From AAS NOVA: “A Young Population of Hidden Jets”

From AAS NOVA

1 July 2020
Susanna Kohler

Artist’s impression of a galaxy forming stars, as powerful jets that are flung from its central black hole collide with the surrounding matter. [ESO/M. Kornmesser]

Looking for a fireworks show this 4th of July? Try checking out the distant universe, where powerful jets flung from supermassive black holes slam into their surroundings, lighting up the sky. Though these jets are hidden behind shrouds of gas and dust, a new study has now revealed some of these young powerhouses.

A Galaxy–Black-Hole Connection

This composite image of Centaurus A shows an example of large-scale jets launched from an AGN, which can eventually extend far beyond the galaxy, as seen here. [ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)]

Wide Field Imager on the 2.2 meter MPG/ESO telescope at Cerro LaSilla

MPG/ESO 2.2 meter telescope at Cerro La Silla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres

ESO/MPIfR APEX high on the Chajnantor plateau in Chile’s Atacama region, at an altitude of over 4,800 m (15,700 ft)

NASA/Chandra X-ray Telescope

In the turbulent centers of active galaxies (active galactic nuclei, or AGN), gas and dust rains onto supermassive black holes of millions to billions of solar masses, triggering dramatic jets that plow into the surrounding matter and light up across the electromagnetic spectrum.

The growth of a supermassive black hole is thought to be closely tied to the evolution of its host galaxy, and feedback like these jets may provide that link. As the jets collide with the gas and dust surrounding the galaxy’s nucleus, they can trigger a range of effects — from shock waves that drive star formation, to gas removal that quenches star formation.

To better understand the connections between supermassive black holes and their host galaxies, we’d especially like to observe AGN at a time known as Cosmic Noon. This period occurred around 10 billion years ago and marks a time when star formation and supermassive black hole growth was at its strongest.

The Hidden World of Cosmic Noon

But there’s a catch: around Cosmic Noon, galaxies were heavily shrouded in thick gas and dust. This obscuring material makes it difficult for us to observe these systems in short wavelengths like optical and X-ray. Instead, we have to get creative by searching for our targets at other wavelengths.

Since AGN emission is absorbed by the surrounding dust and re-radiated in infrared, we can use infrared brightness to find obscured but luminous sources. To differentiate between hidden clumps of star formation and hidden AGN, we also look for a compact radio source — a signature that points to a jet emitted from a central black hole.

A team of scientists led by Pallavi Patil (University of Virginia and the National Radio Astronomy Observatory) has now gone on the hunt for these hidden sources at Cosmic Noon.

Newly-Triggered Jets Caught in the Act

Patil and collaborators observed a sample of 155 infrared-selected sources, following up with high-resolution imaging from the Jansky Very Large Array to identify compact radio sources.

NRAO/Karl V Jansky Expanded Very Large Array, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

From their observations and modeling of the jets, the authors estimate these sources’ properties.

The authors find bright luminosities, small sizes, and high jet pressures — all of which suggest that we’ve caught newly-triggered jets in a short-lived, unique phase of AGN evolution where the jets are still embedded in the dense gas reservoirs of their hosts. The jets are expanding slowly because they have to work hard to push through the thick clouds of surrounding material. Over time, the jets will likely expand to larger scales and clear out the surrounding matter, causing the sources to evolve into more classical looking radio galaxies.

What’s next? The authors are currently working on a companion study to further explore the shapes of the jets and their immediate environments. These young, hidden sources will provide valuable insight into how supermassive black holes evolve alongside their host galaxies.

Citation

“High-resolution VLA Imaging of Obscured Quasars: Young Radio Jets Caught in a Dense ISM,” Pallavi Patil et al 2020 ApJ 896 18.
https://iopscience.iop.org/article/10.3847/1538-4357/ab9011

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Alignment of a Star and a Planet”

From AAS NOVA

29 June 2020
Susanna Kohler

Artist’s impression of a planet orbiting the young star β Pictoris. [ESO L. Calçada/N. Risinger (skysurvey.org)]

The planets in our solar system all orbit in roughly the same direction as the Sun spins — but this isn’t true for all planetary systems! Recent measurements of the spin angle of a nearby, planet-hosting star provide new insight into how solar systems form.

