From AAS NOVA: “Can Magnetic Fields Help Planetesimals Form?”

From AAS NOVA

15 February 2019
Kerry Hensley

This artist’s illustration shows material from the inner edge of a protoplanetary disk following magnetic field lines onto the surface of a young star. [NASA/JPL-Caltech]

Astronomers still don’t fully understand how planets form, especially ultra-dense, iron-rich planets like Mercury. How do trillions of tiny dust grains clump together to make pebbles, planetesimals, and eventually the cores of rocky planets?

Protoplanetary disks are composed of gas and dust, as this artist’s impression shows. How the tenuous gas–dust blend forms planets is still an open question. [NASA/JPL-Caltech]

Arrested (Dust) Development

When iron-rich dust grains in a protoplanetary disk collide, they stick together to form porous dust aggregates. Further collisions increase the size of aggregates, but only to a point; the growth of dust grains is limited by something called the bouncing barrier. The bouncing barrier kicks in when the once-fluffy dust aggregates become so compacted by collisions that incoming grains bounce off rather than stick. This limits the size of dust aggregates to just a couple of millimeters.

If the bouncing barrier stops dust grains from getting progressively larger, how do planets ever manage to form? One possibility is that the presence of an external magnetic field enhances the intrinsic magnetization of the iron in dust grains, which increases the attractive forces between them, making them “stickier.” If magnetic fields can help dust aggregates grow to centimeter size, other growth mechanisms like the streaming instability — a clumping mechanism caused by gas drag in a disk — can take over from there.

From simulations and observations, we expect the inner regions of protoplanetary disks to have strong magnetic fields — somewhere between 1 and 100 mT. How strongly do magnetic fields of this scale affect the growth of iron-rich dust aggregates?

Evolution of the chain length as the magnetic field is turned on and off. [Kruss & Wurm 2018]

Levitation and Magnetization

Maximilian Kruss and Gerhard Wurm (University of Duisburg-Essen, Germany) used laboratory experiments to explore the effects of magnetic fields on the bouncing barrier. Kruss and Wurm used a heat lamp to levitate micron-scale iron–silicate dust grains above a glass lens, which allows them to move and collide freely.

With no external magnetic field, the bouncing barrier stops the grains from growing larger than 2 mm. The authors find that for dust composed of equal amounts of iron and silicate, the bouncing barrier begins to shift when the external magnetic field strength reaches 2.2 mT. The size of the aggregates increases with increasing magnetic field strength, reaching 6 mm in length when the maximum field strength for the experimental setup (7 mT) is applied.

The minimum magnetic field necessary to shift the bouncing barrier as a function of iron mass fraction. Grains with an iron mass fraction below 0.33 didn’t form grains, while those with an iron mass fraction above 0.63 were too dense to be levitated. [Kruss & Wurm 2018]

The Missing Link?

The magnetic field strength necessary to shift the bouncing barrier could be even lower; if dust grains in protoplanetary disks are more iron-rich than those used in this experiment, the required field strength could be below 1 mT — well within the expected range for protoplanetary disks.

It isn’t yet known what proportion of dust grains can be expected to be enriched in iron, but this experiment clearly shows that the presence of an external magnetic field encourages iron-rich dust grains to grow larger.

If magnetic fields can suppress the bouncing barrier so that the grains grow large enough for the streaming instability to take over, we may be able to explain how planet formation gets going on the very smallest scales, especially for iron-rich planets like Mercury.

Citation

“Seeding the Formation of Mercurys: An Iron-sensitive Bouncing Barrier in Disk Magnetic Fields,” Maximilian Kruss and Gerhard Wurm 2018 ApJ 869 45.
https://iopscience.iop.org/article/10.3847/1538-4357/aaec78/meta

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

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From AAS NOVA: “Dwarf Galaxy or Giant Globular Cluster?”

From AAS NOVA

13 February 2019
Susanna Kohler

The recently discovered object FSR 1758 is the bright region pictured in the center of this image. Is this object a globular cluster or a dwarf galaxy? [Barbá et al. 2019]

You might think that we’d already discovered all the large clusters of stars orbiting our galaxy. Surprisingly, there are still detections to be made — such as the recently discovered cluster FSR 1758. But is this large group of stars an enormous globular cluster? Or a newly detected dwarf galaxy?

