Tidying up planetary nurseries

Asia's Tech News Daily

Tidying up planetary nurseries

A group of astronomers, led by scientists from the Max Planck Institute for Astronomy, propose and have tested a mechanism that explains most of the properties observed in dispersing planet-forming disks around newborn stars for the first time. The key ingredients to this new physical concept are X-ray emissions from the central star and a calm inner disk, well shielded from the incident radiation. This approach explains the seemingly contradicting features observed in those dwindling transition disks that previous models have been unable to reconcile. This result, published in the journal “Astronomy and Astrophysics”, is a big step to understanding the evolution from dusty disks to clean planetary systems like the Solar System.

Planets form inside disks made of gas and dust. Each of those disks already gave birth to a new star, or, for that matter, to a predecessor that still has to ignite its nuclear fusion fire, called a protostar. When we look at the Solar System, we recognise that most of that material has long since disappeared. In recent years, research has reached a basic understanding of how these circumstellar disks lose their remnant gas and dust. With the advent of powerful telescopes, astronomers have even identified and studied those dissolving disks coined transition disks.

However, identifying the detailed physical processes remained unsuccessful. The theoretical concepts scientists have explored so far only reproduced a few of the observed properties at a time. Now, a research group led by astronomers from the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, proposes a new scheme that overcomes most of the disadvantages of previous approaches.

“Earlier models failed to reproduce more than only a few of the observational results of transition disks,” says Matias Garate, lead author of the underlying scientific article and scientist at MPIA. “However, we are now able to explain most of the properties that seem to contradict each other: a wide gap in the disk and a sustained accretion of gas and dust from a long-lived inner disk onto the central star.”

Intuitively, it is hard to understand why almost all observed transition disks with a wide gap show signs of accretion. Accretion is the process that feeds the central star with gas and dust from the circumstellar disk. Before the gap opens, material from the thicker outer disk replenishes the inner sectors, sustaining the subsequent transport towards the central star. However, the reservoir is limited, which, in time, reduces the matter flow.

At the same time, X-ray emission from the star hits and heats the disk surface. The radiation gives rise to a wind that expels the then ionised gas into open space. This process is called photoevaporation. As soon as it is more efficient than the outside-in matter flow in the disk, a gap begins to open and disconnects the inner disk from the outer reservoir. At this point, the inner disk should empty very quickly via accretion and disappear rapidly. Accretion onto the star comes to a halt.

“We realised that to extend the lifetime of the inner disk and prolong accretion activity, we had to find a mechanism that reduces the inward drift of the gas and the dust,” Paola Pinilla points out, who is the “Genesis of Planets” research group leader at MPIA and a co-author of the paper. “One way of doing this is to include a generally accepted component of circumstellar disks, a so-called dead zone,” Timmy Delage adds, who is a PhD student at MPIA and another co-author of the research article.

A dead zone is a relatively calm annular region of a circumstellar disk where the random gas motion is reduced compared to other disk components. Consequently, friction between individual particles becomes almost negligible, making it difficult to reduce their orbital velocities, stabilising their orbits. Dead zones may manifest themselves when gas is insufficiently ionised and only poorly affected by magnetic fields. They can occur, for example, when the gas is dense enough to protect the deeper disk layers from ionisation by radiation hitting the disk.

To verify if such a dead zone can explain the observational findings of accreting transition disks with wide gaps, Matias Garate and his colleagues simulated their evolution in time. They constructed a physical disk model while varying the initial conditions for the dead zone and including X-ray irradiation to facilitate photoevaporation. “We were thrilled when we saw the results.

A large majority of the simulated transition disks with a wide range of gap sizes retained a detectable accretion flow to the central solar-type star,” Garate reports. This result demonstrates that dead zones can produce accreting transition disks with wide gaps in large numbers.

Although the result is a big leap in understanding what astronomers find with telescopes when looking at actual transition disks, it still falls short of reproducing the exact numbers. While observations appear to find approximately 3% of the transition disks to be non-accreting, the simulations produce more than ten times this fraction.

