From AAS NOVA: ” Featured Image: A Distant Cluster Tips the Scales”

From AAS NOVA

6 April 2020
Susanna Kohler

You’re looking at SPT-CL J2106-5844, the most massive distant (farther than roughly 8 billion light-years) galaxy cluster known. This composite image (click for the full view) shows the field of the cluster, which spans a distance of roughly 3 million light-years across, in three Hubble color filters. The overlaid contours show the distribution of mass within the cluster, as recently determined by a team of scientists led by Jinhyub Kim (Yonsei University, Republic of Korea; University of California, Davis). Kim and collaborators used weak gravitational lensing — slight distortions in the shapes of background galaxies caused when their light is bent by the massive gravitational pull of this cluster — to map out the tremendous mass of SPT-CL J2106-5844.

Weak gravitational lensing NASA/ESA Hubble

They find this cluster weighs in at a whopping ~1 quadrillion (1015) solar masses! Studying this distant, monster cluster can help us place constraints on how the universe’s large-scale structure formed and evolved. To read more about what the authors learned, check out the article below.

Citation

“Precise Mass Determination of SPT-CL J2106-5844, the Most Massive Cluster at z > 1,” Jinhyub Kim et al 2019 ApJ 887 76.
https://iopscience.iop.org/article/10.3847/1538-4357/ab521e

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: “Peering Into the Atmosphere of the Hottest Planet Known” KELT-9b

From AAS NOVA

3 April 2020
Susanna Kohler

Artist’s impression of KELT-9b, the hottest planet known, and its escaping atmosphere. [NASA/JPL-Caltech]

As the ultra-hot Jupiter KELT-9b blazes across the face of its host star, we have an excellent opportunity to examine its scalding atmosphere. A new study now reports on what we’ve found.

A Passing Glance

In our efforts to learn more about worlds beyond our solar system, atmospheres provide a critical key. Characterizing the atmospheres of exoplanets can provide us with insight into the planets’ compositions and climates, their evolution, and even — with some potential caveats — their habitability.

As a star’s light filters through a planet’s atmosphere on its way to Earth, the atmosphere absorbs certain wavelengths depending on its composition. [European Southern Observatory]

In particular, transiting exoplanets provide us with a unique opportunity. As a planet passes in front of its host star, we briefly observe the star’s light filtering through the planet’s atmosphere. By exploring the spectrum of that light, not only can we identify the presence of specific atoms and molecules in the planet’s atmosphere, but we can also learn more about where they are and what the atmospheric properties are at those locations.

In a new study led by Jake Turner (Cornell University), a team of scientists digs deep into such a transmission spectrum for the exoplanet KELT-9b.

Not Exactly Temperate

KELT-9b is an extreme world. Clocking in with a dayside temperature of more than 4,500 K (~7,600 °F), it is the hottest planet known — hotter than many stars! This ultra-hot Jupiter orbits at a mere 0.035 AU from its scalding A- or B-type host star, whizzing around its host in just 1.5 days.

The intense radiation bombarding KELT-9b almost certainly takes a toll: this energetic light should dissociate molecules into their component atoms and ionize metals in the hot atmosphere, and it may inflate the envelope of hydrogen gas around the planet to the point where the hot gas escapes.

Observed and modeled Hα (top) and Ca II (bottom three) spectral lines in the atmosphere of the ultra-hot Jupiter KELT-9b. [Adapted from Turner et al. 2020]

Turner and collaborators explore the extreme conditions in KELT-9b’s atmosphere with high-resolution transmission spectra taken with the CARMENES instrument on the Calar Alto 3.5-m telescope in Spain.

CARMENES spectrograph, mounted on the Calar Alto 3.5 meter Telescope

Calar Alto 3.5 meter Telescope, located in Almería province in Spain on Calar Alto, a 2,168-meter-high (7,113 ft) mountain in Sierra de Los Filabres

Detecting Atmospheric Thermometers

The authors find absorption lines indicating the presence of ionized calcium, Ca II, in KELT-9b’s atmospheric spectra; this is just the second time that Ca II has been observed in a hot Jupiter’s atmosphere. They also find prominent Hα absorption — evidence that confirms the existence of an extended envelope of hydrogen surrounding the irradiated planet.

