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double neutron star

More than forty years after the first discovery of a double neutron star, we still haven’t found many others — but a new survey is working to change that.

The Hunt for Pairs

Hulse-Taylor binary

The observed shift in the Hulse-Taylor binary’s orbital period over time as it loses energy to gravitational-wave emission. [Weisberg & Taylor, 2004]

In 1974, Russell Hulse and Joseph Taylor discovered the first double neutron star: two compact objects locked in a close orbit about each other. Hulse and Taylor’s measurements of this binary’s decaying orbit over subsequent years led to a Nobel prize — and the first clear evidence of gravitational waves carrying energy and angular momentum away from massive binaries.

Forty years later, we have since confirmed the existence of gravitational waves directly with the Laser Interferometer Gravitational-Wave Observatory (LIGO). Nonetheless, finding and studying pre-merger neutron-star binaries remains a top priority. Observing such systems before they merge reveals crucial information about late-stage stellar evolution, binary interactions, and the types of gravitational-wave signals we expect to find with current and future observatories.

Since the Hulse-Taylor binary, we’ve found a total of 16 additional double neutron-star systems — which represents only a tiny fraction of the more than 2,600 pulsars currently known. Recently, however, a large number of pulsar surveys are turning their eyes toward the sky, with a focus on finding more double neutron stars — and at least one of them has had success.

pulse profile

The pulse profile for PSR J1411+2551 at 327 MHz. [Martinez et al. 2017]

A Low-Mass Double

Conducted with the 1,000-foot Arecibo radio telescope in Puerto Rico, the Arecibo 327 MHz Drift Pulsar Survey has enabled the recent discovery of dozens of pulsars and transients. Among them, as reported by Jose Martinez (Max Planck Institute for Radio Astronomy) and coauthors in a recent publication, is PSR J1411+2551: a new double neutron star with one of the lowest masses ever measured for such a system.

Through meticulous observations over the span of 2.5 years, Martinez and collaborators were able to obtain a number of useful measurements for the system, including the pulsar’s period (62 ms), the period of the binary (2.62 days), and the system’s eccentricity (e = 0.17).

In addition, the team measured the rate of advance of periastron of the system, allowing them to estimate the total mass of the system: M = ~2.54 solar masses. This mass, combined with the eccentricity of the orbit, demonstrate that the companion of the pulsar in PSR J1411+2551 is almost certainly a neutron star — and the system is one of the lightest known to date, even including the double neutron-star merger that was observed by LIGO in August this past year.

Constraining Stellar Physics

recycled pulsar

Based on its measured properties, PSR J1411+2551 is most likely a recycled pulsar in a double neutron-star system. [Martinez et al. 2017]

The intriguing orbital properties and low mass of PSR J1411+2551 have already allowed the authors to explore a number of constraints to stellar evolution models, including narrowing the possible equations of state for neutron stars that could produce such a system. These constraints will be interesting to compare to constraints from LIGO and Virgo in the future, as more merging neutron-star systems are observed.

Meanwhile, our best bet for obtaining further constraints is to continue searching for more pre-merger double neutron-star systems like the Hulse-Taylor binary and PSR J1411+2551. Let the hunt continue!

Citation

J. G. Martinez et al 2017 ApJL 851 L29. doi:10.3847/2041-8213/aa9d87

star formation near Sgr A*

Is it possible to form stars in the immediate vicinity of the hostile supermassive black hole at the center of our galaxy? New evidence suggests that nature has found a way.

infrared galactic center

Infrared view of the central 300 light-years of our galaxy. [Hubble: NASA/ESA/Q.D. Wang; Spitzer: NASA/JPL/S. Stolovy]

Too Hostile for Stellar Birth?

Around Sgr A*, the supermassive black hole lurking at the Milky Way’s center, lies a population of ~200 massive, young, bright stars. Their very tight orbits around the black hole pose a mystery: did these intrepid stars somehow manage to form in situ, or did they instead migrate to their current locations from further out?

For a star to be born out of a molecular cloud, the self-gravity of the cloud clump must be stronger than the other forces it’s subject to. Close to a supermassive black hole, the brutal tidal forces of the black hole dominate over all else. For this reason, it was thought that stars couldn’t form in the hostile environment near a supermassive black hole — until clues came along suggesting otherwise.

