Month: March 2016

Wellspring of New Brown Dwarf Stellar Companions

A new paper published this month in The Astronomical Journal by astronomers from the Sloan Digital Sky Survey (SDSS) reports a wellspring of new brown dwarf stellar companions, throwing cold water on the entire idea of the “brown dwarf desert,” the previously mystifying lack of these sub-stellar objects around stars.

brown-dwarf-plasmaspher

Most stars in our Galaxy have a traveling companion. Often, these companions are stars of similar mass, as is the case for our nearest stellar neighbors, the triple star system Alpha Centauri.

brown_dwarf_size

Our Sun, of course, has companions of its own – the planets of our Solar System. Planetary companions are vastly different from stellar companions: they are much smaller, and they do not shine with their own light created through nuclear fusion. Even the largest planet in our Solar System, Jupiter, would need to be 80 times more massive to even begin to shine this way.

Stuck in the middle are “brown dwarfs,” much bigger than Jupiter but still too small to be shining stars. These brown dwarfs give off merely a dim glow as they slowly cool. The Universe is full of stars, and now we know that it is full of planets too. Astronomers expected that the Universe would also be teeming with brown dwarfs.

But strangely, that’s not what they had been finding. Although astronomers have found plenty of brown dwarfs floating through space on their own, they found very few as stellar companions. Even in recent years, as new and sensitive detection techniques have allowed them to discover thousands of extrasolar planets, brown dwarfs have remained elusive – in spite of the fact that they should be easier to find than planets.

In fact, until recently, so few brown dwarfs have been found orbiting close to other stars that astronomers refer to the phenomenon as the “brown dwarf desert.” This in turn created a problem for theorists, who have been scrambling to explain why astronomers have found so few. Therefore when SDSS astronomers started sifting through their data looking for brown dwarf companions to stars, they were hoping not to come up completely dry.

“We were shocked to find that so many of the stars in our sample have close-orbiting brown dwarf companions,” says Nick Troup of the University of Virginia, lead author of the paper. “We never expected to triple the total number of known brown dwarf companions with only a few years’ worth of observations.”

The team’s success is due to an unlikely tool in the race to find low-mass stellar companions. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) was designed as a substantial survey of stars in our Milky Way to make a large-scale map of their motions and chemical compositions. But the instrument built for the APOGEE project is so sensitive to small stellar motions that companions orbiting these stars can be detected with APOGEE data.

When an object orbits a star, it tugs at it, causing the star to move on a little orbit of its own. For example, Jupiter tugs on the Sun enough to make it wobble around in space by more than its own diameter. To a distant observer, this wobble can be detected—and the mass of the tugging object can be determined—through changes in the motion of the star. This motion is seen through the Doppler effect, the same phenomenon that is the basis of the patrol officer’s speed gun and the meteorologist’s Doppler radar rain map. While APOGEE was designed to measure the grand motions of stars speeding around the Galaxy, it was never intended to do so at the subtle precisions needed to detect the much tinier wobbles induced by small sub-stellar companions.

“This level of precision was a serendipitous bonus of the design of the APOGEE spectrograph”, says John Wilson, University of Virginia astronomer and leader of the APOGEE instrument team. “The entire instrument has to be contained in a giant steel vessel in a vacuum at –320 degrees F, otherwise the instrument’s own heat would swamp the infrared signals from the stars.” It turns out that this tightly controlled environment makes it possible to use the APOGEE instrument to measure Doppler shifts reliably over the course of months or years, a feat not achievable by many other spectrographs.

“Even with the first data obtained a few years ago, it was clear that we could use APOGEE to detect the motions of planet-sized objects around our target stars,” says David Nidever of the University of Arizona and the Large Synoptic Survey Telescope, who was responsible for writing much of the software that measures the Doppler motions in APOGEE spectra. “It definitely opened our eyes to the possibilities of doing a more systematic search for planets and brown dwarfs.”

To undertake such a search, the team started with the 150,000 stars that APOGEE had observed. The astronomers winnowed that collection of stars down to a “prime sample” of about four hundred representing the best examples of stars with companions in the APOGEE data. Among these, they identified about 60 stars with evidence for planetary-mass candidates, which was already exciting.
But the real surprise came with the researchers’ extraordinary haul of 112 brown dwarf candidates – twice as many than had been found in the previous 15 years.

Why has the APOGEE team been so lucky in finding this oasis of brown dwarfs? Troup thinks it may have to do with the types of host stars that they are looking at. “Most people doing planet searches have been interested in finding the next Earth, so they’ve focused their efforts on stars similar to the Sun,” Troup says. “But we had to work with the stars that APOGEE surveyed, which are mostly giant stars.”

The reasons why brown dwarf companions are more common around giant stars is just one of many new questions raised by this new study that the Sloan team is investigating. And the team will continue to test their results with the ever-growing flow of APOGEE data.