The Birth of a Solar System

In a widely accepted theory for solar system formation, a star and its planets are born from the same swirling nebula of gas and dust. As the nebula collapses, it forms a spinning star at its center, with the remaining matter flattening into a rotating disk around the newborn star. Planets later form within this disk.

In this picture, conservation of angular momentum suggests that the spin axis of a star should be aligned with the orbital angular momentum vectors of its planets — a state known as spin–orbit alignment.

This is true in our solar system: our planets’ orbits are aligned to within 7° of the Sun’s spin. But roughly a third of the planets we’ve measured in other systems have significant misalignments — ranging from slightly tilted orbits to orbits that are fully the opposite direction of their star’s spin.

Explaining Crooked Paths

There are two possible explanations for these misaligned orbits:

1. A star’s spin and its planet-forming disk might be misaligned from the start — perhaps due to effects like turbulence or dynamical interactions in the star’s birth environment.
2. Planet orbits and stellar spin start out aligned, but some planets get scattered or nudged onto misaligned orbits after they form.

β Pictoris b is a directly imaged planet that orbits at ~10.6 AU from its host star, as seen at the center of this composite infrared image of the system. [ESO/A.-M. Lagrange et al.]

So far, we’ve only been able to measure spin–orbit alignment angles for short-period hot Jupiters, planets that we already suspect may have formed elsewhere and been driven inward onto their current close orbits. These planets could easily have had their orbits misaligned during this migration — which lends credence to the second explanation above.

But to confirm that this explanation fits, we’d also need to show that the spin–orbit alignments of long–period planets — which are less likely to have been perturbed over their lifetimes — are typically aligned.

In a new study, a team of scientists led by Stefan Kraus (University of Exeter, UK) have now made the first measurement of the spin–orbit alignment of a directly imaged, wide-orbit exoplanet: β Pictoris b.

Confirmation from a Wide Orbiter

Located just ~60 light-years away, the recently formed star β Pictoris hosts a roughly 13-Jupiter-mass exoplanet — β Pictoris b — that orbits with a semimajor axis of 10.6 AU within a young debris disk that surrounds the star.

Schematic illustrating the components of the β Pictoris system. Click to enlarge. [Adapted from Kraus et al. 2020]

Kraus and collaborators conduct high spectral resolution observations of β Pictoris with the GRAVITY instrument on the Very Large Telescope Interferometer in Chile, identifying the angle of the star’s spin from subtle signatures in its spectrum. From these measurements, the authors establish that β Pictoris’s stellar spin, its debris disk rotation, and its planet’s orbit are all aligned to within roughly 3°.

ESO GRAVITY in the VLTI

ESO VLT Interferometer, at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level, • ANTU (UT1; The Sun ),
• KUEYEN (UT2; The Moon ),
• MELIPAL (UT3; The Southern Cross ), and
• YEPUN (UT4; Venus – as evening star).

Kraus and collaborators’ results support the idea that solar systems initially form with aligned stellar spin and planet orbits; misalignments are introduced only later as planets migrate. Additional observations of wide-orbit planets will be needed to confirm this picture — but we can hope to gather more in the future using the techniques demonstrated in this study!

Citation

“Spin–Orbit Alignment of the β Pictoris Planetary System,” Stefan Kraus et al 2020 ApJL 897 L8.
https://iopscience.iop.org/article/10.3847/2041-8213/ab9d27

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Orbits Evolving Under Gravity”

From AAS NOVA

26 June 2020
Tarini Konchady

Artist’s impression of the early solar system, a disk of dust around the young Sun. [NASA/JPL-Caltech]

The solar system extends well beyond Pluto, encompassing small objects on their own unusual orbits around the Sun.

