NASA's Webb Exposes Complex Atmosphere of Starless Super-Jupiter

Isolated Planetary-Mass Object SIMP 0136 (Artist’s Concept)
Credits/Artwork: NASA, ESA, CSA, Joseph Olmsted (STScI)

Isolated Planetary-Mass Object SIMP 0136 (NIRSpec Light Curves)
Credits/Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)

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An international team of researchers has discovered that previously observed variations in brightness of a free-floating planetary-mass object known as SIMP 0136 must be the result of a complex combination of atmospheric factors, and cannot be explained by clouds alone.

Using NASA’s James Webb Space Telescope to monitor a broad spectrum of infrared light emitted over two full rotation periods by SIMP 0136, the team was able to detect variations in cloud layers, temperature, and carbon chemistry that were previously hidden from view

The results provide crucial insight into the three-dimensional complexity of gas giant atmospheres within and beyond our solar system. Detailed characterization of objects like these is essential preparation for direct imaging of exoplanets, planets outside our solar system, with NASA’s Nancy Grace Roman Space Telescope, which is scheduled to begin operations in 2027.

Rapidly Rotating, Free-Floating

SIMP 0136 is a rapidly rotating, free-floating object roughly 13 times the mass of Jupiter, located in the Milky Way just 20 light-years from Earth. Although it is not classified as a gas giant exoplanet — it doesn’t orbit a star and may instead be a brown dwarf — SIMP 0136 is an ideal target for exo-meteorology: It is the brightest object of its kind in the northern sky. Because it is isolated, it can be observed with no fear of light contamination or variability caused by a host star. And its short rotation period of just 2.4 hours makes it possible to survey very efficiently.

Prior to the Webb observations, SIMP 0136 had been studied extensively using ground-based observatories and NASA’s Hubble and Spitzer space telescopes.

“We already knew that it varies in brightness, and we were confident that there are patchy cloud layers that rotate in and out of view and evolve over time,” explained Allison McCarthy, doctoral student at Boston University and lead author on a study published today in The Astrophysical Journal Letters. “We also thought there could be temperature variations, chemical reactions, and possibly some effects of auroral activity affecting the brightness, but we weren’t sure.”

To figure it out, the team needed Webb’s ability to measure very precise changes in brightness over a broad range of wavelengths.

Charting Thousands of Infrared Rainbows

Using NIRSpec (Near-Infrared Spectrograph), Webb captured thousands of individual 0.6- to 5.3-micron spectra — one every 1.8 seconds over more than three hours as the object completed one full rotation. This was immediately followed by an observation with MIRI (Mid-Infrared Instrument), which collected hundreds of spectroscopic measurements of 5- to 14-micron light — one every 19.2 seconds, over another rotation.

The result was hundreds of detailed light curves, each showing the change in brightness of a very precise wavelength (color) as different sides of the object rotated into view.

“To see the full spectrum of this object change over the course of minutes was incredible,” said principal investigator Johanna Vos, from Trinity College Dublin. “Until now, we only had a little slice of the near-infrared spectrum from Hubble, and a few brightness measurements from Spitzer.”

The team noticed almost immediately that there were several distinct light-curve shapes. At any given time, some wavelengths were growing brighter, while others were becoming dimmer or not changing much at all. A number of different factors must be affecting the brightness variations.

“Imagine watching Earth from far away. If you were to look at each color separately, you would see different patterns that tell you something about its surface and atmosphere, even if you couldn’t make out the individual features,” explained co-author Philip Muirhead, also from Boston University. “Blue would increase as oceans rotate into view. Changes in brown and green would tell you something about soil and vegetation.”

Patchy Clouds, Hot Spots, and Carbon Chemistry

To figure out what could be causing the variability on SIMP 0136, the team used atmospheric models to show where in the atmosphere each wavelength of light was originating.

“Different wavelengths provide information about different depths in the atmosphere,” explained McCarthy. “We started to realize that the wavelengths that had the most similar light-curve shapes also probed the same depths, which reinforced this idea that they must be caused by the same mechanism.”

One group of wavelengths, for example, originates deep in the atmosphere where there could be patchy clouds made of iron particles. A second group comes from higher clouds thought to be made of tiny grains of silicate minerals. The variations in both of these light curves are related to patchiness of the cloud layers.

A third group of wavelengths originates at very high altitude, far above the clouds, and seems to track temperature. Bright “hot spots” could be related to auroras that were previously detected at radio wavelengths, or to upwelling of hot gas from deeper in the atmosphere.

Some of the light curves cannot be explained by either clouds or temperature, but instead show variations related to atmospheric carbon chemistry. There could be pockets of carbon monoxide and carbon dioxide rotating in and out of view, or chemical reactions causing the atmosphere to change over time.

“We haven’t really figured out the chemistry part of the puzzle yet,” said Vos. “But these results are really exciting because they are showing us that the abundances of molecules like methane and carbon dioxide could change from place to place and over time. If we are looking at an exoplanet and can get only one measurement, we need to consider that it might not be representative of the entire planet.”

This research was conducted as part of Webb’s General Observer (GO) Program 3548.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency)

Source: Space Telescope Science Institute (STScI)News

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Gliese 229 B’s Newfound Companion Solves Brown Dwarf Mystery

S. Kulkarni (Caltech), D.Golimowski (JHU) and NASA

Astronomers recently discovered a companion to Gliese 229 B, the first confidently identified brown dwarf. This discovery resolves the conflict between Gliese 229 B’s observed mass and the predictions of evolutionary models, potentially illuminating the nature of other poorly understood brown dwarf systems as well.

An illustration of a brown dwarf. Brown dwarfs aren’t actually brown, likely spanning a range of colors from reddish-orange to nearly black. Credit: NASA/JPL-Caltech

First in Its Class

In 1995, Gliese 229 B became the first object to be unambiguously classified as a brown dwarf: an object that bridges the gap between planets and stars. At roughly 13–80 times the mass of Jupiter, brown dwarfs aren’t massive enough to sustain fusion of hydrogen in their cores, as stars do, but they are able to burn a heavier form of hydrogen called deuterium, setting them apart from planets. (The most massive brown dwarfs can burn lithium as well.) After exhausting their supply of deuterium, brown dwarfs steadily cool, sliding down the spectral-type ladder. The youngest and most massive brown dwarfs occupy late M spectral types, while older or less massive brown dwarfs are classified as L, T, or Y dwarfs.

While improved telescopes have advanced our understanding of brown dwarfs, there’s still much we don’t know about these objects, and attempts to study and classify brown dwarfs have been confounded by their complex properties. This is the case for the first confirmed T-class brown dwarf, Gliese 229 B, which recently became the subject of an astronomical mystery.