“It’s completely unprecedented that this many brown dwarf companions have been found at once, so we are anxious to see if the trend persists as the APOGEE sample grows to several times larger,” Troup said.
Read more at: http://phys.org/news/2016-03-oasis-brown-dwarf-desertastronomers-relieved.html#jCp

Andromeda’s First Spinning Neutron Star Found

Decades of searching in the Milky Way’s nearby ‘twin’ galaxy Andromeda have finally paid off, with the discovery of an elusive breed of stellar corpse, a neutron star, by ESA’s XMM-Newton space telescope.

Andromeda galaxy

Andromeda, or M31, is a popular target among astronomers. Under clear, dark skies it is even visible to the naked eye. Its proximity and similarity in structure to our own spiral galaxy, the Milky Way, make it an important natural laboratory for astronomers. It has been extensively studied for decades by telescopes covering the whole electromagnetic spectrum.

Despite being extremely well studied, one particular class of object had never been detected: spinning neutron stars.

Neutron stars are the small and extraordinarily dense remains of a once-massive star that exploded as a powerful supernova at the end of its natural life. They often spin very rapidly and can sweep regular pulses of radiation towards Earth, like a lighthouse beacon appearing to flash on and off as it rotates.

These ‘pulsars’ can be found in stellar couples, with the neutron star cannibalizing its neighbor. This can lead to the neutron star spinning faster, and to pulses of high-energy X-rays from hot gas being funneled down magnetic fields on to the neutron star.

Binary systems hosting a neutron star like this are quite common in our own galaxy, but regular signals from such a pairing had never before been seen in Andromeda.

Now, astronomers systematically searching through the archives of data from XMM-Newton X-ray telescope have uncovered the signal of an unusual source fitting the bill of a fast-spinning neutron star.

It spins every 1.2 seconds, and appears to be feeding on a neighboring star that orbits it every 1.3 days.

“We were expecting to detect periodic signals among the brightest X-ray objects in Andromeda, in line with what we already found during the 1960s and 1970s in our own galaxy,” says Gian Luca Israel, from INAF-Osservatorio Astronomica di Roma, Italy, one of the authors of the paper describing the results, “But persistent, bright X-ray pulsars like this are still somewhat peculiar, so it was not completely a sure thing we would find one in Andromeda.

“We looked through archival data of Andromeda spanning 2000-13, but it wasn’t until 2015 that we were finally able to identify this object in the galaxy’s outer spiral in just two of the 35 measurements.”

While the precise nature of the system remains unclear, the data imply that it is unusual and exotic.

“It could be what we call a ‘peculiar low-mass X-ray binary pulsar’—in which the companion star is less massive than our Sun—or alternatively an intermediate-mass binary system, with a companion of about two solar masses,” says Paolo Esposito of INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan, Italy.

“We need to acquire more observations of the pulsar and its companion to help determine which scenario is more likely.”
“The well-known Andromeda galaxy has long been a source of exciting discoveries, and now an intriguing periodic signal has been detected by our flagship X-ray mission,” adds Norbert Schartel, ESA’s XMM-Newton Project Scientist.

“We’re in a better position now to uncover more objects like this in Andromeda, both with XMM-Newton and with future missions such as ESA’s next-generation high-energy observatory, ATHENA.”

Laser Cloaking Device Can Conceal Earth

Two astronomers at Columbia University in New York suggest humanity could use lasers to conceal the Earth from searches by advanced extraterrestrial civilizations. Professor David Kipping and graduate student Alex Teachey made the proposal in a paper in Monthly Notices of the Royal Astronomical Society.

lasercloakin

Several prominent scientists, including Stephen Hawking, have cautioned against humanity broadcasting our presence to intelligent life on other planets. Other civilisations might try to find Earth-like planets using the same techniques we do, including looking for the dip in light when a planet moves directly in front of the star it orbits.

These events – transits – are the main way that the Kepler mission and similar projects search for planets around other stars. So far Kepler alone has confirmed more than 1,000 planets using this technique, with tens of these worlds similar in size to the Earth. Kipping and Teachey speculate that alien scientists may use this approach to locate our planet, which will be clearly in the ‘habitable zone’ of the Sun, where the temperature is right for liquid water, and so be a promising place for life.

Hawking and others are concerned that extraterrestrials might wish to take advantage of the Earth’s resources, and that their visit, rather than being benign, could be as devastating as when Europeans first travelled to the Americas.

The two authors of the new study suggest that transits could be masked by controlled laser emission, with the beam directed at the star where the aliens might live. When the transit takes place, the laser would be switched on to compensate for the dip in light.