Kuiper Belt. Minor Planet Center

Oort Cloud, The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA, Universe Today

Kuiper Belt and Oort Cloud NASA

How did they get there? A new study attempts to answer this question with simulations.

Models and Moving Objects

The largest objects in the solar system wield the most influence. Models that account for the Sun and the outer planets — Jupiter, Saturn, Uranus, and Neptune — can produce realistic approximations of the solar system’s overall gravitational influence.

So if you have a model of the major gravitational forces at play, you can drop in orbiting objects and see what they do over time. This sounds simple, but it’s a powerful tool when it comes to understanding the current structure of our solar system.

The evolution of the surface density of the disk with time (starting from the upper-left) as seen face-on (top) and edge-on (bottom). Click to enlarge. Yellow regions have a higher density than blue regions. The timescale P represents 1,000 years. The authors note the “cone” of orbits present prior to t = 4,300 P, as well as the coherent ring of orbits most prominent at t = 9,900 P, which corresponds to an “m = 1 mode”. [Zderic et al. 2020]

A new study led by Alexander Zderic (University of Colorado Boulder) looks at what would happen to a large disk of small objects orbiting in the outskirts of our solar system. This study is the latest in a line of similar studies attempting to understand large scale structure in the solar system.

A Disk on the Outskirts

The disk being examined by Zderic and collaborators consists of objects orbiting at roughly 100 to 1,000 astronomical units (au) from the Sun. For context, Pluto’s farthest distance from the Sun is just 50 au, so these distances definitely qualify as the outer solar system. The orbits of the disk objects all start off in the same plane (which is also the plane in which the solar system’s planets orbit), but they have a higher than average eccentricity (as conditions in the outer solar system require).

In previous studies with higher mass disks, the disk conditions have been shown to reach a consistent state within 660 million years of simulated time. Zderic and collaborators were interested in this consistent state, which reflects the long-term behavior of the disk. To reach this state more quickly, the authors used an equivalent setup: they started with a less massive disk, and they ran their simulation for just under 10 million years.

Modes in Models

As the disk of objects evolves, the authors show that the collective gravity of the small bodies can induce an instability. As a result, the final state of the disk has a significant feature: orbits appear to cluster in a particular region. This is called being in a “mode”, which is shorthand for a group of orbital parameters having specific values. Zderic and collaborators note that later in the simulation, objects tend to settle into the m = 1 mode, though objects also fall in and out of the mode. Additionally, adding more particles to the simulation shows that objects stay in the mode longer. Extrapolating to the solar system, the mode may be stable for as long as the solar system is around.

Why is this interesting? These simulations show that the collective gravity of small bodies in a disk can naturally reproduce many of the observed behaviors of objects in our outer solar system — including extreme trans-Neptunian objects (TNOs), small bodies beyond the orbit of Neptune that are on very unusual orbits.

In particular, extreme TNOs have been observed to have clustered orbital properties — a fact that has been used to argue for the presence of an additional, hypothesized giant planet in our outer solar system, Planet Nine. But if Zderic and collaborators are correct, there’s no need for a hidden planet to explain extreme TNO alignments.

Further work will require the simulation of high mass disks that are more similar to the early solar system. Keep an eye out for future studies exploring the cause of our solar system’s structure!

Citation

“Apsidal Clustering following the Inclination Instability,” Alexander Zderic et al 2020 ApJL 895 L27.
https://iopscience.iop.org/article/10.3847/2041-8213/ab91a0

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Featured Image: Forming Betelgeuse from a Stellar Merger”

From AAS NOVA

22 June 2020
Susanna Kohler

This image from a simulation shows how the the large, red supergiant star Betelgeuse may have been created by the tidal disruption and merger of a binary star within the past few hundred thousand years.

QueenBee2 (QB2) computing cluster at LSU’s Center for Computation and Technology (CCT) was mainly utilized for the 3D merger simulation.