Science as an Iterative Process

proplyds

Very Large Array observations of candidate photoevaporative protoplanetary disks discovered in 2015. [Yusef-Zadeh et al. 2015]

Longtime AAS Nova readers might recall that one of our very first highlights on the site, back in August of 2015, was of a study led by Farhad Yusef-Zadeh of Northwestern University. In this study, the authors presented observations of candidate “proplyds” — photoevaporative protoplanetary disks suggestive of star formation — within a few light-years of the galactic center.

While these observations seemed to indicate that stars might, even now, be actively forming near Sgr A*, they weren’t conclusive evidence. Follow-up observations of these and other signs of possible star formation were hindered by the challenges of observing the distant and crowded galactic center.

Two and a half years later, Yusef-Zadeh and collaborators are back — now aided by high-resolution and high-sensitivity observations of the galactic center made with the Atacama Large Millimeter-Submillimeter Array (ALMA). And this time, they consider what they found to be conclusive.

bipolar outflow in galactic center

ALMA observations of BP1, one of 11 bipolar outflows — signatures of star formation — discovered within the central few light-years of our galaxy. BP1 is shown in context at left and zoomed in at right; click for a closer look. [Yusef-Zadeh et al. 2017]

Unambiguous Signatures

The authors’ deep ALMA observations of the galactic center revealed the presence of 11 bipolar outflows within a few light-years of Sgr A*. These outflows appear as approaching and receding lobes of dense gas that were likely swept up by the jets created as stars were formed within the last ~10,000 years. Yusef-Zadeh and collaborators argue that the bipolar outflows are “unambiguous signatures of young protostars.”

Based on these sources, the authors calculate an approximate rate of star formation of ~5 x 10-4 solar masses per year in this region. This is large enough that such low-mass star formation over the past few billion years could be a significant contributor to the stellar mass budget in the galactic center.

bipolar outflow locations

Locations and orientations of the 11 bipolar outflows found. [Yusef-Zadeh et al. 2017]

The question of how these stars were able to form so near the black hole remains open. Yusef-Zadeh and collaborators suggest the possibility of events that compress the host cloud, creating star-forming condensations with enough self-gravity to resist tidal disruption by Sgr A*’s strong gravitational forces.

To verify this picture, the next step is to build a detailed census of low-mass star formation at the galactic center. We’re looking forward to seeing how this field has progressed by the next time we report on it!

Citation

F. Yusef-Zadeh et al 2017 ApJL 850 L30. doi:10.3847/2041-8213/aa96a2

'Oumuamua

What’s the news coming from the research world on the interstellar asteroid visitor, asteroid 1I/’Oumuamua? Read on for an update from a few of the latest studies.

What is ‘Oumuamua?

In late October 2017, the discovery of minor planet 1I/’Oumuamua was announced. This body — which researchers first labeled as a comet and later revised to an asteroid — had just zipped around the Sun and was already in the process of speeding away when we trained our telescopes on it. Its trajectory, however, marked it as being a visitor from outside our solar system: the first known visitor of its kind.

Since ‘Oumuamua’s discovery, scientists have been gathering as many observations of this body as possible before it vanishes into the distance. Simultaneously, theorists have leapt at the opportunity to explain its presence and the implications its passage has on our understanding of our surroundings. Here we present just a few of the latest studies that have been published on this first detected interstellar asteroid — including several timely studies published in our new journal, Research Notes of the AAS.

'Oumuamua velocity

The galactic velocity of ‘Oumuamua does not coincide with any of the nearest stars to us. [Mamajek 2018]

Where Did ‘Oumuamua Come From?

Are we sure ‘Oumuamua didn’t originate in our solar system and get scattered into a weird orbit? Jason Wright (The Pennsylvania State University) demonstrates via a series of calculations that no known solar system body could have scattered ‘Oumuamua onto its current orbit — nor could any still unknown object bound to our solar system.

Eric Mamajek (Caltech and University of Rochester) shows that the kinematics of ‘Oumuamua are consistent with what we might expect of interstellar field objects, though he argues that its kinematics suggest it’s unlikely to have originated from many of the nearest stellar systems.

What Are ‘Oumuamua’s Properties?