By modeling the spectra they obtain for KELT-9b, Turner and collaborators are able to identify the pressures, altitudes, and temperatures at which these spectral lines form in the atmosphere. They find that the Ca II lines probe the atmosphere at an altitude of about 1.32–1.40 times the planet’s radius. The Hα line provides information from higher up, at 1.44 planetary radii.

Together, these absorption lines act as atmospheric thermometers, providing a picture of KELT-9b’s atmospheric temperature profile and yielding insight into the energy that enters and leaves the planet’s atmosphere.

These results demonstrate the power of this technique, revealing the remarkable wealth of information we can glean from some distant starlight filtered through the atmosphere of an extreme world.

Citation

“Detection of Ionized Calcium in the Atmosphere of the Ultra-hot Jupiter KELT-9b,” Jake D. Turner et al 2020 ApJL 888 L13.
https://iopscience.iop.org/article/10.3847/2041-8213/ab60a9

______________________________________________
From JPL-Caltech

KELT-9b will stay firmly categorized among the uninhabitable worlds. Astronomers became aware of its extremely hostile environment in 2017, when it was first detected using the Kilodegree Extremely Little Telescope (KELT) system – a combined effort involving observations from two robotic telescopes, one in southern Arizona and one in South Africa.

KELT South robotic telescope, Southerland, South Africa, jointly operated by Ohio State, Vanderbilt and Lehigh universities.

KELT Kilodegree Extremely Little Telescope at WINER Observatory in Arizona, USA c J.Peppe, operated by Ohio State, Vanderbilt and Lehigh universities

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: “Distant Metals Reveal the Universe’s Evolution”

From AAS NOVA

30 March 2020
Susanna Kohler

This optical/infrared/X-ray composite image of Messier 82 reveals how outflows from a galaxy can enrich the circumgalactic medium that surrounds it. What can we learn about our universe’s evolution from this metal-enriched material? [NASA, ESA, CXC, and JPL-Caltech]

NASA/ESA Hubble Telescope

NASA/Chandra X-ray Telescope

NASA JPL

When did the first sources of light bombard the universe’s gas, tearing electrons from atoms in a period known as reionization? A new study uses the metal-filled gas surrounding galaxies to learn more about this important transition.

Drama in the Early Universe

After the universe’s birth in the hot Big Bang, expansion and cooling allowed the soup of electrons and protons that pervaded space to recombine into neutral hydrogen atoms. But sometime within the first billion years after the Big Bang, these atoms were again ionized by high-energy radiation from the first sources of light in the universe.

How and when, exactly, did this period of reionization occur? One way we can seek to answer these questions is by studying the gas that lies both between and immediately around galaxies.

Clues from Distant Gas

While the broadly dispersed intergalactic medium (IGM) consists largely of hydrogen gas, the circumgalactic medium (CGM) immediately around galaxies is a little more complicated: it’s enriched with elements heavier than helium — “metals” — that have been produced by the galaxy’s stars and flung into the surrounding matter.

Because this distant gas is diffuse and dim, we can’t easily study its emission. Instead, we explore these clouds of gas by looking at how they absorb light from bright background sources.

The authors’ sample. Horizontal lines show the redshift interval over which each line of sight was surveyed for neutral oxygen. Orange dots mark the locations of identified neutral oxygen absorbers. [Becker et al. 2019]

In a new study led by George Becker (University of California, Riverside), a team of scientists has examined the spectra of nearly 200 background quasars — bright, active galaxies — with redshifts up to z = 6.6, corresponding to a time when the universe was less than a billion years old. Their goal: to explore the absorption by clouds of metal-enriched CGM that lie between us and the quasars.

Oxygen Signature Surprise

Becker and collaborators looked for the signatures of several metals in these clouds, including neutral oxygen. From their sample, the authors were able to infer how absorbing clouds containing neutral oxygen are distributed over cosmic time between redshifts of 3.2 < z < 6.5.

If circumgalactic gas were gradually enriched, we would expect to see the number density of neutral oxygen absorbers increase with decreasing redshift (closer to us, or longer time since the Big Bang), as metal-enriched gas continues to accumulate around galaxies over time.

