with the system’s magnetic fields. Image Credit: Stephens et al. 2023 Instead, the polarity comes from the shape of the grains. Grains needn’t be round; they can be prolate, like elongated spheres. And that means they can polarize light. That constrains the size and shape of the grains, which in turn should affect how they clump together. The ALMA image also showed that one side of the protoplanetary disk is more polarized than the other. That’s likely due to asymmetries in the distribution of the dust or how the properties of the grains are different on one side. But there’s no clear answer to it yet. The images revealed another surprise. The polarity of the dust within the gaps is more azimuthal, even though there’s less dust there. That suggests that the dust is more aligned in the gaps. The gaps are where planets form. Do the properties of the dust reflect planet formation? Or does it help account for it? The polarity in the rings themselves is more uniform, indicating that the polarity comes from scattering, adding to the complexity. This figure from the research shows the polarization fraction (L) and polarization intensity (R) of HL Tau’s disk. Polarization fractions are typically much higher in the gaps than in the rings. Even the polarized intensity is frequently higher in the gaps. Image Credit: Stephens et al. 2023. Overall, the polarity has two causes: scattering and the alignment of the dust. But it’s not clear from the images and data what’s causing the dust to align the way it does. It’s unlikely that the dust is aligned with the magnetic fields, though strangely, dust outside of a protoplanetary disk usually is. The current thinking is that the alignment has a mechanical cause rather than a magnetic one. It could result from the movement around the star, but there’s no clear consensus yet. This research doesn’t provide any definitive answers to our questions about planet formation in the disks around young stars. But HL Tau’s disk appears to be highly evolved for its age. It’s probably not more than one million years old, yet it displays the telltale rings and gaps that indicate planet formation. A previous study, also led by Ian Stephens from Worcester State University, suggested that the rapid accretion rate might be due to HL Tau’s complex magnetic fields. “The unexpected morphology suggests that the role of the magnetic field in the accretion of a T Tauri star is more complex than our current theoretical understanding,” Stephens and his colleagues wrote in that research. Unfortunately, even with this exceptional ALMA image, our questions remain unanswered. But this is just one disk. The results show that a high-resolution image of a protoplanetary disk’s polarization reveals details that are otherwise hidden. We need more of these images of more disks around young T Tauri stars like HL Tau. With a large sample size, scientists might make more progress. The post ALMA Takes Next-Level Images of a Protoplanetary Disk appeared first on Universe Today.

[the-telescope-times]

ESO Image of the Week – Worlds With Many Suns

This week’s Picture of the Week highlights another of the 20 images to come out of ALMA’s first Large Program, the Disk Substructures at High Angular Resolution Project (DSHARP). DSHARP explored a number of nearby protoplanetary discs to learn more about the earliest stages of planet formation, and a staggering quantity of data from the project has just been released. Credit: ALMA (ESO/NAOJ/NRAO), S. Andrews et al.; NRAO/AUI/NSF, S. Dagnello

This week’s Picture of the Week highlights another of the 20 images to come out of ALMA’s first Large Program, the Disk Substructures at High Angular Resolution Project (DSHARP).

DSHARP explored a number of nearby protoplanetary discs to learn more about the earliest stages of planet formation, and a staggering quantity of data from the project has just been released.

This object, called AS 205, is notable for being a multiple star system, one of two such systems imaged by DSHARP (the other being HT Lup). While two discs are discernible here, the lower right disc is in fact shared by two stars in a binary system, so we are actually looking at a system of three fledgling stars.

Although most high-resolution studies have so far focused on single stars, multiple systems are far from uncommon in the Universe. It is thought that over half of all stars may exist in multiple systems, an estimate that may be even higher for young stars. The presence of companion stars is likely to have complex implications for a disc and its substructures. This is due to as the gravitational influence of a stellar neighbour, which may distort and redistribute the material within the disc. Data from AS 205 and HT Lup indicate that stars and their neighbouring discs interact strongly.

Despite their unsettled birth environments, planets have been detected in multiple stellar systems — some orbiting just one of the stars, others orbiting the entire system. The latter are more likely to have stable orbits than the former, which get caught up in volatile interstellar dynamics.

~ scitechdaily.com

[morlanwen]

This week’s image shows 20 spectacular protoplanetary discs captured by ALMA’s first Large Program, known as the Disk Substructures at High Angular Resolution Project (DSHARP). In a focused observation effort that included hours of data collected over several months, researchers imaged 20 nearby protoplanetary discs to learn more about the earliest stages of planet formation, and the staggering quantity of data from the project has just been released.

It has long been thought that planetary systems are likely to have their origins in so-called protoplanetary discs — compressed circles, spirals or ellipses of gas and dust, which form around protostars in the early stages of their development. The process by which planets emerge from these diffuse discs, however, is not well understood. It is particularly challenging to understand the very earliest stages of their evolution — when dust within a disc coalesces into planetesimals and the seeds of planets are formed.  