According to the authors, emitting a continuous 30 MW laser for about 10 hours, once a year, would be enough to eliminate the transit signal, at least in visible light. The energy needed is comparable to that collected by the International Space Station in a year. A chromatic cloak, effective at all wavelengths, is more challenging, and would need a large array of tuneable lasers with a total power of 250 MW.

“Alternatively, we could cloak only the atmospheric signatures associated with biological activity, such as oxygen, which is achievable with a peak laser power of just 160 kW per transit. To another civilisation, this should make the Earth appear as if life never took hold on our world”, said Alex.

As well as cloaking our presence, the lasers could also be used to modify the way the light from the Sun drops during a transit to make it obviously artificial, and thus broadcast our existence. The authors suggest that we could transmit information along the laser beams at the same time, providing a means of communication.

David comments: “There is an ongoing debate as to whether we should advertise ourselves or hide from advanced civilisations potentially living on planets elsewhere in the Galaxy. Our work offers humanity a choice, at least for transit events, and we should think about what we want to do.”

Given that humanity is already capable of modifying transit signals, it may just be that aliens have had the same thought. The two scientists propose that the Search for Extraterrestrial Intelligence (SETI), which mostly currently looks for alien radio signals, could be broadened to search for artificial transits.

Gold Star: Seeking The Origin Of Gold In The Universe

Michigan State University researchers, working with colleagues from Technical University Darmstadt in Germany, are zeroing in on the answer to one of science’s most puzzling questions: Where did heavy elements, such as gold, originate?

gold star

Currently there are two candidates, neither of which are located on Earth — a supernova, a massive star that, in its old age, collapsed and then catastrophically exploded under its own weight; or a neutron-star merger, in which two of these small yet incredibly massive stars come together and spew out huge amounts of stellar debris.

In a recently published paper in the journal Physical Review Letters, the researchers detail how they are using computer models to come closer to an answer.

“At this time, no one knows the answer,” said Witold Nazarewicz, a professor at the MSU-based Facility for Rare Isotope Beams and one of the co-authors of the paper. “But this work will help guide future experiments and theoretical developments.”

By using existing data, often obtained by means of high-performance computing, the researchers were able to simulate production of heavy elements in both supernovae and neutron-star mergers.

“Our work shows regions of elements where the models provide a good prediction,” said Nazarewicz, a Hannah Distinguished Professor of Physics who also serves as FRIB’s chief scientist. “What we can do is identify the critical areas where future experiments, which will be conducted at FRIB, will work to reduce uncertainties of nuclear models.”

Other researchers included Dirk Martin and Almudena Arcones from Technical University Darmstadt and Erik Olsen of MSU.

MSU is establishing FRIB as a new scientific user facility for the Office of Nuclear Physics in the U.S. Department of Energy Office of Science.

Titan’s Tallest Peaks: Towering Mountain Discovered On Saturn’s Largest Moon

Titan’s tallest peak is 10,948 feet (3,337 meters) high and is found within a trio of mountainous ridges called the Mithrim Montes. The researchers found that all of Titan’s highest peaks are about 10,000 feet (3,000 meters) in elevation. The study used images and other data from Cassini’s radar instrument, which can peer through the obscuring smog of Titan’s atmosphere to reveal the surface in detail.

titan

“It’s not only the highest point we’ve found so far on Titan, but we think it’s the highest point we’re likely to find,” said Stephen Wall, deputy lead of the Cassini radar team at NASA’s Jet Propulsion Laboratory in Pasadena, California.

The results, which use data collected by Cassini’s radar instrument, are being presented today at the 47th annual Lunar and Planetary Science Conference at The Woodlands, Texas.

Most of Titan’s tallest mountains appear to be close to the equator. The researchers identified other peaks of similar height within the Mithrim Montes, as well as in the rugged region known as Xanadu, and in collections of more isolated peaks called “ridge belts” located near the landing site of ESA’s Huygens probe.

The investigation was originally motivated by a search for active zones within Titan’s crust — places where dynamic forces have shaped the landscape, perhaps in the relatively recent past.

“As explorers, we’re motivated to find the highest or deepest places, partly because it’s exciting. But Titan’s extremes also tell us important things about forces affecting its evolution,” said Jani Radebaugh, a Cassini radar team associate at Brigham Young University in Provo, Utah, who led the research.

Mountains and cliffs on Earth usually are found in locations where forces have shoved the surface upward from underneath. Forces of erosion, including wind, rain and runoff, slowly wear them down over time. The Himalaya and Andes Mountains are examples of places where interior forces are at work today. The Appalachian Mountains represent much more ancient activity that produced similarly gigantic peaks long ago, which have since eroded.

Cassini has found that Titan also has rain and rivers that erode its landscape. According to Radebaugh, the process probably proceeds much more slowly on Titan than on Earth because, at 10 times Earth’s distance from the sun, there is less energy to power erosive processes in the moon’s atmosphere.