Number density of neutral oxygen (black circles), singly ionized magnesium (red squares), and triply ionized carbon (blue triangles) absorbers as a function of redshift. Instead of decreasing monotonically with increasing redshift (as do highly ionized species like the C IV), O I absorber number density dips for redshifts below z ~ 6. [Becker et al. 2019]

Instead, Becker and collaborators see a dip in the number of neutral oxygen absorbers around a redshift of z ~ 6 as the universe ages from high redshift toward today. The reason? The authors argue that it’s because the universe is becoming ionized at this time — so the CGM contains less neutral oxygen in the period right after z ~ 6 because more of the oxygen gas is ionized.

Locking Down a Timeframe

What does this mean? The ionization of the metal-enriched gas immediately surrounding galaxies is directly linked to the reionization of the hydrogen in the broader intergalactic medium: for high-energy background radiation to reach the dense gas around galaxies and ionize it, this means that the surrounding IGM must recently have become ionized.

Becker and collaborators’ observations of metals therefore help us to pinpoint the final stages of the epoch of reionization in the universe, shedding light on how the universe evolved to its current form.

Citation

“The Evolution of O i over 3.2 < z < 6.5: Reionization of the Circumgalactic Medium,” George D. Becker et al 2019 ApJ 883 163.
https://iopscience.iop.org/article/10.3847/1538-4357/ab3eb5

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: ” Signals from Neutron Star Binaries”

From AAS NOVA

27 March 2020
Tarini Konchady

Artist’s illustration of a binary star system consisting of two highly magnetized neutron stars. [John Rowe Animations]

Fast radio bursts (FRBs) are brief radio signals that last on the order of milliseconds. They appear to be extragalactic, coming from small, point-like areas on the sky. Some FRBs are one-off events, while others are periodic or “repeating”. The sources of FRBs are still unknown, but binary neutron star systems might be a piece of the puzzle.

Wanted: A Reliable Source of Repeating Fast Radio Bursts

Any proposed model for a repeating FRB must explain a number of observed behaviors. Among them are the following:

Repeating bursts from a given FRB source are consistent in frequency and overall intensity on the timescale of years.
Bursts exhibit small-scale variations in measures of the source’s magnetic environment.
FRBs seem to be preferentially hosted in massive, Milky-Way-like galaxies.

Example of an FRB from a repeating source, showing the intensity and various frequencies contained in a single burst (darker means more intense, lighter means less intense). The red lines just below and above 550 MHz and those near 450 MHz and 650 MHz indicate frequencies that were unused due to other radio signals interfering [adapted from the CHIME/FRB Collaboration, Andersen et al. 2019].

CHIME Canadian Hydrogen Intensity Mapping Experiment -A partnership between the University of British Columbia, the University of Toronto, McGill University, Yale and the National Research Council in British Columbia, at the Dominion Radio Astrophysical Observatory in Penticton, British Columbia, CA Altitude 545 m (1,788 ft)

Binary neutron stars (BNSs) have been considered as possible solutions to the repeating FRB puzzle. Specifically, binary neutron star mergers might produce FRBs, along with gamma-ray bursts and gravitational waves. But how could BNSs produce repeating, consistent FRBs?

In a recent study, Bing Zhang (University of Nevada Las Vegas; Kyoto University, Japan) attempts to explain repeating FRBs using BNSs in a novel way. Instead of considering the neutron-star merger itself, Zhang examined whether the years leading up to the merger could produce repeating FRBs.

A Magnetic Dance

Repeating FRBs put out an enormous amount of energy over a few milliseconds — at least as much energy as the Sun puts out over three days. To put constraints on the average FRB-producing BNS, Zhang used the double-pulsar system PSR J0737-3039A/B (pulsars are fast-rotating neutron stars with strong magnetic fields), which is very well characterized in terms of its component stars and overall structure.

Aside from having enormous amounts of rotational energy intrinsically and in their orbits, BNSs also have strong magnetic fields. These magnetic fields are key to the production of FRBs in Zhang’s scenario — as the neutron stars orbit each other, their magnetic fields interact, possibly triggering a flow of particles that would produce FRBs.