A New Cluster

A wide-field view (2.5° x 2.5°; top) and a zoomed-in view (18’ x 18’; bottom) centered on FSR 1758 from the DECaPS survey. [Barbá et al. 2019]

FSR 1758 was first discovered last year, hiding in the extremely dense bulge at the center of our galaxy. Objects in the galactic bulge are very difficult to detect: due to the high density of surrounding stars and dust, not much of the light of bulge objects makes it to us.

Based on the limited observations we initially had of FSR 1758 — and because clusters residing in the galactic bulge are typically expected to be of low mass — it was assumed that this object was a globular cluster: a spherical collection of stars that all formed around the same time from the same cloud and are bound by their mutual gravity.

But could the difficulty peering into the galactic bulge mean that we’re missing important details? Another theory posits that the part of FSR 1758 we’re seeing is instead the nucleus of a faint dwarf galaxy orbiting the Milky Way; we simply can’t see the fainter outer reaches of the galaxy.

So which is it: globular cluster or dwarf galaxy? A team of scientists led by Rodolfo Barbá (University of La Serena, Chile) have gathered observations to find out.

Revealing Details

Barbá and collaborators use three different sets of observations to explore FSR 1758: optical data from Gaia’s DR2 and the DECam Plane Survey, and near-infrared data from the VISTA Variables in the Via Lactea Extended Survey. From these data, the authors determine the cluster’s position and distance, as well as its size, metallicity, absolute magnitude, and proper motion.

ESA/GAIA satellite

Dark Energy Survey

Dark Energy Camera [DECam], built at FNAL

NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

Part of ESO’s Paranal Observatory, the VLT Survey Telescope (VISTA) observes the brilliantly clear skies above the Atacama Desert of Chile. It is the largest survey telescope in the world in visible light.
Credit: ESO/Y. Beletsky, with an elevation of 2,635 metres (8,645 ft) above sea level

Spatial distribution of stars that have common proper motion, suggesting that they belong to FSR 2758. Beyond the visible custer of stars at the center of the group, FSR 1758 appears to have a possible larger extended structure, suggesting it may be the nucleus of a dwarf galaxy. [Barbá et al. 2019]

FSR 1758 has a number of intriguing properties. If it’s a globular cluster, it’s one of the largest around our galaxy — and the part that we see is probably just the metaphorical tip of the iceberg, as much of its population is likely hidden by contamination and reddening due to its location in the galactic bulge. Furthermore, FSR 1758’s properties don’t fit known relationships for globular clusters, such as the correlation between size and metallicity.

Lastly, the authors find additional asymmetrically distributed stars further out in the field with motions and colors indicating that they also belong to FSR 1758. These suggest that the cluster may be more extended than originally thought and might have tidal tails. These signs support a picture in which FSR 1758 is the nucleus of a dwarf galaxy — which the authors tentatively name the Scorpius dwarf galaxy.

Though we still don’t have a definitive answer about FSR 1758’s nature, we can hope that future spectral data for its stars will settle the debate. And in the meantime, it’s good to be reminded that our galaxy is still hiding some surprising discoveries.

Citation

“A Sequoia in the Garden: FSR 1758—Dwarf Galaxy or Giant Globular Cluster?,” Rodolfo H. Barbá et al 2019 ApJL 870 L24.
https://iopscience.iop.org/article/10.3847/2041-8213/aaf811/meta

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: Tracking Motions of Local Galaxies”

From AAS NOVA

11 February 2019
Susanna Kohler

What’s with all the dots? You’re looking at the positions of thousands of stars observed by the Gaia mission in and around two nearby galaxies: Andromeda (Messier 31) and Triangulum (Messier 33). In a new study led by Roeland van der Marel (Space Telescope Science Institute and Johns Hopkins University), a team of scientists used stellar proper-motion observations from Gaia’s second data release, DR2, to track the 3D movement of these two galaxies. The precision of the Gaia data allowed the authors to update our best estimates about how these galaxies are interacting with each other and with the Milky Way, both now and in the future. Van der Marel and collaborators find that the Triangulum galaxy is likely on its very first infall into Andromeda, suggesting it’s not to blame for Andromeda’s previously formed tidal warps and tails. And Andromeda itself appears to be on a less direct path toward us than we’d previously thought, suggesting the collision between Andromeda and the Milky Way may be only glancing, and it won’t occur for another 4.5 billion years. For more on the authors’ conclusions, check out the article below.

