NASA’s Webb Telescope to Search for Young Brown Dwarfs and Rogue Planets

Scientists will use Webb to search the nearby stellar nursery NGC 1333 for its smallest, faintest residents. It is an ideal place to look for very dim, free-floating objects, including those with planetary masses. Credits: NASA/JPL-Caltech/R. A. Gutermuth (Harvard-Smithsonian CfA). Hi-res image

How small are the smallest celestial objects that form like stars, but don't produce their own light? How common are they compared to full-fledged stars? How about “rogue planets,” which formed around stars before being tossed into interstellar space? When NASA’s James Webb Space Telescope launches in 2021, it will shed light on these questions

Answering them will set a boundary between objects that form like stars, which are born out of gravitationally collapsing clouds of gas and dust, and those that form like planets, which are created when gas and dust clump together in a disk around a young star. It will also distinguish among competing ideas about the origins of brown dwarfs, objects with masses between 1% and 8% of the Sun that cannot sustain hydrogen fusion at their cores.

In a study led by Aleks Scholz of the University of St Andrews in the United Kingdom, researchers will use Webb to discover the smallest, faintest residents of a nearby stellar nursery called NGC 1333. Located about 1,000 light-years away in the constellation Perseus, the stellar cluster NGC 1333 is fairly close in astronomical terms. It is also very compact and contains many young stars. These three factors make it an ideal place to study star formation in action, particularly for those interested in very faint, free-floating objects.

“The least massive brown dwarfs identified so far are only five to 10 times heftier than the planet Jupiter,” explained Scholz. “We don’t yet know whether even lower mass objects form in stellar nurseries. With Webb, we expect to identify cluster members as puny as Jupiter for the first time ever. Their numbers relative to heftier brown dwarfs and stars will shed light on their origins and also give us important clues about the star formation process more broadly.”

A Fuzzy Boundary

Very low-mass objects are cool, meaning they emit most of their light in infrared wavelengths. Observing infrared light from ground-based telescopes is challenging because of interference from Earth's atmosphere. Due to its sheer size and ability to see infrared light with unprecedented sensitivity, Webb is ideally suited for finding and characterizing young free-floating objects with masses below five Jupiters.

The distinction between brown dwarfs and giant planets is blurry.

“There are some objects with masses below the 10-Jupiter mark freely floating through the cluster. As they don’t orbit any particular star, we may call them brown dwarfs, or planetary-mass objects, since we don’t know better,” said team member Koraljka Muzic of the University of Lisbon in Portugal. “On the other hand, some massive giant planets may have fusion reactions. And some brown dwarfs may form in a disk.”

There is also the issue of “rogue planets”—objects that form like planets and then later get ejected from their solar systems. These free-floating bodies are doomed to wander between the stars forever.

Dozens at Once

The team will use Webb’s Near Infrared Imager and Slitless Spectrograph (NIRISS) to study these various low-mass objects. A spectrograph breaks the light from a single source into its component colors the way a prism splits white light into a rainbow. That light carries fingerprints produced when material emits or interacts with light. Spectrographs allow researchers to analyze those fingerprints and discover properties like temperature and composition.

NIRISS will give the team simultaneous information for dozens of objects. “That is key. For an unambiguous confirmation of a brown dwarf or rogue planet we need to see the absorption signatures of molecules — water and methane primarily — in the spectra,” explained team member Ray Jayawardhana of Cornell University. “Spectroscopy is time consuming, and being able to observe many objects simultaneously helps enormously. The alternative is to take images first, measure colors, select candidates, and then go and take spectra, which will take much more time and relies on more assumptions.”

This work is being conducted as part of a Webb Guaranteed Time Observations (GTO) program. This program is designed to reward scientists who helped develop the key hardware and software components or technical and interdisciplinary knowledge for the observatory. Jayawardhana has been involved in the design and development of NIRISS, as well as its key science programs, as a core member of the instrument team since 2004.

The James Webb Space Telescope will be the world’s premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe 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.

For more information about Webb, visit www.nasa.gov/webb.

By Ann Jenkins
Space Telescope Science Institute
Baltimore, Md.