On the scale of centuries or even decades pre-merger, these triggers could occur repeatedly and consistently, satisfying a key requirement for repeating FRBs. This picture of interacting magnetic fields would also explain the small-scale variations in the magnetic environment measures, and there is an overlap between the sorts of galaxies that host FRBs and those that host the gamma-ray bursts that could be associated with BNS mergers.

By Way of Gravitational Waves

An observational test for this scenario is the detection of gravitational waves from an FRB source. Space-based gravitational wave detectors, such as the Laser Interferometer Space Antenna, would be well-suited for this.

Gravity is talking. Lisa will listen. Dialogos of Eide

ESA/NASA eLISA space based, the future of gravitational wave research

Ground-based detectors would also play a role, picking up waves from the BNSs actually merging.

MIT /Caltech Advanced aLigo

VIRGO Gravitational Wave interferometer, near Pisa, Italy

And of course, the more FRBs we observe, the more we can narrow down their properties and sources. Fortunately, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) is predicted to detect 2 to 50 FRBs per day, and other radio telescopes are hard at work as well. So maybe this FRB mystery will be solved sooner than we think!

Citation

“Fast Radio Bursts from Interacting Binary Neutron Star Systems,” Bing Zhang 2020 ApJL 890 L24.

https://iopscience.iop.org/article/10.3847/2041-8213/ab7244

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: Evidence for Planets in Disks?”

From AAS NOVA

23 March 2020
Susanna Kohler

Disk Substructures at High Angular Resolution Project (DSHARP) ESO/ALMA

Are baby planets responsible for the gaps and rings we’ve spotted in the disks that surround distant, young stars? A new study led by Christophe Pinte (Monash University, Australia; Univ. Grenoble Alpes, France) has found evidence supporting this theory in the images of eight circumstellar disks observed in the Disk Substructures at High Angular Resolution (DSHARP) project. DSHARP uses the Atacama Large Millimeter/submillimeter Array (ALMA) to explore the gas distributed within the disks around young stars.

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

In the image above the left-most panel shows the 1.3-millimeter dust continuum images of five complex circumstellar disks. The panels to the right show gas measurements for each disk in different velocity channels, revealing “velocity kinks” — deviations from the normal Keplerian velocity expected from unperturbed, orbiting gas. According to Pinte and collaborators, the kinks signatures of planets that perturb the gas flow in their vicinity. For more information, check out the article below.

Citation

“Nine Localized Deviations from Keplerian Rotation in the DSHARP Circumstellar Disks: Kinematic Evidence for Protoplanets Carving the Gaps,” C. Pinte et al 2020 ApJL 890 L9.

https://iopscience.iop.org/article/10.3847/2041-8213/ab6dda

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: “Learning from LIGO’s Second Binary Neutron Star Detection”

From AAS NOVA

20 March 2020
Susanna Kohler

LIGO has discovered another likely binary neutron star merger — and this one has new, interesting implications. [NASA/Goddard Space Flight Center]

In case you missed the news in January: the Laser Interferometer Gravitational-Wave Observatory (LIGO) has detected its second merger of two neutron stars — probably. In a recent publication, the collaboration details the interesting uncertainties and implications of this find.

MIT /Caltech Advanced aLigo

VIRGO Gravitational Wave interferometer, near Pisa, Italy

Artist’s illustration of a binary neutron star merger. [National Science Foundation/LIGO/Sonoma State University/A. Simonnet]

What We Saw and Why It’s Weird

On April 25, 2019, the LIGO detector in Livingston, Louisiana, spotted a gravitational-wave signal from a merger roughly 520 million light-years away. This single-detector observation — LIGO Hanford was offline at the time, and the Virgo detector in Europe didn’t spot it — was nonetheless strong enough to qualify as a definite detection of a merger.

Analysis of the GW190425 signal indicates that we saw the collision of a binary with a total mass of 3.3–3.7 times the mass of the Sun. While the estimated masses of the merging objects — between 1.1 and 2.5 solar masses — are consistent with the expected masses of neutron stars, that total mass measurement is much larger than any neutron star binary we’ve observed in our galaxy. We know of 17 galactic neutron star pairs with measured total masses, and these masses range from just 2.5 to 2.9 times that of the Sun. Why is GW190425 so heavy?

