Revealing the Explosive Heart of Eta Carinae

Using adaptive optics to remove atmospheric blurring, Gemini Observatory released an image today showing previously hidden forensic secrets at the ballistic core of the Homunculus Nebula, part of the explosive Eta Carinae star system.

The infrared image, revealed at the 215th American Astronomical Society meeting in Washington DC, is a high-resolution view of the complex tendrils and puffs of glowing gas and dust surrounding the violent and convulsive death of an exceptionally massive, short-lived star.

The compelling modern history of Eta Carinae began in April 1843 when the system underwent a huge 20-year outburst that, throughout some of that period, made it the sky’s second brightest stellar object. During the “Great Eruption” astronomers estimate that about 20 times the mass of our Sun was ejected into interstellar space. Today, astronomers study this relatively nearby stellar oddity to help understand the late evolution of massive stars – a messy process involving outflows, eruptions, strong magnetic fields and powerful jets. The result of this activity is reflected in the new Gemini image presented by John Martin of the University of Illinois Springfield who, along with an international team of researchers, obtained their data using the Near-Infrared Coronagraphic Imager (NICI) at the Gemini South telescope in Chile.

Martin’s team used NICI to study gas and dust features surrounding the central star where the complex structure includes an intricate network of wispy clouds, inspiring the “Butterfly Nebula” moniker. The data also uncover a feature never directly imaged before called the Little Homunculus Nebula. “The Homunculus is an evolving corpse of a dying star and most of what we see is the visible outer layer, like a skin, from the Great Eruption. The Little Homunculus is under that skin,” said Martin. “The Gemini images have allowed us to perform something akin to an autopsy by peeling away the obscuring, outer dusty skin and giving us a glimpse of what’s inside. In the process we're finding things we have never imaged before and didn't expect. It’s like finding your murder victim has a third lung, an extra liver, or something more exotic hidden away under their skin!” Martin and his team hope that these observations will soon trace the uncertain history of a minor eruption in the Eta Carinae system in the late 1890s. The research team also includes Etienne Artigau (University of Montréal, Canada, lead author on subsequent paper and previously at Gemini South), Kris Davidson (University of Minnesota), Roberta Humphreys (University of Minnesota), Olivier Chesneau (FIZEAU, France), and Nathan Smith (University of California).

Eta Carinae, located only about 7,500-8,000 light years away, consists of at least two stars at its core, the largest of which is among the most luminous and massive stars in our galaxy having a mass of at least 100 times that of our sun. The stellar component is visible to the naked eye from the southern hemisphere and very low northern latitudes. Because of the complexity and advanced age of this stellar system, Eta Carinae has displayed consistently odd behavior and its brightness has varied greatly over the centuries. During its massive explosion (that lasted from 1843 through the 1850’s) it gave off as much light energy as a typical supernova but somehow survived the normally annihilating event. What we see as the Homunculus Nebula are the remains of that explosion–sometimes called the supernova imposter event. The gasses expelled from this explosion are hurtling outward at up to 2 million kilometers per hour and are comprised of a mixture of diverse elements (from nitrogen to iron) formed by the massive star.

NICI, the Gemini South instrument used to obtain the data for this result, incorporates a built-in curvature-sensing adaptive optics system and is optimized for the detection of faint, sub-stellar companions. It images over a field of about 18 arcseconds from 1 – 5 microns. In addition to images like the one featured in this release, NICI is currently being utilized in an aggressive planet-finding campaign targeting about 300 nearby stars for possible planetary companions.

gemini.edu

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Looks Can Be Deceiving

Does it matter if nature solves the same problem multiple ways? A NSF-supported study of lizard populations in White Sands, New Mexico has helped researcher Erica Rosenblum of the University of Idaho begin to answer that question. Published December 28 in the Proceedings of the National Academy of Sciences, the article describes genetic differences between lizards found in habitats that contain white or dark soils. These stark differences in color are an ideal environment to study natural selection and gene flow.

In three separate lizard species, Rosenblum and her team identified mutations in the gene encoding the melanocortin-1 receptor (Mc1r), all resulting in lizards with light skin. Further biochemical characterization of the mutations revealed that, although the same gene is affected in two of the species, the functional changes caused by the mutations were distinct. In one species the receptor is in the wrong location in the cell, while in a different species the receptor is in the correct location, but it is unable to transmit signal.