The large relative radial velocity between Gliese 229 A and 229 B and the large difference in Gliese 229 B’s radial velocity between the two time periods provides firm evidence for the existence of an unseen companion. Credit: Whitebook et al. 2024

A Mass Mystery

Soon after Gliese 229 B was discovered, researchers used substellar evolution models to interpret the object’s spectrum and luminosity and estimate its mass at 30–50 Jupiter masses. More than two decades later, refined observations of the brown dwarf’s orbit around its red dwarf host star allowed researchers to calculate its mass dynamically. The newly calculated mass — 71 Jupiter masses — was troubling. According to models of how substellar objects cool as they age, it simply wasn’t possible for a 71-Jupiter-mass object of Gliese 229 B’s age to have cooled to its present temperature.

This conflict between dynamical mass measurements and evolutionary model predictions led researchers to suspect that Gliese 229 B is actually a binary system — a brown dwarf harboring an unseen companion. In March and November of 2022, Samuel Whitebook (University of California, Santa Barbara; California Institute of Technology) and coauthors turned one of the giant telescopes of Keck Observatory toward the Gliese 229 system, using the sensitive High Resolution Echelle Spectrometer to search for evidence of a companion tugging on Gliese 229 B. The team found a clear difference in Gliese 229 B’s radial velocity compared to expectations for an orderly orbit around its host star. Its radial velocity changed by 11σ between the observations, completely ruling out the possibility that Gliese 229 B is a single object.

 

 Likelihood distribution of the orbital period and mass for the companion object.
Credit: Whitebook et al. 2024

Single No More

What do these observations tell us about the newfound companion? While it’s not possible to fully pin down the properties of the companion object from current observations, Whitebook’s team estimated the companion’s mass to be somewhere between 15 and 35 Jupiter masses with an orbital period between a few days and 60 days. Future observations will refine the companion’s orbit and provide an accurate estimate of the masses of the two components.

In addition to solving the mystery of Gliese 229 B, this discovery may help to explain other seemingly over-massive T dwarfs orbiting main-sequence stars, several of which have been discovered in the past decade. If future work reveals that these too-massive T dwarfs are actually pairs of brown dwarfs, that may suggest that T dwarfs orbiting main-sequence stars are more likely to host companions than T dwarfs in the field, which are usually solo.

By Kerry Hensley

Citation

“Discovery of the Binarity of Gliese 229B, and Constraints on the System’s Properties,” Samuel Whitebook et al 2024 ApJL 974 L30. doi:10.3847/2041-8213/ad7714

Source: American Astronomical Society/AAS-Nova

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NASA's Hubble Finds that Aging Brown Dwarfs Grow Lonely

Hubble Brown Dwarf Survey Illustration
Credits: Artwork: NASA, ESA, Joseph Olmsted (STScI)

Images

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It takes two to tango, but in the case of brown dwarfs that were once paired as binary systems, that relationship doesn't last for very long, according to a recent survey from NASA's Hubble Space Telescope.

Brown dwarfs are interstellar objects larger than Jupiter but smaller than the lowest-mass stars. They are born like stars – out of a cloud of gas and dust that collapses – but do not have enough mass to sustain the fusion of hydrogen like a normal star.

Astronomers using Hubble confirm that companions are extremely rare around the lowest-mass and coldest brown dwarfs. Hubble can detect binaries as close to each other as a 300-million-mile separation – the approximate separation between our Sun and the asteroid belt. But they didn't find any binary pairs in a sample of brown dwarfs in the solar neighborhood. This implies that a binary pair of dwarfs is so weakly linked by gravity that they drift apart over a few hundred million years due to the pull of bypassing stars.

"Our survey confirms that widely separated companions are extremely rare among the lowest-mass and coldest isolated brown dwarfs, even though binary brown dwarfs are observed at younger ages. This suggests that such systems do not survive over time," said lead author Clémence Fontanive of the Trottier Institute for Research on Exoplanets, Université de Montréal, Canada.

In a similar survey Fontanive conducted a couple of years ago, Hubble looked at extremely young brown dwarfs and some had binary companions, confirming that star-forming mechanisms do produce binary pairs among low-mass brown dwarfs. The lack of binary companions for older brown dwarfs suggests that some may have started out as binaries, but parted ways over time.

The new Hubble findings published in The Monthly Notices of the Royal Astronomical Society further support the theory that brown dwarfs are born the same way as stars, through the gravitational collapse of a cloud of molecular hydrogen. The difference being that they do not have enough mass to sustain nuclear fusion of hydrogen for generating energy, whereas stars do. More than half of the stars in our galaxy have a companion star that resulted from these formation processes, with more massive stars more commonly found in binary systems. "The motivation for the study was really to see how low in mass the trends seen among multiple stars systems hold up," said Fontanive.

"Our Hubble survey offers direct evidence that these binaries that we observe when they're young are unlikely to survive to old ages, they're likely going to get disrupted. When they're young, they're part of a molecular cloud, and then as they age the cloud disperses. As that happens, things start moving around and stars pass by each other. Because brown dwarfs are so light, the gravitational hold tying wide binary pairs is very weak, and bypassing stars can easily tear these binaries apart," said Fontanive.

The team selected a sample of brown dwarfs previously identified by NASA's Wide-Field Infrared Survey Explorer. It sampled some of the coldest and lowest-mass old brown dwarfs in the solar neighborhood. These old brown dwarfs are so cool (a few hundred degrees warmer than Jupiter in most cases) that their atmospheres contain water vapor that condensed out.

To find the coolest companions, the team used two different near-infrared filters, one in which cold brown dwarfs are bright, and another covering specific wavelengths where they appear very faint due to water absorption in their atmospheres.

"This is the best observational evidence to date that brown dwarf pairs drift apart over time," said Fontanive. "We could not have done this kind of survey and confirmed earlier models without Hubble's sharp vision and sensitivity."

The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. Goddard also conducts mission operations with Lockheed Martin Space based in Denver, Colorado. The Space Telescope Science Institute in Baltimore, Maryland, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.

Source: HubbleSite/News

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• iREx, Université de Montréal's Release

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Tilted Orbits

This illustration shows a brown dwarf with no orbital tilt (above), versus one with a high orbital tilt (below). Astronomers think that brown dwarfs with no, or low, tilts likely formed like planets, while those with high tilts formed like stars. Credit: Caltech/S. Giacalone

Steven Giacalone
Credit: Caltech/S. Giacalone

How the orbital inclinations of brown dwarfs reveal clues about their formation

Within the family of celestial orbs in the universe, brown dwarfs are somewhat like misfits. They are less massive and cooler than stars but are 10 to 80 times more massive than Jupiter. Brown dwarfs are sometimes called "failed stars," because they lack the mass to ignite nuclear fusion and shine with starlight.