Indeed, since computing power is limited, the model used in this study only reflects a simplified version of the real world and does not include all possible mechanisms suspected to occur in such disks. Some of them may even increase the longevity of the inner disk. On the other hand, it is well possible astronomers have to revisit some of their conclusions drawn from observations, and there may actually be more non-accreting disks than previously thought.

During their study, the MPIA-led team explored the accretion activity by focussing on the gas. Still, the dust can behave quite differently. When astronomers take images of such planet-forming disks, it is often the distribution of the dust they see radiating at millimetre wavelengths, frequently shaped in the form of concentric rings. Therefore, the MPIA astronomers investigated if their simulations also treat the dust realistically.

“To compare our calculations with highly resolved images of real transitions disks we had obtained with the ALMA interferometer, we produced a synthetic picture of one of the simulated dust disks,” says co-author Jochen Stadler, a master student at MPIA and Heidelberg University. The result is a stunning confirmation. The image of the computer-generated dust distribution shows the elements typical of transition disks: a small inner disk and an outer ring, both separated by a wide gap.

As often, the devil is in the details. While the structures appear to be a good match, the brightnesses disagree. The dust emission of the simulated transition disks is considerably fainter than one would expect from observations. Hence, the synthetic disks probably possess less dust than the real ones. However, the authors have a reasonable solution for this discrepancy.

“We think this is a consequence of planet formation we have not included in our models,” Garate points out. Studies frequently show that newly formed planets carve gaps along their orbits through the disk. Such rifts function like barriers for the dust drifting radially. Garate adds: “It is well possible the planetary gaps escape detection by observation due to insufficient spatial resolution. If planets form in the inner disk, that may help prevent dust from accreting onto the central star. We will extend our models accordingly and explore if we can also solve this puzzle.”

Research Report: “Large gaps and high accretion rates in photoevaporative transition disks with a dead zone”

Internet Explorer Channel Network
Asia's Tech News Daily
News Related


NASA awards contract for bed rest studies

NASA has selected Deutsches Zentrum fur Luft-und Raumfahrt (DLR) of Cologne, Germany, to provide use of its facility to support long-duration bed rest research. The $49.9 million Bedrest Studies Contract ... Read more »

Magellanic Stream arcing over Milky Way may be five times closer than previously thought

Our galaxy is not alone. Swirling around the Milky Way are several smaller, dwarf galaxies – the biggest of which are the Small and Large Magellanic Clouds, visible in the ... Read more »

Research in Brief: First-ever interior Earth mineral discovered in nature

UNLV geochemists have discovered a new mineral on the surface of the Earth. There’s just one catch: it shouldn’t be here. The mineral – entrapped in a diamond – traveled ... Read more »

Crew operations aboard Space Station return to normal

NASA and U.S. Space Command continue to monitor the debris cloud created by a recent Russian anti-satellite test. The International Space Station and crew members are safe and have resumed ... Read more »

Aerospike engine from Pangea Aerospace trialled on DLR test stand

Unique test stands, comprehensive expertise and decades of experience – the Lampoldshausen site of the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR) specialises in developing and testing ... Read more »

Solar Orbiter returns to Earth before starting its main science mission

Solar Orbiter is returning to Earth for a flyby before starting its main science mission to explore the Sun and its connection to ‘space weather’. During the flyby Solar Orbiter ... Read more »

Maritime Launch Services announces Nanoracks as payload provider; Unveils Spaceport Nova Scotia design

Maritime Launch Services, one of Canada’s leading aerospace firms and the owner of the country’s first commercial spaceport, announced that Nanoracks, a Voyager Space company and the leading commercial payload ... Read more »

Satellite operator Telesat goes public

Telesat Corporation announced today that it is now a public company and will begin trading on the Nasdaq Global Select Market and the Toronto Stock Exchange under the ticker symbol ... Read more »

