In The Heart Of Cygnus, NASA's Fermi Reveals A Cosmic-ray CocoonNovember 29, 2011
Located in the vicinity of the second-magnitude star Gamma Cygni, the star-forming region was named Cygnus X when it was discovered as a diffuse radio source by surveys in the 1950s. Now, a study using data from NASA's Fermi Gamma-ray Space Telescope finds that the tumult of star birth and death in Cygnus X has managed to corral fast-moving particles called cosmic rays.
Cosmic rays are subatomic particles -- mainly protons -- that move through space at nearly the speed of light. In their journey across the galaxy, the particles are deflected by magnetic fields, which scramble their paths and make it impossible to backtrack the particles to their sources.
Yet when cosmic rays collide with interstellar gas, they produce gamma rays -- the most energetic and penetrating form of light -- that travel to us straight from the source. By tracing gamma-ray signals throughout the galaxy, Fermi's Large Area Telescope (LAT) is helping astronomers understand the sources of cosmic rays and how they're accelerated to such high speeds. In fact, this is one of the mission's key goals.
The galaxy's best candidate sites for cosmic-ray acceleration are the rapidly expanding shells of ionized gas and magnetic field associated with supernova explosions. For stars, mass is destiny, and the most massive ones -- known as types O and B -- live fast and die young.
They're also relatively rare because such extreme stars, with masses more than 40 times that of our sun and surface temperatures eight times hotter, exert tremendous influence on their surroundings. With intense ultraviolet radiation and powerful outflows known as stellar winds, the most massive stars rapidly disperse their natal gas clouds, naturally limiting the number of massive stars in any given region.
Which brings us back to Cygnus X. Located about 4,500 light-years away, this star factory is believed to contain enough raw material to make two million stars like our sun. Within it are many young star clusters and several sprawling groups of related O- and B-type stars, called OB associations. One, called Cygnus OB2, contains 65 O stars -- the most massive, luminous and hottest type -- and nearly 500 B stars.
Astronomers estimate that the association's total stellar mass is 30,000 times that of our sun, making Cygnus OB2 the largest object of its type within 6,500 light-years. And with ages of less than 5 million years, few of its most massive stars have lived long enough to exhaust their fuel and explode as supernovae.
Intense light and outflows from the monster stars in Cygnus OB2 and from several other nearby associations and star clusters have excavated vast amounts of gas from their vicinities. The stars reside within cavities filled with hot, thin gas surrounded by ridges of cool, dense gas where stars are now forming. It's within the hollowed-out zones that Fermi's LAT detects intense gamma-ray emission, according to a paper describing the findings that was published in the Nov. 25 edition of the journal Science.
"We are seeing young cosmic rays, with energies comparable to those produced by the most powerful particle accelerators on Earth. They have just started their galactic voyage, zig-zagging away from their accelerator and producing gamma rays when striking gas or starlight in the cavities," said co-author Luigi Tibaldo, a physicist at Padova University and the Italian National Institute of Nuclear Physics.
The energy of the gamma-ray emission, which is measured up to 100 billion electron volts by the LAT and even higher by ground-based gamma-ray detectors, indicates the extreme nature of the accelerated particles. (For comparison, the energy of visible light is between 2 and 3 electron volts.) The environment holds onto its cosmic rays despite their high energies by entangling them in turbulent magnetic fields created by the combined outflows of the region's numerous high-mass stars.
"These shockwaves stir the gas and twist and tangle the magnetic field in a cosmic-scale jacuzzi so the young cosmic rays, freshly ejected from their accelerators, remain trapped in this turmoil until they can leak into quieter interstellar regions, where they can stream more freely," said co-author Isabelle Grenier, an astrophysicist at Paris Diderot University and the Atomic Energy Commission in Saclay, France.
The well known Gamma Cygni supernova remnant - so named for its proximity to the star -- also lies within this region; astronomers estimate its age at about 7,000 years. The Fermi team considers it possible that the supernova remnant spawned the cosmic rays trapped in the Cygnus X "cocoon," but they also suggest an alternative scenario where the particles became accelerated through repeated interaction with shockwaves produced inside the cocoon by powerful stellar winds.
"Whether the particles further gain or lose energy inside this cocoon needs to be investigated, but its existence shows that cosmic-ray history is much more eventful than a random walk away from their sources," Tibaldo added.
Fermi is providing a never-before-seen glimpse of the early life of cosmic rays, long before they diffuse into the galaxy at large. Astronomers know of a dozen stellar clusters at least as young and rich as Cygnus OB2, including the Arches and Quintuplet clusters near the galaxy's center. Energetic gamma rays are detected in the vicinity of several of them, so perhaps they also corral cosmic rays in their own high-energy cocoons.
NASA's Fermi is an astrophysics and particle physics partnership managed by NASA's Goddard Space Flight Center in Greenbelt, Md., and developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.
Nursery of Giants Captured in New Spitzer Image
NASA's Fermi Telescope Detects Gamma-Rays From 'Star Factories' in Other Galaxies
What is Cygnus X?
NASA's Goddard Space Flight Center
Related Cosmic Rays Current Events and Cosmic Rays News Articles
Scientists successfully use krypton to accurately date ancient Antarctic ice
A team of scientists has successfully identified the age of 120,000-year-old Antarctic ice using radiometric krypton dating - a new technique that may allow them to locate and date ice that is more than a million years old.
Krypton-dating technique allows researchers to accurately date ancient Antarctic ice
A team of scientists, funded by the National Science Foundation (NSF), has successfully used a new technique to confirm the age of a 120,000-year-old sample of Antarctic ice.
Researchers Find 3-million-year-old Landscape Beneath Greenland Ice Sheet
Glaciers and ice sheets are commonly thought to work like a belt sander. As they move over the land they scrape off everything - vegetation, soil and even the top layer of bedrock.
Frozen in time: Three-million-year-old landscape still exists beneath the Greenland Ice Sheet
Some of the landscape underlying the massive Greenland ice sheet may have been undisturbed for almost 3 million years, ever since the island became completely ice-covered, according to researchers funded by the National Science Foundation (NSF).
Meteorites Yield Clues to Red Planet's Early Atmosphere
Geologists who analyzed 40 meteorites that fell to Earth from Mars unlocked secrets of the Martian atmosphere hidden in the chemical signatures of these ancient rocks.
SU plays key role in search for elusive dark matter
Physicist Richard Schnee hopes to find traces of dark matter by studying particles with low masses and interaction rates, some of which have never been probed before.
SU professors test boundaries of 'new physics' with discovery of 4-quark hadron
Physicists in Syracuse University's College of Arts and Sciences have helped confirm the existence of exotic hadrons-a type of matter that cannot be classified within the traditional quark model.
Current ice melt rate in Pine Island Glacier may go on for decades
A study of the Pine Island Glacier could provide insight into the patterns and duration of glacial melt.
LUX dark matter results confirmed
A new calibration of the Large Underground Xenon (LUX) dark matter detector brought a 10-fold increase in calibration accuracy, confirming findings announced last October from the instrument's first 90-day run. If low-mass "WIMP" particles had passed through the detector, LUX would have found them.
IBEX research shows influence of galactic magnetic field extends well beyond our solar system
In a report published today, new research suggests the enigmatic "ribbon" of energetic particles discovered at the edge of our solar system by NASA's Interstellar Boundary Explorer (IBEX) may be only a small sign of the vast influence of the galactic magnetic field.
More Cosmic Rays Current Events and Cosmic Rays News Articles