Archive for the ‘Gamma Ray Bursts’ Category

Left-Handed Cosmic Magnetic Field Could Explain Missing Antimatter

An artist’s concept of the Fermi Gamma ray Space Telescope (FGST) in orbit. Credit: NASA

An artist’s concept of the Fermi Gamma ray Space Telescope (FGST) in orbit. Credit: NASA

The discovery of a ‘left-handed’ magnetic field that pervades the universe could help explain a long standing mystery – the absence of cosmic antimatter. A group of scientists, led by Prof Tanmay Vachaspati from Arizona State University in the United States, with collaborators at the University of Washington and Nagoya University, announce their result in Monthly Notices of the Royal Astronomical Society.

Planets, stars, gas and dust are almost entirely made up of ‘normal’ matter of the kind we are familiar with on Earth. But theory predicts that there should be a similar amount of antimatter, like normal matter, but with the opposite charge. For example, an antielectron or positron has the same mass as its conventional counterpart, but a positive rather than negative charge.

In 2001 Prof Vachaspati published theoretical models to try to solve this puzzle, which predict that the entire universe is filled with helical (screw-like) magnetic fields. He and his team were inspired to search for evidence of these fields in data from the NASA Fermi Gamma ray Space Telescope (FGST).

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Strange Supernova Is “Missing Link” In Gamma-Ray Burst Connection



Astronomers using the National Science Foundation’s Very Large Array (VLA) have found a long-sought “missing link” between supernova explosions that generate gamma-ray bursts (GRBs) and those that don’t. The scientists found that a stellar explosion seen in 2012 has many characteristics expected of one that generates a powerful burst of gamma rays, yet no such burst occurred.

“This is a striking result that provides a key insight about the mechanism underlying these explosions,” said Sayan Chakraborti, of the Harvard-Smithsonian Center for Astrophysics (CfA). “This object fills in a gap between GRBs and other supernovae of this type, showing us that a wide range of activity is possible in such blasts,” he added.

The object, called Supernova 2012ap (SN 2012ap) is what astronomers term a core-collapse supernova. This type of blast occurs when the nuclear fusion reactions at the core of a very massive star no longer can provide the energy needed to hold up the core against the weight of the outer parts of the star. The core then collapses catastrophically into a superdense neutron star or a black hole. The rest of the star’s material is blasted into space in a supernova explosion.

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Unusual Light Signal Yields Clues About Elusive Black Hole Merger

January 8, 2015 Leave a comment

Credit: Santiago Lombeyda/Caltech Center for Data-Driven Discovery

Credit: Santiago Lombeyda/Caltech Center for Data-Driven Discovery

The central regions of many glittering galaxies, our own Milky Way included, harbor cores of impenetrable darkness—black holes with masses equivalent to millions, or even billions, of suns. What is more, these supermassive black holes and their host galaxies appear to develop together, or “co-evolve.” Theory predicts that as galaxies collide and merge, growing ever more massive, so too do their dark hearts.

Black holes by themselves are impossible to see, but their gravity can pull in surrounding gas to form a swirling band of material called an accretion disk. The spinning particles are accelerated to tremendous speeds and release vast amounts of energy in the form of heat and powerful X-rays and gamma rays. When this process happens to a supermassive black hole, the result is a quasar—an extremely luminous object that outshines all of the stars in its host galaxy and that is visible from across the universe. “Quasars are valuable probes of the evolution of galaxies and their central black holes,” says George Djorgovski, professor of astronomy and director of the Center for Data-Driven Discovery at Caltech.

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NASA’s Fermi Satellite Finds Hints Of Starquakes In Magnetar ‘Storm’

October 24, 2014 Leave a comment

Image Credit: NASA's Goddard Space Flight Center/S. Wiessinger

Image Credit: NASA’s Goddard Space Flight Center/S. Wiessinger

NASA’s Fermi Gamma-ray Space Telescope detected a rapid-fire “storm” of high-energy blasts from a highly magnetized neutron star, also called a magnetar, on Jan. 22, 2009. Now astronomers analyzing this data have discovered underlying signals related to seismic waves rippling throughout the magnetar.