Milkdromeda -Andromeda on the left-Earth’s night sky in 3.75 billion years-NASA

Citation

“First Gaia Dynamics of the Andromeda System: DR2 Proper Motions, Orbits, and Rotation of M31 and M33,” Roeland P. van der Marel et al 2019 ApJ 872 24.
https://iopscience.iop.org/article/10.3847/1538-4357/ab001b/meta

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: “When Stellar and Black-Hole Binaries Meet”

From AAS NOVA

6 February 2019
Susanna Kohler

Artist’s impression of supermassive black holes that have formed a binary as they’ve sunk to the center of their merged galaxies. What happens when such a black-hole binary encounters a stellar binary? [NAOJ]

You might think that a passing star getting ripped apart by a supermassive black hole sounds like more than enough drama. But a new study takes this picture a step further, exploring what happens when a stellar binary interacts with a pair of supermassive black holes.

Illustration of a tidal disruption event, in which a star is torn apart by a black hole’s gravitational forces and its material falls onto the black hole. [NASA/CXC/M. Weiss]

Stellar Destruction

First suggested in the 1970s, the theory of tidal disruption events (TDEs) has since been supported by the discovery of many dozens of observed candidates. These spectacular eruptions often arise from previously dark regions, and they’re thought to indicate the accretion of debris after a star is torn apart by a lurking supermassive black hole.

But this simple model can’t adequately explain all of the disruption-like signals we’ve observed. Could more complex interactions be at play too? Two clues support this possibility:

1.A large fraction of stars exist in binary pairs.
2.Supermassive black holes can also form binaries, when their host galaxies merge.

With this in mind, a team of scientists led by Eric Coughlin (an Einstein Postdoctoral Fellow at UC Berkeley at the time) has explored a more complicated tidal disruption scenario: that in which a stellar binary interacts with a supermassive black-hole binary.

In some of the authors’ simulated encounters, both stars are tidally disrupted, but with a delay between the two disruptions. This plot shows the distribution of times (measured in number of orbits of the black holes) for the delay between the two disruptions. [Adapted from Coughlin et al. 2018]

Simulating Paired Encounters

By performing hundreds of thousands of simulations of the gravitational interactions between a stellar binary and a supermassive black-hole binary, Coughlin and collaborators conclude that there are a number of possible outcomes.

Most encounters result either in the entire intact stellar binary being ejected from the system, or in the two stars being ejected one after the other, after the stellar binary is broken up. But several more interesting outcomes are also possible:

Hills capture, in which one star is ejected and the other is captured into orbit around one of the black holes.
Single and double TDEs, in which either one or both stars are torn apart and their material accretes onto the black-hole binary.
Stellar mergers, in which the two stars lose angular momentum and merge with each other as a result of interacting with and being ejected by the black-hole binary.

Telltale Signals

Coughlin and collaborators point out that these exotic possibilities are interesting because they create distinctive signals — some of which are consistent with signals that we’ve observed, and some of which we can hope to look for in the future.

Artist’s impression of a hypervelocity star escaping a galaxy. [ESO]

A double TDE, for instance, could nicely account for the very bright, double-peaked transient known as ASASSN-15lh.

The Resurgence of the Brightest Supernova, ASASSN-15lh – Sky & Telescope

The accelerated inspiral of a stellar binary — after having been flung from its galaxy by the supermassive black-hole binary — could account for some calcium-rich transient signals we’ve spotted. And two members of a stellar binary, individually ejected from a galaxy, may later be detectable as hypervelocity stars that have similar spectroscopic properties despite being thousands of light-years apart.

The intriguingly broad range of outcomes that result from the meeting of stellar and black-hole binaries demonstrates that these possibilities are worth exploring further. It would seem that in some cases, this extra drama may be just what we’ve been missing.

Citation

“Stellar Binaries Incident on Supermassive Black Hole Binaries: Implications for Double Tidal Disruption Events, Calcium-rich Transients, and Hypervelocity Stars,” Eric R. Coughlin et al 2018 ApJL 863 L24. https://iopscience.iop.org/article/10.3847/2041-8213/aad7bd/meta

Related Journal Articles

The Fastest Unbound Stars in the Universe doi: 10.1088/0004-637X/806/1/124
A Milliparsec Supermassive Black Hole Binary Candidate in the Galaxy SDSS J120136.02+300305.5 doi: 10.1088/0004-637X/786/2/103
Relaxation near Supermassive Black Holes Driven by Nuclear Spiral Arms: Anisotropic Hypervelocity Stars, S-stars, and Tidal Disruption Events doi: 10.3847/1538-4357/aa7f29
Tidal Disruption of Stellar Objects by Hard Supermassive Black Hole Binaries doi: 10.1086/527412
Boosted Tidal Disruption by Massive Black Hole Binaries During Galaxy Mergers from the View of N-Body Simulation doi: 10.3847/1538-4357/834/2/195
Periodic Accretion-powered Flares from Colliding EMRIs as TDE Imposters doi: 10.3847/1538-4357/aa7a16