One mystery that surrounds these oddballs is how they formed: Some theories propose that they form like stars do, out of collapsing clouds of material, while others suggest they form like planets, taking shape within rotating dusty disks that circle young stars. It is also possible, scientists propose, that brown dwarfs may form both like stars and planets.

Steven Giacalone, a National Science Foundation (NSF) Postdoctoral Scholar Fellowship Trainee in Astronomy at Caltech, and his colleagues are addressing the mystery by studying the orbital tilts of brown dwarfs that circle very closely around companion stars. Brown dwarfs, as well as some other exoplanets, can have orbits that are tilted to varying degrees relative to the rotational direction of their host stars. If a brown dwarf has an orbital tilt, then it is out of whack with its partner star: the brown dwarf will loop above and below a plane that aligns with the star's equator. This is unlike the planets in our own solar system that orbit in a plane that aligns with the Sun's rotational direction.

Using the Keck Planet Finder (KPF), a new planet-hunting instrument at the W. M. Keck Observatory in Hawaiʻi, Giacalone and his colleagues wanted to assess whether a brown dwarf named GPX-1b has an orbital tilt. They say that a tilt would indicate that the object probably formed like a star and not like a planet.

"For a brown dwarf to have made its way into a tilted close-in orbit, it would have had to have been knocked around by a larger planetary body or captured by the star as the brown dwarf passed by," explains Giacalone, who works in the group of Andrew Howard, a professor of astronomy at Caltech and the principal investigator of KPF. "That would mean it started out like a star."

On the other hand, if the brown dwarf has an orbit aligned with the equatorial plane of its central star, then "it most likely migrated inward similar to planets via interactions with the disk in which it formed," Giacalone says.

The results revealed GPX-1b is not tilted in its orbit, but that it circles in a plane that aligns with the host star's equator.

"This is only one data point, and preliminary, but it suggests that the brown dwarf migrated close to its companion star in a similar manner to planets," says Giacalone, who presented the results at the 243rd meeting of the American Astronomical Society (AAS) in New Orleans on January 10, 2024. "Theory has predicted that brown dwarfs should be able to form like planets, but observational evidence is only just beginning to be gathered to support that idea."

The result contrasts with what is known about brown dwarfs with wide separations from their companion stars. "The wide-separation brown dwarfs are known to have high orbital tilts and do not form in a disk, but rather, like stars," Giacalone says. "The short-separation ones like GPX-1b, on the other hand, probably do form in the disk if they have low orbital tilts, meaning they form like planets. In other words, we think brown dwarfs can form either like stars or planets."

KPF, a high-precision spectrograph, was able to determine the orbital inclination of the object by watching it pass in front of, or transit, its star. The brown dwarf was discovered by NASA's TESS (Transiting Exoplanet Survey Satellite) mission and the Galactic Plane eXoplanet Survey (GPX) in 2021. It is one of a small number of brown dwarfs known to pass in front of, or transit, its host star.

The researchers hope to use KPF to study the orbital inclinations of more brown dwarfs in the future. "We have demonstrated the power of KPF for studying these systems," Giacalone says. "Because close-in brown dwarfs are so rare, they are mostly found around relatively faint and distant stars. That means we need large telescopes like Keck and advanced instruments like KPF to study them accurately."

Written by Whitney Clavin

Contact:

Whitney Clavin
(626) 395‑1944
wclavin@caltech.edu

Source: Caltech/News

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NASA's Webb Finds Signs of Possible Aurorae on Isolated Brown Dwarf

Brown Dwarf W1935 (Artist Concept)
Credits: Artwork: NASA, ESA, CSA, Leah Hustak (STScI)

Atmospheric Methane of Brown Dwarfs W1935 and W2220 (NIRSpec)
Credits: Illustration: NASA, ESA, CSA, Leah Hustak (STScI)

Release Images

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Astronomers using NASA’s James Webb Space Telescope have found a brown dwarf (an object more massive than Jupiter but smaller than a star) with infrared emission from methane, likely due to energy in its upper atmosphere. This is an unexpected discovery because the brown dwarf, W1935, is cold and lacks a host star; therefore, there is no obvious source for the upper atmosphere energy. The team speculates that the methane emission may be due to processes generating aurorae.

These findings are being presented at the 243rd meeting of the American Astronomical Society in New Orleans.

To help explain the mystery of the infrared emission from methane, the team turned to our solar system. Methane in emission is a common feature in gas giants like Jupiter and Saturn. The upper-atmosphere heating that powers this emission is linked to aurorae.

On Earth, aurorae are created when energetic particles blown into space from the Sun are captured by Earth’s magnetic field. They cascade down into our atmosphere along magnetic field lines near Earth’s poles, colliding with gas molecules and creating eerie, dancing curtains of light. Jupiter and Saturn have similar auroral processes that involve interacting with the solar wind, but they also get auroral contributions from nearby active moons like Io (for Jupiter) and Enceladus (for Saturn).

For isolated brown dwarfs like W1935, the absence of a stellar wind to contribute to the auroral process and explain the extra energy in the upper atmosphere required for the methane emission is a mystery. The team surmises that either unaccounted internal processes like the atmospheric phenomena of Jupiter and Saturn, or external interactions with either interstellar plasma or a nearby active moon may help account for the emission.

A Detective Story

The aurorae’s discovery played out like a detective story. A team led by Jackie Faherty, an astronomer at the American Museum of Natural History in New York, was awarded time with the Webb telescope to investigate 12 cold brown dwarfs. Among those were W1935 – an object that was discovered by citizen scientist Dan Caselden, who worked with the Backyard Worlds Zooniverse project – and W2220, an object that was discovered using NASA’s Wide Field Infrared Survey Explorer. Webb revealed in exquisite detail that W1935 and W2220 appeared to be near clones of each other in composition. They also shared similar brightness, temperatures, and spectral features of water, ammonia, carbon monoxide and carbon dioxide. The striking exception was that W1935 showed emission from methane, as opposed to the anticipated absorption feature that was observed toward W2220. This was seen at a distinct infrared wavelength to which Webb is uniquely sensitive.

“We expected to see methane because methane is all over these brown dwarfs. But instead of absorbing light, we saw just the opposite: The methane was glowing. My first thought was, what the heck? Why is methane emission coming out of this object?” said Faherty.

