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Brown dwarfs and planets

Brown dwarfs and planets


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As far as I know, a brown dwarf is a 'star' whose core never underwent a fusion reaction, so it never became a star.

So I was wondering if, apart from orbiting a star, is there any difference between a massive planet and a brown dwarf?

I heard that they found an exoplanet 5 times the mass of Jupiter, and say a brown dwarf was in a binary pair where the other is a star: What stops it from being classified as a planet?

I guess what I am really asking for is a clearer definition of a brown dwarf.


Stanley, there really isn't a very clear definition and this is still a keenly argued point.

Definitions include:

Browns dwarfs burn deuterium. In models this happens if they are more massive than about 13 times Jupiter. The weakness of this that we think isolated brown dwarfs could condense from a gas cloud that are less massive than this; and young brown dwarfs won't have got around to fusing deuterium.

Planets must form from the disk around a star. This is ok, but: brown dwarfs may also form from the disk and it is also possible for planets to be tidally stripped from their stars and be found alone in space.

Planets must have a rocky core. This used to be thought definite, but now we think maybe sometimes planets can collapse from a gas instability in the disk in some circumstances, without the need for a rocky/icy core. It is true that brown dwarfs should not have a rocky core. However as an observational definition this is fairly hopeless since we can't even tell yet if Jupiter has a rocky core.

A flavour of the controversy can be gleaned from reading between the lines of the IAU statement on the definition of planets vs brown dwarfs.


Making Planets Around Brown Dwarfs

By: John Bochanski December 5, 2012 10

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Astronomers searching for forming planets have a new place to look. Even the thin disks around brown dwarfs are capable of forming grains large enough that, one day, they could potentially coalesce into a rocky planet.

An artist imagines what the debris disk surrounding a brown dwarf might look like.The tiny grains in this disk, called dust by astronomers, are similar in size to fine soot and sand.

ALMA (ESO/NAOJ/NRAO)/M. Kornmesser (ESO)

While debris disks have been observed around many young stars, the exact details of how planets form in these disks is an open question. Now, with new observations from one of the most sensitive telescopes on the planet, astronomers have added yet another clue to the planet-formation mystery.

Astronomer Luca Ricci (California Institute of Technology) led an international team that recently released results stemming from observations of the brown dwarf Rho-Oph 102. They observed the failed star using the combined power of 15 to 16 radio antennas, part of the Atacama Large Millimeter/submillimeter Array (ALMA). Located high in the Chilean desert, ALMA’s dishes will number 66 when the telescope finishes construction in 2013. But already the collection of 7-meter and 12-meter antennas makes up one of the most sensitive telescopes in the world. ALMA has been conducting science observations since the end of 2011.

The brown dwarf calls the Rho Ophiuchi star-forming region its home. Cross-hairs mark Rho-Oph 102's location.

ALMA (ESO / NAOJ / NRAO) / DSS2 / D. Martin


Formation failure

Brown dwarfs start out just like their main-sequence siblings. A cloud of dust and gas collapses, gravity piling the components in tightly and forming a young protostar at its center.

For main sequence stars, the gravity pushes inward until hydrogen fusion is jump-started in their core. But brown dwarfs never reach this crucial stage. Instead, before the temperatures get hot enough for hydrogen fusion to start, the close-packed material reaches a stable state and becomes a brown dwarf.

"Brown dwarfs are the missing link between gas giant planets like Jupiter and small stars like red dwarfs," Ian McLean, an astronomer at the University of California, Los Angeles, said in a statement.


Radio Transmission from a Brown Dwarf

By: Govert Schilling November 11, 2020 0

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The radio discovery of a brown dwarf holds promise for future exoplanet detections.

Artist’s impression of the cold brown dwarf BDR J1750+3809. 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.
ASTRON / Danielle Futselaar

For the first time ever, astronomers have found a cool brown dwarf with a radio telescope. The discovery suggests that future radio surveys may even turn up radio-emitting exoplanets that are too cool to detect by any other means. “It’s a very exciting result,” says David Charbonneau (Center for Astrophysics, Harvard & Smithsonian).