"The mutations we observed resulted in two distinct changes in how the Mc1 receptor functioned. Mc1r acts like a light switch for melanin, so even though the way the signaling is disrupted is different, outwardly we see the same result: light-skinned lizards," Rosenblum explained.

Although the end point, light skin, is the same, the different ways the reptiles achieve this have important implications for gene flow in each species. For instance, the dominance pattern of the mutated genes is different in the two species. The mutation that results in improperly located Mc1r protein is dominant, meaning it takes only one copy of the new gene to result in light-skinned lizards. In contrast, the lizards that appear white due to faulty receptor signal transmission must harbor two copies of the mutant gene because the trait is recessive.

Rosenblum added, "There is preliminary evidence that suggests the genes involved in adaptation can also affect speciation. Changes in melanin affect coloration on the top of the body, which predators see, and also the sides of the body, which other lizards use to decide who to mate with. Therefore both natural selection and sexual selection appear to play a role in this system."

This habitat provides researchers the unique opportunity to observe natural selection and speciation in progress. New species can form relatively quickly (over a few thousand years) in some selection environments, but catching organisms in the act is rare. The more researchers understand the speciation process, the better equipped we will be to try to preserve this process as our landscape changes.

-NSF-

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Marine Scientists Discover Deepest Undersea Erupting Volcano

Scientists funded by the National Science Foundation (NSF) and NOAA have recorded the deepest erupting volcano yet discovered --West Mata Volcano-- describing high-definition video of the undersea eruption as "spectacular."

"For the first time we have been able to examine, up close, the way ocean islands and submarine volcanoes are born," said Barbara Ransom, program director in NSF's Division of Ocean Sciences. "The unusual primitive compositions of the West Mata eruption lavas have much to tell us."

The volcanic eruption, discovered in May, is nearly 4,000 feet below the surface of the Pacific Ocean, in an area bounded by Fiji, Tonga and Samoa.

"We found a type of lava never before seen erupting from an active volcano, and for the first time observed molten lava flowing across the deep-ocean seafloor," said the expedition's chief scientist Joseph Resing, a chemical oceanographer at the University of Washington.

"It was an underwater Fourth of July, a spectacular display of fireworks nearly 4,000 feet deep," said co-chief scientist Bob Embley, a marine geologist at NOAA's Pacific Marine Environmental Laboratory in Newport, Ore.

"Since the water pressure at that depth suppresses the violence of the volcano's explosions, we could get an underwater robot within feet of the active eruption. On land, or even in shallow water, you could never hope to get that close and see such great detail."

Imagery includes large molten lava bubbles three feet across bursting into cold seawater, glowing red vents exploding lava into the sea, and the first-observed advance of lava flows across the deep-ocean floor.

Sounds of the eruption were recorded by a hydrophone and later matched with the video footage.

Expedition scientists released the video and discussed their observations at a Dec. 17 news conference at the American Geophysical Union (AGU)'s annual fall meeting in San Francisco.

The West Mata Volcano is producing boninite lavas, believed to be among the hottest on Earth in modern times, and a type seen before only on extinct volcanoes more than one million years old.

University of Hawaii geochemist Ken Rubin believes that the active boninite eruption provides a unique opportunity to study magma formation at volcanoes, and to learn more about how Earth recycles material where one tectonic plate is subducted under another.

Water from the volcano is very acidic, with some samples collected directly above the eruption, the scientists said, as acidic as battery acid or stomach acid.

Julie Huber, a microbiologist at the Marine Biological Laboratory, found diverse microbes even in such extreme conditions.

Tim Shank, a biologist at the Woods Hole Oceanographic Institution (WHOI), found that shrimp were the only animals thriving in the acidic vent water near the eruption. Shank is analyzing shrimp DNA to determine whether they are the same species as those found at seamounts more than 3,000 miles away.

The scientists believe that 80 percent of eruptive activity on Earth takes place in the ocean, and that most volcanoes are in the deep sea.

Further study of active deep-ocean eruptions will provide a better understanding of oceanic cycles of carbon dioxide and sulfur gases, how heat and matter are transferred from the interior of the Earth to its surface, and how life adapts to some of the harshest conditions on Earth.

The science team worked aboard the University of Washington's research vessel Thomas Thompson, and deployed Jason, a remotely-operated vehicle owned by WHOI.