The team used computer models to infer what might be behind the emission. The modeling work showed that W2220 had an expected distribution of energy throughout the atmosphere, getting cooler with increasing altitude. W1935, on the other hand, had a surprising result. The best model favored a temperature inversion, where the atmosphere got warmer with increasing altitude.

“This temperature inversion is really puzzling,” said Ben Burningham, a co-author from the University of Hertfordshire in England and lead modeler on the work. “We have seen this kind of phenomenon in planets with a nearby star that can heat the stratosphere, but seeing it in an object with no obvious external heat source is wild.”

Clues from our Solar System

For clues, the team looked in our own backyard, to the planets of our solar system. The gas giant planets can serve as proxies for what is seen going on more than 40 light-years away in the atmosphere of W1935.

The team realized that temperature inversions are prominent in planets like Jupiter and Saturn. There is still ongoing work to understand the causes of their stratospheric heating, but leading theories for the solar system involve external heating by aurorae and internal energy transport from deeper in the atmosphere (with the former a leading explanation).

Brown Dwarf Aurora Candidates in Context

This is not the first time an aurora has been used to explain a brown dwarf observation. Astronomers have detected radio emission coming from several warmer brown dwarfs and invoked aurorae as the most likely explanation. Searches were conducted with ground-based telescopes like the Keck Observatory for infrared signatures from these radio-emitting brown dwarfs to further characterize the phenomenon, but were inconclusive.

W1935 is the first auroral candidate outside the solar system with the signature of methane emission. It’s also the coldest auroral candidate outside our solar system, with an effective temperature of about 400 degrees Fahrenheit (200 degrees Celsius), about 600 degrees Fahrenheit warmer than Jupiter.

In our solar system the solar wind is a primary contributor to auroral processes, with active moons like Io and Enceladus playing a role for planets like Jupiter and Saturn, respectively. W1935 lacks a companion star entirely, so a stellar wind cannot contribute to the phenomenon. It is yet to be seen whether an active moon might play a role in the methane emission on W1935.

“With W1935, we now have a spectacular extension of a solar system phenomenon without any stellar irradiation to help in the explanation,” Faherty noted. “With Webb, we can really ‘open the hood’ on the chemistry and unpack how similar or different the auroral process may be beyond our solar system,” she added.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Want to help discover a new world? Join the Backyard Worlds: Planet 9 citizen science project and search the realm beyond Neptune for new brown dwarfs and planets. Or try NASA’s new Burst Chaser citizen science project, which launched Jan. 9.

Source: NASA's James Webb Space Telescope/News

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Baby Brown Dwarf Might be Growing: JWST Observations of TWA 27B

An image of the TWA 27 system, taken with a ground-based telescope in 2004.
Credit:ESO; CC BY 4.0

Having caught the gigantic, golden eye of JWST several times now, brown dwarfs are having a moment. A new article in The Astrophysical Journal Letters describes the latest planetary-mass companion to take the spotlight, and how our understanding of these mysterious objects is rapidly evolving.

A Popular Runt

Of all the known tiny, barely glowing “failed stars” known to astronomers as brown dwarfs, TWA 27B stands out as a particularly rich target for a number of reasons. As a member of the TW Hydrae association, the youngest group of stars within the nearest few hundred light-years of the Sun, TWA 27B is both exceptionally young and helpfully close by. Also, as a product of the earliest successful campaign to directly image small companions of larger objects, it has the longest track record of observations that can compared with new measurements. Acting on these temptations, JWST took a look at TWA 27B and its slightly larger partner, TWA 27A, in February of this year.

Images of the TWA 27 system created using three different grisms aboard the NIRSpec instrument. The top row shows both objects, while the bottom shows an enhanced view of TWA 27B created by subtracting out its brighter companion. Credit: Luhman et al. 2023

Methane-Free Zone

For about half an hour, JWST aimed at the TWA 27 system and dutifully collected photons with its onboard Near-Infrared Spectrograph (NIRSpec) instrument across three different wavelength ranges. Piecing the data together back on the ground, a team led by Kevin Luhman, Pennsylvania State University, revealed the atmosphere of a 10 million years young, 5–6-Jupiter-mass object, interestingly devoid of any methane and with only a small whiff of carbon monoxide. Both of these chemical species are common in older brown dwarfs but seem to vanish among younger ones due to non-equilibrium chemistry– a recently noted trend that these observations bolster.

The full 1–5-micron spectrum obtained of TWA 27B, compared to the best-fitting model spectrum derived from a simulation of a cloudless atmosphere. Although the model qualitatively follows the spectrum well, it overpredicts both the strength of the methane absorption and the object’s temperature. The discrepancies might be corrected with a more complex model that includes clouds. Credit: Luhman et al. 2023

Hungry Brown Dwarf?

Tantalizingly, the team also noticed that while their spectra did not indicate the smoking-gun signatures of a large circumstellar disk (an apparent “excess” of infrared emission), they did reveal that TWA 27B was emitting at specific wavelengths usually associated with accretion. This raises the possibility that the object is still growing slowly, and that it’s ringed by a tiny disk never before inferred over the long and distinguished trail of previous studies.

Thankfully, this cliffhanger provides a possible resolution: if such a disk exists, it will be obvious in observations taken at longer wavelengths. JWST, once again demonstrating its abilities to see what has never before been seen, has already taken these measurements. Data collected with its Mid-Infrared Instrument (MIRI) are being processed now, meaning the flood of unprecedented observations and accompanying discoveries about brown dwarfs is unlikely to stop soon.

By Ben Cassese

Citation

“JWST/NIRSpec Observations of the Planetary Mass Companion TWA 27B,” K. L. Luhman et al 2023 ApJL 949 L36. doi:10.3847/2041-8213/acd635

Source: American Astronomical Society/AAS Nova

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The Mouse That Roared: The Strange Tale of a Brown Dwarf

A brown dwarf was found in an unusual place
Credit: NRAO/AUI/NSF

Recently the Atacama Large Millimeter/Submillimeter Array (ALMA) found an unusual object during observations for the Ophiuchus Disk Survey Employing ALMA (ODISEA). It looked unusual since the data didn’t match the rotating protoplanetary disks the ODISEA project was designed to study, and the closer Dary Ruíz-Rodríguez and her team looked, the stranger the object became.