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: “Update on the Search for Planets with TESS”

From AAS NOVA

1 February 2019
Kerry Hensley

This artist’s conception shows the Transiting Exoplanet Survey Satellite (TESS), which travels in a never-before-used 2:1 lunar resonance orbit. [NASA’s Goddard Space Flight Center]

What’s the news coming from NASA’s newest planet hunter, the Transiting Exoplanet Survey Satellite (TESS)? Launched in April 2018, TESS is expected to discover tens of thousands of exoplanets orbiting the nearest and brightest stars. Now that observations are underway, what exciting discoveries have been made? Read on for an update from just a few of the latest TESS studies published in AAS journals.

Raw and corrected TESS light curves showing the five transits of π Men c. The bottom panel shows the folded light curve. [Huang et al. 2018]

Around a Far Sun-like Star

Within the first six months of TESS’s launch, a team led by Chelsea Huang (MIT) reported the first official discovery of a planet by TESS — a super-Earth orbiting the Sun-like star π Men.

At a distance of about 59 light-years, π Men is dimly visible to the naked eye near the south celestial pole. Over a decade ago, the Anglo-Australian Planet Search discovered a giant planet — π Men b — orbiting the star every 5.7 years. What TESS’s high-cadence observations revealed was a second, smaller planet orbiting the star every 6.27 days. By combining TESS photometry with precise radial-velocity measurements, Huang and collaborators determined the parameters of the planetary system, including the mass and radius of the newly discovered π Men c.

With a radius twice that of Earth and a mass nearly five times greater, π Men c isn’t an entirely “rocky” planet like the terrestrial planets in our solar system. Instead, it probably has a hydrogen-helium or water-methane envelope. We hope to learn more from future observations with the James Webb Space Telescope, Gaia, or even TESS itself!

Physical parameters of LHS 3844 b compared to other known exoplanets. [Vanderspek et al. 2019]

Another First for TESS

TESS won’t only find planets around Sun-like stars. Thanks to its redder observing bandpass (600–1000 nm, as opposed to Kepler’s 420–900 nm), TESS is especially sensitive to planets orbiting the small, reddish stars called M dwarfs. Because M dwarfs are so small and cool, planets in their habitable zones complete orbits in days rather than years, making them great observing targets.

A team led by Roland Vanderspek (MIT) analyzed data from the first month of TESS’s science operations, leading to the discovery of the first M-dwarf-orbiting planet detected by TESS. The planet, dubbed LHS 3844 b, has a radius 32% larger than Earth’s and orbits its small parent star at a distance of just 0.006 AU — swinging around LHS 3844 in just 11 hours. Although it’s unclear whether or not LHS 3844 b will have an atmosphere — it orbits so close to its host star that any atmosphere may have been torn away by stellar winds long ago — it’s definitely worth investigating the first (of many!) M-dwarf planets discovered by TESS.

Seeking Confirmation

As always with new detections, astronomers are rushing to confirm TESS’s discoveries with other telescopes and instruments. HD 202772A b is the first TESS hot Jupiter to have been confirmed by follow-up observations. In a recent study led by Songhu Wang (Yale University), the authors detail radial-velocity measurements made with the CHIRON, HARPS, and TRES spectrographs that confirm the planetary nature of HD 202772A b.

CHIRON spectrogaph at CTIO SMARTS 1.5-meter telescope at La Serena, Chile, Altitude 2,207 m (7,241 ft)

ESO/HARPS at La Silla

ESO 3.6m telescope & HARPS at Cerro LaSilla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

TILLINGHAST REFLECTOR ECHELLE SPECTROGRAPH (TRES) on the 1.5-meter Tillinghast telescope at the Smithsonian Astrophysical Observatory’s Fred L. Whipple Observatory, outside Tucson, AZ, USA

This inflated gas giant is orbiting a quickly evolving star that’s one of the brightest and most massive stars known to host a hot Jupiter. As a result, HD 202772A b is one of the most strongly irradiated hot Jupiters currently known.

