NASA's Fermi Telescope Detects Gamma Rays From 'Star Factories' In Other Galaxies

Nearby galaxies undergoing a furious pace of star formation also emit lots of gamma rays, say astronomers using NASA's Fermi Gamma-ray Space Telescope. Two so-called "starburst" galaxies, plus a satellite of our own Milky Way galaxy, represent a new category of gamma-ray-emitting objects detected both by Fermi and ground-based observatories.

"Starburst galaxies have not been accessible in gamma rays before," said Fermi team member Seth Digel, a physicist at SLAC National Accelerator Laboratory in Menlo Park, Calif. "Most of the galaxies Fermi sees are exotic and distant blazars, which produce jets powered by matter falling into enormous black holes. But these new galaxies are much closer to us and much more like our own."

Gamma rays are the most energetic form of light. Fermi has detected more than a thousand point sources and hundreds of gamma-ray bursts, but the satellite also detects a broad glow that roughly follows the plane of our galaxy. This diffuse gamma-ray emission results when fast-moving particles called cosmic rays strike galactic gas or even starlight.

Cosmic rays are hyperfast electrons, positrons, and atomic nuclei moving at nearly the speed of light. But, although Earth is constantly bombarded by these particles, their origin remains a mystery nearly a century after their discovery. Astronomers suspect that the rapidly expanding shells of exploded stars somehow accelerate cosmic ray particles to their fantastic energy.

"For the first time, we're seeing diffuse emission from star-forming regions in galaxies other than our own," noted Jürgen Knödlseder, a Fermi collaborator at the Center for the Study of Space Radiation in Toulouse, France. He spoke to reporters today at the 2009 Fermi Symposium, a Washington gathering of hundreds of astrophysicists involved in the Fermi mission and related studies. The meeting continues through Nov. 5.

Knödlseder revealed an image captured by Fermi's Large Area Telescope (LAT) of a star-forming region known as 30 Doradus within the Large Magellanic Cloud (LMC). Located 170,000 light-years away in the southern constellation Dorado, the LMC is the largest of several small satellite galaxies that orbit our own.

More stars form in the 30 Doradus "star factory" than in any similar location in the Milky Way. "The region is an intense source of gamma rays, and the diffuse emission we see with Fermi follows the glowing gas we see in visible light," Knödlseder explained.

The region lights up in gamma rays for the same reason the Milky Way does -- because cosmic rays strike gas clouds and starlight. But Fermi shows that the LMC's brightest diffuse emission remains close to 30 Doradus and doesn't extend across the galaxy. This implies that the stellar factory itself is the source of the cosmic rays producing the glow.

"Star-forming regions produce lots of massive, short-lived stars, which explode when they die," Digel said. "The connection makes sense."

"The tangled magnetic fields near 30 Doradus probably confine the cosmic rays to their acceleration sites," Knödlseder said.

Fermi's LAT sees diffuse emission from the starburst galaxies M82 and NGC 253, both of which were also seen this year by ground-based observatories sensitive to gamma rays hundreds of times more energetic than the LAT can detect. They do this by imaging faint flashes in the upper atmosphere caused by the absorption of gamma rays carrying trillions of times the energy of visible light.

"The core of M82 forms stars at a rate ten times greater than the entire Milky Way galaxy," said Niklas Karlsson, a postdoctoral fellow at Adler Planetarium in Chicago. He is also a member of the science team for VERITAS, an array of gamma-ray telescopes in Arizona that detected M82, which lies 12 million light-years away in the constellation Ursa Major.

"These very-high-energy gamma rays probe physical processes in other galaxies that will help us understand how and where cosmic rays become accelerated," Karlsson explained.

"Our sensitivity to gamma-rays -- both in space and on the ground -- has increased enormously thanks to Fermi and observatories like VERITAS," Digel said. "This is opening up the detailed study of high-energy processes in galaxies very close to home." NASA's Fermi Gamma Ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Newly Discovered Ankylosaur Dinosaur Is 'Biological Version Of An Army Tank'

A husband and wife team of American paleontologists has discovered a new species of dinosaur that lived 112 million years ago during the early Cretaceous of central Montana.

The new dinosaur, a species of ankylosaur, is documented in the October issue of the Canadian Journal of Earth Sciences. Ankylosaurs are the biological version of an army tank. They are protected by a plate-like armour with two sets of sharp spikes on each side of the head, and a skull so thick that even 'raptors' such as Deinonychus could leave barely more than a scratch.