What It Suggests For Formation Channels

Blue and orange curves show the estimated total mass of GW190425 under different spin assumptions. In either case, the estimated mass is dramatically different from the total masses for the known galactic population of binary neutron stars, indicated with the grey histogram bars and the dashed line. [Abbott et al. 2020]

GW190425’s unusual mass may indicate that it formed differently from known galactic neutron star binaries.

Theory suggests that massive, fast-merging neutron-star pairs like GW190425 could potentially result from especially low-metallicity stars evolving in close binary systems. Under the right conditions, the energetic kicks caused by supernova explosions might be suppressed, allowing the objects to stay together in the close binary even after their evolution into neutron stars.

If this is the case, GW190425 could represent a population of binary neutron stars that we haven’t observed before. These binaries have remained invisible due to their ultra-tight orbits with sub-hour periods; the rapid accelerations of these objects would obscure their signals in pulsar surveys. The shortest-period neutron star binary we’ve detected with pulsar surveys has a period of 1.88 hours, and it won’t merge for another 46 million years. GW190425 could represent a very different binary neutron star population that’s just as common as the galactic population we know.

What If It’s Not Neutron Stars?

Unfortunately, the single-detector observation of GW190425 means we couldn’t pin down the gravitational-wave source’s location well — so follow-up observations haven’t yet spotted an electromagnetic counterpart like the one we had for GW170817, the first binary neutron star merger LIGO observed.

GW190425’s signal was localized to an unfortunately large area of ~16% of the sky, providing a challenge for electromagnetic and neutrino observatories hoping to discover counterparts. [Abbott et al. 2020]

This means we’re missing outside information confirming that this was a neutron star binary; it’s therefore possible that one or both of the merging objects was actually a black hole. If so, this would be smaller than any black holes we’ve detected so far, and we would need to significantly revamp our models of black hole binary formation.

There are clearly still a lot of open questions, but it’s early days yet! With the many recent upgrades to the LIGO and Virgo detectors, we can hope for more binary neutron star detections soon — and every new signal brings us a wealth of information in this rapidly developing field.

Citation

“GW190425: Observation of a Compact Binary Coalescence with Total Mass ~ 3.4 M⊙,” B. P. Abbott et al 2020 ApJL 892 L3.
https://iopscience.iop.org/article/10.3847/2041-8213/ab75f5

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: “Cloudy Challenges to Exploring Exoplanet Atmospheres”

From AAS NOVA

18 March 2020
Susanna Kohler

Artist’s impression of a planet with water vapor in its atmosphere. Could clouds get in the way of us being able to detect atmospheric signatures? [ESA/Hubble, M. Kornmesser.]

One of our goals with the soon-to-launch James Webb Space Telescope (JWST) is to better characterize the atmospheres of exoplanets. But will clouds get in the way of our chances?

As a star’s light filters through a planet’s atmosphere on its way to Earth, the atmosphere absorbs certain wavelengths depending on its composition. [European Southern Observatory]

The Hunt for Water

When an exoplanet transits across the face of its host star, it presents us with a golden opportunity: with a sensitive enough telescope — like the upcoming JWST, scheduled to launch a year from now — we can explore the atmosphere of the planet as it filters the light from its host. Through this transmission spectroscopy, we can look for spectral features that indicate the presence of specific atoms and molecules in the planet’s atmospheric gas.

In the search for life beyond our solar system, surface liquid water is generally considered a necessary ingredient for a habitable world — so signatures of water vapor in planet atmospheres are a prime target for transmission spectroscopy. But any planet with abundant surface water is likely to have something else, too: clouds of liquid and ice condensing in its atmosphere.

A new study led by Thaddeus Komacek (The University of Chicago) explores whether these clouds will foil our chances of detecting water vapor in the atmospheres of terrestrial exoplanets.

Transmission spectra for planets with clouds (open markers) and without clouds (closed markers), for rotation periods of 8 (orange) and 16 (blue) days. Clouds significantly mute the spectral features, especially for long-period planets. JWST’s expected noise floor is ~20 ppm. [Komacek et al. 2020]

An Obstructed View

Komacek and collaborators examine the results of three-dimensional general circulation models of tidally locked planets orbiting M-dwarf stars. The authors generate simulated transit spectra for planets with different rotation rates, incoming starlight, surface pressure, radius, and more. They then explore whether the presence of clouds in the atmospheres of these planets will impede JWST’s ability to detect the water vapor features that arise from lower in the atmosphere.