It began with the detection of an elliptical shell, or bubble of carbon monoxide within an interstellar molecular cloud. This type of gas shell is the type of thing scientists expect to see around AGB stars, which are medium-mass stars at the end of their lives. Such a spherical shell of gas is likely to be formed by our Sun in a few billion years. The Sun shines by fusing hydrogen in its core, which also creates the pressure needed to prevent the Sun from collapsing under its own weight. But in a few billion years the Sun will run out of hydrogen to burn. So it will start to fuse other elements such as helium, which burns much hotter. As a result, the Sun will swell into a red giant, and for a time cast off a bit of its outer layer to create a shell of gas surrounding the star.

When scientists see a shell of gas like this, they expect to see it centered around a red giant star. Sure enough, there was an object in the center of this carbon monoxide shell. The object has a surface temperature of about 3,000 K or less, just as scientists expect from a red giant, but it is very dim. Too dim to be a red giant. The object is so dim it looks like a brown dwarf. This didn’t make any sense. Brown dwarfs are too small to undergo hydrogen fusion in their core, and they don’t cast off an outer layer of gas at the end of their lives.

But looks can be deceiving, so the team looked for alternatives. Perhaps the dim object is a red giant, but much more distant than the shell of gas they observed. The Ophiuchus Molecular cloud, where the target was expected to be, is about 450 light-years from Earth, but given the observed brightness, the red giant would have to be 15,000 to 30,000 light-years away, behind the center of our Galaxy. When the team compared the proper motions and radial velocities of the Ophiuchus members and the target, it strongly suggested that the mysterious object was a member of the Ophiuchus Molecular Cloud and could not be a distant. This means it can’t be a red giant. Just to be sure, the team also looked at near-infrared observations of the object gathered from the European Southern Observatory’s Very Large Telescope (VLT), which further confirmed it isn’t a red giant star.

The behavior of a dying red giant or first hydrostatic core doesn’t fit the data
Credit: Ruíz-Rodríguez et al, 2022

Another idea is that it might be a very young star. Stars form when a region within a molecular cloud gravitationally collapses into a protostar. Early on there is a period where gravitational squeezing of the protostar collapses the central region into a dense core. This is known as the first hydrostatic core mass and is expected to be highly embedded in a dense environment and surrounded by a massive, optically thick disk. As material constantly feeds the central object, it can sometimes leave behind a thin shell of gas surrounding it. But if that were the case, then ALMA should see a dense carbon monoxide core collapsing inward as it falls toward the protostellar core. Surprisingly, ALMA showed a tenuous carbon monoxide shell expanding outward; and on top of that, did not detect any signs of circumstellar disk material. So this isn’t the answer either.

All of the observational data, both from ALMA and the VLT, lead to the same conclusion. This object is a brown dwarf surrounded by an expanding shell of gas. It’s a very strange thing, and Dary Ruíz-Rodríguez and her team think it could be the first observation of a phenomenon known as a deuterium flash.

Brown dwarfs lie in the middle ground between planets and stars. They are about the size of Jupiter, but about 30-70 times more massive. They aren’t stars because they don’t have enough mass to trigger the fusion of hydrogen to helium in the usual way. But they can massive enough to fuse an isotope of hydrogen known as deuterium. Elements are defined by the number of protons they have in their nucleus, but many elements have multiple varieties, or isotopes, that have different numbers of neutrons. The nucleus of regular hydrogen is just a single proton. Deuterium, also known as hydrogen-2 has one proton and one neutron. There is only about 1 deuterium atom for every 500 hydrogen atoms, but brown dwarfs are justmassive enough to fuse deuterium with hydrogen and harness it as a power source for a short while.

We still don’t understand all the details of deuterium fusion, but astronomers think that when brown dwarfs form the early onset of deuterium fusion triggers a rapid release of energy known as a deuterium flash. Such a flash could eject an outer layer of gas, just as we see with this particular brown dwarf.

The data can’t completely prove a deuterium flash as the cause, and the team is careful to note other possible solutions such as a collision between the brown dwarf and a small planet. But it’s clear that whatever the cause, this mousey brown dwarf has a very strange tale indeed.

Ruíz-Rodríguez, Dary A., et al. “Discovery of a brown dwarf with quasi-spherical mass-loss.” arXiv preprint arXiv:2209.00759 (2022), accepted for publication in The Astrophysical Journal.

By Brian Koberlein

About the Author:

Brian Koberlein is a science writer for NRAO. He has a Ph.D. in Physics from the University of Connecticut, and has published research in physics and astrophysics. Together with David Meisel, he is the author of Astrophysics Through Computation, published by Cambridge University Press.

Recent Articles

• The Mouse That Roared: The Strange Tale of a Brown Dwarf
• ALMA: Visit to an Alien World
• From the Moon to the Earth

Source: National Radio Astronomy Observatory (NRAO)/News

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A planet-forming disk still fed by the mother cloud

This false-colour image shows the filaments of accretion around the protostar [BHB2007] 1. The large structures are inflows of molecular gas (CO) nurturing the disk surrounding the protostar. The inset shows the dust emission from the disk, which is seen edge-on. The "holes" in the dust map represent an enormous ringed cavity seen (sideways) in the disk structure. © MPE 

Two different observations of the protoplanetary disk show signatures of the formation of a companion to the protostar . The grey scale represents the dust thermal emission from the disk, same as in the inset of Fig. 1. The red/blue contours show the molecular CO brightness emission levels from the northern/southern side of the dust cavity observed with ALMA. The brighter CO emission from the south indicates that the gas is hotter there. This location coincides with a zone of non-thermal emission tracing ionised gas (green contours) observed with the VLA (middle), which is observed in addition to the protostar (centre of the image). The team proposes that both the ionised gas and the hot molecular gas are due to the presence of a protoplanet or a brown dwarf in the cavity. The configuration of such a system is shown in the sketch on the right. © MPE; illustration: Gabriel A. P. Franco 

Stellar systems like our own form inside interstellar clouds of gas and dust that collapse producing young stars surrounded by protoplanetary disks. Planets form within these protoplanetary disks, leaving clear gaps, which have been recently observed in evolved systems, at the time when the mother cloud has been cleared out. ALMA has now revealed an evolved protoplanetary disk with a large gap still being fed by the surrounding cloud via large accretion filaments. This shows that accretion of material onto the protoplanetary disk is continuing for times longer than previously thought, affecting the evolution of the future planetary system.