Some other analyses were done on the SuperMike II cluster also at CCT

Betelgeuse — a prominent star in our night sky — has recently made headlines due to its unexpected, sudden dimming and rebrightening. But the supergiant has other quirks, like how it’s hurtling rapidly through space as a “runaway” star, or how it spins unusually fast for its size. A team of Louisiana State University researchers led by Manos Chatzopoulos has now performed simulations that show that Betelgeuse’s odd properties could be explained if the supergiant was formed by the merger of an unequal-mass binary star system in the relatively recent past. To learn more about the authors’ results, check out the original article below.

Betelgeuse merger full
The full view of two frames from one of the authors’ simulations. The left image shows the original configuration of the unequal-mass binary star system; the right image shows the tidal disruption of the secondary around the core of the primary. [Chatzopoulos et al. 2020]

Citation

“Is Betelgeuse the Outcome of a Past Merger?,” E. Chatzopoulos et al 2020 ApJ 896 50.
https://iopscience.iop.org/article/10.3847/1538-4357/ab91bb

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Exploring Links Between Nearby Asteroids”

From AAS NOVA

19 June 2020
Susanna Kohler

Artist’s illustration of the near-Earth asteroid 3200 Phaethon, one target of an upcoming fly-by mission. [Heather Roper/University of Arizona]

It’s not easy being a speeding rock in our solar system.

Illustration of an asteroid breaking apart into smaller fragments. [NASA/JPL]

Over their lifetimes, the millions of minor rocky bodies of our solar system — asteroids — are subject to extreme conditions. Some experience dramatic collisions, some are spun up to such high rotation speeds that they fly apart, and some venture so close to the Sun that our star’s heat cracks them into pieces.

Over time, these violent processes create families of asteroids that dance around our solar system on similar paths. Where one rock once orbited, there might now be a group of genetically linked asteroids that follow similar trajectories — all produced by the splitting of one parent rock.

In a new study, scientists have explored two especially nearby asteroids to determine whether they might be linked.

A Visit to a “Potentially Hazardous” Neighbor

The orbital path of the near-Earth asteroid Phaethon. [Sky&Tel]

Asteroids whose orbits bring them close to the Earth are of particular interest to us: we like to keep an eye on those bodies that might threaten our planet.

Perhaps 22,000 near-Earth asteroids are currently known, with just over 2,000 that are large enough and swing close enough to Earth’s orbit to be considered “potentially hazardous” — though it should be noted that the vast majority of these have been ruled out as being an impact threat in at least the next 100 years.

Artist’s illustration of the DESTINY+ spacecraft. [JAXA]

To learn more about these nearby bodies, the Japanese Aerospace Exploration Agency is sending a spacecraft, DESTINY+, to fly by a large (~5-km) near-Earth asteroid. The target is 3200 Phaethon — an unusual blue-toned, dust-producing asteroid thought to be the source of the Geminid meteor stream — and other minor bodies that might be associated with it.

As DESTINY+ is currently scheduled to launch in 2022, scientists are currently preparing by learning all they can about the possible mission targets using ground- and space-based observatories. In a new study led by Maxime Devogèle (Lowell Observatory), a team of scientists presents detailed observations of (155140) 2005 UD, another near-Earth object and potential DESTINY+ target that might be related to Phaethon.

Signs Point to a Linked Pair

Devogèle and collaborators gathered an impressive array of observations of 2005 UD, using dozens of telescopes to obtain photometry, polarimetry, and spectroscopy, and also reanalyzing thermal imaging.

2005 UD and Phaethon exhibit very similar spectra, including rare spectroscopic (B-type) signatures. [Devogèle et al. 2020]

By combining new observations with archival data and detailed modeling, the team constrained 2005 UD’s size (just over 1 km across) and rotation rate (it spins roughly once every 5.2 hours), as well as many other properties like its albedo, spectroscopic class, and even the size of the grains on its surface — knowledge that will all help with mission planning for DESTINY+.

