In a recent issue of Science Magazine, the Major Atmospheric Gamma-ray ImagingCherenkov (MAGIC) Telescope has reported the discovery of variable very high energy (VHE) gamma-ray emission from a microquasar. Microquasars are binary star systems, composed of a massive ordinary star and a compact object, which can be either a neutron star or a black hole (see Fig. 1). The stars orbit around one another and, when they are close enough, there is a transfer of matter from the massive one toward the compact object, due to gravitational attraction. This matter forms a disk around the compact object and is heated-up due to viscosity, producing X-rays. In addition, the collapse of matter from the disk into the compact object produces the ejection of jets of particles that travel in opposite directions at velocities close to the speed of light. In particular the jets contain electrons that undergo the so-called synchrotron radiation, which can be detected by radio telescopes. These jets remain among the most spectacular, yet poorly explained astrophysical phenomena. Microquasars can be considered as scaled-down versions of active galactic nuclei, or quasars. Quasars display also jets of relativistic particles, but in their case the compact object is a black hole of millions of solar masses located at the center of a galaxy. In contrast to quasars, where phenomena of jet formation and matter ejection can take years, microquasar jets evolve in time scales of days, a fact that makes them more suitable for human observations. Microquasars are also candidates to be one of the sites of production of the cosmic rays, a mystery unsolved since their discovery almosta hundred years ago.
The study of microquasars represents one of the most important additions to the recently born field of VHE gamma-ray astrophysics. VHE gamma-rays are a kind of radiation which is produced in the most violent phenomena of our Universe, like e.g. supernova explosions or quasars. They can reach the Earth, albeit at a very low rate (typically less than one gamma-ray per square meter and per week). MAGIC detects gamma-rays through the short light flashes that they produce as they enter the atmosphere. MAGIC is the largest telescope exploiting this experimental technique, with a 17 m diameter mirror. It is located at the observatory Roque de los Muchachos on the Canary Island of La Palma (Spain). The MAGIC team is composed of more than 130 scientists coming from 9 countries, namely: Spain, Germany, Italy, Switzerland, Poland, Armenia, Finland, Bulgaria and USA.
MAGIC has observed, between October 2005 and March 2006, one of the approximately 20 known microquasars, called LS I +61 303. VHE gamma-rays coming from LS I +61 303 have been detected at an approximate rate of one gamma-ray per square meter and per month. Only one other binary star system (LS 5039) is known to emit VHE gamma-rays. This new discovery points to the fact that gamma-ray production could be a common property of microquasars. The results of the MAGIC team have revealed a very interesting property: the intensity of the gamma-ray emission coming from LS I +61 303 varies with time (see Fig. 2). The binary system was observed at different 2 moments along the orbital cycle of the compact object around the massive star. The time scale of variability was similar to the orbital period, showing that the VHE emission is directly related to the interplay between the two stars of the system. Furthermore, some theorists expected the gamma-ray emission to happen when the two stars are closest to one another (i.e. at periastron passage, Fig. 2a) since it is at this moment when the particles accelerated in the jet find the largest density of potential targets to produce the gammarays. However, a relatively strong gamma-ray flux was observed only when the compact object had completed about one third of the whole orbital cycle (Fig 2b). Future observations of LS I +61 303 with MAGIC, together with theoretical interpretation of the present results will help elucidate the mechanisms of gamma-ray production and absorption in microquasars and in objects displaying relativistic jets in general.
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22.09.2017 | Forschungszentrum MATHEON ECMath
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
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