A team of astronomers led by Dr. Felipe Alves from the Center for Astrochemical Studies (CAS) at the Max Planck Institute for Extraterrestrial Physics (MPE) used the Atacama Large Millimeter/submillimeter Array (ALMA) to study the accretion process in the stellar object [BHB2007] 1, a system located at the tip of the Pipe Molecular Cloud. The ALMA data reveal a disk of dust and gas around the protostar, and large filaments of gas around this disk. The scientists interpret these filaments as accretion streamers feeding the disk with material extracted from the ambient cloud. The disk reprocesses the accreted material, delivering it to the protostar. The structure observed is very unusual for stellar objects at this stage of evolution — with an estimated age of 1,000,000 years — when circumstellar disks are already formed and matured for planet formation. “We were quite surprised to observe such prominent accretion filaments falling into the disk”, said Alves. “The accretion filament activity demonstrates that the disk is still growing while simultaneously nurturing the protostar.”

The team also reports the presence of an enormous cavity within the disk. The cavity has a width of 70 astronomical units, and it encompasses a compact zone of hot molecular gas. In addition, supplementary data at radio frequencies by the Very Large Array (VLA) point to the existence of non-thermal emission in the same spot where the hot gas was detected. These two lines of evidence indicate that a substellar object — a young giant planet or brown dwarf — is present within the cavity. As this companion accretes material from the disk, it heats up the gas and possibly powers strong ionized winds and/or jets. The team estimates that an object with a mass between 4 and 70 Jupiter masses is needed to produce the observed gap in the disk.

“We present a new case of star and planet formation happening in tandem,” states Paola Caselli, director at MPE and head of the CAS group. “Our observations strongly indicate that protoplanetary disks keep accreting material also after planet formation has started. This is important because the fresh material falling onto the disk will affect both the chemical composition of the future planetary system and the dynamical evolution of the whole disk.” These observations also put new time constraints for planet formation and disk evolution, shedding light on how stellar systems like our own are sculpted from the original cloud.

 Source:  Max Planck Institute for Extraterrestrial Physics

Contacts

Dr. Felipe De Oliveira Alves
postdoc
+49 (0)89 30000-3897
0049(0)17637101004
+49 (0)89 30000-3950

Prof. Dr. Paola Caselli
acting director
+49 (0)89 30000-3400
+49 (0)89 30000-3399

Original publication

1. Felipe O. Alves, L. Ilsedore Cleeves, Josep M. Girart, Zhaohuan Zhu, Gabriel A. P. Franco, Alice Zurlo and Paola Caselli

A case of simultaneous star and planet formation
Astrophysical Journal Letters, 904 L6
DOI

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First direct detection of a brown dwarf with a radio telescope

Artist’s impression of Elegast. The blue loops depict the magnetic field lines. Charged particles moving along these lines emit radio waves that LOFAR detected. Some particles eventually reach the poles and generate aurorae similar to the northern lights on Earth. (Image credit: ASTRON / Danielle Futselaar)

Astronomers at ASTRON have used the LOFAR radio telescope to discover a “brown dwarf” – a faint object more massive than Jupiter, but significantly less massive than the Sun. The discovery of the object dubbed Elegast, opens up a new path that uses radio telescopes to discover faint objects that are close-cousins of Jupiter-like exoplanets. 

Radio waves emitted by brown dwarfs carry information about their magnetic field strength. Until now radio observations could only measure strong magnetic fields – about a hundred times the strength of a common fridge magnet. LOFAR’s low frequency of observation makes it sensitive to magnetic fields comparable to that of a fridge magnet, which is within the range postulated to exist on the coldest brown dwarfs and large exoplanets.

“Magnetic fields control the atmospheric properties and radiation environment around exoplanets and radio observations are our best hope of measuring them. With this discovery, we have taken an important step towards realising the promise of radio astronomy to exoplanet science,” said Dr. Harish Vedantham, ASTRON staff scientist and lead author of the study published today in the Astrophysical Journal Letters.

New discovery technique

The group used a new discovery technique to spot Elegast. Previously, astronomers pointed radio telescopes at known and catalogued brown dwarfs that were all found from their faint glow at infrared wavelengths. “With LOFAR, we want to go down the mass-ladder all the way to Jupiter-like planets that are too faint to have been found in existing infrared surveys, so we decided to search for these objects directly in our radio images,” said Dr. Joe Callingham, a VENI postdoctoral fellow at Leiden Observatory and co-author of the study.

Objects such as Elegast (and exoplanets) stand out in special “polarised” radio images because the electric field of the radio waves they emit rotates in a characteristic circular pattern as it propagates – a phenomenon called circular polarisation. “We could not have picked out Elegast in our standard radio images from among the crowd of millions of galaxies, but Elegast immediately stood out when we made circularly polarised images,” said Dr. Tim Shimwell, ASTRON staff and project scientist of the LOFAR survey that led to Elegast’s discovery. The group then used infrared follow-up observations from the Gemini telescope, a program of NSF's NOIRLab, and NASA’s Infrared Telescope Facility to confirm that Elegast was indeed a cold brown dwarf.

Elegast is the first object of its kind that has been directly identified in radio images. The group is now busy acquiring follow-up observations of Elegast to measure its magnetic field and compare the results with theory. They are also busy sifting through LOFAR data to identify more objects like Elegast.

“Our ultimate goal is to understand magnetism in exoplanets and how it impacts their ability to host life. Because magnetic phenomena of cold brown dwarfs like Elegast are so similar to what is seen on solar system planets, we expect our work to provide a vital datapoint to test theoretical models that predict the magnetic fields of extrasolar bodies,” said Vedantham.

The published journal article can be found here.

An open-access pre-print of the paper can be found here.

 

Source:  Astron/Astronomy/News

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100 Cool Worlds Found Near The Sun

Artist’s impression of one of this study’s superlative discoveries, the oldest known wide-separation white dwarf plus cold brown dwarf pair. the small white orb represents the white dwarf (the remnant of a long-dead sun-like star), while the brown/orange foreground object is the newly discovered brown dwarf companion. this faint brown dwarf was previously overlooked until it was spotted by citizen scientists because it lies right within the plane of the milky way. Credit: NOIRLab/NSF/AURA/P. Marenfeld; Acknowledgement: William Pendrill

Maunakea, Hawaii –  How complete is our census of the Sun’s closest neighbors? Astronomers and a team of data-sleuthing volunteers participating in Backyard Worlds: Planet 9, a citizen science project, have discovered roughly 100 cool worlds near the Sun — objects more massive than planets but lighter than stars, known as brown dwarfs.

With the help of W. M. Keck Observatory on Maunakea in Hawaii, the research team found several of these newly discovered worlds are among the very coolest known, with a few approaching the temperature of Earth — cool enough to harbor water clouds.

The study will be published in the August 20, 2020 issue of The Astrophysical Journal and is available in preprint format on arXiv.org.