Such signals were first identified during the fadeout of rare giant flares produced by magnetars. Over the past 40 years, giant flares have been observed just three times — in 1979, 1998 and 2004 — and signals related to starquakes, which set the neutron stars ringing like a bell, were identified only in the two most recent events.

“Fermi’s Gamma-ray Burst Monitor (GBM) has captured the same evidence from smaller and much more frequent eruptions called bursts, opening up the potential for a wealth of new data to help us understand how neutron stars are put together,” said Anna Watts, an astrophysicist at the University of Amsterdam in the Netherlands and co-author of a new study about the burst storm. “It turns out that Fermi’s GBM is the perfect tool for this work.”

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NASA’s Fermi Space Telescope Reveals New Source Of Gamma Rays

Image Credit: NASA/DOE/Fermi LAT Collaboration

Image Credit: NASA/DOE/Fermi LAT Collaboration

Observations by NASA’s Fermi Gamma-ray Space Telescope of several stellar eruptions, called novae, firmly establish these relatively common outbursts almost always produce gamma rays, the most energetic form of light.

“There’s a saying that one is a fluke, two is a coincidence, and three is a class, and we’re now at four novae and counting with Fermi,” said Teddy Cheung, an astrophysicist at the Naval Research Laboratory in Washington, and the lead author of a paper reporting the findings in the Aug. 1 edition of the journal Science.

A nova is a sudden, short-lived brightening of an otherwise inconspicuous star caused by a thermonuclear explosion on the surface of a white dwarf, a compact star not much larger than Earth. Each nova explosion releases up to 100,000 times the annual energy output of our sun. Prior to Fermi, no one suspected these outbursts were capable of producing high-energy gamma rays, emission with energy levels millions of times greater than visible light and usually associated with far more powerful cosmic blasts.

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Black Hole ‘Batteries’ Keep Blazars Going And Going

Astronomers studying two classes of black-hole-powered galaxies monitored by NASA’s Fermi Gamma-ray Space Telescope have found evidence that they represent different sides of the same cosmic coin. By unraveling how these objects, called blazars, are distributed throughout the universe, the scientists suggest that apparently distinctive properties defining each class more likely reflect a change in the way the galaxies extract energy from their central black holes.

“We can think of one blazar class as a gas-guzzling car and the other as an energy-efficient electric vehicle,” said lead researcher Marco Ajello, an astrophysicist at Clemson University in South Carolina. “Our results suggest that we’re actually seeing hybrids, which tap into the energy of their black holes in different ways as they age.”

Active galaxies possess extraordinarily luminous cores powered by black holes containing millions or even billions of times the mass of the sun. As gas falls toward these supermassive black holes, it settles into an accretion disk and heats up. Near the brink of the black hole, through processes not yet well understood, some of the gas blasts out of the disk in jets moving in opposite directions at nearly the speed of light.

Blazars are the highest-energy type of active galaxy and emit light across the spectrum, from radio to gamma rays. They make up more than half of the discrete gamma-ray sources cataloged by Fermi’s Large Area Telescope, which has detected more than 1,000 to date. Astronomers think blazars appear so intense because they happen to tip our way, bringing one jet nearly into our line of sight. Looking almost directly down the barrel of a particle jet moving near the speed of light, emissions from the jet and the region producing it dominate our view.

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Fermi Data Tantalize With New Clues To Dark Matter

Image Credit: T. Linden, Univ. of Chicago

Image Credit: T. Linden, Univ. of Chicago

A new study of gamma-ray light from the center of our galaxy makes the strongest case to date that some of this emission may arise from dark matter, an unknown substance making up most of the material universe. Using publicly available data from NASA’s Fermi Gamma-ray Space Telescope, independent scientists at the Fermi National Accelerator Laboratory (Fermilab), the Harvard-Smithsonian Center for Astrophysics (CfA), the Massachusetts Institute of Technology (MIT) and the University of Chicago have developed new maps showing that the galactic center produces more high-energy gamma rays than can be explained by known sources and that this excess emission is consistent with some forms of dark matter.