China launches new satellite

China launched a new satellite from the Taiyuan Satellite Launch Center in the northern province of Shanxi on Saturday. The satellite, Gaofen-11 03, was launched by a Long March-4B rocket ... Read more »

Stanford researchers are using AI to create better VR experiences

Virtual and augmented reality headsets are designed to place wearers directly into other environments, worlds and experiences. While the technology is already popular among consumers for its immersive quality, there ... Read more »

Bezos' Blue Origin hires lobbyist after 'Space Tax' proposed

This year, the company spent over $1.3 million on lobbying, in addition to $2 million in 2020. Jeff Bezos’ Blue Origin hired Mac Campbell from Capitol Counsel – a lobbyist ... Read more »

Decisions from the ESA Intermediate Ministerial Meeting 2021

Government ministers in charge of space activities in ESA’s Member States today met at an Intermediate Ministerial Meeting held in Matosinhos, Portugal. The Council of Ministers unanimously adopted a Resolution ... Read more »

Turning space junk into rocket fuel

While SpaceX is working hard to make reusable rockets a new reality, the launches still leave behind massive amounts of debris in orbit, posing a potential hazard to communication satellites ... Read more »

BlackSky set to expand its EO constellation for real-time global intelligence

BlackSky’s latest satellites reached orbit and delivered first insights within 14 hours of launch. The company’s constellation growth signals a return to space and an increased capacity for global customers. ... Read more »

Japanese space tourists arrive at launch site ahead of ISS trip

Japanese billionaire Yusaku Maezawa arrived at the Baikonur cosmodrome in Kazakhstan on Friday for training ahead of his flight to the International Space Station on a Russian-operated spacecraft. Maezawa’s mission ... Read more »

Bacteria may be key to sustainably extracting earth elements for tech

Rare earth elements from ore are vital for modern life but refining them after mining is costly, harms the environment and mostly occurs abroad. A new study describes a proof ... Read more »

ESA selects revolutionary Venus EnVision mission

EnVision will be ESA’s next Venus orbiter, providing a holistic view of the planet from its inner core to upper atmosphere to determine how and why Venus and Earth evolved ... Read more »

Meet VMS - the briefcase-sized chemistry lab headed to Venus

Short for Venus Mass Spectrometer, VMS is one of five instruments aboard the DAVINCI descent probe. Launching in 2029, DAVINCI will be the first US probe mission to enter Venus’ ... Read more »

Scientists eagerly await James Webb telescope to discover stars, exoplanets

Scientists around the world eagerly await discoveries of early galaxies and exoplanets after the James Webb Space Telescope, the most powerful telescope ever conceived, is launched Dec. 18, a panel ... Read more »

US still characterizing damage of satellite struck in Russian missile test

The United States is still characterising the damage from an anti-satellite missile test allegedly conducted by Russia earlier this week, US Space Command Deputy Commander John Shaw said on Wednesday. ... Read more »

SES orders 2 new sats for Prime TV Neighbourhood serving 118 million homes

SES has ordered two geostationary (GEO) Ku-band satellites for its prime orbital slot at 19.2 degrees East to maintain the premium services it provides to its European video customers and ... Read more »

When debris disaster strikes

In 2021 so far, some 2467 new objects large enough to be tracked have been added to world catalogues of orbital objects, out of which 1493 are new satellites and ... Read more »

Astronomical object found by amateur identified as new dwarf galaxy

Enthusiast Giuseppe Donatiello spotted the galaxy while scrutinising publicly available data and his finding was investigated by professional astrophysicists, led by Dr. David Martinez-Delgado from the Instituto de Astrofisica de ... Read more »

Hubble Takes a Grand Tour of the Solar System

The NASA/ESA Hubble Space Telescope has completed its annual grand tour of the outer Solar System. This is the realm of the giant planets – Jupiter, Saturn, Uranus, and Neptune ... Read more »