Discovering and characterizing astronomical objects near the Sun is fundamental to our understanding of our place in, and the history of, the universe. Yet astronomers are still unearthing new residents of the solar neighborhood. The new Backyard Worlds discovery bridges a previously empty gap in the range of low-temperature brown dwarfs, identifying a long-sought missing link within the brown dwarf population.

“These cool worlds offer the opportunity for new insights into the formation and atmospheres of planets beyond the solar system,” said lead author Aaron Meisner from the National Science Foundation’s NOIRLab. “This collection of cool brown dwarfs also allows us to accurately estimate the number of free-floating worlds roaming interstellar space near the Sun.

To identify several of the faintest and coolest of the newly discovered brown dwarfs, UC San Diego’s Professor of Physics Adam Burgasser and researchers from the Cool Star Lab used Keck Observatory’s sensitive Near-Infrared Echellette Spectrometer, or NIRES, instrument.

“We used the NIRES spectra to measure the temperature and gases present in their atmospheres. Each spectrum is essentially a fingerprint that allows us to distinguish a cool brown dwarf from other kinds of stars,” said Burgasser, a co-author of the study.

Artist’s impression of the oldest known wide-separation white dwarf plus cold brown dwarf pair. The small white orb represents the white dwarf (the remnant of a long-dead Sun-like star), while the brown/orange foreground object is the newly discovered brown dwarf companion. This faint brown dwarf was previously overlooked until it was spotted by citizen scientists, because it lies right within the plane of the Milky Way. Credit: NOIRLab/NSF/AURA/P. Marenfeld 

Follow-up observations using NASA’s Spitzer Space Telescope, Mont Mégantic Observatory, and Las Campanas Observatory also contributed to the brown dwarf temperature estimates.

Brown dwarfs lie somewhere between the most massive planets and the smallest stars. Lacking the mass needed to sustain nuclear reactions in their core, brown dwarfs are sometimes referred to as “failed stars.” Their low mass, low temperature, and lack of internal nuclear reactions make them extremely faint — and therefore extremely difficult to detect. Because of this, when searching for the very coolest brown dwarfs, astronomers can only hope to detect such objects relatively close to the Sun.

To help find our Sun’s coldest, nearest neighbors, astronomers with the Backyard Worlds project turned to a worldwide network of more than 100,000 citizen scientists. These volunteers diligently inspect trillions of pixels of telescope images to identify the subtle movements of nearby brown dwarfs and planets. Despite the advances of machine learning and supercomputers, there’s still no substitute for the human eye when it comes to finding faint, moving objects.

Backyard Worlds volunteers have already discovered more than 1,500 stars and brown dwarfs near the Sun; this new discovery represents about 100 of the coldest in that sample. Meisner says this is a record for any citizen science program, and 20 of the citizen scientists are listed as co-authors of the study.

The availability of decades of astronomical catalogs through NOIRLab’s Astro Data Lab helped make the discoveries possible.

“The technical burden of downloading billion-object astronomical catalogs is typically insurmountable for individual investigators—including most professional astronomers,” said Meisner. “Thankfully, the Astro Data Lab’s open and accessible web portal allowed Backyard Worlds citizen scientists to easily query massive catalogs for brown dwarf candidates.”

Data sets from NASA’s WISE satellite as well as archival observations from telescopes at Cerro Tololo Inter-American Observatory and Kitt Peak National Observatory were also key to these brown dwarf discoveries.

“It’s exciting these could be spotted first by a citizen scientist,” said Meisner. “The Backyard Worlds discoveries show that members of the public can play an important role in reshaping our scientific understanding of our solar neighborhood.”

Source: W. M. Keck Observatory

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About NIRES

The Near Infrared Echellette Spectrograph (NIRES) is a prism cross-dispersed near-infrared spectrograph built at the California Institute of Technology by a team led by Chief Instrument Scientist Keith Matthews and Prof. Tom Soifer. Commissioned in 2018, NIRES covers a large wavelength range at moderate spectral resolution for use on the Keck II telescope and observes extremely faint red objects found with the Spitzer and WISE infrared space telescopes, as well as brown dwarfs, high-redshift galaxies, and quasars. Support for this technology was generously provided by the Mt. Cuba Astronomical Foundation.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems.

Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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The Formative Years: Giant Planets vs. Brown Dwarfs

GPI Survey from Franck Marchis on Vimeo.

Animation showing the 617 observations conducted during GPIES from November 2014 to April 2019 (right) and the location of the stars in the southern sky (left). Open circles indicate system (like 51 Eri at 2 o’clock) which have been visited multiple times. Stars indicated by a red dot have a disk of material. Blue dots are planetary systems (with one planet at least). Brown dot are binary systems with a brown dwarf. Credits: P. Kalas, D. Savransky, R. De Rosa and GPIES.

Based on preliminary results from a new Gemini Observatory survey of 531 stars with the Gemini Planet Imager (GPI), it appears more and more likely that large planets and brown dwarfs have very different roots.

The GPI Exoplanet Survey (GPIES), one of the largest and most sensitive direct imaging exoplanet surveys to date, is still ongoing at the Gemini South telescope in Chile. “From our analysis of the first 300 stars observed, we are already seeing strong trends,” said Eric L. Nielsen of Stanford University, who is the lead author of the study, published in The Astronomical Journal.

In November 2014, GPI Principal Investigator Bruce Macintosh of Stanford University and his international team set out to observe almost 600 young nearby stars with the newly commissioned instrument. GPI was funded with support from the Gemini Observatory partnership, with the largest portion from the US National Science Foundation (NSF). The NSF, and the Canadian National Research Council (NRC; also a Gemini partner), funded researchers participating in GPIES.

Imaging a planet around another star is a difficult technical challenge possible with only a few instruments. Exoplanets are small, faint, and very close to their host star — distinguishing an orbiting planet from its star is like resolving the width of a dime from several miles away. Even the brightest planets are ten thousand times fainter than their parent star. GPI can see planets up to a million times fainter, much more sensitive than previous planet-imaging instruments. “GPI is a great tool for studying planets, and the Gemini Observatory gave us time to do a careful, systematic survey,” said Macintosh.

GPIES is now coming to an end. From the first 300 stars, GPIES has detected six giant planets and three brown dwarfs. “This analysis of the first 300 stars observed by GPIES represents the largest, most sensitive direct imaging survey for giant planets published to date,” added Macintosh.

Brown dwarfs are more massive than planets, but not massive enough to fuse hydrogen like stars. “Our analysis of this Gemini survey suggests that wide-separation giant planets may have formed differently from their brown dwarf cousins,” Nielsen said.