Electrons spiraling in the brown dwarf’s magnetic field produce the radio emission we see. According to study lead Harish Vedantham (ASTRON Netherlands Institute for Radio Astronomy), the radio waves are a low-energy form of synchrotron radiation. “Most likely, the same electrons also produce aurorae in the dwarf star’s atmosphere,” he says.

Radio-emitting brown dwarfs aren’t surprising by themselves: Radio waves from a known brown dwarf were first detected in 2001. And in 2012, Matthew Route and Aleksander Wolszczan (both at Penn State) detected radio emission from a cool “methane dwarf,” which has a surface temperature of just 900 degrees above absolute zero. However, that dwarf had first been found by its infrared glow in the Two Micron All-Sky Survey (2MASS), so the astronomers knew where to point their radio dish.

But until now, astronomers have never detected brown dwarfs solely by their radio emission. Now, the Low-Frequency Array (LOFAR) Two-metre Sky Survey has detected the new object, dubbed BDR 1750+380, in the constellation Hercules, based only on its strongly polarized radio waves.

LOFAR is an international network of more than 100,000 simple antennas, with its core in The Netherlands. Because of the low frequencies it detects, the array is sensitive to emissions from brown dwarfs, and maybe even planets with relatively small magnetic fields.

Vedantham and his colleagues used the Gemini North telescope and NASA’s Infrared Telescope Facility, both on Mauna Kea, Hawai‘i, to confirm that their radio source is a bona fide methane dwarf with spectral type T6.5 at a distance of just over 200 light-years. Its magnetic field is at least 25 Gauss strong, comparable to planetary-scale magnetic fields. The discovery appears in the November 10th Astrophysical Journal Letters.

“It’s essential that the existence of the brown dwarf has been confirmed by infrared observations,” comments Charbonneau. “A radio signal alone would certainly not be enough.” Wolszczan agrees. “Radio detection tells you nothing about the spectral type of the object, although you get its magnetic field, and, possibly its rotation period, if the detected emission is periodic,” he says.

The authors believe there’s more in store. “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,” says co-discoverer Joe Callingham (Leiden Observatory). He has bestowed the brown dwarf with the name Elegast, after a dwarf-like spirit in a 12th-century Middle Dutch poem.

“I’m particularly excited whenever a new method is developed to study exoplanets, since each method offers unique information,” Charbonneau says. “I’ll be following this project closely to see if this detection is followed by others.”


Coldest Brown Dwarf Ever Observed: Closing The Gap Between Stars And Planets

An international team of astronomers has discovered the coldest brown dwarf star ever observed. This finding, to be published in Astronomy & Astrophysics, is a new step toward filling the gap between stars and planets.

An international team [1] led by French and Canadian astronomers has just discovered the coldest brown dwarf ever observed. Their results will soon be published in Astronomy & Astrophysics. This new finding was made possible by the performance of telescopes worldwide [2]: Canada France Hawaii Telescope (CFHT) and Gemini North Telescope, both located in Hawaii, and the ESO/NTT located in Chile.

The brown dwarf is named CFBDS J005910.83-011401.3 (it will be called CFBDS0059 in the following). Its temperature is about 350°C and its mass about 15-30 times the mass of Jupiter, the largest planet of our solar system [3]. Located about 40 light years from our solar system, it is an isolated object, meaning that it doesn't orbit another star.

Brown dwarfs are intermediate bodies between stars and giant planets (like Jupiter). The mass of brown dwarfs is usually less than 70 Jupiter masses. Because of their low mass, their central temperature is not high enough to maintain thermonuclear fusion reactions over a long time. In contrast to a star like our Sun, which spends most of its lifetime burning hydrogen, hence keeping a constant internal temperature, a brown dwarf spends its lifetime getting colder and colder after its formation.