But what about 2005 UD’s potential link to Phaethon? Based on Devogèle and collaborators’ observations, 2005 UD and Phaethon appear to share more than just orbital characteristics. They also have very similar — and rare, among asteroids — physical properties as shown by their spectroscopy and polarimetry.

More study is needed, but the data suggest that the two are, indeed, genetically linked — perhaps 2005 UD and Phaethon both split from the same parent thousands of years ago. With any luck, DESTINY+ will soon reveal more about these close-swinging rocky bodies!

Citation

“New Evidence for a Physical Link between Asteroids (155140) 2005 UD and (3200) Phaethon,” Maxime Devogèle et al 2020 Planet. Sci. J. 1 15.
https://iopscience.iop.org/article/10.3847/PSJ/ab8e45

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Spotted: A Galactic PeVatron?”

From AAS NOVA

17 June 2020
Susanna Kohler

HAWC High Altitude Čerenkov Experiment, />US Mexico Europe collaboration located on the flanks of the Sierra Negra volcano in the Mexican state of Puebla at an altitude of 4100 meters(13,500ft), at WikiMiniAtlas 18°59′41″N 97°18′30.6″W. searches for cosmic rays

Speeding charged particles — far more energetic than any we can create in laboratory particle accelerators — constantly bombard the Earth’s atmosphere. But what extreme environments produce these high-energy particles? A new study may have identified one cosmic accelerator in our galaxy.

Charged Arrivals

At any given moment, protons and atomic nuclei are whizzing through our galaxy, sometimes at nearly the speed of light. These charged particles — cosmic rays —span a wide range of energies, with the most energetic packing the same punch as a 90 kilometer-per-hour (56 mph) baseball!

Cosmic rays produced by high-energy astrophysics sources (ASPERA collaboration – AStroParticle ERAnet)

More modest cosmic rays reach “only” peta-electron-volt (PeV) energies — that’s 10^15 eV, still more than 100 times more energetic than the particles accelerated by the record-holding Large Hadron Collider. We think that these PeV particles were produced somewhere within our own galaxy.

If we could unravel their secrets, these cosmic rays could provide clues about how stars evolve and how energy is transported throughout the galaxy. First, however, we need to figure out where they came from. Are their sources supernova remnants? Microquasars? Superbubbles? What galactic PeVatrons accelerated these particles to their tremendous speeds?

Road Map to a Birthplace

Unfortunately, we can’t just trace cosmic rays backwards to figure out their origins. Because these particles are charged, their trajectories are deflected by interstellar magnetic fields — which means that the direction a cosmic ray arrived from probably isn’t the direction of its source.

To address this challenge, high-energy astronomers search for more direct messengers that are produced as cosmic rays are accelerated — like extremely energetic gamma-ray radiation.

When PeV particles accelerated by a galactic PeVatron collide with gas and dust in the vicinity of their origin, they should produce very high-energy tera-electron-volt (TeV, or 10^12 eV) gamma-ray photons. These photon by-products won’t be deflected by magnetic fields, so their arrival at gamma-ray observatories on Earth provides a clearer path back to the source of the PeV cosmic rays.

Top: significance map from HAWC showing the location of gamma-ray emission from near SNR G106.3+2.7. Bottom: Molecular hydrogen column density around the HAWC-detected source (shown in gray contours). The detectors VERITAS and Milagro have also observed very high-energy gamma-ray emission from this region; their detection centers are also marked. [Adapted from Albert et al. 2020]

Hunting for Galactic Accelerators

So how’s the search for these characteristic TeV gamma-rays going? With one possible success on the books so far — scientists think there’s a galactic PeVatron at the center of our galaxy, but we haven’t yet determined the source — we’ve now identified a new potential galactic PeVatron: the remnant produced by a past supernova explosion just 2,600 light-years from Earth.

In a new publication, a team of scientists from the High-Altitude Water Čerenkov Gamma-Ray Observatory (HAWC) announces the detection of TeV gamma-ray emission from the same region as supernova remnant SNR G106.3+2.7.