Astronomers know that a planet’s first growth spurt, from individual grains to a body a few kilometres across, must happen quickly in astronomical terms, but the lack of observational data has made pinning down the physics of this growth challenging. Fortunately, this recently changed with the opening of new telescopes such as ALMA.

Eventually, astronomers hope to be able to accurately predict what type of planetary system will evolve from any particular disc. The DSHARP program takes us a step towards this goal by providing a detailed view of the substructures (the varied patterns of dark and light circles and spirals you can see in each disc) — helping us to understand their significance.

The story continues next week — this is the first instalment in a trio of Pictures of the Week that will delve into recent discoveries made by DSHARP.

Credit:

ALMA (ESO/NAOJ/NRAO), S. Andrews et al.; NRAO/AUI/NSF, S. Dagnello Source

[mitchbattros]

Gas 'Waterfalls' Reveal Infant Planets Around Young Star

The birthplaces of planets are disks made out of gas and dust. Astronomers study these so-called protoplanetary disks to understand the processes of planet formation. Beautiful images of disks made with the Atacama Large Millimeter/submillimeter Array (ALMA) how distinct gaps and ring features in dust, which may be caused by infant planets.

To get more certainty that these gaps are actually caused by planets, and to get a more complete view of planet formation, scientists study the gas in the disks in addition to dust. 99 percent of a protoplanetary disk's mass is gas, of which carbon monoxide (CO) gas is the brightest component, emitting at a very distinctive millimeter-wavelength light that ALMA can observe. Last year, two teams of astronomers demonstrated a new planet-hunting technique using this gas. They measured the velocity of CO gas rotating in the disk around the young star HD 163296. Localized disturbances in the movements of the gas revealed three planet-like patterns in the disk. In this new study, lead author Richard Teague from the University of Michigan and his team used new high-resolution ALMA data from the Disk Substructures at High Angular Resolution Project (DSHARP) to study the gas's velocity in more detail. "With the high fidelity data from this program, we were able to measure the gas's velocity in three directions instead of just one," said Teague. "For the first time, we measured the motion of the gas rotating around the star, towards or away from the star, and up- or downwards in the disk." Unique gas flows Teague and his colleagues saw the gas moving from the upper layers towards the middle of the disk at three different locations. "What most likely happens is that a planet in orbit around the star pushes the gas and dust aside, opening a gap," Teague explained. "The gas above the gap then collapses into it like a waterfall, causing a rotational flow of gas in the disk." This is the best evidence to date that there are indeed planets being formed around HD 163296. But astronomers cannot say with one hundred percent certainty that the gas flows are caused by planets. For example, the star's magnetic field could also cause disturbances in the gas. "Right now, only a direct observation of the planets could rule out the other options. But the patterns of these gas flows are unique and it is very likely that they can only be caused by planets," said co-author Jaehan Bae of the Carnegie Institution for Science, who tested this theory with a computer simulation of the disk. The location of the three predicted planets in this study correspond to the results from last year: they are likely located at 87, 140 and 237 AU. (An astronomical unit -- AU -- is the average distance from the Earth to the Sun.) The closest planet to HD 163296 is calculated to be half the mass of Jupiter, the middle planet is Jupiter-mass, and the farthest planet is twice as massive as Jupiter. Planet atmospheres Gas flows from the surface towards the midplane of the protoplanetary disk have been predicted by theoretical models to exist since the late '90s, but this is the first time that they have been observed. Not only can they be used to detect infant planets, they also shape our understanding of how gas giant planets obtain their atmospheres. "Planets form in the middle layer of the disk, the so-called midplane. This is a cold place, shielded from radiation from the star," Teague explained. "We think that the gaps caused by planets bring in warmer gas from the more chemically active outer layers of the disk, and that this gas will form the atmosphere of the planet." Teague and his team did not expect that they would be able to see this phenomenon. "The disk around HD 163296 is the brightest and biggest disk we can see with ALMA," said Teague. "But it was a big surprise to actually see these gas flows so clearly. The disks appears to be much more dynamic than we thought." "This gives us a much more complete picture of planet formation than we ever dreamed," said co-author Ted Bergin of the University of Michigan. "By characterizing these flows we can determine how planets like Jupiter are born and characterize their chemical composition at birth. We might be able to use this to trace the birth location of these planets, as they can move during formation." The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. Read the full article

[sciencespies]

Gas 'waterfalls' reveal infant planets around young star

https://sciencespies.com/space/gas-waterfalls-reveal-infant-planets-around-young-star/

Gas 'waterfalls' reveal infant planets around young star

Artist impression of gas flowing like a waterfall into a protoplanetary disk gap, which is most likely caused by an infant planet. Credit: NRAO/AUI/NSF, S. Dagnello

More

The birthplaces of planets are disks made out of gas and dust. Astronomers study these so-called protoplanetary disks to understand the processes of planet formation. Beautiful images of disks made with the Atacama Large Millimeter/submillimeter Array (ALMA) how distinct gaps and ring features in dust, which may be caused by infant planets.