The team’s paper advances the idea that massive planets form due to the slow accumulation of material surrounding a young star, while brown dwarfs come about due to rapid gravitational collapse. “It’s a bit like the difference between a gentle light rain and a thunderstorm,” said Macintosh.

“With six detected planets and three detected brown dwarfs from our survey, along with unprecedented sensitivity to planets a few times the mass of Jupiter at orbital distances well beyond Jupiter’s, we can now answer some key questions, especially about where and how these objects form,” Nielsen said.

This discovery may answer a longstanding question as to whether brown dwarfs — intermediate-mass objects — are born more like stars or planets. Stars form from the top down by the gravitational collapse of large primordial clouds of gas and dust, while planets are thought — but have not been confirmed — to form from the bottom up by the assembly of small rocky bodies that then grow into larger ones, a process also termed “core accretion.”

“What the GPIES team’s analysis shows is that the properties of brown dwarfs and giant planets run completely counter to each other,” said Eugene Chiang, professor of astronomy at the University of California Berkeley and a co-author of the paper. “Whereas more massive brown dwarfs outnumber less massive brown dwarfs, for giant planets the trend is reversed: less massive planets outnumber more massive ones. Moreover, brown dwarfs tend to be found far from their host stars, while giant planets concentrate closer in. These opposing trends point to brown dwarfs forming top-down, and giant planets forming bottom-up.”

More Surprises

Of the 300 stars surveyed thus far, 123 are at least 1.5 times more massive than our Sun. One of the most striking results of the GPI survey is that all hosts of detected planets are among these higher-mass stars — even though it is easier to see a giant planet orbiting a fainter, more Sun-like star. Astronomers have suspected this relationship for years, but the GPIES survey has unambiguously confirmed it. This finding also supports the bottom-up formation scenario for planets.

One of the study’s greatest surprises has been how different other planetary systems are from our own. Our Solar System has small rocky planets in the inner parts and giant gas planets in the outer parts. But the very first exoplanets discovered reversed this trend, with giant planets skimming closer to their stars than does moon-sized Mercury. Furthermore, radial-velocity studies — which rely on the fact that a star experiences a gravitationally induced “wobble” when it is orbited by a planet — have shown that the number of giant planets increases with distance from the star out to about Jupiter’s orbit. But the GPIES team’s preliminary results, which probe still larger distances, has shown that giant planets become less numerous farther out.

“The region in the middle could be where you're most likely to find planets larger than Jupiter around other stars," added Nielsen, “which is very interesting since this is where we see Jupiter and Saturn in our own Solar System.” In this regard, the location of Jupiter in our own Solar System may fit the overall exoplanet trend.

But a surprise from all exoplanet surveys is how intrinsically rare giant planets seem to be around Sun-like stars, and how different other solar systems are. The Kepler mission discovered far more small and close-in planets — two or more “super-Earth” planets per Sun-like star, densely packed into inner solar systems much more crowded than our own. Extrapolation of simple models suggested GPI would find a dozen giant planets or more, but it only saw six. Putting it all together, giant planets may be present around only a minority of stars like our own.

In January 2019, GPIES observed its 531st, and final, new star, and the team is currently following up the remaining candidates to determine which are truly planets and which are distant background stars impersonating giant planets.

The next-generation telescopes — such as NASA’s James Webb Space Telescope and WFIRST mission, the Giant Magellan Telescope, Thirty Meter Telescope, and Extremely Large Telescope — should be able to push the boundaries of study, imaging planets much closer to their star and overlapping with other techniques, producing a full accounting of giant planet and brown dwarf populations from 1 to 1,000 AU.

“Further observations of additional higher mass stars can test whether this trend is real,” said Macintosh, “especially as our survey is limited by the number of bright, young nearby stars available for study by direct imagers like GPI.”

Source:  Gemini Observatory/Releases

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Science Contacts:

• Eric Nielsen
  Stanford University
  Email: enielsen@standard.edu
  Phone: (408) 394-4582


• Bruce Macintosh
  Stanford University
  Email: bmacint@standard.edu
  


• Franck Marchis
  SETI Institute
  Email: fmarchis@seti.org
  Phone: (510) 599-0604

Media Contact:

• Peter Michaud
  Gemini Observatory, PIO Manager
  Email: pmichaud@gemini.edu
  Desk phone: 808-974-2510
  Cell phone: 808-936-6643

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Background:

GPI is specifically designed to search for planets and brown dwarfs around other stars, using a mask known as a coronagraph to partially block a star’s light. Together with adaptive optics correcting for turbulence in the Earth’s atmosphere and advanced image processing, researchers can search the star’s neighborhood for Jupiter-like exoplanets and brown dwarfs up to a million times fainter than the host star.

In our Solar System, Jupiter is the largest planet, being about 318 times as massive as the Earth and lying about five times farther from the Sun than does the Earth. Brown dwarfs range from 13 to 90 times the mass of Jupiter; and while they can be up to a tenth the mass of the Sun, they lack the nuclear fusion in their core to burn as a star — so they lie somewhere between a diminutive star and a super-planet.

An early success of GPIES was the discovery of 51 Eridani b in December 2014, a planet about two-and-a-half times more massive than Jupiter, that orbits its star beyond the distance that Saturn orbits our own Sun. The host star, 51 Eridani, is just 97 light-years away, and is only 26 million years old (nearby and young, by astronomy standards). The star had been observed by multiple planet-imaging surveys with a variety of telescopes and instruments, but its planet was not detected until GPI’s superior instrumentation was able to suppress the starlight enough for the planet to be visible.

GPIES also discovered the brown dwarf HR 2562 B, which is at a separation similar to that between the Sun and Uranus, and is 30 times more massive than Jupiter.

Most exoplanets discovered thus far, including those found by NASA’s Kepler spacecraft, are found via indirect methods, such as observing a dimming in the star’s light as the orbiting planet eclipses its parent star, or by observing the star’s wobble as the planet’s gravity tugs on the star. These methods have been very successful, but they only probe the central regions of planetary systems. Those regions outside the orbit of Jupiter, where the giant planets are in our Solar System, are usually out of their reach. GPI, however, endeavors to directly detect planets in this parameter space by taking a picture of them alongside their parent stars.

The Gemini results support those from these other techniques, including a recent study of exoplanets discovered by the radial velocity method that found the most likely separation for a giant planet around Sun-like stars is about 3 AU. The finding that brown dwarfs occur with a frequency of only about 1%, independent of stellar mass, is also consistent with previous results from direct imaging surveys.

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