Though the team can’t rule out other causes of the emission, this signal has a spectrum that’s consistent with what we’d expect to be produced by PeV protons colliding with gas and dust. The origin near SNR G106.3+2.7 supports a picture in which charged particles can be accelerated across the shocks of supernova remnants and flung into space with PeV energies.

So might the mystery of galactic PeVatrons be solved with supernova remnants? We don’t know for sure yet, but future high-energy gamma-ray observations are sure to help us further identify the sources of the speeding charged particles in our galaxy.

Citation

“HAWC J2227+610 and Its Association with G106.3+2.7, a New Potential Galactic PeVatron,” A. Albert et al 2020 ApJL 896 L29.
https://iopscience.iop.org/article/10.3847/2041-8213/ab96cc

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Seeing Things in Threes”

From AAS NOVA

12 June 2020
Tarini Konchady

The molecular ring associated with the Lambda Orionis cluster, as seen by NASA’s Wide-Field Infrared Survey Explorer. In the full image, Betelgeuse is visible as a bright blue star in the lower left corner. [NASA/JPL/Caltech/UCLA]

GW Ori is a system of three stars that are gravitationally bound. Aside from being a triple system, GW Ori also stands out for another reason — it harbors a circumtriple disk, which is a disk of gas and dust surrounding all three stars.

The dust component of GW Ori’s disk as seen by ALMA, showing the three rings discussed in this study. The x- and y-axes of the plot are position offsets, with (0,0) being the position of GW Ori. The color of the rings indicate intensity of emission, with yellow being more intense than purple. The circle in the lower left corner shows the size of the beam used by ALMA to image the disk. [Bi et al. 2020]

A Tricky Triple

GW Ori lives in a star cluster called Lambda Orionis, which appears near Betelgeuse on the sky. The inner stars of the system, GW Ori A and GW Ori B, orbit each other and are separated by about 1 astronomical unit (au). The third star, GW Ori C, revolves around its two companions at a distance of roughly 8 au.

GW Ori’s circumtriple disk is enormous relative to the orbits of its stars. The dust component of the disk is about 400 au across, with the gas component spanning roughly 1,300 au. For scale, Neptune is only about 30 au from the Sun!

Models of GW Ori have suggested a gap in the disk between 25 and 55 au from its center. A recent study led by Jiaqing Bi (University of Victoria) attempted to test these models and probe the structure of GW Ori directly using observations by the Atacama Large Millimeter/submillimeter Array (ALMA).

ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

Finding Rings in Radio

Bi and collaborators used ALMA observations taken at multiple frequencies to probe the gas and dust of the circumtriple disk. The dust component has characteristic emission that can be observed at 1.3 millimeters, while the gas can be studied using a particular transition of carbon monoxide.

The gas observations showed the expected disk rotation, and additional structure in the disk was immediately apparent in the dust observations. Bi and collaborators identified three dust rings in GW Ori’s disk at roughly 46, 88, and 338 au from its center, the innermost ring being the one that was suggested by past models. Additionally, an unexpected result was brought to fore — the dust rings may be very misaligned relative to one another!

Out of Balance But It’s Fine

Bi and collaborators found that the dust rings showed significant inclinations relative to the plane of the orbit of GW Ori A and B — specifically 11, 35, and 40 degrees starting from the innermost ring. The gas observations back this up, requiring a model that assumes some distortion from an undisturbed disk.

Additional analysis and simulations by Bi and collaborators suggest that the stars of GW Ori alone could not be responsible for this misalignment. The innermost ring also adds another puzzle to this system: in addition to being misaligned, it also has a non-zero eccentricity, meaning its center is different than those of the other rings.

A possible explanation could be additional companions to GW Ori, which are also carving out paths in the disk. This phenomenon has been observed by ALMA before in protoplanetary disks. If this is the case, it would be the first time circumtriple companions were detected. Only time will tell!