Light Curves All Around

Want a chance to explore some TESS data on your own? Ryan Oelkers and Keivan Stassun (Vanderbilt University) have extracted and made available light curves from all the stars in TESS Sector 1, which is home to all three of the stars discussed above. Their website provides both raw and cleaned (systematic trends removed) light curves for each star, as well as information about each target (mass, luminosity class, magnitude, etc.).

As more TESS data rolls in, Oelkers and Stassun plan to update their website with the latest light curves for each observing sector. Happy planet hunting!

Citation

“TESS Discovery of a Transiting Super-Earth in the pi Mensae System,” Chelsea X. Huang et al. 2018 ApJL 868 L39. https://iopscience.iop.org/article/10.3847/2041-8213/aaef91/meta

“TESS Discovery of an Ultra-short-period Planet Around the Nearby M Dwarf LHS 3844,” Roland Vanderspek et al. 2019 ApJL 871 L24. doi:10.3847/2041-8213/aafb7a

“HD 202772A b: A Transiting Hot Jupiter around a Bright, Mildly Evolved Star in a Visual Binary Discovered by TESS,” Songhu Wang et al 2019 AJ 157 51. doi:10.3847/1538-3881/aaf1b7

“Light Curves for All Stars Observed in TESS Full-frame Images: Sector 1 and Beyond,” Ryan J. Oelkers and Keivan G. Stassun 2019, Res. Notes AAS 3 1. doi:10.3847/2515-5172/aafc34

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 Societyis 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 Hunt for Enormous Early Stars”

From AAS NOVA

30 January 2019
Susanna Kohler

Artist’s illustration of a primordial galaxy dominated by the supermassive black hole in its center. How did these earliest quasars form? [NASA/ESA/ESO/Wolfram Freudling et al. (STECF)]

The collapse of enormous stars in our early universe may have given birth to the first supermassive black holes. But will we be able to find these early, giant stars to test this theory?

Considering Giant Seeds

An unsolved mystery of our universe is how the very first quasars — powerful, accreting supermassive black holes — formed. Based on our observations, these earliest quasars had less than a billion years to grow to a billion solar masses. So what seeded these monsters, jump-starting them on their way to this tremendous size?

One theory is that they resulted from the direct collapse of enormous early stars, known as supermassive primordial stars. These giant stars are a little different from typical Population III stars, the first generation of stars theorized to form from the metal-poor gas of our early universe.

While ordinary Pop III stars cap out at around 1,000 solar masses, supermassive primordial stars form in primordial halos that are — by one means or another — prevented from collapsing into stars until after they reach masses of 107-108 solar masses. According to models, these halos then undergo sudden cooling and catastrophic collapse, resulting in rapidly accreting stars that are much larger than typical Pop III stars.

An accretion disk at 0.625 Myr in the authors’ simulations of forming supermassive primordial stars. [Surace et al. 2018]

Hide and Seek

The theory of supermassive primordial stars suggests that these giants could undergo gravitational instabilities and directly collapse into black holes, seeding the earliest quasars in our universe. So how do we test this picture?

The first step is to find observational evidence of supermassive primordial stars! Unfortunately, there’s a catch: these stars would generally evolve as cool, red hypergiants, possibly shrouded by the dense flows of gas accreting onto them. Do we stand a chance of being able to spot these giants with upcoming technology? Or will they remain hidden to us?

In a recent study led by Marco Surace (University of Portsmouth, UK), a team of scientists have modeled supermassive primordial stars to answer these questions.

Near-infared AB magnitudes for two primordial stars formed in the authors’ simulations (solid and dashed lines), shown in the JWST NIRCam bands (different colors). JWST NIRCam’s predicted detection limits are at ~31.5. [Surace et al. 2018]

Exploring Visibility

Surace and collaborators used simulations of a rapidly cooled halo to create their supermassive primordial stars. They then calculated what the spectra of these stars would look like to telescopes near Earth, such as the upcoming James Webb Space Telescope (JWST), Euclid, and Wide-Field Infrared Space Telescope (WFIRST).

NASA/ESA/CSA Webb Telescope annotated

ESA/Euclid spacecraft

NASA WFIRST

The authors find that the accretion envelopes surrounding these stars may be helpful rather than detrimental: rather than obscuring the stars, this gas can enhance the stars’ visibility by reprocessing the short-wavelength radiation from the star into photons that we can detect with our near-infrared telescopes.