'Oumuamua light curve

‘Oumuamua’s light curve. [Bannister et al. 2017]

A team of University of Maryland scientists led by Matthew Knight captured a light curve of ‘Oumuamua using Lowell Observatory’s 4.3-m Discovery Channel Telescope. The data indicate that the asteroid’s period is at least 3 hours in length, and most likely more than 5 hours. Assuming the light curve’s variation is caused by the tumbling asteroid’s changing cross-section, ‘Oumuamua must be a minimum of 3 times as long as it is wide. Knight and collaborators see no signs in their images of a coma or tail emitted from ‘Oumuamua, suggesting there is no volatile material sublimating from its surface under the heat of the Sun.

coma

No coma is visible around ‘Oumuamua. [Knight et al. 2017]

A study of the asteroid’s photometry, led by Michele Bannister (Queen’s University Belfast, UK), used the Gemini-North telescope in Hawaii and the William Herschel Telescope in Spain to explore the asteroid’s shape and color. Bannister and collaborators refined the estimate of the asteroid’s shape to be at least 5.3 times as long as it is wide, which requires this body to have significant internal cohesion to hold together as it tumbles. Their measured color for ‘Oumuamua is largely neutral.

What Does This Visitor Imply?

missing planets

Masses and semimajor axes of known exoplanets. Colors correspond to the ratio of escape velocity to circular velocity. The presence of ‘Oumuamua implies a vast and cool, still undetected population of planets. [Laughlin & Batygin, 2017]

Gregory Laughlin of Yale University and Konstantin Batygin of Caltech (and Planet Nine fame) explore some of the consequences of ‘Oumuamua’s parameters. They argue that its current passage, if it’s not a fluke, suggests the presence of an enormous number (1027) of such objects in our galaxy alone — enough to account for two Earth-masses of material for every star in the galaxy. Flinging asteroids like ‘Oumuamua out into interstellar space isn’t easy, though; the necessary multi-body interaction requires the system to contain a giant and long-period planet like our Neptune or Jupiter. Taken together, this information suggests that every star in the galaxy may host a Neptune-like planet at a Neptune-like distance.

More information on ‘Oumuamua is sure to come in the next few months as scientists continue to process their data from the asteroid’s swift passage. In the meantime, this interstellar visitor continues to challenge our understanding of our nearby surroundings and the broader context of the galaxy around us.

Citation

Jason T. Wright 2017 Res. Notes AAS 1 38. doi:10.3847/2515-5172/aa9f23
Eric Mamajek 2017 Res. Notes AAS 1 21. doi:10.3847/2515-5172/aa9bdc
Matthew M. Knight et al 2017 ApJL 851 L31. doi:10.3847/2041-8213/aa9d81
Michele T. Bannister et al 2017 ApJL 851 L38. doi:10.3847/2041-8213/aaa07c
Gregory Laughlin and Konstantin Batygin 2017 Res. Notes AAS 1 43. doi:10.3847/2515-5172/aaa02b

cataclysmic variable

What can you do with a team of people armed with backyard telescopes and a decade of patience? Test how binary star systems evolve under Einstein’s general theory of relativity!

Unusual Variables

Cataclysmic variables — irregularly brightening binary stars consisting of an accreting white dwarf and a donor star — are a favorite target among amateur astronomers: they’re detectable even with small telescopes, and there’s a lot we can learn about stellar astrophysics by observing them, if we’re patient.

CV

Diagram of a cataclysmic variable. In an AM CVn, the donor is most likely a white dwarf as well, or a low-mass helium star. [Philip D. Hall]

Among the large family of cataclysmic variables is one unusual type: the extremely short-period AM Canum Venaticorum (AM CVn) stars. These rare variables (only ~40 are known) are unique in having spectra dominated by helium, suggesting that they contain little or no hydrogen. Because of this, scientists have speculated that the donor stars in these systems are either white dwarfs themselves or very low-mass helium stars.

Why study AM CVn stars? Because their unusual configuration allows us to predict the behavior of their orbital evolution. According to the general theory of relativity, the two components of an AM CVn will spiral closer and closer as the system loses angular momentum to gravitational-wave emission. Eventually they will get so close that the low-mass companion star overflows its Roche lobe, beginning mass transfer to the white dwarf. At this point, the orbital evolution will reverse and the binary orbit will expand, increasing its period.

Enrique de Miguel

CBA member Enrique de Miguel, lead author on the study, with his backyard telescope in Huelva, Spain. [Enrique de Miguel]

Backyard Astronomy Hard at Work

Measuring the evolution of an AM CVn’s orbital period is the best way to confirm this model, but this is no simple task! To observe this evolution, we first need a system with a period that can be very precisely measured — best achieved with an eclipsing binary system. Then the system must be observed regularly over a very long period of time.

