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NASA’s Webb Telescope to investigate mysterious brown dwarfs

Twinkle, twinkle, little star, how I wonder what you are. Astronomers are hopeful that the powerful infrared capability of NASA’s James Webb Space Telescope will resolve a puzzle as fundamental as stargazing itself – what IS that dim light in the sky? Brown dwarfs muddy a clear distinction between stars and planets, throwing established understanding of those bodies, and theories of their formation, into question.

Several research teams will use Webb to explore the mysterious nature of brown dwarfs, looking for insight into both star formation and exoplanet atmospheres, and the hazy territory in-between where the brown dwarf itself exists. Previous work with Hubble, Spitzer, and ALMA have shown that brown dwarfs can be up to 70 times more massive than gas giants like Jupiter, yet they do not have enough mass for their cores to burn nuclear fuel and radiate starlight.

Though brown dwarfs were theorized in the 1960s and confirmed in 1995, there is not an accepted explanation of how they form: like a star, by the contraction of gas, or like a planet, by the accretion of material in a protoplanetary disk? Some have a companion relationship with a star, while others drift alone in space.

At the Université de Montréal, Étienne Artigau leads a team that will use Webb to study a specific brown dwarf, labeled SIMP0136. It is a low-mass, young, isolated brown dwarf – one of the closest to our Sun – all of which make it fascinating for study, as it has many features of a planet without being too close to the blinding light of a star.

SIMP0136 was the object of a past scientific breakthrough by Artigau and his team, when they found evidence suggesting it has a cloudy atmosphere. He and his colleagues will use Webb’s spectroscopic instruments to learn more about the chemical elements and compounds in those clouds.

“Very accurate spectroscopic measurements are challenging to obtain from the ground in the infrared due to variable absorption in our own atmosphere, hence the need for space-based infrared observation. Also, Webb allows us to probe features, such as water absorption, that are inaccessible from the ground at this level of precision,” Artigau explains.

These observations could lay groundwork for future exoplanet exploration with Webb, including which worlds could support life. Webb’s infrared instruments will be capable of detecting the types of molecules in the atmospheres of exoplanets by seeing which elements are absorbing light as the planet passes in front of its star, a scientific technique known as transit spectroscopy.

“The brown dwarf SIMP0136 has the same temperature as various planets that will be observed in transit spectroscopy with Webb, and clouds are known to affect this type of measurement; our observations will help us better understand cloud decks in brown dwarfs and planet atmospheres in general,” Artigau says.

The search for low-mass, isolated brown dwarfs was one of the early science goals put forward for the Webb telescope in the 1990s, says astronomer Aleks Scholz of the University of St. Andrews.

Brown dwarfs have a lower mass than stars and do not “shine” but merely emit the dim afterglow of their birth, and so they are best seen in infrared light, which is why Webb will be such a valuable tool in this research.

Scholz, who also leads the Substellar Objects in Nearby Young Clusters (SONYC) project, will use Webb’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) to study NGC 1333 in the constellation of Perseus. NGC 1333 is a stellar nursery that has also been found to harbor an unusually high number of brown dwarfs, some of them at the very low end of the mass range for such objects - in other words, not much heavier than Jupiter.

“In more than a decade of searching, our team has found it is very difficult to locate brown dwarfs that are less than five Jupiter-masses - the mass where star and planet formation overlap. That is a job for the Webb telescope,” Scholz says. “It has been a long wait for Webb, but we are very excited to get an opportunity to break new ground and potentially discover an entirely new type of planets, unbound, roaming the Galaxy like stars.”

Both of the projects led by Scholz and Artigau are making use of Guaranteed Time Observations (GTOs), observing time on the telescope that is granted to astronomers who have worked for years to prepare Webb’s scientific operations.

TOP IMAGE….Artist’s conception of a brown dwarf, featuring the cloudy atmosphere of a planet and the residual light of an almost-star. Credit NASA/ESA/JPL

LOWER IMAGE….Stellar cluster NGC 1333 is home to a large number of brown dwarfs. Astronomers will use Webb’s powerful infrared instruments to learn more about these dim cousins to the cluster’s bright newborn stars. Credit NASA/CXC/JPL

The window for saving the world’s coral reefs is rapidly closing

The world’s reefs are under siege from global warming, according to a novel study published today in the prestigious journal Science

The world’s reefs are under siege from global warming, according to a novel study published today in the prestigious journal Science.

For the first time, an international team of researchers has measured the escalating rate of coral bleaching at locations throughout the tropics over the past four decades. The study documents a dramatic shortening of the gap between pairs of bleaching events, threatening the future existence of these iconic ecosystems and the livelihoods of many millions of people.

“The time between bleaching events at each location has diminished five-fold in the past 3-4 decades, from once every 25-30 years in the early 1980s to an average of just once every six years since 2010,” says lead author Prof Terry Hughes, Director of the ARC Centre of Excellence for Coral Reef Studies (Coral CoE).

