Archives 2010

A team of astronomers, including two from KIPAC, have created a map of X-ray emission from around the central galaxy of a galaxy group. Along with data from other wavelengths, it dramatically shows the effects of outbursts from the central active galactic nucleus that occurred millions of years ago.

Galaxy clusters are a well known source of X-rays. KIPAC researchers have shown that at least one cluster, the famous 'Bullet' Cluster, has an extra component of X-ray emission detectable beyond the dominant one seen ubiquitously elsewhere.

The Crab Nebula is a system with a pulsar and a surrounding ball of material that emits light all across the electromagnetic spectrum. For many years it was thought to be a constant steady source and was used as a calibration reference for telescopes. Now, KIPAC scientists using the Fermi Space telescope have shown that the emission from the Crab in gamma rays varies with time.

The Fermi Gamma-Ray Space Telescope has seen giant unexpected gamma-ray structures in the center of our Milky Way galaxy. The structures, which protrude above and below the Galactic plane in the center of the Galaxy like two opposing bubbles being blown up, are approximately 50,000 light-years tall.

By most accounts, the Milky Way is a fairly unexceptional galaxy in the Universe at large. However, a team of KIPAC scientists has shown that it has one very unusual feature: its two lesser companions, the Magellanic Clouds.

For the first time, thanks to the Fermi Space Telescope, high energy gamma rays gave been detected coming from another spiral galaxy much like our own Milky Way. It is now evident that the differences in gamma-ray luminosity among galaxies show that the density of cosmic rays varies and is correlated with the formation of new stars.

A KIPAC astrophysicist has published some of the first constraints on dark energy and other cosmological parameters using the measured signal from "shadows" of galaxy clusters in the CMB.

The question of whether we receive microwave radiation from spinning dust grains in our Galaxy has been debated for 15 years. A collaboration including a KIPAC scientist has provided valuable data indicating that the answer is probably yes.

Of the four established ways to study dark matter astronomically, looking at the evolving properties of galaxy clusters is the most reliant on non-optical observations of our Universe. A KIPAC faculty member has proposed satellite observations for a new era of cluster constraints on dark energy.

Creating the first ever catalog of the entire Galactic plane in hard x-rays, a KIPAC scientist has paved the way for a deeper understanding of the most luminous compact objects in our Galaxy, and of the x-ray emission from other galaxies.

The extent to which the cool, dense gas at the centers of massive galaxy clusters can be disrupted remains an outstanding question in astrophysics. Although physical processes such as mergers and central galaxy activity have been shown to suppress cooling and therefore star formation in the central gas, the cool core has almost always been observed to remain more or less intact. Recently, however, a team of KIPAC researchers has found the most extreme example yet of these processes disrupting the core.

The Fermi LAT has observed, for the first time, gamma-rays produced in cosmic-ray interactions in several neighboring galaxies - and is even able to spatially resolve one of those galaxies. This has given us a unique global view of cosmic ray acceleration, that previous Milky Way studies could not provide.

Core-collapse supernovae are some of the biggest explosions in the universe - but exactly how the immense amount of energy released is converted into a form we can observe has puzzled astrophysicists for many decades. The Computational Astrophysics Consortium, which includes KIPAC, studies these systems via state-of-the-art hydrodynamic (HD) and magneto-hydrodynamic (MHD) simulations, and met in May to discuss their recent results. Making the step up from two to three dimensions, they have found that neutrino heating can provide a robust explosion mechanism, while their advances in the 2D MHD simulations suggest that magnetic instability-induced gas mixing is an important new process in the explosion. The team is proving that combining expertise from astrophysics, applied mathematics, and the computer science community makes for a successful way of exploiting the enormous computational power available today.

Among the many opportunities in the LSST project, it necessitates a new understanding of our own atmosphere. LSST science depends on photometric redshift determination, which in turn depends on accurate measurements of the flux from celestial objects. At wavelengths where our atmosphere glows, this presents a novel challenge.

Cosmic inflation may have imprinted a distinctive pattern, associated with so-called B-Modes, on the polarization pattern of the Cosmic Microwave Background radiation on degree angular scales. A team including several KIPAC researchers will be attempting to detect this key signal using the BICEP2 telescope over the next two years, following its "first light" observations of spinning dust in our galaxy this spring.

Centaurus A (Cen A) is one of the brightest radio sources in the sky: it is a giant elliptical Galaxy about 10 million light years away, making it the closest active galaxy we know. A remarkable feature of the radio image of this galaxy is that the bright central source is accompanied by a pair of giant radio "lobes," thought to be fuelled by relativistic jets generated in the dynamical process of gas accretion around the super-massive black hole residing at the galaxy's center. New Fermi observations provide direct evidence of electrons with energies beyond 100 GeV in these lobes - either they are being accelerated in situ, or the ride from the galaxy center was easier than previously thought...