To get more certainty that these gaps are actually caused by planets, and to get a more complete view of planet formation, scientists study the gas in the disks in addition to dust. 99 percent of a protoplanetary disk’s mass is gas, of which carbon monoxide (CO) gas is the brightest component, emitting at a very distinctive millimeter-wavelength light that ALMA can observe.

Last year, two teams of astronomers demonstrated a new planet-hunting technique using this gas. They measured the velocity of CO gas rotating in the disk around the young star HD 163296. Localized disturbances in the movements of the gas revealed three planet-like patterns in the disk.

In this new study, lead author Richard Teague from the University of Michigan and his team used new high-resolution ALMA data from the Disk Substructures at High Angular Resolution Project (DSHARP) to study the gas’s velocity in more detail. “With the high fidelity data from this program, we were able to measure the gas’s velocity in three directions instead of just one,” said Teague. “For the first time, we measured the motion of the gas rotating around the star, towards or away from the star, and up- or downwards in the disk.”

This animation shows the computer simulation of how the gas flows in the disk as a result of three planets in formation. Credit: ALMA (ESO/NAOJ/NRAO), J. Bae; NRAO/AUI/NSF, S. Dagnello

More

Unique gas flows

Teague and his colleagues saw the gas moving from the upper layers towards the middle of the disk at three different locations. “What most likely happens is that a planet in orbit around the star pushes the gas and dust aside, opening a gap,” Teague explained. “The gas above the gap then collapses into it like a waterfall, causing a rotational flow of gas in the disk.”

This is the best evidence to date that there are indeed planets being formed around HD 163296. But astronomers cannot say with one hundred percent certainty that the gas flows are caused by planets. For example, the star’s magnetic field could also cause disturbances in the gas. “Right now, only a direct observation of the planets could rule out the other options. But the patterns of these gas flows are unique and it is very likely that they can only be caused by planets,” said co-author Jaehan Bae of the Carnegie Institution for Science, who tested this theory with a computer simulation of the disk.

The location of the three predicted planets in this study correspond to the results from last year: they are likely located at 87, 140 and 237 AU. (An astronomical unit—AU—is the average distance from the Earth to the Sun.) The closest planet to HD 163296 is calculated to be half the mass of Jupiter, the middle planet is Jupiter-mass, and the farthest planet is twice as massive as Jupiter.

An artist’s conception of the disk of gas and dust rotating around the young star HD 163296. Gas can be seen cascading into gaps in the disk–likely indicating the formation of baby planets in these locations. Credit: Robin Dienel, Carnegie Institution for Science.

More

Scientists measured the motion of gas (arrows) in a protoplanetary disk in three directions: rotating around the star, towards or away from the star, and up- or downwards in the disk. The insert shows a close-up of where a planet in orbit around the star pushes the gas and dust aside, opening a gap. Credit: NRAO/AUI/NSF, B. Saxton

More

Planet atmospheres

Gas flows from the surface towards the midplane of the protoplanetary disk have been predicted by theoretical models to exist since the late ’90s, but this is the first time that they have been observed. Not only can they be used to detect infant planets, they also shape our understanding of how gas giant planets obtain their atmospheres.

“Planets form in the middle layer of the disk, the so-called midplane. This is a cold place, shielded from radiation from the star,” Teague explained. “We think that the gaps caused by planets bring in warmer gas from the more chemically active outer layers of the disk, and that this gas will form the atmosphere of the planet.”

Teague and his team did not expect that they would be able to see this phenomenon. “The disk around HD 163296 is the brightest and biggest disk we can see with ALMA,” said Teague. “But it was a big surprise to actually see these gas flows so clearly. The disks appears to be much more dynamic than we thought.”

“This gives us a much more complete picture of planet formation than we ever dreamed,” said co-author Ted Bergin of the University of Michigan. “By characterizing these flows we can determine how planets like Jupiter are born and characterize their chemical composition at birth. We might be able to use this to trace the birth location of these planets, as they can move during formation.”

Explore further

New and improved way to find baby planets

More information: Meridional flows in the disk around a young star, Nature, DOI: 10.1038/s41586-019-1642-0 , https://nature.com/articles/s41586-019-1642-0

Provided by National Radio Astronomy Observatory

Citation: Gas ‘waterfalls’ reveal infant planets around young star (2019, October 16) retrieved 16 October 2019 from https://phys.org/news/2019-10-cascades-gas-young-star-early.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

#Space

[sciencebulletin]