Bill and Kris Parsons, Research associates of the Buffalo Museum of Science, found much of the skull of the newly described Tatankacephalus cooneyorum resting on the surface of a hillside in 1997. Because the skull was 90% complete, it was possible to justify this fossil as a new species.

"This is the first member of Ankylosauridae to be found within the Early Cretaceous Cloverly Geologic Formation," said Bill Parsons, who characterized the fossil as a transitional evolutionary form between the earlier Jurassic ankylosaurs and the better known Late Cretaceous ankylosaurs.

The skull is heavily protected by two sets of lateral horns, two thick domes at the back, and smaller thickenings around the nasal region. "Heavy ornamentation and horn-like plates would have covered most of the dorsal surface of this dinosaur" said Bill Parsons.

"For years, Bill and Kris have been collecting fossils from a critical time in Earth's history, and their hard work has paid off," said Lawrence Witmer, professor of paleontology at Ohio University who was not involved with this study. "This is a really important find and gives us a clearer view of the evolution of armored dinosaurs. But this is just the first; I'm sure, of what will be a series of important discoveries from this team."

Parsons also illustrated the dermal armour of this new species based on the theory by Museum of the Rockies paleontologist John R. Horner that there was an outer keratinous sheathing on it as found in modern turtle shells and bird beaks. In his new reconstruction, Parsons suggests that Tatankacephalus exhibited complex and colorful patterns rather than the dull appearance suggested in earlier ankylosaur portraits. "According to Horner's theory, many other dinosaurs also had this kind of sheathing and also may have been diversely colored," said Parsons.

As to its name, the broad, short horns on the back of its skull resemble the horns found on a modern buffalo skull and Tatankacephalus loosely translates as 'Buffalo head.' Parsons also noted, "of course any further allusions to the city of Buffalo are completely intentional as well."

New Analyses Of Dinosaur Growth May Wipe Out One-third Of Species

Paleontologists from the University of California, Berkeley, and the Museum of the Rockies have wiped out two species of dome-headed dinosaur, one of them named three years ago -- with great fanfare -- after Hogwarts, the school attended by Harry Potter.

Their demise comes after a three-horned dinosaur, Torosaurus, was assigned to the dustbin of history last month at the Society of Vertebrate Paleontology meeting in the United Kingdom, the loss in recent years of quite a few duck-billed hadrosaurs and the probable disappearance of Nanotyrannus, a supposedly miniature Tyrannosaurus rex.

These dinosaurs were not separate species, as some paleontologists claim, but different growth stages of previously named dinosaurs, according to a new study. The confusion is traced to their bizarre head ornaments, ranging from shields and domes to horns and spikes, which changed dramatically with age and sexual maturity, making the heads of youngsters look very different from those of adults.

"Juveniles and adults of these dinosaurs look very, very different from adults, and literally may resemble a different species," said dinosaur expert Mark B. Goodwin, assistant director of UC Berkeley's Museum of Paleontology. "But some scientists are confusing morphological differences at different growth stages with characteristics that are taxonomically important. The result is an inflated number of dinosaurs in the late Cretaceous."

Goodwin and John "Jack" Horner of the Museum of the Rockies at Montana State University in Bozeman, are the authors of a new paper analyzing North American dome-headed dinosaurs that appeared this week in the public access online journal PLoS One.

Unlike the original dinosaur die-off at the end of the Cretaceous period 65 million years ago, this loss of species is the result of a sustained effort by paleontologists to collect a full range of dinosaur fossils -- not just the big ones. Their work has provided dinosaur specimens of various ages, allowing computed tomography (CT) scans and tissue study of the growth stages of dinosaurs.

In fact, Horner suggests that one-third of all named dinosaur species may never have existed, but are merely different stages in the growth of other known dinosaurs.

"What we are seeing in the Hell Creek Formation in Montana suggests that we may be overextended by a third," Horner said, a "wild guess" that may hold true for the various horned dinosaurs recently discovered in Asia from the Cretaceous. "A lot of the dinosaurs that have been named recently fall into that category."