Long (up to Megaparsec scale), highly collimated jets of magnetized plasma emanating from the active nuclei of galaxies pose many astrophysical puzzles - including the mechanism by which those outflows are accelerated to relativistic velocities, and the structure of the jet magnetic field. Recent high resolution X-ray imaging of the jet in famous radio galaxy Pictor A shows some surprising and unexpected variability. This suggests that the local magnetic field within the jet of Pictor A may have been much stronger than previously thought, affecting dramatically the high energy emission of extremely energetic, ultrarelativistic jet particles.

It has long been suspected that the processes at the center of active galaxies prevent the gas from forming stars. Now, for the first time, a KIPAC team has seen that happening before our eyes.

Huge natural thermonuclear explosions, so called stellar novae, are observed in binary systems consisting of a dense compact white dwarf circling a star. The Fermi LAT has for the first time ever detected gamma-ray emission from such an event. This observation indicates particle acceleration in the shock wave produced by the nova explosion to at least GeV energies.

Clusters of galaxies are the most massive structures in the universe. Most of the mass in these clusters is considered to be dark matter. The Fermi LAT monitors these clusters for a gamma-ray signal from dark matter annihilation. No such signal has been found yet, but the non-observation starts to constrain a wide range of proposed dark matter models.

In recent years a dozen small 'dwarf' galaxies that surround our Milky Way have been discovered. A KIPAC team shows how these tiny galaxies are great places to look for the signatures of dark matter and determine its properties.

The only way to accurately predict the conditions near black holes is with extensive computer simulations of the complicated physics involved. While black holes are the quintessential manifestation of Einstein's General Relativity, very few precision tests of the theory have been based on actual observations of black holes. New simulation results point to an observable property of such systems that could be used as a precision test of Einstein's theory.

Astronomers have discovered that most of the matter in the universe is quite different from normal matter and does not shine - they call it dark matter. Physicists believe that they may be able to create some of this dark matter at article accelerators like the Large Hadron Collider in Switzerland, or indirectly detect its presence from the occasional annihilations that occur in our galaxy or in the Sun. In addition, it should also be possible to directly detect our galaxy's dark matter as it flows through the Earth in detectors placed deep underground. One such experiment is run by the the CDMS collaboration, in which members of the Stanford physics department play a key role. They recently released 2 tantalising events detected in their final exposure dataset - leaving the dark matter community wanting more. KIPAC is helping to foster a new partnership between Stanford and SLAC, as the experiment steps up its sensitivity and aims to home in on the elusive dark matter particle.

Our galaxy is bathed in Extragalactic Gamma-ray Background light (EGB), which we suppose to be coming from some superposition of not only the various unresolved astrophysical sources in the Universe, but also diffuse processes, including - perhaps - the annihilation or decay of dark matter.

A California-based team of astronomers, including KIPAC's Brian Gerke, have discovered 33 pairs of waltzing black holes in distant merging galaxies, showing that supermassive black hole pairs are more common than previously thought. These black hole pairings can be used to estimate how often galaxies merge with each other, an important piece of the puzzle of how galaxies form and evolve.

The Fermi LAT collaboration, with significant contributions from KIPAC researchers Seth Digel and James Chiang, has compiled its first all-sky catalog of gamma-ray sources above 200 MeV and released it to the public. It contains 1451 sources with a detection significance above 4.1 sigma found in 11 months of LAT observations. This is not only a major step forward in number of known gamma-ray sources from the about 200 sources discovered during the lifetime of the EGRET experiment. The highly improved resolution of the LAT instrument allows to localize the sources on the sky with higher precision allowing more accurate identification of the sources through counterpart searches in other parts of the electromagnetic spectrum.

The KIPAC X-ray Astronomy and Observational Cosmology group recently used their new analysis and measurements of the abundance of galaxy clusters to constrain dark energy parameters via the growth of structure in the Universe. Now, in a paper led by David Rapetti, they ask: what if General Relativity is not how gravity works?

Low frequency gravitational waves are predicted to be emitted by a variety of cosmological sources, from cosmic strings to binary black holes to the big bang itself. Undetectable with ground-based detectors, pulsar timing measurements offer our best chance of detecting these signals. The Fermi LAT, in tandem with a global network of radio astronomers, is enlarging the sample of the best reference clocks - millisecond pulsars - at an impressive rate.