Surace and collaborators show that some of these supermassive primordial stars will, indeed, be visible to JWST out to redshifts of z ~ 20, and they may even be detectable by the wide-field Euclid and WFIRST missions if some of these stars are modestly gravitationally lensed by foreground objects. This is a promising result, leaving us with some hope that the next generation of telescopes will help us to finally address the mystery of how the first quasars formed in our universe.

Citation

“On the Detection of Supermassive Primordial Stars,” Marco Surace et al 2018 ApJL 869 L39. https://iopscience.iop.org/article/10.3847/2041-8213/aaf80d/meta

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 Societyis 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: “Taking Note of Molecules in Space”

From AAS NOVA

23 January 2019
Susanna Kohler

Artist’s impression of the molecules found in a hot molecular core in the Large Magellanic Cloud. [FRIS/Tohoku University; ESO/M. Kornmesser; NASA/ESA/S. Beckwith (STScI)/HUDF Team; Hubble Heritage Team (AURA/STScI)/HEI]

What do methylidyne, cyanamide, vinyl alcohol, and rugbyballene all have in common? They’re all molecules that have been detected in space — and they’re all included in a recent census of our universe’s chemical makeup.

Cumulative number of known interstellar molecules over time. Commissioning dates of major contributing facilities are noted with arrows. [McGuire 2018]

Looking For Complexity

Since the first detection of methylidyne (CH) in the interstellar medium in the 1930s, scientists have been on the lookout for the many molecules — groups of two or more atoms held together by chemical bonds — they know must exist beyond our own planet.

Observations of molecules can help us to understand the chemical evolution of the interstellar medium, the formation of planets, and the physical conditions and processes of the universe around us. But molecules produce complex spectral features that are difficult to correctly attribute, making definitive observations of specific molecules challenging — which means that we’re still only just beginning to understand the chemical composition of our universe.

In a recent publication, scientist Brett McGuire (Hubble Fellow of the National Radio Astronomy Observatory, Harvard-Smithsonian Center for Astrophysics) provides an overall summary of observed interstellar, circumstellar, extragalactic, protoplanetary-disk, and exoplanetary molecules. This publication marks the first “living paper” published in AAS journals — a paper that will continue to be updated over years to come as our observations amass and our understanding of the universe around us grows.

Location, Location, Location

Percentage of known molecules that were detected for the first time in carbon stars, dark clouds, LOS clouds, and SFRs. [McGuire 2018]

McGuire’s census, which includes observations from dozens of facilities across the electromagnetic spectrum, identifies the molecules that have been discovered in various locations.

-Interstellar and circumstellar molecules
All of the molecules that we’ve detected beyond Earth have been spotted in the interstellar or circumstellar medium in our galaxy. In total, 204 different molecules have been identified, ranging in size from two atoms (like methylidyne) to 70 atoms (like rugbyballene, C70).
-Extragalactic molecules
67 of the known interstellar and circumstellar molecules (33%) have also been detected in observations of external galaxies.
-Protoplanetary-disk molecules
Only 36 of the known interstellar and circumstellar molecules have been found in protoplanetary disks, in part due to the harsh physical environment around young stars and the challenge of maintaining gas-phase molecules under these conditions.
-Exoplanetary molecules
Just five molecules — CO, TiO, H2O, CO2, and CH4 — have been found in exoplanetary atmospheres thus far.

Periodic table of the elements color-coded by number of detected species containing each element. [McGuire 2018]

Analyzing Detections

What can we learn from this census? It’s interesting to note that the entirety of the known molecular inventory is constructed from just 16 of the 118 known elements. As for where they form, more than 90% of the detected molecules were made in a carbon star, a dark cloud, a diffuse/translucent/dense cloud that lies between us and a background source, or a star-forming region.

McGuire points out that our detection of new molecules has progressed at a fairly constant rate since the 1960s. Nonetheless, there are many prospects for future advances — such as the upcoming James Webb Space Telescope’s ability to study exoplanet atmospheres in greater detail. Be sure to check back with this living paper in the future to see how our knowledge of the universe’s chemistry changes!

Citation

“2018 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules,” Brett A. McGuire 2018 ApJS 239 17.
https://iopscience.iop.org/article/10.3847/1538-4365/aae5d2/meta

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 Societyis 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: “Can Blue Stragglers Be Used to Tell Time?”