Editor: Lynn Jenner

Source: NASA/Webb Telescope

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Free-floating planets may be born free

Tiny, round, cold clouds in space have all the right characteristics to form planets with no parent star. New observations, made with Chalmers University of Technology telescopes, show that not all free-floating planets were thrown out of existing planetary systems. They can also be born free. 

​Previous research has shown that there may be as many as 200 billion free-floating planets in our galaxy, the Milky Way. Until now scientists have believed that such “rogue planets”, which don’t orbit around a star, must have been ejected from existing planetary systems.

New observations of tiny dark clouds in space point out another possibility: that some free-floating planets formed on their own.

A team of astronomers from Sweden and Finland used several telescopes to observe the Rosette Nebula, a huge cloud of gas and dust 4600 light years from Earth in the constellation Monoceros (the Unicorn).

They collected observations in radio waves with the 20-metre telescope at Onsala Space Observatory in Sweden, in submillimetre waves with APEX in Chile, and in infrared light with the New Technology Telescope (NTT) at ESO’s La Silla Observatory in Chile.

”The Rosette Nebula is home to more than a hundred of these tiny clouds – we call them globulettes”, says Gösta Gahm, astronomer at Stockholm University, who led the project.

“They are very small, each with diameter less than 50 times the distance between the Sun and Neptune. Previously we were able to estimate that most of them are of planetary mass, less than 13 times Jupiter’s mass. Now we have much more reliable measures of mass and density for a large number of these objects, and we have also precisely measured how fast they are moving relative to their environment”, he says.

 “We found that the globulettes are very dense and compact, and many of them have very dense cores. That tells us that many of them will collapse under their own weight and form free-floating planets. The most massive of them can form so-called brown dwarfs”, says team member Carina Persson, astronomer at Chalmers University of Technology.

Brown dwarfs, sometimes called failed stars, are bodies whose mass lies between that of planets and stars.

The study shows that the tiny clouds are moving outwards through the Rosette Nebula at high speed, about 80 000 kilometres per hour.

”We think that these small, round clouds have broken off from tall, dusty pillars of gas which were sculpted by the intense radiation from young stars. They have been accelerated out from the centre of the nebula thanks to pressure from radiation from the hot stars in its centre”, explains Minja Mäkelä, astronomer at the University of Helsinki.

According to Gösta Gahm and his team, the tiny dark clouds are being thrown out of the Rosette Nebula. During the history of the Milky Way, countless millions of nebulae like the Rosette have bloomed and faded away. In all of these, many globulettes would have formed.

Astronomers have found that tiny, round, dark clouds called globulettes have the right characteristics to form free-floating planets. The graph shows the spectrum of one of the globulettes taken at the 20-metre telescope at Onsala Space Observatory. Radio waves from molecules of carbon monoxide (13CO) give information on the mass and structure of these clouds. ESO/M. Mäkelä

More about exoplanets and free-floating planets

Astronomers know of almost 900 planets which orbit around other stars than the Sun, but free-floating planets have also been found. Some have been discovered using a technique called microlensing, in which the planet is found when it passes in front of a background star, temporarily making it look brighter. This is an effect predicted by Einstein’s theory of general relativity, in which the light from the star is bent when the planet passes in front of it, a so-called gravitational lens. Scientists have estimated that the number of free-floating planets in our galaxy may exceed 200 billion.

More about the research

The study has been published in the article Mass and motion of globulettes in the Rosette Nebula​ in the July issue of the journal Astronomy & Astrophysics. The team consists of Gösta Gahm (Stockholm University, Sweden), Carina M. Persson (Onsala Space Observatory at Chalmers University of Technology, Sweden), Minja M. Mäkelä (Department of Physics, University of Helsinki, Finland) and Lauri K. Haikala (Finnish Centre for Astronomy with ESO [FINCA], University of Turku, Finland).

More about the telescopes

The team observed radio waves from molecules of carbon monoxide using the 20-metre radio telescope at Onsala Space Observatory, Sweden, and submillimetre light with the telescope APEX at 5100 metres altitude in the Atacama desert in northern Chile. APEX is a collaboration between the Max Planck Institute for Radio Astronomy in Bonn, Germany, Onsala Space Observatory and ESO, with operations of the telescope entrusted to ESO. Observations in infrared light were made using the 3.58 metre New Technology Telescope (NTT) at ESO’s La Silla Observatory.