The first brown dwarfs were detected in 1995. Since then, this type of stellar object has been found to share common properties with giant planets, even though differences remain. For example, clouds of dust and aerosols, as well as large amounts of methane, were detected in their atmosphere (for the coldest ones), just as in the atmosphere of Jupiter and Saturn. However, there were still two major differences. In the brown dwarf atmospheres, water is always in gaseous state, while it condenses into water ice in giant planets and ammonia has never been detected in the brown dwarf near-infrared spectra, while it is a major component of Jupiter's atmosphere. CFBDS0059, the newly-discovered brown dwarf, looks much more like a giant planet than the known classes of brown dwarfs, both because of its low temperature and because of the presence of ammonia.

To date, two classes of brown dwarfs have been known: the L dwarfs (temperature of 1200-2000°C), which have clouds of dust and aerosols in their high atmosphere and the T dwarfs (temperature lower than 1200°C), which have a very different spectrum because of methane forming in their atmospheres. Because it contains ammonia and has a much lower temperature than do L and T dwarfs, CFBDS0059 might be the prototype of a new class of brown dwarfs to be called the Y dwarfs. This new class would then become the missing link in the sequence from the hottest stars to giant planets of less than -100°C, by filling the gap now left in the midrange.

This discovery also has important implications in the study of extrasolar planets. The atmosphere of brown dwarfs looks very much like that of giant planets, therefore the same models are used to reproduce their physical conditions. Such modeling needs to be tested against observations. Observing the atmospheres of extrasolar planets is indeed very hard because the light from the planets is embedded in the much stronger light from their parent stars. Because brown dwarfs are isolated bodies, they are much easier to observe. Thus, looking to brown dwarfs with a temperature close to that of the giant planets will help in testing the models of extrasolar planets' atmospheres.

[1] The team of astronomers includes P. Delorme, X. Delfosse (Observatoire de Grenoble, France), L. Albert (CFHT, Hawaii), E. Artigau (Gemini Observatory, Chile), T. Forveille (Obs. Grenoble/France, IfA/Hawaii), C. Reylé (Observatoire de Besançon, France), F. Allard, A. C. Robin (CRAL, Lyon, France), D. Homeier (Göttingen, Germany), C.J. Willott (University of Ottawa, Canada), M. C. Liu, T. J. Dupuy (IfA, Hawaii).

[2] CFBDS0059 was discovered in the framework of the Canada-France Brown-Dwarfs survey. The object was first identified in pictures from the wide-field camera Megacam installed on the CFHT (Canada France Hawaii Telescope). Infrared pictures were then obtained with the NTT telescope (La Silla, ESO, Chile) and confirmed the low temperature of the object. Finally, the spectrum showing the presence of ammonia was obtained using the Gemini North Telescope (Hawaii).

[3] The mass of Jupiter is about 300 times the Earth's mass and about 1/1000e of the Sun's mass.

Reference: CFBDS J005910.90-011401.3: reaching the T-Y brown dwarf transition? by P. Delorme, X. Delfosse, L. Albert, E. Artigau, T. Forveille, C. Reylé, F. Allard, D. Homeier, A. C. Robin, C.J. Willott, M. C. Liu, and T. J. Dupuy. Astronomy & Astrophysics, 2007, 473, p. 511. Full article available in PDF format.

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Failed Stars: Brown Dwarfs

Astronomers realized decades ago that the star formation process does not always produce a star. In order for an object to become a star, it has to achieve hydrostatic equilibrium by generating energy via nuclear fusion in its core. Do all protostellar cores eventually get hot enough to ignite nuclear fusion? The answer is NO.

We will be reminded frequently that the property that is most important for stars is their mass. Inside of GMCs, the clumps that form stars have a range of masses, and the stars that eventually form can be as large as 100 times the mass of the Sun or as small as 1/10 th the mass of the Sun. If a protostar has less than approximately 8% of the mass of the Sun (about 80 times the mass of the planet Jupiter), the temperature in the core will never reach a high enough point for the proton-proton chain to begin. Objects like this can be considered failed stars since they never achieve steady nuclear fusion in their core. They are usually referred to as brown dwarfs.