The result? Bad news. The authors find that the presence of clouds significantly mutes spectral features; when clouds are present, JWST would typically need to observe 10–100 times more transits of the planet to be able to detect the water vapor features in its atmosphere.

This impact is especially strong for slower-rotating planets. The climate models show that planets with periods longer than about 12 days form significantly more cloud cover on their daysides, due to more water vapor being carried to high altitudes. This leads to even stronger muting of these planets’ spectral features.

Hope for the Future

NASA/ESA/CSA Webb Telescope annotated

The authors summarize with the disappointing conclusion that, with JWST, we’re going to have a tough time using atmospheric transmission spectroscopy to spot signs of surface water from the tantalizing targets of terrestrial planets orbiting in M-dwarf habitable zones.

There is still some hope, however. An extended mission lifetime for JWST, lowered signal-to-noise threshold for detection, or the discovery of a habitable-zone planet that JWST can monitor continuously could all push the spectral features above the telescope’s noise limit.

What’s more, since only the features from the atmosphere below the clouds will be affected, species that are well-mixed above the cloud deck may still be detectable. Even on cloudy worlds, we’re sure to have plenty to learn with JWST!

Citation

“Clouds will Likely Prevent the Detection of Water Vapor in JWST Transmission Spectra of Terrestrial Exoplanets,” Thaddeus D. Komacek et al 2020 ApJL 888 L20.

https://iopscience.iop.org/article/10.3847/2041-8213/ab6200

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: “A Star-Bursting Galaxy Born from the Collision of Dwarfs”

From AAS NOVA

16 March 2020
Susanna Kohler

This 2.5 x 2.5 arcminute image shows VCC 848, a compact dwarf galaxy that scientists think formed from the merger of two smaller galaxies. Click for the full view! [Adapted from Zhang et al. 2020]

What happens when the large-scale drama of a violent galaxy merger plays out on small scales for a pair of dwarf galaxies? New observations document the scene of a recent dwarf-galaxy collision.

Dramatic Encounters

The Antennae Galaxies are an example of a starburst galaxy with rapid star-formation activity driven by a recent merger. [NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration]

When two galaxies merge, the collision can have dramatic consequences — particularly if the galaxies are rich in gas. The gravitational interaction of galaxies oscillating during a merger drives shock waves through their gas. This can trigger bursts of star formation, launch jets from active galactic nuclei, and result in the eventual formation of a new galaxy with drastically different morphology than the original merging pair.

We’ve seen this drama play out on large scales between giant galaxies, but we know a lot less about what happens when dwarf galaxies collide. Dwarf galaxies are the most abundant type of galaxy in the universe, but they’re also very small and faint. This poses a significant challenge to finding and studying dwarfs — which means there’s a lot we don’t know about how the mergers of dwarf galaxies impact overall star formation and the shape of the new galaxy that forms in the collision.

Fortunately, we may now have an opportunity to learn more. In a recent publication led by Hong-Xin Zhang (University of Science and Technology of China), a team of scientists reports on the discovery of a small, compact galaxy formed by the collision of two dwarfs.

This g-band image of VCC 848 better shows the galaxy’s three extended shell-like structures (outlined with red arcs) surrounding the central body of stars. [Adapted from Zhang et al. 2020]

Feeling Shell-Shocked

VCC 848 is what’s known as a blue compact dwarf galaxy — a small galaxy that’s actively undergoing a burst of star formation. Located in the outskirts of the Virgo Cluster some 65 million light-years away, this little dwarf shows telltale signs of a recent merger: careful analysis reveals a complex set of three extended shell-like structures of stars around the bright stellar main body.

Shell structures — which, previously, had only been detected in larger galaxies — are known to be a signature of a recent minor or major galaxy merger; they are formed as the merger sends ripples through the galaxy and disrupts its structure. The detection of these shells in such a small galaxy provides evidence that we’re looking at the recent merger of two dwarfs.

A Flurry of Activity

Zhang and collaborators use their observations of VCC 848 — made with the MegaCam instrument on the Canada–France–Hawaii Telescope in Hawaii — to analyze the stars of the galaxy and learn more about its history.