Citation

“GW Ori: Interactions between a Triple-star System and Its Circumtriple Disk in Action,” Jiaqing Bi et al 2020 ApJL 895 L18.
https://iopscience.iop.org/article/10.3847/2041-8213/ab8eb4

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Featured Image: Fractals in Cosmic Gas”

From AAS NOVA

8 June 2020
Susanna Kohler

What happens in galactic and intergalactic settings when cold, dense gas moves through hot, diffuse gas? You can see the result in the complex simulations shown above, as reported in a recent publication led by scientist Drummond Fielding (Center for Computational Astrophysics, Flatiron Institute). Turbulent mixing layers like those simulated by Fielding and collaborators form in a vast variety of cosmic environments: the interstellar medium, the circumgalactic medium, expanding supernova remnants, cosmic filaments, galactic winds, protoplanetary disks, the solar corona, and many more. The authors’ new models show the fractal nature of the cooling surface that arises within these layers as the gases mix.

You can watch the animated version of the simulation below, which shows how eight different fluid properties evolve over time in a turbulent layer containing mixing cold and hot gas. For more information, check out the original article, linked below.

Citation

“Multiphase Gas and the Fractal Nature of Radiative Turbulent Mixing Layers,” Drummond B. Fielding et al 2020 ApJL 894 L24.
https://iopscience.iop.org/article/10.3847/2041-8213/ab8d2c

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: ” Are We Watching a Planet Disintegrate?”

From AAS NOVA

27 May 2020
Susanna Kohler

Artist’s illustration of the possible disintegrating planet in the nearby planetary system DMPP-1. [Mark A. Garlick/Haswell/ Barnes/Staab/Open University]

Among the wealth of exoplanets we’ve discovered beyond our solar system, some are temperate, some less so. New observations have now revealed what may be a particularly inhospitable environment: a planet literally disintegrating as it orbits its host.

Artist’s illustration of another DMPP-discovered planetary system, DMPP-2. [Mark A. Garlick/Haswell/ Barnes/Staab/Open University]

Peering Through the Shroud

With initial observations in 2015, the Dispersed Matter Planet Project (DMPP) promised an innovative approach to hunting for exoplanets closely orbiting their hosts. Using high-cadence, high-precision radial velocity measurements, the project targets bright nearby stars that shows signatures of being shrouded in hot circumstellar gas. By looking for tiny radial-velocity wiggles in the star’s signal, the DMPP team hopes to detect small planets that are losing mass as they orbit close to their hot hosts.

Radial Velocity Method-Las Cumbres Observatory

In December 2019, DMPP announced its first discoveries: six planets orbiting around three different target stars. Now, in a new publication led by scientist Mark Jones (The Open University, UK), the team has revisited the first of these systems, DMPP-1, with follow-up photometry from the Transiting Exoplanet Survey Satellite (TESS).

NASA/MIT TESS replaced Kepler in search for exoplanets

Intriguingly, the radial-velocity-detected planets are not the only signals from this system.

Missing the Expected, but Finding the Unexpected

DMPP-1 is a 2-billion-year-old star located just over 200 light-years away. The radial-velocity observations of this system revealed the gravitational tugs of four planets all orbiting with periods of less than 19 days. The radial-velocity data suggest that this system is probably near edge-on and contains three super-Earths and one Neptune-like planet.

Jones and collaborators began their photometric follow-up by searching TESS data for evidence of these four planets transiting across the host star’s face. Interestingly, they found no sign of transits at the predicted periods — indicating that the four radial-velocity planets are either smaller than expected, or that the system isn’t quite edge-on after all, so the planets don’t pass directly in front of the star.

The authors did, however, find a new signal: a weak transit detection with a period of just ~3.3 days. This signal doesn’t match any of the known radial-velocity planets.

A Disappearing Planet?

What might this marginal detection be? Its variable transit depths, short period, and apparent small size are all consistent with a catastrophically disintegrating exoplanet — a close-in, small, rocky planet that is so irradiated by its host that its rocky surface is being sublimated. As time goes on, such a planet will eventually disintegrate into nothing.