Recall that even before a protostar begins fusion, it is giving off light. This happens because the gravitational contraction is generating thermal energy inside the object. So, brown dwarfs do emit some light, however they are cool, so the peak of their spectrum is in the infrared. They are extremely faint, which makes them difficult to detect with all but the most sensitive telescopes. You may have seen in some of the images or external websites linked on previous pages that the standard list of spectral types (OBAFGKM) occasionally includes a few extra spectral types. Today, the most widely used set of stellar spectral types is OBAFGKMLT, and the last two classes, L and T, are the spectral types of brown dwarfs.

The direct observation of brown dwarfs is a relatively young area of study in astronomy. The object considered to be the first brown dwarf to be detected is Gliese 229B, and the press release at Hubblesite provides an excellent overview of that discovery. More recently, astronomers, including Professor Kevin Luhman of Penn State, have found many more objects they classify as brown dwarfs, but these faint, small, low mass objects remain difficult to detect.

Want to learn more?

There are many exciting discoveries of brown dwarfs that have been in the news lately, but here are three by Penn State's Kevin Luhman that you may wish to read:


Are brown dwarfs failed stars or super-planets?

Brown dwarfs fill the "gap" between stars and the much smaller planets -- two very different types of astronomical objects. But how they originate has yet to be fully explained. Astronomers from Heidelberg University may now be able to answer that question. They discovered that the star &nu Ophiuchi in the Milky Way is being orbited by two brown dwarfs, which in all probability formed along with the star from a gas and dust disk, just as planets do. The research results were published in Astronomy & Astrophysics.

Brown dwarfs orbit either one star or travel in isolation in the vast expanse of the Milky Way. Their mass -- they are at least 13 times heavier than the planet Jupiter -- is sufficient to generate, at least temporarily, energy in their core through nuclear fusion. They are not sufficiently massive, however, to ignite hydrogen in their cores and hence to create their own light. The heat they continue to radiate after formation is how astronomers are able to locate them. It is estimated that up to 100 billion brown dwarfs make their home in the Milky Way. Yet it remains unclear how they form -- whether they are "failed" stars or possibly even super-planets.

The recent discoveries made at the Centre for Astronomy of Heidelberg University (ZAH) could provide an answer. Prof. Dr Andreas Quirrenbach and his team at the Königstuhl State Observatory of the ZAH analysed the variations in radial velocity of the star &nu Ophiuchi. Using telescopes in the USA and Japan, the Heidelberg astronomers and others measured the velocity of the star for 11 years. The star has a mass slightly greater than two and half times that of the Sun, and is located approximately 150 light years from Earth in the constellation Ophiuchus.

The Heidelberg team noticed a certain pattern in the measurements, similar to those caused by orbiting planets or binary stars, which is usually nothing out of the ordinary. But in this case, in-depth analysis of the data revealed something extraordinary: apparently, &nu Ophiuchi is being orbited by two brown dwarfs with an orbital period of approximately 530 and 3,185 days, which puts them in a 6:1 resonant configuration. So, the brown dwarf closest to &nu Ophiuchi orbits its star exactly six times while the other, more distant brown dwarf completes only one orbit.

This discovery sheds completely new light on the evolution of brown dwarfs. Do they develop exclusively like normal stars in interstellar clouds, or can they also form in the so-called protoplanetary disk of gas and dust that surrounds the parent star in the early phase of its formation? "The 6:1 resonance is a strong indication for the latter scenario," explains Prof. Quirrenbach. "Only then could the orbits of the newly developing brown dwarfs adjust to a stable resonance over millions of years."