Jason collected samples using its manipulator arms, and obtained imagery using a prototype still and HD imaging system developed and operated by the Advanced Imaging and Visualization Lab at WHOI.

-NSF-

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Newly Discovered Dinosaur Illuminates Ancient Lineage

When Darwin's finches diverged from their common ancestor, the isolation of their island home allowed many species to arise from one.

When their dinosaur ancestors emerged in the Triassic, the island home was the unified landmass Pangea, and the evolution was far more complicated.

In the Dec. 11, 2009, issue of Science, a team of paleontologists introduces the Triassic dinosaur Tawa hallae, an animal that may answer longstanding questions about the earliest years of dinosaur evolution.

The Tawa fossils, collected along with other specimens during recent field excursions to Ghost Ranch in New Mexico, are some of the most complete and best preserved dinosaur skeletons from the Late-Triassic time period.

Tawa possesses features that appear in its contemporaries and features that do not, a finding that helps unite all Triassic carnivorous dinosaurs into one group, the theropods, the same group that included Tyrannosaurus rex, and now includes birds.

The recent finds also support the hypothesis that dinosaurs first originated in what is now South America and soon after diverged into theropods, sauropodomorphs (the line that includes the ground-shaking giants like Apatosaurus) and ornithischians (a line that includes a range of body types, including Stegosaurus and Triceratops).

Only after this divergence did dinosaurs disperse across the Triassic world more than 220 million years ago.

"Tawa gives us an unprecedented window into early dinosaur evolution, solidifying the relationships of early dinosaurs, revealing how they spread across the globe, and providing new insights into the evolution of their characteristics," says Sterling Nesbitt of the University of Texas at Austin, the lead author on the paper.

Nesbitt's co-authors included Nathan Smith of the University of Chicago and the Field Museum of Natural History; Randall Irmis of the Utah Museum of Natural History, University of Utah; Alan Turner of Stony Brook University; Alex Downs of the Ruth Hall Museum of Paleontology in Abiquiu, N.M.; and Mark Norell of the American Museum of Natural History, where Nesbitt was a researcher at the time of the discovery.

"If you have continents splitting apart, you get isolation," says Nesbitt. "So when barriers develop, you would expect that multiple carnivorous dinosaurs in a region should represent a closely related, endemic radiation," similar to what occurred with Darwin's finches. "But that is what we don't see in early dinosaur evolution," adds Nesbitt.

Instead, Nesbitt and his colleagues observed three distantly related carnivores in the fossil-rich, Late Triassic beds, implying that each carnivore descended from a separate lineage before arriving in North America, instead of all evolving from a local ancestor. In addition to Tawa, the researchers found fossils from a carnivorous dinosaur related to Coelophysis, common to that region, and fossils from a carnivore closely related to Herrerasaurus, which lived in South America.

The two- to four-meter-long skeletons of Tawa display characteristics that exist in both of its contemporaries, and features found in neither, implying a separate lineage. Unlike many theropods, Tawa's lineage does not lead directly to birds.

According to Nesbitt, the old view held that Herrerasaurus split off of the family tree after the ornithischians, but before the sauropods and theropods diverged. "Tawa now appears to show that the three groups split from each other as soon as dinosaurs evolved," he adds, though paleontologists have not yet found a concrete example of a dinosaur that existed before the divergence.

"Tawa is a very good example of a fossil that fills in what we call a morphological gap," says Nesbitt, referring to a gap in knowledge about how morphology, or body structures, changed over time, a result of the incomplete nature of the fossil record. While theropods were changing quickly in the Triassic, paleontologists have found few animals that preserve the "steps" that define the sequence of changes.

One of the most significant morphological gaps for early dinosaurs lies between Herrerasaurus and animals that are clearly more closely related to birds, such as Coelophysis. According to Nesbitt, Tawa fits perfectly in between. "It is not a missing link," he adds, "It evolved on its own lineage, but it retains characteristics that existed in Herrerasaurus that we thought were more primitive while also possessing features seen in unmistakable theropods, including birds, such as the presence of air sacs surrounding the braincase and neck."