Get ready for more interstellar objects, astronomers say

Gregory Laughlin and Malena Rice weren't exactly surprised a few weeks ago when they learned that a second interstellar object had made its way into our solar system. The Yale University astronomers had just put the finishing touches on a new study suggesting that these strange, icy visitors from other planets are going to keep right on coming. We can expect a few large objects showing up every year, they say; smaller objects entering the solar system could reach into the hundreds each year. The study has been accepted for publication in The Astrophysical Journal Letters. "There should be a lot of this material floating around," said Rice, a graduate student at Yale and first author of the study. "So much more data will be coming out soon, thanks to new telescopes coming online. We won't have to speculate." The first interstellar object known to pass through our solar system was 'Oumuamua, first spotted in October 2017. Its arrival generated intense debate over its origins and how to classify it. Laughlin, an astronomy professor at Yale, has contributed valuable research indicating 'Oumuamua likely has properties similar to a comet, despite the fact that it doesn't have a comet's telltale tail, called a coma. The new object, recently dubbed 2I/Borisov, came on the scene this summer. Amateur astronomer Gennady Borisov first noticed 2I/Borisov in August, and researchers will have about a year to observe the object with telescopes—a considerably longer time than the few weeks they had to observe 'Oumuamua. The new object is also larger than 'Oumuamua and has a pronounced coma. Of course, for scientists one of the big questions arising from the appearance of interstellar objects is: "Where did they come from?" An easy answer would be that they are ejected planetary building blocks—planetesimals—from other solar systems. But upon first look, there's a problem with that theory, say researchers: A close study of the roughly 4,000 confirmed planets outside of our solar system shows that most of them are located too close to their parent stars to readily eject a planetesimal. Planetesimals stirred up by most currently known planets would remain stuck in orbits in the systems where they formed. So where do the interstellar objects originate? Rice and Laughlin's work proposes for the first time that interstellar objects could be material ejected from large, newborn planets, orbiting farther away from their sun, which have carved out pronounced gaps in the cosmic platters of gas and dust that astronomers call protoplanetary disks. When a star is newly formed, it is surrounded by a thin, rotating "protoplanetary" disk of dense gas and dust. The disk is a volatile environment in which gas and dust are heated up by the young star, as well as the star's gravitational energy, leading to movement, collisions, and eventually, the formation of planets. Although most known planets form close to their sun, there are some that develop much farther away and create large gaps in the protoplanetary disk. According to Rice and Laughlin, those more distant planets are able to fling out material that could leave their home solar systems. However, they are also much more difficult to directly observe than their closer-in counterparts, which is why not many of these planets have been confirmed, the researchers said. To test their theory, the researchers looked at three protoplanetary disks from the Disk Substructures at High Angular Resolution Project (DSHARP), a survey conducted by a large consortium of astronomers. DSHARP focuses on images of 20 nearby, bright and large protoplanetary disks taken by the Atacama Large Millimeter/submillimeter Array telescope in Chile. "We were looking for disks in which it was pretty clear a planet was there," Rice said. "If a disk has clear gaps in it, like several of the DSHARP disks do, it's possible to extrapolate what type of planet would be there. Then, we can simulate the systems to see how much material should be ejected over time." "This idea nicely explains the high density of these objects drifting in interstellar space, and it shows that we should be finding up to hundreds of these objects with upcoming surveys coming online next year," Laughlin said. Beyond the mere novelty of noticing interstellar objects passing through our solar system, the idea of observing such objects offers major possibilities for advancing our knowledge of the cosmos, the researchers added. Unlike many astronomical discoveries, in which data is observed and interpreted from tremendous distances, interstellar objects are an up-close look at another part of the galaxy, they said. "You're not looking at a distant star through a telescope," Rice said. "This is actual material that makes up planets in other solar systems, being flung at us. It's a completely unprecedented way to study extrasolar systems up close—and this field is going to start exploding with data, very soon." Provided by: Yale University More information:  Malena Rice et al. Hidden Planets: Implications from 'Oumuamua and DSHARP. Astrophysical Journal Letters (2019).  arxiv.org/abs/1909.06387 Image: An image of a protoplanetary disk, from the Atacama Large Millimeter/submillimeter Array telescope in Chile. The black interior rings are gaps in the disk. Credit: ALMA (ESO/NAOJ/NRAO), S. Andrews et al.; N. Lira Read the full article

[citevibes-blog]

ESO Image of the Week

ESO Image of the Week

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By European Southern Observatory February 13, 2019

This week’s Picture of the Week highlights another of the 20 images to come out of ALMA’s first Large Program, the Disk Substructures at High Angular Resolution Project (DSHARP). DSHARP explored a number of nearby protoplanetary discs to learn more about the earliest stages of planet formation, and a staggering quantity of data from…

[arxt1]

The formation of rings and gaps in magnetically coupled disk-wind systems: ambipolar diffusion and reconnection. (arXiv:1712.06217v1 [astro-ph.SR])