The galactic center teems with gamma-ray sources, from interacting binary systems and isolated pulsars to supernova remnants and particles colliding with interstellar gas. It’s also where astronomers expect to find the galaxy’s highest density of dark matter, which only affects normal matter and radiation through its gravity. Large amounts of dark matter attract normal matter, forming a foundation upon which visible structures, like galaxies, are built.

No one knows the true nature of dark matter, but WIMPs, or Weakly Interacting Massive Particles, represent a leading class of candidates. Theorists have envisioned a wide range of WIMP types, some of which may either mutually annihilate or produce an intermediate, quickly decaying particle when they collide. Both of these pathways end with the production of gamma rays — the most energetic form of light — at energies within the detection range of Fermi’s Large Area Telescope (LAT).

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Gamma-Rays Tighten Window On Dark Matter Theories

February 28, 2014 Leave a comment

Observed data fitting the dark matter component, after subtracting all other components toward the Galactic Center.

Observed data fitting the dark matter component, after subtracting all other components toward the Galactic Center.

UC Irvine astrophysicists report that gamma-ray photons observed from the center of the Milky Way Galaxy are consistent with the intriguing possibility of dark matter annihilation, according to research submitted to the journal Physical Review D.

Kevork Abazajian, Nicolas Canac, Shunsaku Horiuchi and Manoj Kaplinghat analyzed data from NASA’s space-borne Fermi Gamma-ray Space Telescope and found that only a narrow range of dark matter models can produce an excess of gamma rays coming from the Milky Way. These gamma rays could be produced as particles of dark matter annihilate one another.

“The data provides a better-than 10 percent precise determination of the dark matter’s particle mass with the best estimates we have of what else is going on in the Galactic Center,” says Abazajian.

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NASA’s Fermi Makes First Gamma-ray Study Of A Gravitational Lens

January 7, 2014 Leave a comment

An international team of astronomers, using NASA’s Fermi observatory, has made the first-ever gamma-ray measurements of a gravitational lens, a kind of natural telescope formed when a rare cosmic alignment allows the gravity of a massive object to bend and amplify light from a more distant source.

This accomplishment opens new avenues for research, including a novel way to probe emission regions near supermassive black holes. It may even be possible to find other gravitational lenses with data from the Fermi Gamma-ray Space Telescope.

“We began thinking about the possibility of making this observation a couple of years after Fermi launched, and all of the pieces finally came together in late 2012,” said Teddy Cheung, lead scientist for the finding and an astrophysicist at the Naval Research Laboratory in Washington.

In September 2012, Fermi’s Large Area Telescope (LAT) detected a series of bright gamma-ray flares from a source known as B0218+357, located 4.35 billion light-years from Earth in the direction of a constellation called Triangulum. These powerful flares, in a known gravitational lens system, provided the key to making the lens measurement.

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Glimpsing The Infrastructure Of A Gamma-Ray Burst Jet

December 6, 2013 Leave a comment

A new study using observations from a novel instrument provides the best look to date at magnetic fields at the heart of gamma-ray bursts, the most energetic explosions in the universe. An international team of astronomers from Britain, Slovenia and Italy has glimpsed the infrastructure of a burst’s high-speed jet.

Gamma-ray bursts are the most luminous explosions in the cosmos. Most are thought to be triggered when the core of a massive star runs out of nuclear fuel, collapses under its own weight, and forms a black hole. The black hole then drives jets of particles that drill all the way through the collapsing star and erupt into space at nearly the speed of light.

On March 8, 2012, NASA’s Swift satellite detected a 100-second pulse of gamma rays from a source in the constellation Ursa Minor. The spacecraft immediately forwarded the location of the gamma-ray burst, dubbed GRB 120308A, to observatories around the globe.

The world’s largest fully autonomous robotic optical telescope, the 2-meter Liverpool Telescope located at Roque de los Muchachos Observatory on La Palma in the Canary Islands, automatically responded to Swift’s notification.

“Just four minutes after it received Swift’s trigger, the telescope found the burst’s visible afterglow and began making thousands of measurements,” said lead researcher Carole Mundell, who heads the gamma-ray burst team at the Astrophysics Research Institute at Liverpool John Moores University in the U.K.

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