From AAS NOVA

18 January 2019
Kerry Hensley

This Hubble image of the center of globular cluster NGC 6362 shows an impressive spectrum of stellar colors. Particularly interesting are the bright blue stars in this image, which should have left the main sequence already. [ESA/Hubble & NASA]

NASA/ESA Hubble Telescope

As stars age, they gradually lose angular momentum and spin more slowly. This process occurs so predictably for normal, solar-type stars that we can treat them as cosmic clocks using a technique called gyrochronology. But could the same strategy be applied to an unusual type of main-sequence star called blue stragglers?

The blue stragglers in globular cluster M55 are easily identified in a color-magnitude diagram (cyan circle). [Adapted from B.J. Mochejska, J. Kaluzny (CAMK), 1-m Swope Telescope]

Carnegie Institution Swope telescope at Las Campanas, Chile, 100 kilometres (62 mi) northeast of the city of La Serena. near the north end of a 7 km (4.3 mi) long mountain ridge. Cerro Las Campanas, near the southern end and over 2,500 m (8,200 ft) high, at Las Campanas, Chile

Stars That Linger

Based on their mass and age, we would expect blue-straggler stars to have exhausted their core hydrogen and evolved off the main sequence already. Instead, these oddball objects have managed to loiter long past their time by gaining mass — either by siphoning it from a binary companion star or by consuming another star altogether through a collision.

Blue stragglers are easy to pick out in a star cluster, where they are bluer and brighter than the main-sequence turnoff point on a color–magnitude diagram. Post-mass-transfer stars like blue stragglers also exist outside of clusters, where they can be identified by abnormal chemical abundances or the presence of a white-dwarf companion.

To better understand post-mass-transfer stars like blue stragglers, we would like to know how long ago they accreted mass from their companions. We know that these stars experience a jump in spin rate immediately after mass accretion — but what happens after that point? Do they undergo predictable spin-down like normal, solar-type stars, allowing us to use gyrochronology to determine their post-mass-transfer ages?

Going for a Spin

To explore this question, a team led by Emily Leiner (Northwestern University) studied the rotation-rate slowdown of blue-straggler and other post-mass-transfer stars. Leiner and collaborators compiled a sample of post-mass-transfer binaries of varying ages by selecting stars with spectral types F, G, and K with white-dwarf companions in close orbits. Here, age doesn’t refer to time since the star formed, but rather time since the mass transfer took place.

The very young systems were selected by direct detection of the white-dwarf companion in the extreme ultraviolet. In older systems, the white-dwarf companion is too cool to be visible but can be detected by gravitational microlensing.

Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835

Leiner and collaborators combined the age estimates from white-dwarf cooling models with rotation periods derived from photometric or spectral measurements. The authors found that the stars spin faster after the mass transfer, then steadily slow down after about 100 million years since the mass transfer have passed.

Ages and rotation periods for this sample of post-mass-transfer systems. The purple and gold lines are single-star models, while the red and cyan lines are collisional-product models.

A Model for Spin-down

To understand the physics of post-mass-transfer star spin-down, the authors compared the observed spin-down to models for single solar-type stars and stellar collision products. They found that the models for the stellar collision products showed distinctly different behavior; the collision products maintained their rapid rotation rates far longer than the single stars or post-mass-transfer stars.

Leiner and collaborators attributed this to the possibility that the collision products don’t form normal stellar magnetic fields and can’t lose angular momentum through magnetic braking the way single main-sequence stars do.

On the other hand, the models for spin-down of single solar-type stars matched the blue-straggler observations well. This suggests that blue stragglers and other post-mass-transfer stars have a promising future as gyrochronometers!

Citation

“Observations of Spin-down in Post-mass-transfer Stars and the Possibility for Blue Straggler Gyrochronology,” Emily Leiner, Robert D. Mathieu, Natalie M. Gosnell, and Alison Sills 2018 ApJL 869 L29. http://iopscience.iop.org/article/10.3847/2041-8213/aaf4ed/meta

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 Societyis 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 Fast Radio Bursts from Flaring Magnetars?”

From AAS NOVA

16 January 2019
Susanna Kohler

Artist’s impression of a magnetized neutron star. Could these objects be responsible for fast radio bursts? [ESO/L. Calçada]

Could the mysterious fast-radio-burst signal FRB 121102 be emitted from a flaring, strongly magnetic neutron star? In a new study, two scientists explore the evidence.

Mysterious Signals

More than a decade ago, a powerful burst of coherent radio emission lasting only a few milliseconds mystified astronomers. The dispersion of the signal — the delay of its component frequencies by different amounts of time, depending on the wavelength — indicated that this pulse came from beyond our galaxy. But what was it?