CFHT MegaCam

CFHT Telescope, Maunakea, Hawaii, USA, at Maunakea, Hawaii, USA,4,207 m (13,802 ft) above sea level

They determine that the two dwarfs that collided were likely similar in mass to within a factor of a few, and the merger triggered a burst of star formation over the past billion years that was ~7–10 times higher than normal. This enhancement in star formation peaked near the center of the galaxy a few hundred million years ago, and it’s since declined; current star formation activity is primarily in VCC 848’s outer regions.

VCC 848 is just one of several blue compact dwarfs with hints of tidal shells that the authors uncovered in their survey, so there’s more data on the way! We have a lot more to learn about what happens when tiny galaxies collide.

Citation

“The Blue Compact Dwarf Galaxy VCC 848 Formed by Dwarf–Dwarf Merging,” Hong-Xin Zhang et al 2020 ApJL 891 L23.

https://iopscience.iop.org/article/10.3847/2041-8213/ab7825

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: “CHIME Detects Even More Repeating Bursts”

From AAS NOVA

13 March 2020
Susanna Kohler

Photograph of the CHIME radio telescope in British Columbia. [Andre Renard/Dunlap Institute/CHIME Collaboration] CHIME Canadian Hydrogen Intensity Mapping Experiment -A partnership between the University of British Columbia, the University of Toronto, McGill University, Yale and the National Research Council in British Columbia, at the Dominion Radio Astrophysical Observatory in Penticton, British Columbia, CA Altitude 545 m (1,788 ft)

In October of 2018, we wrote about a new project to study fast radio bursts (FRBs) — brief, energetic flashes of light from beyond our galaxy. At the time, we knew of about 30 FRB sources; the new project by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope in British Columbia promised to dramatically increase that number.

Now, a year and a half later, we can see the impressive progress made: CHIME has already detected around 700 bursts from FRB sources! Included among those is the collaboration’s latest announcement: nine new repeating sources.

Artist’s impression of a fast radio burst detection. [CSIRO/Andrew Howells]

A Question of Repetition

FRBs were first discovered more than a decade ago. These bright, short (around a millisecond) flashes of radio emission are a million times brighter than the brightest pulses from galactic pulsars, and they carry the signature of being produced at a great distance — something that has been further confirmed by the localization of several FRBs to faraway galaxies.

Despite all we’ve learned about FRBs, we still don’t know how they’re produced — though the list of theories has now grown large enough that there’s actually a living catalog of them. One particular puzzlement is that some FRBs have been observed to repeat, whereas others have produced only one detected flash.

Burst profiles for some of the new fast radio bursts detected by CHIME.[Fonseca et al. 2020]

Does this mean that the two types of FRBs — repeating and non-repeating — are produced in two different ways? Or in two different environments? Or is there another explanation for why some repeat and others don’t?

Clues from New Flashes

To answer these questions, our best bet is to find enough FRBs to be able to make statistical inferences — and CHIME is helping to build a large sample. In a new publication led by Emmanuel Fonseca (McGill University, Canada), the CHIME collaboration presents a collection of bursts from nine new repeating FRB sources, bringing the total number of known repeaters to 20.

What does this new sample tell us? So far, it’s confirmed previous assessments of the two populations of repeaters and non-repeaters:

1.The dispersion measures — a measure of the matter the signals travel through to reach us — for repeaters have the same distribution as those for non-repeaters, suggesting the two populations originate in similar local environments and have similar distributions in space.
2.The pulse widths are larger for repeaters than for non-repeaters, meaning that repeating sources have slightly longer-duration bursts. This may point to different emission mechanisms for the two types of bursts.
3.The Faraday rotation measures — a measure of the magnetized environment around the burst source — were obtained for two of the new repeaters, and they are lower than the surprisingly high rotation measure of FRB 121102, the first known repeater. We don’t have enough measurements to tell for certain yet, but it’s starting to look like FRB 121102 is an anomaly, and both repeaters and non-repeaters typically originate from more modestly magnetized environments.