More about Onsala Space Observatory

Onsala Space Observatory is Sweden's national facility for radio astronomy. The observatory provides researchers with equipment for the study of the earth and the rest of the universe. In Onsala, 45 km south of Gothenburg, it operates two radio telescopes and a station in the international telescope Lofar. It also participates in several international projects. The observatory is hosted by Department of Earth and Space Sciences at Chalmers University of Technology, and is operated on behalf of the Swedish Research Council.

For more information, please contact:

Robert Cumming, 

astronomer and communications officer, 

Onsala Space Observatory at Chalmers University of Technology, 

+46 31-772 55 00 or +46-70-493 31 14, 

email:   robert.cumming@chalmers.se

Gösta Gahm, astronomer, 

Stockholm University, 

+46-73-785 70 71,

email: gahm@astro.su.se

Carina Persson, 

astronomer, 

Onsala Space Observatory at Chalmers University of Technology, 

+46 31-772 55 37, 

email: carina.persson@chalmers.se

Minja Mäkelä, 

Department of Physics, 

University of Helsinki, 

+358-9-191 50811,

email:  minja.makela@helsinki.fi​

 

Some Stars Capture Rogue Planets

In this artist's conception, a captured world drifts at the outer edge of a distant star system, so far from its Sun-like host that the star's disk is barely resolvable at upper right. New research shows that one in 20 stars within our galaxy might have captured a free-floating planet. Credit: Christine Pulliam (CfA). High Resolution Image (jpg) -Low Resolution Image (jpg)

Cambridge, MA - New research suggests that billions of stars in our galaxy have captured rogue planets that once roamed interstellar space. The nomad worlds, which were kicked out of the star systems in which they formed, occasionally find a new home with a different sun. This finding could explain the existence of some planets that orbit surprisingly far from their stars, and even the existence of a double-planet system.

"Stars trade planets just like baseball teams trade players," said Hagai Perets of the Harvard-Smithsonian Center for Astrophysics.

The study, co-authored by Perets and Thijs Kouwenhoven of Peking University, China, will appear in the April 20th issue of The Astrophysical Journal.

To reach their conclusion, Perets and Kouwenhoven simulated young star clusters containing free-floating planets. They found that if the number of rogue planets equaled the number of stars, then 3 to 6 percent of the stars would grab a planet over time. The more massive a star, the more likely it is to snag a planet drifting by.

They studied young star clusters because capture is more likely when stars and free-floating planets are crowded together in a small space. Over time, the clusters disperse due to close interactions between their stars, so any planet-star encounters have to happen early in the cluster's history.

Rogue planets are a natural consequence of star formation. Newborn star systems often contain multiple planets. If two planets interact, one can be ejected and become an interstellar traveler. If it later encounters a different star moving in the same direction at the same speed, it can hitch a ride.

A captured planet tends to end up hundreds or thousands of times farther from its star than Earth is from the Sun. It's also likely to have a orbit that's tilted relative to any native planets, and may even revolve around its star backward.

Astronomers haven't detected any clear-cut cases of captured planets yet. Imposters can be difficult to rule out. Gravitational interactions within a planetary system can throw a planet into a wide, tilted orbit that mimics the signature of a captured world.

Finding a planet in a distant orbit around a low-mass star would be a good sign of capture, because the star's disk wouldn't have had enough material to form the planet so far out.

The best evidence to date in support of planetary capture comes from the European Southern Observatory, which announced in 2006 the discovery of two planets (weighing 14 and 7 times Jupiter) orbiting each other without a star.

"The rogue double-planet system is the closest thing we have to a 'smoking gun' right now," said Perets. "To get more proof, we'll have to build up statistics by studying a lot of planetary systems."

Could our solar system harbor an alien world far beyond Pluto? Astronomers have looked, and haven't found anything yet.

"There's no evidence that the Sun captured a planet," said Perets. "We can rule out large planets. But there's a non-zero chance that a small world might lurk on the fringes of our solar system."

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

Source:Harvard-Smithsonian Center for Astrophysics