“Before the 1980s, mass bleaching of corals was unheard of, even during strong El Niño conditions, but now repeated bouts of regional-scale bleaching and mass mortality of corals has become the new normal around the world as temperatures continue to rise.”

The study establishes a transition from a period before the 1980s when bleaching only occurred locally, to an intermediate stage in the 1980s and 1990s when mass bleaching was first recorded during warmer than average El Niño conditions, and finally to the current era when climate-driven bleaching is now occurring throughout ENSO cycles.

The researchers show that tropical sea temperatures are warmer today during cooler than average La Niña conditions than they were 40 years ago during El Niño periods.

“Coral bleaching is a stress response caused by exposure of coral reefs to elevated ocean temperatures. When bleaching is severe and prolonged, many of the corals die. It takes at least a decade to replace even the fastest-growing species,” explained co-author Prof Andrew Baird of Coral CoE.

“Reefs have entered a distinctive human-dominated era - the Anthropocene,” said co-author, Dr C. Mark Eakin of the National Oceanic & Atmospheric Administration, USA. “The climate has warmed rapidly in the past 50 years, first making El Niños dangerous for corals, and now we’re seeing the emergence of bleaching in every hot summer.” For example, the Great Barrier Reef has now bleached four times since 1998, including for the first time during back-to-back events in 2016 and 2017, causing unprecedented damage. Yet the Australia government continues to support fossil fuels.

“We hope our stark results will help spur on the stronger action needed to reduce greenhouse gases in Australia, the United States and elsewhere,” says Prof Hughes.

IMAGE….A researcher from the ARC Centre of Excellence for Coral Reef Studies surveys the bleached/dead corals at Zenith Reef, Nov 2016. Credit Andreas Dietzel

New observations and modeling by a NASA-led team can help scientists understand a fast and furious jet stream high above Jupiter’s equator. This jet has a counterpart on Earth that seems to influence the transport of ozone, water vapor and pollution in the upper atmosphere, as well as the production of hurricanes. Credits: NASA’s Goddard Space Flight Center/Scientific Visualization Studio/Dan Gallagher

(NASA)  NASA Solves How a Jupiter Jet Stream Shifts into Reverse

Speeding through the atmosphere high above Jupiter’s equator is an east–west jet stream that reverses course on a schedule almost as predictable as a Tokyo train’s. Now, a NASA-led team has identified which type of wave forces this jet to change direction.

Similar equatorial jet streams have been identified on Saturn and on Earth, where a rare disruption of the usual wind pattern complicated weather forecasts in early 2016. The new study combines modeling of Jupiter’s atmosphere with detailed observations made over the course of five years from NASA’s Infrared Telescope Facility, or IRTF, in Hawai’i. The findings could help scientists better understand the dynamic atmosphere of Jupiter and other planets, including those beyond our solar system.

Earth’s equatorial jet stream was discovered after observers saw debris from the 1883 eruption of the Krakatoa volcano being carried by a westward wind in the stratosphere, the region of the atmosphere where modern airplanes achieve cruising altitude. Later, weather balloons documented an eastward wind in the stratosphere. Scientists eventually determined that these winds reversed course regularly and that both cases were part of the same phenomenon.

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Argyre Impact basin

Credits on photo

A NEW APPROACH FOR DETECTING PLANETS IN THE ALPHA CENTAURI SYSTEM

Yale astronomers have taken a fresh look at the nearby Alpha Centauri star system and found new ways to narrow the search for habitable planets there.

According to a study led by Professor Debra Fischer and graduate student Lily Zhao, there may be small, Earth-like planets in Alpha Centauri that have been overlooked. Meanwhile, the study ruled out the existence of a number of larger planets in the system that had popped up in previous models.

“The universe has told us the most common types of planets are small planets, and our study shows these are exactly the ones that are most likely to be orbiting Alpha Centauri A and B,” said Fischer, a leading expert on exoplanets who has devoted decades of research to the search for an Earth analog.

The new study appears in the Astronomical Journal. Co-authors are John Brewer and Matt Giguere of Yale and Bárbara Rojas-Ayala of Universidad Andrés Bello in Chile.

The Alpha Centauri system is located 1.3 parsecs (24.9 trillion miles) from Earth, making it our closest neighboring system. It has three stars: Centauri A, Centauri B, and Proxima Centauri. Last year, the discovery of an Earth-like planet orbiting Proxima Centauri set off a new wave of scientific and public interest in the system.

“Because Alpha Centauri is so close, it is our first stop outside our solar system,” Fischer said. “There’s almost certain to be small, rocky planets around Alpha Centauri A and B.”

The findings are based on data coming in from a new wave of more advanced spectrographic instruments at observatories located in Chile: CHIRON, a spectrograph built by Fischer’s team; HARPS, built by a team from Geneva; and UVES, part of the Very Large Telescope Array. “The precision of our instruments hasn’t been good enough, until now,” Fischer said.