Radial substructures in circumstellar disks are now routinely observed by ALMA. There is also growing observational evidence that such disks can accrete through angular momentum removal by rotating disk winds. We show through idealized 2D (axisymmetric) simulations that rings and gaps develop naturally in magnetically coupled disk-wind systems on the scale of tens of au, where ambipolar diffusion (AD) is the dominant non-ideal MHD effect. In simulations where the magnetic field and bulk neutral matter are only moderately coupled, relatively laminar disk accretion occurs while the spatial distribution of radial electric current is steepened by AD into a thin layer near the midplane. The toroidal magnetic field sharply reverses polarity in this current layer, generating a large magnetic torque that drives fast accretion and drags the poloidal magnetic field into an elongated radial configuration. The reconnection of this radial field creates magnetic loops where the net poloidal magnetic flux is greatly reduced. The regions with reduced poloidal magnetic flux accrete more slowly creating dense rings and the neighboring regions where the magnetic flux is concentrated accrete faster and form gaps. In better magnetically coupled simulations, we find the continuous development of the so-called `avalanche accretion streams' near the disk surface that render the disk-wind system more chaotic. Nevertheless, prominent rings and gaps are still present. We suggest that they are also produced, at least in part, by reconnection, which again enables the segregation of the poloidal field and the disk material similar to the more diffusive disks. However, the reconnection is now driven by the non-linear growth of MRI channel flows. The formation of rings and gaps in rapidly accreting yet laminar disks has interesting implications for dust settling and trapping, grain growth, and planet formation.

from astro-ph.HE updates on arXiv.org http://ift.tt/2AVRyZW

[spacetimewithstuartgary]

Super-resolution imaging reveals the first step of planet formation after star birth

Identifying the formation period of planetary systems, such as our solar system, could be the beginning of the journey to discover the origin of life. The key to this is the unique substructures found in protoplanetary disks—the sites of planet formation.

A protoplanetary disk is composed of low-temperature molecular gas and dust, surrounding a protostar. If a planet exists in the disk, its gravity will gather or eject materials within the disk, forming characteristic substructures such as rings or spirals. In other words, various disk substructures can be interpreted as "messages" from the forming planets. To study these substructures in detail, high-resolution radio observations with ALMA are required.

Numerous ALMA observations of protoplanetary disks (or circumstellar disks) have been conducted so far. In particular, two ALMA large programs, DSHARP and eDisk, have revealed the detailed distribution of dust in protoplanetary disks through high-resolution observations.

The DSHARP project discovered that distinctive structures are common in circumstellar disks around 20 young stars, each exceeding 1 million years since the onset of star formation (see note below).

On the other hand, fewer distinctive structures were found by the eDisk project that investigated disks around 19 protostars in the accretion phase (the stage where mass accretion onto the star and the disk is active). This phase occurs approximately 10,000 to 100,000 years after star birth. This suggests that disks have diverse characteristics depending on the age of the star.

Here, the question is: When do substructures, the signs of planet formation, appear in disks? To find the answer, it is necessary to observe disks of a wide range of intermediate ages that have yet to be explored. However, limitations on the number of disks observable at high resolution, due to distance and observational time, make it challenging to conduct a statistically significant survey with a sufficiently large sample size.

To overcome these limitations, the research team turned to super-resolution imaging with sparse modeling. In radio astronomy, images are commonly restored based on a specific assumption to compensate for missing observation data. The imaging method employed reconstructs based on a more accurate assumption than the conventional approach, producing higher-resolution images even though the same observation data is used. The findings are published in the Publications of the Astronomical Society of Japan.

PRIISM (Python module for Radio Interferometry Imaging with Sparse Modeling), the public software developed by a Japanese research team, was used in this study. The research team utilized this new imaging technique on ALMA archival data, targeting 78 disks in the Ophiuchus star-forming region, located 460 light years from the solar system.

As a result, more than half of the images produced in this study achieved a resolution over three times higher than that of the conventional method, which is comparable to that of the DSHARP and eDisk projects.

Moreover, the total number of samples in this study is nearly four times larger than that of the previous two projects, significantly improving the robustness of our statistical analysis. Among the analyzed 78 disks, 27 disks were revealed to have ring or spiral structures, 15 of which were identified for the first time in this study.

The team combined the Ophiuchus sample with those of the eDisk project to conduct a statistical analysis. As a result, they found that the characteristic disk substructures emerge in disks with radii larger than 30 astronomical units (au) during the early stage of star formation, just a few hundred thousand years after a star was born

This suggests that planets begin to form at a much earlier stage than previously believed, when the disk still possesses abundant gas and dust . In other words, planets grow together with their very young host stars.

Ayumu Shoshi says, "These findings, bridging the gap between the eDisk and DSHARP projects, were enabled by the innovative imaging that allows for both achieving high resolution and a large number of samples. While these findings only pertain to the disks in the constellation Ophiuchus, future studies of other star-forming regions will reveal whether this tendency is universal."

Note: The evolutionary stage of a protostar is estimated using the bolometric temperature around the star. The bolometric temperature is an apparent temperature derived from the total brightness of an object across all wavelengths. A higher bolometric temperature indicates a more advanced evolutionary stage, and a temperature of 650 K suggests that approximately 1 million years have passed since the birth of the star.