That is what the extensive dynamic analyses for possible configurations of the &nu Ophiuchi system suggest, reports the researcher. This superplanetary system is the first of its kind as well as the first sure sign that brown dwarfs can form in a protoplanetary disk, Prof. Quirrenbach stresses. The researcher and his team hope for other such discoveries that may one day allow them to clarify how many of the "failed" stars are actually more massive siblings of Jupiter and Saturn.


UCLA Astronomers obtain "Molecular Fingerprints" for Celestial "Brown Dwarfs," Missing Link between Stars and Planets

NIRSPEC instrument on the Nasmyth platform of the Keck II 10-m telescope.

Elusive brown dwarfs, the missing link between gas giant planets like Jupiter and small, low-mass stars, have now been “fingerprinted” by UCLA astronomy professor Ian S. McLean and colleagues, using the Keck II Telescope at the W.M. Keck Observatory in Hawaii.

McLean and his research team will publish the most systematic and comprehensive near-infrared spectral analysis of more than 50 brown dwarfs in the Oct. 10 issue of the Astrophysical Journal, the premier journal in astronomy, published by the American Astronomical Society.

“The infrared spectra of brown dwarfs reveal their atomic and molecular fingerprints,” said McLean. “Each class of brown dwarfs has a unique fingerprint. We have taken the spectra of more than 50 of them, which reveal their physical and chemical properties.”

Brown dwarfs are failed stars about the size of Jupiter, with a much larger mass -but not quite large enough to become stars. Like the sun and Jupiter, they are composed mainly of hydrogen gas, perhaps with swirling cloud belts. Unlike the sun, they have no internal energy source, and emit almost no visible light. Brown dwarfs are formed along with stars by the contraction of gases and dust in the interstellar medium, McLean said. The first brown dwarf was not discovered until 1995, yet McLean suspects the galaxy is teeming with them.

“Brown dwarfs are so elusive, so hard to find,” McLean said. “They can be detected best in the infrared, and even within the infrared, they are very difficult to detect,” McLean said. “We detect the heat glow from these faint objects in the infrared. Typically, they have to be relatively close by, within 100 light years, for us to even detect the heat signature.”

McLean and his colleagues do so using a sophisticated instrument that McLean designed and built at UCLA with other astronomers from UCLA and UC Berkeley. The instrument, attached to the W.M. Keck Observatory’s 10-meter Keck II Telescope atop Mauna Kea in Hawaii – the world’s largest optical and infrared telescope – is called NIRSPEC. It is six feet high, weighs one ton, and contains the most powerful infrared spectrometer in the world.

“This is the first time a large quantity of high quality spectral data are presented systematically in the infrared, where brown dwarfs emit most of their light,” said Davy Kirkpatrick, staff scientist at Caltech’s NASA-funded Infrared Processing and Analysis Center. “Approximately two percent of brown dwarfs near the sun are oddballs, and we are starting to be able to identify them and understand what makes them different. In addition, many brown dwarfs have been reported in different ways, and we now present them in a consistent manner that will become a standard reference for the future.”

McLean built the world’s first infrared camera for wide use by astronomers in 1986, and has built six increasingly sophisticated infrared cameras and spectrometers since then. (A spectrometer splits light into its component colors.)

“The quality of infrared spectra has improved drastically over the last decade,” he said.

The detectors in McLean’s spectrometers, such as NIRSPEC, have over 250 times as many picture elements as in the 1980s.

“The spectrum reveals what’s present and what’s missing,” McLean said. “What’s missing in the light tells us something in the atmosphere of the brown dwarf has absorbed the light.

“When we first studied the brown dwarf spectra, they were peculiar – like no star we had ever seen before. The reason we saw missing light in the spectra of the coolest brown dwarfs is the presence of methane in the atmosphere, which we also see in the outer gas giants of the solar system: Jupiter, Saturn, Uranus, Neptune.

“We also see evidence of water in the form of superheated steam, which we don’t see in any normal star like the sun. The sun is much too hot to have water molecules. Methane and water sculpt the infrared spectrum in a very distinctive way. The spectra of brown dwarfs show a gradual change from that of a star to that of Jupiter.