Teledyne e2v HiRel offers new radiation dosimeters for space applications

Teledyne e2v HiRel has announced availability of 3 new radiation dosimeter models that further broaden its popular range of radiation measurement devices. Aimed at high altitude aerospace applications and all ... Read more »

Planetary defenders: after NASA's DART comes ESA's Hera

The world will be watching the milestone launch of NASA’s Double Asteroid Redirection Test, DART, spacecraft on Wednesday, 24 November, intended to alter one small part of the Solar System ... Read more »

RocketStar gets SBIR contract to develop new plasma thrusters

RocketStar, an industry leader transforming access to space with fully reusable rockets, has announced that the company has been selected by the U.S Air Force to participate in a Small ... Read more »

CGI selected for GSA's ASTRO space and development IDIQ contract

CGI has been selected by the General Services Administration (GSA) for the multi-award ASTRO Indefinite-Delivery/Indefinite-Quantity (IDIQ) contract. This 10-year award provides CGI the opportunity to compete for task orders with ... Read more »

First all-private space station mission to include two dozen experiments

A private space company that’s planning to send the first all-private crew to the International Space Station announced on Wednesday that they will conduct medical and scientific experiments during their ... Read more »

Arianespace to launch Australian satellite Optus-11 with Ariane 6

Arianespace and Australian operator SingTel Optus signed the launch contract for the Optus-11 communications satellite. The launch, scheduled for the second half of 2023, will use the Ariane 64 version ... Read more »

Rocket Lab launches 107th satellite; Tests helicopter recovery operations

Rocket Lab has successfully deployed two satellites to orbit for real-time geospatial monitoring company BlackSky. Rocket Lab also successfully introduced helicopter operations to a recovery mission for the first time, ... Read more »

Latest Vega launch paves way for Vega-C

Arianespace announced liftoff of Vega’s twentieth flight from Europe’s Spaceport in French Guiana at 9:27 GMT (10:27 CET; 06:27 local time). Vega delivered three CERES payloads for the French Ministry ... Read more »

Pangea Aerospace hot fire tests the first MethaLox aerospike engine in the world

Pangea Aerospace, a company from Barcelona (Spain), has fired several times the first MethaLox aerospike engine in the world in their first try, at DLR Lampoldshausen facilities. The company has ... Read more »

PLD Space exhibits the first privately-developed Spanish rocket

PLD Space has achieved a new milestone with the official presentation in Madrid of its MIURA 1 rocket, that has been exhibited fully assembled for the first time in the ... Read more »

LeoLabs Australia's Space Tracking Centre releases first images of Russian space debris field

As reported, the Russian Federation tested a probable ‘Nudol’ direct ascent anti-satellite missile yesterday at 150250Z from Pllesetk, Russia with the target a defunct Russian satellite called Cosmos 1408. The ... Read more »

The worlds next door: Looking for habitable planets around Alpha Centauri

A mission to discover new planets potentially capable of sustaining life around Earth’s nearest neighbor, Alpha Centauri, was announced this week by Sydney University. The proposed telescope project will look ... Read more »

"Alien" invasions and the need for planetary biosecurity

The era of space exploration brings with it a new risk: invasion. The peril comes not from little green men arriving on flying saucers but, rather, from microbiological contamination of ... Read more »

Research casts new light on processes behind solar eruptions

Their work could provide a key piece to help solve a puzzle which solar astronomers have been aiming to solve for decades – what is the origin of magnetic twist ... Read more »

Alien organisms - hitchhikers of the galaxy

Scientists warn, without good biosecurity measures ‘alien organisms’ on Earth may become a reality stranger than fiction. Published in international journal BioSciences, a team of scientists, including Dr Phill Cassey, ... Read more »

NASA's next steps to return Hubble to normal operation status

The Hubble Space Telescope’s Advanced Camera for Surveys has continued collecting science data as NASA works to address the anomaly that started Oct 25. Missed synchronization messages halted science production ... Read more »
On free-english-test.com you will find lots of free English exam practice materials to help you improve your English skills: grammar, listening, reading, writing, ielts, toeic