Artist’s impression of a fast radio burst observed by the Parkes Radio Telescope. [Swinburne Astronomy Productions]

Today, we’ve detected many dozens of these odd fast radio bursts (FRBs), including two sources that appear to repeat. The repetition has allowed scientists to learn more about the best studied of these, FRB 121102: this burst has been localized to a star-forming dwarf galaxy that lies three billion light-years from Earth. Upon closer inspection of the region, scientists found that in addition to FRB 121102’s repeating bursts, a dim and steady source of radio emission lies nearby.

These accumulating clues all address a broad mystery: what object could be responsible for the bursting and steady emission we observe? What is the source of an FRB?

A Magnetized Solution

Two scientists at Columbia University, former graduate student Ben Margalit (now a NASA Einstein Postdoctoral Fellow at UC Berkeley) and advisor Brian Metzger, recently proposed an explanation for FRB 121102: perhaps this source is a young, flaring, highly magnetized neutron star that is embedded in a decades-old supernova remnant.

Neutron stars are dense cores left behind after a star’s spectacular death in a supernova or a gamma-ray burst. In particular, a magnetar is a type of neutron star with an extremely powerful magnetic field that causes flares and bursts early in the object’s life. Such flares from a distant young magnetar, Margalit and Metzger argue, could explain the FRB signals we observe.

Schematic of the authors’ model, in which a young, flaring magnetar is embedded in a magnetized nebula trapped behind the shell of supernova ejecta. Electrons in the magnetized nebula emit the persistent radio radiation, and the nebula leaves an imprint on the burst emission — which originates from the magnetar — as well. [Margalit & Metzger 2018]

In addition, the newly-formed magnetar may rest in the center of a compact, magnetized nebula that’s trapped behind the expanding shell of supernova ejecta created when the magnetar was born. This magnetized nebula could power persistent radio emission like what we observed near FRB 121102.

As a final piece of the puzzle, the authors point out that the identified home for FRB 121102 is consistent with the type of galaxy in which magnetars often form. Such small galaxies with high specific star formation rates are known to preferentially host long gamma-ray bursts and superluminous supernovae, events in which magnetars are born.

Predicting the Future

To test their theory, Margalit and Metzger develop a detailed time-dependent model of an expanding, magnetized electron-ion nebula inflated by a flaring, young magnetar. They then show that the energetics of their model beautifully match the properties of both the bursting and persistent radio emission from FRB 121102.

Does this mean the mystery’s solved? We can’t say for sure yet — but the authors make specific predictions for future observations of FRB 121102 that will provide a robust test of their model. In addition, the very recent discovery of a second repeating burst, FRB 180814.J0422+73, will hopefully allow us to further explore these mysterious sources and confirm their origin.

Citation

“A Concordance Picture of FRB 121102 as a Flaring Magnetar Embedded in a Magnetized Ion–Electron Wind Nebula,” Ben Margalit and Brian D. Metzger 2018 ApJL 868 L4.
http://iopscience.iop.org/article/10.3847/2041-8213/aaedad/meta

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 Societyis 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: Star Formation in a Long Tail”

From AAS NOVA

The distant Coma Cluster contains over a thousand identified galaxies.

Coma cluster via NASA/ESA Hubble

The rapid motions of such galaxies in large clusters can drive a process known as ram-pressure stripping, in which gas is torn away from the galaxies as the galaxies speed through the intercluster medium. In the spectacular composite image shown above — created by combining false-color Hubble imaging with Hα data from the ground-based Subaru Suprime-Cam — a remarkable 200,000-light-year-long and extremely narrow (only 5,000 light-years wide) ram-pressure-stripped tail of gas can be seen to stream out from the center of the spiral galaxy D100 in the Coma Cluster.

NAOJ Subaru Hyper Suprime-Cam

NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level

In a new study led by William Cramer (Yale University), a team of scientists has now used deep Hubble imaging to explore this tail in greater detail, particularly studying young stars that have formed in the tail. For more information and beautiful images, check out the paper below!

Citation

“Spectacular Hubble Space Telescope Observations of the Coma Galaxy D100 and Star Formation in Its Ram Pressure–stripped Tail,” W. J. Cramer et al 2019 ApJ 870 63. http://iopscience.iop.org/article/10.3847/1538-4357/aaefff/meta

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 Societyis 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