The new paper, published online Oct. 27, contains a thorough analysis of three of the four named dome-headed dinosaurs from North America, including Pachycephalosaurus wyomingensis, the first "thick-headed" dinosaur discovered. After that dinosaur's description in 1943, many speculated that male pachycephalosaurs used their bowling ball-like domes to head-butt one another like big-horn sheep, though Goodwin and Horner disproved that notion in 2004 after a thorough study of the tissue structure of the dome.

Many paleontologists now realize that the elaborate head ornaments of dinosaurs, from the huge bony shield and three horns of Triceratops to the coxcomb-like head gear of some hadrosaurs, were not for combat, but served the same purpose as feathers in birds: to distinguish between species and indicate sexual maturity.

"Dinosaurs, like birds and many mammals, retain neoteny, that is, they retain their juvenile characteristics for a long period of growth," Horner said, "which is a strong indicator that they were very social animals, grouping in flocks or herds with long periods of parental care."

These head ornaments, which probably had horny coverings of keratin that may have been brightly-colored as they are in many birds, started growing when these dinosaurs reached about half their adult size, and were remodeled as these dinosaurs matured, continuing to change shape even into adulthood and old age, according to the researchers.

In the new paper, Horner and Goodwin compared the bone structures of Pachycephalosaurus with that of a domeheaded dinosaur, Stygimoloch spinifer, discovered in Montana by UC Berkeley paleontologists in 1973, and a dragon-like skull discovered in South Dakota and named in 2006 as a new species, Dracorex hogwartsia.

With the help of CT scans and microscopic analysis of slices through the bones of Pachycephalosaurus and Stygimoloch, the team concluded that Stygimoloch, with its high, narrow dome, growing tissue and unfused skull bones, was probably a pachycephalosaur subadult, in a stage just before sexual maturity.

Dracorex is one of a kind, and thus unavailable for dissection, but morphological analysis indicates it is a juvenile that hasn't yet formed a dome, although the top of its skull shows thickening suggestive of an emerging dome.

"Dracorex's flat skull, nodules on the front end and small spikes on back, and thickened but undomed frontoparietal bone all confirm that, ontogenetically, it is a juvenile Pachycephalosaurus," Goodwin said.

Comparison of these skulls to other fossils in the hands of private collectors confirm the conclusions, they said. In all, they looked at 21 dome-headed dinosaur skulls and cranial elements from North America.

The key to this analysis, Horner said, was years of field work in Montana by his team and Goodwin's in search of fossils of all sizes.

"We have gone out in the Hell Creek Formation for 11 years doing nothing but collecting absolutely everything we could find, which is the kind of collecting that is required," he said. "If you think about Triceratops, people had collected for 100 years and still hadn't found any juveniles. And we went out and spent 11 years collecting everything, and we found all kinds of them."

"Early paleontologists recognized the distinction between adults and juveniles, but people have lost track of looking at ontogeny -- how the individual develops -- when they discover a new fossil," Goodwin said. "Dinosaurs are not mammals, and they don't grow like mammals."

In fact, the so-called metaplastic bone on the heads of horned dinosaurs grows and dissolves, or resorbs, throughout life like no other bone, Horner said, and is reminiscent of the growth and loss of horns today in elk and deer. In earlier studies, Horner and Goodwin found dramatic remodeling of metaplastic bone in Triceratops, which led to their subsequent focus on dome-headed dinosaurs.

"Metaplastic bones get long and shorten, as in Triceratops, where the horn orientation is backwards in juveniles and forward in adults," Horner said. Even in older specimens, such as the fossil previously named Torosaurus, bone in the face shield resorbs to create holes along the margin. John Scannella, Horner's student at Montana State, presented a paper reclassifying Torosaurus as an old Triceratops at the Society for Vertebrate Paleontology meeting in Bristol, U.K., on Sept. 25.

"In order for that huge amount of bone to move, there has to be a lot of deposition and resorption," Horner said.

Horner and Goodwin continue to search for dinosaur fossils in the Hell Creek Formation, which is rich in Triceratops, dome-headed dinosaurs, hadrosaurs and tyrannosaurs. Analysis of growth stages in these taxa will have implications for other horned dinosaurs that are being uncovered in Asia and elsewhere.

"There are other horned dinosaurs I think may be over split," that is, split into too many new species rather than being lumped together as one species, Goodwin said.

The work was supported by grants from the UC Museum of Paleontology and the Museum of the Rockies.