Though such a feat is challenging, a team of astronomers has done precisely this. The Center for Backyard Astrophysics (CBA) — a group of primarily amateur astronomers located around the world — has collectively observed the AM CVn star system ES Ceti using seven different telescopes over more than a decade. In total, they now have measurements of ES Ceti’s period spanning 2001–2017. Now, in a publication led by Enrique de Miguel (CBA-Huelva and University of Huelva, Spain), the group details the outcomes of their patience.

Testing the Model

ES Ceti period

This O–C diagram of the timings of minimum light relative to a test ephemeris demonstrates that ES Ceti’s orbital period is steadily increasing over time. [de Miguel et al. 2017]

De Miguel and collaborators find that ES Ceti’s ~10.3-minute orbital period has indeed increased over time — as predicted by the model — at a relatively rapid rate: the timescale for change, described by P/(dP/dt), is ~10 million years. This outcome is consistent with the hypothesis that the mass transfer and binary evolution of such systems is driven by gravitational radiation — marking one of the first such demonstrations with a cataclysmic variable.

What’s next for ES Ceti? Systems such as this one will make for interesting targets for the Laser Interferometer Space Antenna (LISA; planned for a 2034 launch). The gravitational radiation emitted by AM CVns like ES Ceti should be strong enough and in the right frequency range to be detected by LISA, providing another test of our models for how these star systems evolve.

Citation

Enrique de Miguel et al 2018 ApJ 852 19. doi:10.3847/1538-4357/aa9ed6

Millennium Simulation

Editor’s note: Kerrin Hensley is a third-year graduate student in Boston University’s astronomy department, and she was recently selected as the inaugural AAS Media Fellow. We’re excited to welcome Kerry to the team and look forward to featuring her writing on AAS Nova regularly!

As effective laboratories for studying the impact of nature on galaxy evolution without the influence of nurture, galaxies in cosmic voids stand alone. What does the dearth of galactic neighbors mean for the morphology of galaxies in cosmic voids?

Bubbles on a Megaparsec Scale

Cosmic voids are roughly spherical regions of the cosmic web with lower-than-average density of matter. Though far less populated than dense galaxy clusters, cosmic voids aren’t empty; delicate filaments beaded with galactic pearls cut across their centers, hosting sites of galaxy formation. Because of their low density, voids represent a laboratory within which galaxy properties and evolution are largely determined independent of the influence of neighboring galaxies.

What is life like for a galaxy in the proximity of a cosmic void? To answer this question, Elena Ricciardelli (École Polytechnique Fédérale de Lausanne, Switzerland) and collaborators analyze the properties of galaxies residing in and around cosmic voids in the nearby (0.01 < z < 0.12) universe.

Exploring Void Galaxy Morphology

elliptical and spiral fractions

Fraction of elliptical and spiral galaxies as a function of absolute magnitude in and outside of voids. Voids contain a higher fraction of spirals and a lower fraction of ellipticals than the control sample. [Adapted from Ricciardelli et al. 2017]

Ricciardelli and collaborators search for the effects cosmic voids have on galaxy morphology by analyzing a sample of galaxies drawn from the Sloan Digital Sky Survey. In total, they consider roughly 6,000 void galaxies and a control sample of 200,000 galaxies from environments of average density. They use the Galaxy Zoo morphological classification tool to identify the spiral and elliptical galaxies in their sample.

Lastly, they calculate the fraction of spiral and elliptical galaxies present in their void and control samples, while correcting for the fact that faint spiral galaxies are more likely to be misclassified as ellipticals than their bright counterparts. They find that galaxies near voids are more likely to be spirals than galaxies far from voids, indicating that nearby cosmic voids have a marked effect on galaxy evolution.

galaxy fractions

Clockwise from top left: elliptical fraction, spiral fraction, star-forming fraction, and stellar mass for galaxies in and around voids out to a redshift of z = 0.065. The dashed line marks the median value for each variable for the control galaxies. The dotted lines indicate the boundaries of the zone of influence of the voids. [Ricciardelli et al. 2017]

Life in and Around the Void

The authors find that not only does a galaxy’s distance from the void affect its properties, but the size of the adjacent void has a measurable impact as well. Within the voids, they find a larger fraction of spiral galaxies compared to the control sample. This effect persists after removing the mass bias due to the fact that the low-density void environments are preferentially populated with low-mass galaxies; for a given mass or absolute magnitude, voids contain a higher proportion of spiral galaxies than the control sample.