"Usually, early dinosaur specimens are not as complete or well preserved, so they spur a lot more questions than answers," says Nesbitt. "Tawa is so well preserved that every bone we have, we can examine it in three dimensions. And we can analyze five of the skeletons this way, with examples of both mature and immature animals. This is just the tip of the iceberg. All dinosaurs share a common feature, an open hip socket, and you can dissect your Thanksgiving turkey and still see that original feature. But the earliest lineages that lie in between are far from understood."

-NSF-

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The Snows of Kilimanjaro: For How Much Longer?

The iconic snows of Kilimanjaro still exist--but for how long? The remaining ice fields atop famed Mount Kilimanjaro in Tanzania could be gone within two decades and perhaps even sooner, based on the latest survey of the ice fields on the mountain.

These predictions, published this week in the journal Proceedings of the National Academy of Sciences (PNAS), are among the latest dramatic physical evidence of global climate change.

The findings, by paleoclimatologist Lonnie Thompson at Ohio State University and co-authors, indicate that a major cause of this ice loss is likely to be the rise in global temperatures.

Although changes in cloudiness and precipitation may also play a role, they appear less important, particularly in recent decades.

"The loss of Mount Kilimanjaro's ice cover has attracted worldwide attention because of its impact on regional water resources," said David Verardo, director of NSF's Paleoclimate Program, which funded the research along with Ohio State University's Climate, Water and Carbon Program. "The remaining ice fields are melting from all sides," said Verardo. "Like many glaciers in mid-to-low latitudes, Kilimanjaro's may only be with us for a short time longer."

This first calculation of ice volume loss indicates that from 2000 to 2007, the loss by thinning is now roughly equal to that by shrinking.

Thompson and colleagues have amassed a trail of data showing the rapid loss of ice atop Africa's highest mountain:

•85 percent of the ice that covered the mountain in 1912 had been lost by 2007, and 26 percent of the ice there in 2000 is now gone.

•A radioactive signal marking the 1951-52 "Ivy" atomic tests that was detected in 2000 some 1.6 meters (5.25 feet) below the surface of the Kilimanjaro ice is now lost, with an estimated 2.5 meters (8.2 feet) missing from the tops of the current ice fields.

•The presence of elongated bubbles trapped in the frozen ice at the top of one of the cores shows that surface ice has melted and refrozen. There is no evidence of sustained melting anywhere in the rest of the core material which dates back 11,700 years.

•Even 4,200 years ago, a drought in this part of Africa that lasted about 300 years and left a thick (about 1-inch) dust layer, was not accompanied by any evidence of melting.

These observations confirm that the current climate conditions at Mount Kilimanjaro are unique over the last 11 millennia.

"This is the first time researchers have calculated the volume of ice lost from the mountain's ice fields," said Thompson, a scientist at Ohio State's Byrd Polar Research Center. "If you look at the percentage of volume lost since 2000 versus the percentage of area lost as the ice fields shrink, the numbers are very close."

While the loss of mountain glaciers is most apparent from the retreat of their margins, Thompson said an equally troubling effect is the thinning of the ice fields from the surface.

The summits of both the Northern and Southern Ice Fields atop Kilimanjaro have thinned by 1.9 meters (6.2 feet) and 5.1 meters (16.7 feet), respectively.

The smaller Furtwangler Glacier, which was melting and water-saturated in 2000 when it was drilled for samples, has thinned as much as 50 percent between 2000 and 2009.

"It has lost half of its thickness," Thompson said. "In the future, there will be a year when Furtwängler is present and by the next year, it will have disappeared.

"The whole thing will be gone!"

Thompson's team drilled six cores through Kilimanjaro's ice fields in 2000 and published their findings in the journal Science two years later. That work established a detailed baseline against which more recent data can be compared.

Thompson said the changes occurring on Mount Kilimanjaro mirror those on Mount Kenya and the Rwenzori Mountains in Africa, as well as tropical glaciers high in the South American Andes and in the Himalayas.

"The fact that so many glaciers throughout the tropics and subtropics are showing similar responses suggests an underlying common cause," he said.

"The increase of Earth's near-surface temperatures, coupled with even greater such increases in the mid- to upper-tropical troposphere, as documented in recent decades, would at least partially explain the observed widespread similarity in glacier behavior."

Along with Thompson, Ellen Mosley-Thompson, Henry Brecher and Bryan Mark, all with Ohio State's Byrd Polar Research Center, and Douglas Hardy from the University of Massachusetts contributed to the study.

-NSF-

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