TOP IMAGE: New high-resolution images of protoplanetary disks in the Ophiuchus star-forming region, created with improved analysis. The resolution is shown by the white ellipse in the lower left of each panel, with a smaller ellipse indicating higher resolution. The white line in the lower right of each panel indicates a scale of 30 au. The evolution stage of the central stars progresses from left to right, and from top to bottom in the same row. Credit: ALMA(ESO/NAOJ/NRAO), A. Shoshi et al.

CENTRE IMAGE: A scatter plot of bolometric temperatures and dust disk radii of the sources investigated in this study and those observed in the eDisk project. Purple, red, and yellow markings indicate disks with characteristic structures or potential ones with substructures. A bolometric temperature of 650 K corresponds to a disk around a central star that has evolved for about 1 million years since its formation, suggesting that characteristic substructures begin to emerge at even earlier stages. Credit: A. Shoshi et al

LOWER IMAGE: Artist’s impression of the distinctive substructure in a protoplanetary disk formed a few hundred thousand years after the birth of the central star. Credit: Y. Nakamura, A. Shoshi et al

[spacenutspod]

The JWST has delivered a breakthrough in planetary science. Its observations show that a long-proposed theory of planet formation is true. Up until now, thick veils of dust in young solar systems have obscured the evidence. But the JWST saw through it all, and now we know the truth: Ice-covered pebbles from outer solar systems deliver water to still-forming planets closer to their stars. The debate over Earth’s water has raged for decades. Somehow, Earth ended up with oceans of water, but it’s not clear where it came from. Earth formed about 4.5 billion years ago in the inner Solar System. It formed inside the rotating disk of gas and dust called the protoplanetary disk. These disks form around young stars throughout the galaxy. The most persistent idea is that the water came from elsewhere in the protoplanetary disk and not from Earth’s vicinity in the inner Solar System. The most well-known hypothesis is that Earth received its water from comets and asteroids after it formed and cooled. The protoplanetary disks around young stars are still a bit of a mystery. We can see them around other stars in the galaxy, and we can even see the gaps traced in the disk by young, still-forming planets. But seeing inside these disks is tough. One of the reasons the JWST was built was to probe these disks better than any other telescope. “This finding opens up exciting prospects for studying rocky planet formation with Webb!”Andrea Banzatti, Texas State University Protoplanetary disks are a very active area of research because there’s so much we don’t know about how solar systems and planets form. But the origin of Earth’s water is also a hot topic, and the two are linked. The idea that our planet’s water came from objects further out in the Solar System has staying power. The inner Solar System was too hot for water to stick around, the hypothesis goes. But further away, beyond the frost line, frozen water was taken up by comets and asteroids. These are ALMA‘s high-resolution images of nearby protoplanetary disks, which come from the Disk Substructures at High Angular Resolution Project (DSHARP). The gaps and rings are where planets are forming. Credit: ALMA (ESO/NAOJ/NRAO), S. Andrews et al.; NRAO/AUI/NSF, S. Dagnello The early Solar System was a chaotic place, and asteroids, comets, and even icy planetesimals from the outer Solar System continually rained down on the Earth. Over time, water accumulated and formed the oceans, according to this explanation. Now we have an Earth rich in water. But there’s always been some stubborn problems with this hypothesis. Some isotope ratios indicate that Earth had a sizeable portion of its water very early in its lifetime. Studies of lunar isotope ratios also show that Earth received much of its water prior to the Giant Impact that created the Moon only a few million years after the Solar System formed. But now, the powerful JWST has entered the chat. Its evidence supports another long-held theory of planet formation. That theory states that Earth’s water arrived as Earth formed. Ice-covered pebbles drifted inward from the outer Solar System, and as they reached the warmer inner Solar System, the water sublimated into vapour. The vapour and the pebbles were both accreted into young planets. This is known as the icy pebble drift theory. These findings are in a new paper in The Astrophysical Journal Letters titled “JWST Reveals Excess Cool Water near the Snow Line in Compact Disks, Consistent with Pebble Drift.” The lead author is Andrea Banzatti, an assistant professor of physics at Texas State University, San Marcos, Texas. “Webb finally revealed the connection between water vapour in the inner disk and the drift of icy pebbles from the outer disk,” said Banzatti. “This finding opens up exciting prospects for studying rocky planet formation with Webb!” Banzatti and his colleagues used the JWST’s MIRI (Mid-Infrared Instrument) to study four young, Sun-like stars only two or three million years old and surrounded by protoplanetary disks. Two of them were compact disks about 10 to 20 AU in size, and two of them were extended disks around 100 to 150 AU. The extended disks also have large radial gaps in them. The pebble drift theory states that compact disks deliver icy pebbles more efficiently into the inner solar system, well within the equivalent of Neptune’s orbit in our Solar System. Conversely, the theory also states that extended disks are less efficient at it. The JWST’s powerful Medium-Resolution Spectrometer (MRS) works in conjunction with MIRI. The MRS can differentiate cool water from warm water, a critical part of untangling the complicated picture in protoplanetary disks. MRS data shows that there’s more cool water in the compact disks than there is in the extended disks. “We present new JWST-MIRI spectra of four disks, two compact and two large with multiple radial gaps, selected to test the scenario that water vapour inside the snow line is regulated by pebble drift,” the article states. “Observation of this process opens up multiple exciting prospects to study planet formation chemistry in inner