“Brown dwarfs are the missing link between gas giant planets like Jupiter and small stars like red dwarfs.”

If large numbers of brown dwarfs exist, they “could make a small, but significant contribution to dark matter,” the so-called “missing mass” in the universe, McLean said.

“Brown dwarfs won’t account for all of the so-called dark matter,” he said. “There is mass in the form of ordinary matter that is unaccounted for because we don’t yet have the technology to find it. There are brown dwarfs, and maybe small black holes, and faint white dwarfs – regular stars that lost their outer gaseous envelopes leaving the burned-out core of old stars. White dwarfs, brown dwarfs, black holes, and gas account for some of the dark matter. The rest is presumably a new form of matter.”

McLean and his colleagues – Kirkpatrick Adam Burgasser, a UCLA postdoctoral scholar in McLean’s group and recipient of a NASA-funded Hubble fellowship UCLA graduate student Mark McGovern and postdoctoral scholar Lisa Prato, who both work in McLean’s group and former UCLA postdoctoral scholar Sungsoo Kim – will publish an atlas and analysis of brown dwarf infrared spectra in the Oct. 10 Astrophysical Journal. Kirkpatrick and Burgasser were responsible for most of the initial brown dwarf identifications using an infrared all-sky survey called 2MASS. McLean praised the members of his research team as “instrumental to the success” of the research.

“After four years of data gathering from NIRSPEC, we have obtained and studied spectra from more than 50 brown dwarfs, and analyzed the variations,” McLean said. “Astronomers in the future will be able to obtain the infrared spectrum of a newly discovered brown dwarf and compare the spectrum with those we have published and instantly identify what kind of brown dwarf they have found. Probing more distant regions of the galaxy to study the youngest, recently-formed brown dwarfs is the next step.”

His research, including NIRSPEC, was funded by the California Association for Research in Astronomy, the entity that operates the W.M. Keck Observatory.

To do his research, McLean designs and builds spectrometers, and analyzes astrophysics data.

“The astronomy motivates me, but I have to be a bit of an engineer and experimental physicist as well,” he said, “because technology is the key to new discoveries.”


Brown Dwarfs Mimic Their Big Stellar Siblings

By: John Bochanski May 24, 2017 1

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Two recent studies suggest that brown dwarfs, or so-called “failed stars,” are nevertheless more like stars than planets.

Artist's conception of a brown dwarf.
NASA / JPL-Caltech

Brown dwarfs are the exceedingly common runts of the stellar litter. But even though they’re everywhere, their faint glow makes them difficult to observe and understand. Two recent studies shed light on the formation of these once-exotic objects.

First proposed as an idea in the 1960s and finally discovered in the 1990s, brown dwarfs bridge the gap between the smallest stars and the largest planets, never igniting hydrogen fusion in their cores. They cool off over time, slowly shedding the nascent heat leftover from their formation as a dim glow.

In the last two decades, astronomers have scrutinized hundreds of these objects, studying their properties and pondering their formation. Did brown dwarfs form like stars, condensing out of gigantic clouds of dust and gas? Or did they come together in the same way as planets do, within the disk around another star? The debate rang out in meetings all over the world, but gradually evidence pointed to a scaled-down version of star formation.

Now, two exciting new studies suggest that brown dwarfs (including one with a mass of just 12 times that of Jupiter) are mimicking their bigger stellar siblings in other ways.

A Brown Dwarf’s Star-Like Jet

This image shows the jet launched by a brown dwarf in the outer periphery of the sigma Ori cluster. Traced by emission from singly ionized sulfur, which appears green in the image, the jet extends 0.7 light years northwest of the brown dwarf. Click image for larger version.
NOAO

Basmah Riaz (Max Planck Institute for Extraterrestrial Physics, Germany) and colleagues used the Southern Astrophysical Research telescope (SOAR) to study a young brown dwarf, dubbed Mayrit 1701117, in the 3 million-year old sigma Ori star cluster. The observations, to be published in the Astrophysical Journal, showed the brown dwarf to be powering a jet of material that launches gas up to 0.7 light-years from the object.