This effect is not limited to the volume within the voids; Ricciardelli and collaborators find that the properties of void-adjacent galaxies are altered out to twice the radius of the void, with a higher fraction of spiral galaxies found closer to voids. The size of a void has an effect as well; larger-than-average voids harbor a larger fraction of spiral galaxies than smaller-than-average voids.

The authors caution that this final result depends on how the voids are defined; the effect disappears if the voids are defined using their dynamical properties rather than their size. Future research will help further disentangle the role that cosmic voids play in galaxy evolution.

Citation

Elena Ricciardelli et al 2017 ApJL 846 L4. doi:10.3847/2041-8213/aa84ad

quadruple star system

Editor’s note: In these last two weeks of 2017, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume in January.

The Age of the KIC 7177553 System

Published January 2017

 

Main takeaway:

Two scientists from the University of Delaware, James MacDonald and Dermott Mullan, recently derived the age of the quadruple star system KIC 7177553. The system appears to be younger than originally thought — it’s best modeled as being 32–36 million years old.

stellar ages

Based on stellar models and the observed radii of the stars, their ages are likely between 32 and 36 million years. [MacDonald & Mullan et al. 2017]

Why it’s interesting:

The KIC 7177553 system is intriguing because of its complex structure: it consists of two binaries (one of which is eclipsing) orbiting each other in a hierarchical structure. Observations of KIC 7177553 can teach us how hierarchical systems like this one form and evolve, but first we need to determine how old the system is so we know what stage of its evolution we’re seeing. The authors’ estimate of 32–36 million years is relatively young for stars; this age places them in the pre-main-sequence phase.

The additional intrigue of KIC 7177553:

KIC 7177553 is of further interest to astronomers because it might host a super-Jupiter-sized planet in an eccentric orbit around the system. If true, this system may provide an excellent opportunity to learn more about how planets in hierarchical star systems are born and evolve. Having an accurate determination of the age of the system is therefore especially important so that we can constrain possible planet formation scenarios.

Citation

James MacDonald and D. J. Mullan 2017 ApJ 834 99. doi:10.3847/1538-4357/834/2/99

COSMOS field

Editor’s note: In these last two weeks of 2017, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume in January.

CANDELS Multi-Wavelength Catalogs: Source Identification and Photometry in the CANDELS COSMOS Survey Field

Published January 2017

 

Main takeaway:

A publication led by Hooshang Nayyeri (UC Irvine and UC Riverside) early this year details a catalog of sources built using the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), a survey carried out by cameras on board the Hubble Space Telescope. The catalog lists the properties of ~38,000 distant galaxies visible within the COSMOS field, a two-square-degree equatorial field explored in depth to answer cosmological questions.

Why it’s interesting:

dark matter and COSMOS

Illustration showing the three-dimensional map of the dark matter distribution in the
COSMOS field. [Adapted from NASA/ESA/R. Massey
(California Institute of Technology)]

The depth and resolution of the CANDELS observations are useful for addressing several major science goals, including the following:

  1. Studying the most distant objects in the universe at the epoch of reionization in the cosmic dawn.
  2. Understanding galaxy formation and evolution during the peak epoch of star formation in the cosmic high noon.
  3. Studying star formation from deep ultraviolet observations and studying cosmology from supernova observations.

Why CANDELS is a major endeavor:

CANDELS is the largest multi-cycle treasury program ever approved on the Hubble Space Telescope — using over 900 orbits between 2010 and 2013 with two cameras on board the spacecraft to study galaxy formation and evolution throughout cosmic time. The CANDELS images are all publicly available, and the new catalog represents an enormous source of information about distant objects in our universe.

Citation

H. Nayyeri et al 2017 ApJS 228 7. doi:10.3847/1538-4365/228/1/7

Titan's atmosphere

Editor’s note: In these last two weeks of 2017, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume in January.

Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan’s Ionosphere

Published July 2017

 

Main takeaway:

Titan atmosphere chemical reactions

Graphic depicting some of the chemical reactions taking place in Titan’s atmosphere, leading to the generation of organic haze particles. [ESA]

In a recently published study led by Ravi Desai (University College London), scientists used data from the Cassini mission to identify negatively charged molecules known as “carbon chain anions” in the atmosphere of Saturn’s largest moon, Titan.