disks with JWST.” This graphic compares the spectral data for warm and cool water in the GK Tau disk, which is a compact disk without rings, and the extended CI Tau disk, which has at least three rings on different orbits. MRS can separate the spectra into individual lines that probe water at different temperatures. These spectra, seen in the top graph, clearly reveal excess cool water in the compact GK Tau disk, compared with the large CI Tau disk. The bottom graph shows the excess cool water data in the compact GK Tau disk minus the cool water data in the extended CI Tau disk. The actual data, in purple, are overlaid on a model spectrum of cool water. Note how closely they align. Image Credit: NASA, ESA, CSA, Leah Hustak (STScI) The pebble drift theory says that pebbles behave differently in different-sized disks. Some disks are much larger than others, and the hydrodynamical forces are much stronger in these larger disks. They effectively lock pebbles in place in their outer rings, inhibiting inward drift. But compact rings don’t have the same strong hydrodynamical forces. Icy pebbles are freer to drift inward, becoming part of the rocky planets that typically form in the inner regions of Solar Systems. Up until now, researchers have had trouble gathering observations to test this theory. Researchers using ALMA imaged numerous protoplanetary disks around young stars with telltale gaps showing where planets are forming. Based on these images and other data, scientists developed models showing that the presence or lack of gaps in protoplanetary disks regulated pebble drift into the inner solar systems. However, previous observations lacked the high resolution needed to see inside these disks and test these ideas. Thanks to the James Webb Space Telescope and MIRI, scientists have finally observed the predicted pebble drift behaviour in both large and compact disks. This graphic is an interpretation of data from Webb’s MIRI and its MRS, which is sensitive to water vapour in disks. It shows the difference between pebble drift and water content in a compact disk versus an extended disk with rings and gaps. Image Credit: NASA, ESA, CSA, Joseph Olmsted (STScI) Here’s how pebble drift works. In compact disks like the one on the left in the above image, ice-covered pebbles drift inward toward the warmer region closer to the star unimpeded. When they cross the snow line, or astrophysical frost line, their ice sublimates to vapour. That delivers a large amount of water to the still-forming, rocky planets nearer the star. The right side of the above image shows an extended disk with rings and gaps likely created by large planets that are still forming. These rings have higher pressure than the gaps. As the ice-covered pebbles drift inward, more of them are stopped by the rings in the protoplanetary disk and trapped there. So fewer icy pebbles make it across the snow line to deliver water to the inner regions. It took a while for Banzatti and his colleagues to understand the Webb data. It wasn’t initially clear what the observations were telling them. “For two months, we were stuck on these preliminary results that were telling us that the compact disks had colder water, and the large disks had hotter water overall,” remembered Banzatti. “This made no sense because we had selected a sample of stars with very similar temperatures.” The answer became clear when the researchers combined the data from compact and large rings. It showed that the compact disks have extra cool water just inside their snowlines, at about ten times closer than the orbit of Neptune. This figure from the research article shows how pebble drift is more efficient in compact disks. Compact disks that lack the large rings where massive planets form. These rings have higher pressure and impede icy pebbles from delivering their water to the inner solar system. Image Credit: Banzatti et al. 2023. “Now we finally see unambiguously that it is the colder water that has an excess,” said Banzatti. “This is unprecedented and entirely due to Webb’s higher resolving power!” Now that scientists have observed this in other solar systems it’s very likely and almost certain that this is how Earth got its water. It also shows how the regions of a solar system interact with each other and that the inner regions of a solar system aren’t isolated from the outer regions. “In the past, we had this very static picture of planet formation, almost like there were these isolated zones that planets formed out of,” explained team member Colette Salyk of Vassar College in Poughkeepsie, New York. “Now we actually have evidence that these zones can interact with each other. It’s also something that is proposed to have happened in our solar system.” This is a huge finding. But scientists are cautious by nature, so the door isn’t closed on other explanations for the origins of Earth’s water. Earth may have gotten its water through different pathways, and icy impactors could still have delivered some of our planet’s water. Artist’s rendering of a comet headed towards Earth. Comets, asteroids, and icy planetesimals could still have delivered some of Earth’s water. Image Credit: Public Domain. But the results lead to some other intriguing avenues of inquiry. It starts with observing more disks beyond the four in this study. “The findings of this work open up a number of exciting prospects,” the authors write in their article. “While this work includes the first four spectra from program GO-1640, which was set up with the specific goal of studying water emission in connection to pebble drift, a large number of disk spectra will be observed with MIRI in Cycle 1 and future cycles.” That means a larger sample size, a critical part of solidifying these findings. With that in hand, researchers can start to piece together more detail in the pebble drift scenario by asking some pertinent questions. How common is the cool water excess? Does it vary with disk size? How does the size of the disk and the location and size of the dust rings affect everything? How does stellar size and luminosity affect it all? How do all of these factors affect the molecular chemistry in inner solar systems? Stay tuned. The JWST isn’t finished yet. The post JWST Shows Ice-Covered Pebbles Delivering Water to New Planets appeared first on Universe Today.