Jets have often been observed coming from young stars as well as brown dwarfs, but brown dwarf jets have typically been much smaller than their stellar counterparts. This jet, though, is the largest ever observed from a brown dwarf. And just like jets coming from more massive stars, this one also varies with time, its gas clumping as it flows outward. That kind of knottiness indicates that the gas is probably powered by accreting material that falls irregularly onto the brown dwarf.

“The jet shows all the familiar hallmarks of outflows from stars . . . it checks all the boxes quite convincingly,” says coauthor Emma Whelan (National University of Ireland, Maynooth).

Star-like Disk Feeds Infant Brown Dwarf

Artists' impression of the gas and dust disk around the planet-like object OTS44. First radio observations indicate that OTS44 has formed in the same way as a young star.
Johan Olofsson (Univ. Valparaiso & MPIA)

Young stars are often found surrounded by disks of gas and dust leftover from their formation. Some of this disk material falls onto the star itself, while other parts eventually form planets and other small objects. Some brown dwarfs have such disks too, but until now, such disks have only been discovered around much more massive brown dwarfs.

In another study, published in Astrophysical Journal Letters and led by Amelia Bayo (University of Valparaíso, Chile), focused on OST44, a planetary-mass object in the Chameleon star-forming region. It isn’t a brown dwarf exactly — the boundaries that divide stars, brown dwarfs and planets are fuzzy. Brown dwarfs traditionally contain between 13 and 75 times the mass of Jupiter, but the exact boundaries can shift depending on what the object’s made of. With a mass 12 times Jupiter’s, OST44 lies right on the planet-brown dwarf boundary. .

Bayo used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to examine the disk of cool gas around OST44, the least massive brown dwarf-ish object to host an accretion disk. At just 2 million years old, the object is an infant in astronomical terms and it’s still growing, as gas flows inward from its disk.

From the ALMA data Bayo and colleagues measured the amount of dust around OST44 and found that it matched what’s expected based on observations of disks around other stars and more massive brown dwarfs. So it seems the astronomers have caught this object in the act of forming like a star.

But these new observations present a new challenge: From what we know, star formation methods shouldn’t be able to produce planet-mass objects. Yet that seems to be exactly what happened here.

To understand how these runts can act like their bigger stellar siblings, producing large-scale jets and feeding from swirling disks of gas, astronomers will need more data. You can expect more exciting results from ALMA in this regime, as it studies more young, low-mass objects in the future.


Brown dwarfs and planets - Astronomy

A planetary atmosphere is the outer gas layer of a planet. Besides its scientific significance among the first and most accessible planetary layers observed from space, it is closely connected with planetary formation and evolution, surface and interior processes, and habitability of planets. Current theories of planetary atmospheres were primarily obtained through the studies of eight large planets, Pluto and three large moons (Io, Titan, and Triton) in the Solar System. Outside the Solar System, more than four thousand extrasolar planets (exoplanets) and two thousand brown dwarfs have been confirmed in our Galaxy, and their population is rapidly growing. The rich information from these exotic bodies offers a database to test, in a statistical sense, the fundamental theories of planetary climates. Here we review the current knowledge on atmospheres of exoplanets and brown dwarfs from recent observations and theories. This review highlights important regimes and statistical trends in an ensemble of atmospheres as an initial step towards fully characterizing diverse substellar atmospheres, that illustrates the underlying principles and critical problems. Insights are obtained through analysis of the dependence of atmospheric characteristics on basic planetary parameters. Dominant processes that influence atmospheric stability, energy transport, temperature, composition and flow pattern are discussed and elaborated with simple scaling laws. We dedicate this review to Dr. Adam P. Showman (1968-2020) in recognition of his fundamental contribution to the understanding of atmospheric dynamics on giant planets, exoplanets and brown dwarfs.