Pulse widths for repeating (orange) vs. nonrepeating (blue) fast radio bursts show a distinct difference between the two populations. [Adapted from Fonseca et al. 2020]

We still have a lot to figure out, but as we build up FRB statistics with samples like these, we can start to rule out some of the many origin theories for fast radio bursts. It’s exciting to watch this field as it rapidly evolves!

Citation

“Nine New Repeating Fast Radio Burst Sources from CHIME/FRB,” E. Fonseca et al 2020 ApJL 891 L6.
https://iopscience.iop.org/article/10.3847/2041-8213/ab7208

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: ” Jet-Setting in the Infrared”

From AAS NOVA

11 March 2020
Tarini Konchady

Artist’s now iconic impression of an X-ray binary, in which a black hole accretes matter from a stellar companion. [NASA/CXC/M.Weiss]

An X-ray binary consists of a dense compact object that strips material off its stellar companion, producing X-rays in the process. These binaries are surrounded by radiating accretion disks of infalling material, but they also sometimes fling matter out in powerful relativistic jets. What can their infrared emission tell us about the speed of these jets?

Looking for Lorentz Factors

A schematic of a black hole X-ray binary highlighting the black hole, the accretion disk, and the jets. The expected IR emissions at different inclinations are also explained. [Saikia et al. 2019.]

Black hole X-ray binaries (BHXBs) are X-ray binaries where the accreting compact object is a black hole. The jets in BHXBs can approach the speed of light, and they can even give the false appearance of moving faster than light. This relativistic illusion is characterized by something called a Lorentz factor, Γ, which quantifies the distortions that come from moving at near light-speed. Unfortunately, the Lorentz factors of BHXB jets haven’t yet been well measured — which limits our understanding of how these speedy outflows may be launched, accelerated, and collimated as they are flung from the black holes.

Luckily we may have a new way of measuring these Lorentz factors: by looking at the BHXBs in infrared (IR) light. In a recent study, a group of scientists led by Payaswini Saikia (New York University Abu Dhabi, UAE) explored what a BHXB’s IR emission says about its structure and its jet’s Lorentz factor.

Transitions between the “on” (“hard”) to “off” (“soft”) states for the black hole X-ray binary GX 339–4. Multiple light curves are shown to emphasize the repeated transitions between the “on” and “off” states. Top: transition from “on” to “off” (“flux drop”), bottom: transition from “off” to “on” (“flux recovery”). [Saikia et al. 2019]

Eyes on IR Emissions

The IR emission from a BHXB can be largely attributed to two things: the accretion disk and synchrotron emission from the jets. Saikia and collaborators explored the infrared emission from 14 BHXBs, gauging how it changed when the BHXB jets turned “on”, emitting highly energetic X-rays, and “off”, emitting less energetic X-rays. Saika and collaborators argue that when the jets were “off”, any observed IR emission could be attributed to the disk; when they were “on”, the excess IR emission was due to the jets. This framework for looking at the BHXBs allowed the authors to isolate the jet emission and characterize the Lorentz factors for some of these outflows.

Inclined to Model

To determine the Lorentz factors, Saikia and collaborators used the IR flux ratio between the states when the jets were “on” and “off”. Here disk inclination comes into play: due to a combination of disk geometry and relativistic beaming of the jet, at high and low disk inclinations, the ratio between the “on” and “off” states ought to be high. For intermediate inclinations, the ratio should be low.

The modeled flux ratios between the “on” and “off” states versus disk inclination for different Lorentz factors, with observed BHXBs overplotted. [Saikia et al. 2019]

Using observed ratios and disk inclinations, Saikia and collaborators were able to model and constrain the Lorentz factors for nine BHXBs for the first time, finding a range of Γ = 1.3–3.5 — which means the jet bulk flows are moving at 64–96% of the speed of light. In addition, the authors put limits on the underlying distribution of BHXB Lorentz factors and could confidently attribute the variations in excess IR emission to disk inclination and jet direction.

With more observations of BHXBs across the spectrum, the techniques in this work should be more widely applicable and could help us better understand these highly energetic objects.

Citation

“Lorentz Factors of Compact Jets in Black Hole X-Ray Binaries,” Payaswini Saikia et al 2019 ApJ 887 21.
https://iopscience.iop.org/article/10.3847/1538-4357/ab4a09

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