[sciencebulletin]

Get ready for more interstellar objects, astronomers say

Gregory Laughlin and Malena Rice weren't exactly surprised a few weeks ago when they learned that a second interstellar object had made its way into our solar system. The Yale University astronomers had just put the finishing touches on a new study suggesting that these strange, icy visitors from other planets are going to keep right on coming. We can expect a few large objects showing up every year, they say; smaller objects entering the solar system could reach into the hundreds each year. The study has been accepted for publication in The Astrophysical Journal Letters. "There should be a lot of this material floating around," said Rice, a graduate student at Yale and first author of the study. "So much more data will be coming out soon, thanks to new telescopes coming online. We won't have to speculate." The first interstellar object known to pass through our solar system was 'Oumuamua, first spotted in October 2017. Its arrival generated intense debate over its origins and how to classify it. Laughlin, an astronomy professor at Yale, has contributed valuable research indicating 'Oumuamua likely has properties similar to a comet, despite the fact that it doesn't have a comet's telltale tail, called a coma. The new object, recently dubbed 2I/Borisov, came on the scene this summer. Amateur astronomer Gennady Borisov first noticed 2I/Borisov in August, and researchers will have about a year to observe the object with telescopes—a considerably longer time than the few weeks they had to observe 'Oumuamua. The new object is also larger than 'Oumuamua and has a pronounced coma. Of course, for scientists one of the big questions arising from the appearance of interstellar objects is: "Where did they come from?" An easy answer would be that they are ejected planetary building blocks—planetesimals—from other solar systems. But upon first look, there's a problem with that theory, say researchers: A close study of the roughly 4,000 confirmed planets outside of our solar system shows that most of them are located too close to their parent stars to readily eject a planetesimal. Planetesimals stirred up by most currently known planets would remain stuck in orbits in the systems where they formed. So where do the interstellar objects originate? Rice and Laughlin's work proposes for the first time that interstellar objects could be material ejected from large, newborn planets, orbiting farther away from their sun, which have carved out pronounced gaps in the cosmic platters of gas and dust that astronomers call protoplanetary disks. When a star is newly formed, it is surrounded by a thin, rotating "protoplanetary" disk of dense gas and dust. The disk is a volatile environment in which gas and dust are heated up by the young star, as well as the star's gravitational energy, leading to movement, collisions, and eventually, the formation of planets. Although most known planets form close to their sun, there are some that develop much farther away and create large gaps in the protoplanetary disk. According to Rice and Laughlin, those more distant planets are able to fling out material that could leave their home solar systems. However, they are also much more difficult to directly observe than their closer-in counterparts, which is why not many of these planets have been confirmed, the researchers said. To test their theory, the researchers looked at three protoplanetary disks from the Disk Substructures at High Angular Resolution Project (DSHARP), a survey conducted by a large consortium of astronomers. DSHARP focuses on images of 20 nearby, bright and large protoplanetary disks taken by the Atacama Large Millimeter/submillimeter Array telescope in Chile. "We were looking for disks in which it was pretty clear a planet was there," Rice said. "If a disk has clear gaps in it, like several of the DSHARP disks do, it's possible to extrapolate what type of planet would be there. Then, we can simulate the systems to see how much material should be ejected over time." "This idea nicely explains the high density of these objects drifting in interstellar space, and it shows that we should be finding up to hundreds of these objects with upcoming surveys coming online next year," Laughlin said. Beyond the mere novelty of noticing interstellar objects passing through our solar system, the idea of observing such objects offers major possibilities for advancing our knowledge of the cosmos, the researchers added. Unlike many astronomical discoveries, in which data is observed and interpreted from tremendous distances, interstellar objects are an up-close look at another part of the galaxy, they said. "You're not looking at a distant star through a telescope," Rice said. "This is actual material that makes up planets in other solar systems, being flung at us. It's a completely unprecedented way to study extrasolar systems up close—and this field is going to start exploding with data, very soon." Provided by: Yale University More information:  Malena Rice et al. Hidden Planets: Implications from 'Oumuamua and DSHARP. Astrophysical Journal Letters (2019).  arxiv.org/abs/1909.06387 Image: An image of a protoplanetary disk, from the Atacama Large Millimeter/submillimeter Array telescope in Chile. The black interior rings are gaps in the disk. Credit: ALMA (ESO/NAOJ/NRAO), S. Andrews et al.; N. Lira Read the full article