Titan’s icy crust sits atop a deep ocean of liquid water that probably acts much like Earth’s upper mantle — the layer of hot, high-pressure rock below the crust that can slowly flow and deform over time. Once a period of mountain-building ends, these fluid layers (Earth’s upper mantle and Titan’s liquid ocean) allow the crust to relax, like a person settling into a waterbed. Also, at great depth, the water-ice bedrock of Titan is softer than rock on Earth. Because of these characteristics, scientists didn’t expect mountains on Titan would tower quite as high as those on Earth, which can rise to more than 5 miles (nearly 9 kilometers) tall.

The fact that Titan has significant mountains at all suggests that some active tectonic forces could be affecting the surface, for example, related to Titan’s rotation, tidal forces from Saturn or cooling of the crust. The next step for the researchers will be trying to figure out what could produce such tall peaks on an icy ocean world.

“There is lot of value in examining the topography of Titan in a broad, global sense, since it tells us about forces acting on the surface from below as well as above,” said Radebaugh.

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. JPL designed, developed and assembled the Cassini orbiter. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the US and several European countries.

Scientists Explain Evolution Of Some Of The Largest Dinosaurs

Scientists from the University of Liverpool have developed computer models of the bodies of sauropod dinosaurs to examine the evolution of their body shape.

dinosaurs

Sauropod dinosaurs include the largest land animals to have ever lived. Some of the more well-known sauropods include Diplodocus, Apatosaurus and Brontosaurus. They are renowned for their extremely long necks, long tails as well as four thick, pillar-like legs and small heads in relation to their body.

To date, however, there have been only limited attempts to examine how this unique body-plan evolved and how it might be related to their gigantic body size. Dr Karl Bates from the University’s Department of Musculoskeletal Biology and his colleagues used three-dimensional computer models reconstructing the bodies of sauropod dinosaurs to analyse how their size, shape and weight-distribution evolved over time.

Evolutionary history

Dr Bates found evidence that changes in body shape coincided with major events in sauropod evolutionary history such as the rise of the titanosaurs. The early dinosaurs that sauropods evolved from were small and walked on two legs, with long tails, small chests and small forelimbs. The team estimate that this body shape concentrated their weight close to the hip joint, which would have helped them balance while walking bipedally on their hind legs.

As sauropods evolved they gradually altered both their size and shape from this ancestral template, becoming not only significantly larger and heavier, but also gaining a proportionally larger chest, forelimbs and in particular a dramatically larger neck.

The team’s findings show that these changes altered sauropods’ weight distribution as they grew in size, gradually shifting from being tail-heavy, two-legged animals to being front-heavy, four-legged animals, such as the large, fully quadrupedal Jurassic sauropods Diplodocus and Apatosaurus.

The team found that these linked trends in size, body shape and weight distribution did not end with the evolution of fully quadrupedal sauropods. In the Cretaceous period — the last of the three ages of the dinosaurs — many earlier sauropod groups dwindled. In their place, a new and extremely large type of sauropod known as titanosaurs evolved, including the truly massive Argentinosaurus and Dreadnoughtus, among the largest known animals ever to have lived.

Front heavy

The team’s computer models suggest that in addition to their size, the titanosaurs evolved the most extreme ‘front heavy’ body shape of all sauropods, as a result of their extremely long necks.

Dr Bates said: “As a result of devising these models we were able to ascertain that the relative size of sauropods’ necks increased gradually over time, leading to animals that were increasingly more front-heavy relative to their ancestors.”

Dr Philip Mannion from Imperial College London, a collaborator in the research, added: “These innovations in body shape might have been key to the success of titanosaurs, which were the only sauropod dinosaurs to survive until the end-Cretaceous mass extinction, 66 million years ago.”

Dr Vivian Allen from the Royal Veterinary College London, who also collaborated in the research, added: “What’s important to remember about studies like this is that there is a very high degree of uncertainty about exactly how these animals were put together. While we have good skeletons for many of them, it’s difficult to be sure how much meat there was around each of the bones. We have built this uncertainly into our models, ranging each body part from emaciated to borderline obesity, and even using these extremes we still find these solid, trending changes in body proportions over sauropod evolution.”

Quiet Sunspot

Sunspot AR2526 is big enough to swallow our entire planet–twice–and today it is crossing the center of the solar disk, directly facing Earth. Amateur astronomer J. P. Brahic took advantage of the crossing to photograph the behemoth from his backyard observatory in Uzès, France.

quietsunspot_strip

Surrounded by a maelstrom of swirling red-hot plasma, the sunspot’s dark core looks menacing indeed. But looks can be deceiving. In fact, sunspot AR2526 is one of the least threatening sunspots to come along this year. AR2526 has a stable magnetic field that resists exploding. As a result, NOAA forecasters say there is no more than a 1% chance of a strong solar flare for the next three days.