This transit signal still needs to be confirmed with additional follow-up photometric observations. Assuming it proves to be a true detection, however, such a disintegrating, rocky planet orbiting a bright nearby star would provide a veritable gold mine of information.

By exploring the transit signals from DMPP-1 with future technology like the James Webb Space Telescope, we will be able to examine the composition of the ablated material, potentially revealing clues as to how hot, rocky inner planets form and evolve.

Citation

“A Possible Transit of a Disintegrating Exoplanet in the Nearby Multiplanet System DMPP-1,” Mark H. Jones et al 2020 ApJL 895 L17.
https://iopscience.iop.org/article/10.3847/2041-8213/ab8f2b

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “The Case of the Missing CO”

From AAS NOVA

8 May 2020
Tarini Konchady

By now iconic artist’s illustration of a protoplanetary disk. [ESO/L. Calçada]

Planets start their lives in disks of gas and matter around stars, so understanding these so-called protoplanetary disks is key to decoding planet formation. One interesting feature of protoplanetary disks is that they contain less carbon monoxide gas than the typical interstellar medium. When and how does this deficit arise?

Radio observations of the disk around the star DG Tau, with separate plots for each form or isotopologue of CO. The contours designate varying intensity and the colors indicate the velocity of the gas (red is faster than blue). The arrows in the bottom-most plot indicate outflows associated with DG Tau. [Adapted from Zhang et al. 2020]

Protostellar to Protoplanetary

Carbon monoxide (CO) is one of the most common compounds found in space and can be used to trace other chemical compounds along with the structure and mass distribution of objects. However, protoplanetary disks appear to lack CO gas to a startling degree relative to the interstellar medium (ISM). CO gas can be destroyed by chemical processes or be frozen out of the gas state, but these mechanisms alone can’t explain the deficit of CO gas seen in protoplanetary disks.

Protoplanetary disks are an evolved form of protostellar disks, which are created when a cloud of gas collapses to birth a star. Could CO be dissipated at this earlier protostellar disk stage? Or does the depletion only occur when the disk is older?

This question of timing is what motivated a recent study by a group of researchers led by Ke Zhang (University of Michigan). Zhang and collaborators used radio observations of three young (less than a million years old) protostellar disks to measure their levels of CO gas and compare them to that of the typical ISM.

COuld It Be at a Higher Level?

Zhang and collaborators selected their disks based on whether the disk structure could be seen in radio observations. They searched for three different forms of CO that, taken together with models, could probe the CO content of the entire disk. Different models were used to fit the disks, with adjustments to parameters like the gas-to-dust ratio and levels of molecular hydrogen.

The CO content and ages of various protostellar and protoplanetary disks. The average ISM value is shown for comparison. The disks used in this study are TMC1A, HL Tau, and DG Tau. The circles indicate disks and the squares indicate the average value for disks in star-forming regions. Disks younger than 1 million years are considered protostellar disks and disks older than one million years are considered protoplanetary disks.[Zhang et al. 2020]

Zhang and collaborators found that the CO gas content of all three protostellar disks is similar to that of the ISM. This puts them at a higher level relative to disks that are older than a million years.

What does this mean for the missing CO problem? The dropoff in CO appears to occur around the million year mark. This means that the CO depletion process is fairly rapid — on astronomical scales — and puts tight constraints on the responsible mechanisms.It also restricts the depletion to occurring within the disk rather than in the surrounding envelope of infalling gas.

It may take exploring combinations of physical and chemical processes to solve this puzzle, as well as observing a larger sample of disks. Either way, CO continues to be a useful molecule to find (or not find) in space!

Citation

“Rapid Evolution of Volatile CO from the Protostellar Disk Stage to the Protoplanetary Disk Stage,” Ke Zhang et al 2020 ApJL 891 L17.

https://iopscience.iop.org/article/10.3847/2041-8213/ab7823

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009