The researchers set up a grid system for the Alpha Centauri system and asked, based on the spectrographic analysis, “If there was a small, rocky planet in the habitable zone, would we have been able to detect it?” Often, the answer came back: “No.”

Zhao, the study’s first author, determined that for Alpha Centauri A, there might still be orbiting planets that are smaller than 50 Earth masses. For Alpha Centauri B there might be orbiting planets than are smaller than 8 Earth masses; for Proxima Centauri, there might be orbiting planets that are less than one-half of Earth’s mass.

In addition, the study eliminated the possibility of a number of larger planets. Zhao said this takes away the possibility of Jupiter-sized planets causing asteroids that might hit or change the orbits of smaller, Earth-like planets.

“This is a very green study in that it recycles existing data to draw new conclusions,” said Zhao. “By using the data in a different way, we are able to rule out large planets that could endanger small, habitable worlds and narrow down the search area for future investigations.”

This new information will help astronomers prioritize their efforts to detect additional planets in the system, the researchers said. Likewise, the continuing effort by Fischer and others to improve spectrographic technology will help identify and understand the composition of exoplanets.

Illustration by Michael S. Helfenbein

Omega Centauri (ω Cen), or NGC 5139; globular cluster in the constellation of Centaurus.

Cut Timber

LIBRARY OF GALAXY HISTORIES RECONSTRUCTED FROM MOTIONS OF STARS

** Synopsis: The CALIFA survey allows to map the orbits of the stars of a sample of 300 galaxies, a fundamental information to know how they formed and evolved. **

Just like the Sun is moving in our galaxy, the Milky Way, all the stars in galaxies are moving, but with very different orbits: some of the stars have strong rotations, while others may be moving randomly with no clear rotation. Comparing the fraction of stars on different orbits we can find out how galaxies form and evolve. An international team of astronomers has derived directly, for the first time, the orbital distribution of a galaxy sample, containing more than 300 galaxies of the local universe. The results, published in Nature Astronomy, are based on the CALIFA survey, a project developed at Calar Alto Observatory and conceived from the Institute of Astrophysics of Andalusia (IAA-CSIC).

Galaxies are the largest structures in the universe, and scientist study how they evolve to understand the history of the universe. Galaxy formation entails the hierarchical assembly of halos of dark matter (a type of matter that has not been directly observed and whose existence and properties are inferred from its gravitational effects), along with the condensation of normal matter at the halos’ center, where stellar formation takes place. Stars that formed from a settled, thin gas disk and then lived though dynamically quiescent times will present near circular orbits, while stars with random motions are the result of turbulent environments, either at birth or later, with galactic mergers.

Thus, the motions of stars in a galaxy are like a history book; they record the information about their birth and growth environment, and it may tell us how the galaxy was formed. “However, the motion of each single star is not directly observable in external galaxies. External galaxies are projected on the observational plane as an image and we cannot resolve the discrete stars in it,” says Ling Zhu, researcher from the Max Planck Institute for Astronomy who leads the study. “The CALIFA survey uses a recently developed technique, integral field spectroscopy, which can observe the external galaxies in such a way that it provides the overall motion of stars. Thus, we can get kinematic maps of each galaxy.”

The researchers then build models for each galaxy by superposing stars on different types of orbits. By constraining the model with the observed image and kinematic maps, they can find out the amount of stars moving on different types of orbits in each galaxy. They call it the stellar orbit distribution and, for this study, the team has built models for all 300 galaxies, representative of the general properties of galaxies in the local universe.

The maps show changes in galactic orbit distribution depending on the total stellar mass of the galaxies. The ordered-rotating orbits are most prominent in galaxies with total stellar masses of 10 billion solar masses, and least important for the most massive ones. Random-motion orbits unsurprisingly dominate the most massive galaxies (more than 100 billion solar masses). “This is the first orbit-based mass sequence across all morphological types. It includes flourishing information of a galaxy’s past, basically whether it had been a quiet succession of only smaller mergers or shaped by a violent major merger. Further studies are needed to understand the details,” says Glenn van de Ven (ESO).

The researchers had found a new and accurate method of reading off a galaxy’s history – and their survey with its data sets for 300 galaxies turned out to be the largest existing library of galaxy history books.

“This work highlights the importance of integral field spectroscopy and, in particular, of large-scale surveys such as the CALIFA project. The significant contribution of what we call ‘hot’ orbits, a mixture of rotation and random movements of the stellar component, poses important challenges to cosmological models of galaxy formation and evolution,” says Rubén García Benito, a researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) participating in the project.

CALIFA’s results represent an observationally-determined orbit distribution of galaxies in the present-day universe. They lend themselves thus to direct comparison with samples of cosmological simulations of galaxies in a cosmological context. In this sense, these results open a new window for comparing galaxy simulations to the observed galaxy population in the present-day universe.