Why it’s interesting:

Carbon chain anions are the building blocks of more complex molecules, and Titan’s thick nitrogen and methane atmosphere might mimic the atmosphere of early Earth. This first unambiguous detection of carbon chain anions in a planet-like atmosphere might therefore teach us about the conditions and chemical reactions that eventually led to the development of life on Earth. And if we can use Titan to learn about how complex molecules grow from these anion chains, we may be able to identify a universal pathway towards the ingredients for life.

What we’ve learned so far:

Cassini measured fewer and fewer lower-mass anions the deeper in Titan’s ionosphere that it looked — and at the same time, an increase in the number of precursors to larger aerosol molecules further down. This tradeoff strongly suggests that the anions are indeed involved in building up the more complex molecules, seeding their eventual growth into the complex organic haze of Titan’s lower atmosphere.

Citation

R. T. Desai et al 2017 ApJL 844 L18. doi:10.3847/2041-8213/aa7851

AIJ example plot

Editor’s note: In these last two weeks of 2017, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume in January.

AstroImageJ: Image Processing and Photometric Extraction for Ultra-Precise Astronomical Light Curves

Published January 2017

 

AIJ

The AIJ image display. A wide range of astronomy specific image display options and image analysis tools are available from the menus, quick access icons, and interactive histogram. [Collins et al. 2017]

Main takeaway:

AstroImageJ is a new integrated software package presented in a publication led by Karen Collins (Vanderbilt University, Fisk University, and University of Louisville). It enables new users — even at the level of undergraduate student, high school student, or amateur astronomer — to quickly start processing, modeling, and plotting astronomical image data.

Why it’s interesting:

Science doesn’t just happen the moment a telescope captures a picture of a distant object. Instead, astronomical images must first be carefully processed to clean up the data, and this data must then be systematically analyzed to learn about the objects within it. AstroImageJ — as a GUI-driven, easily installed, public-domain tool — is a uniquely accessible tool for this processing and analysis, allowing even non-specialist users to explore and visualize astronomical data.

Some features of AstroImageJ:

(as reported by Astrobites)

  • Image calibration: generate master flat, dark, and bias frames
  • Image arithmetic: combine images via subtraction, addition, division, multiplication, etc.
  • Stack editing: easily perform operations on a series of images
  • Image stabilization and image alignment features
  • Precise coordinate converters: calculate Heliocentric and Barycentric Julian Dates
  • WCS coordinates: determine precisely where a telescope was pointed for an image by PlateSolving using Astronomy.net
  • Macro and plugin support: write your own macros
  • Multi-aperture photometry with interactive light curve fitting: plot light curves of a star in real time

Citation

Karen A. Collins et al 2017 AJ 153 77. doi:10.3847/1538-3881/153/2/77

GJ 1132 b

Editor’s note: In these last two weeks of 2017, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume in January.

Detection of the Atmosphere of the 1.6 M ⊕ Exoplanet GJ 1132 b

Published March 2017

 

Main takeaway:

An atmosphere was detected around the roughly Earth-size exoplanet GJ 1132 b using a telescope at the European Southern Observatory in Chile. A team of scientists led by John Southworth (Keele University) found features indicating the presence of an atmosphere in the observations of this 1.6-Earth-mass planet as it transits an M-dwarf host star. This is the lowest-mass planet with a detected atmosphere thus far.

Why it’s interesting:

M dwarfs are among the most common stars in our galaxy, and we’ve found many Earth-size exoplanets in or near the habitable zones around M-dwarf hosts. But M dwarfs are also more magnetically active than stars like our Sun, suggesting that the planets in M-dwarf habitable zones may not be able to support life due to stellar activity eroding their atmospheres. The detection of an atmosphere around GJ 1132 b suggests that some planets orbiting M dwarfs are able to retain their atmospheres — which means that these planets may be an interesting place to search for life after all.

How the atmosphere was detected:

GJ 1132 b radius

The measured planetary radius for GJ 1132 b as a function of the wavelength used to observe it. [Southworth et al. 2017]

When measuring the radius of GJ 1132 b based on its transits, the authors noticed that the planet appeared to be larger when observed in some wavelengths than in others. This can be explained if the planet has a “surface radius” of ~1.4 Earth radii, overlaid by an atmosphere that extends out another few tenths of an Earth radius. The atmosphere, which may consist of water vapor or methane, is transparent to some wavelengths and absorbs others — which is why the apparent size of the planet changes across wavelength bands.

Citation

John Southworth et al 2017 AJ 153 191. doi:10.3847/1538-3881/aa6477

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