#h.e.s.s.

[skycrorg]

✨ Nuevo estudio revela un “chorro cósmico” saliendo de Westerlund 1 — Astrónomos detectaron por primera vez un flujo de partículas cargadas (electrones cósmicos) abandonando este enorme cúmulo estelar, lo que podría abrir un canal para que rayos cósmicos alcancen el halo galáctico.

Westerlund 1: Primera evidencia de un flujo de partículas desde un cúmulo estelar masivo joven

[delectatiosola]

H.E.S.S. - The High Energy Stereoscopic System

[scifigeneration]

Source of unprecedented energy found in Milky Way

For more than ten years the H.E.S.S. observatory in Namibia, run by an international collaboration of 42 institutions in 12 countries, has been mapping the centre of our galaxy in very-high-energy gamma rays. These gamma rays are produced by cosmic rays from the innermost region of the Galaxy. A detailed analysis of the latest H.E.S.S. data, published on 16th March 2016 in Nature, reveals for the first time a source of this cosmic radiation at energies never observed before in the Milky Way: the supermassive black hole at the centre of the Galaxy, likely to accelerate cosmic rays to energies 100 times larger than those achieved at the largest terrestrial particle accelerator, the LHC at CERN.

The Earth is constantly bombarded by high energy particles (protons, electrons and atomic nuclei) of cosmic origin, particles that comprise the so-called "cosmic radiation." These "cosmic rays" are electrically charged, and are hence strongly deflected by the interstellar magnetic fields that pervade our galaxy. Their path through the cosmos is randomised by these deflections, making it impossible to directly identify the astrophysical sources responsible for their production. Thus, for more than a century, the origin of the cosmic rays remains one of the most enduring mysteries of science.

Fortunately, cosmic rays interact with light and gas in the neighbourhood of their sources, producing gamma rays. These gamma rays travel in straight lines, undeflected by magnetic fields, and can therefore be traced back to their origin. When a very-high-energy gamma ray reaches the Earth, it interacts with a molecule in the upper atmosphere, producing a shower of secondary particles that emit a short pulse of "Cherenkov light." By detecting these flashes of light using telescopes equipped with large mirrors, sensitive photo-detectors, and fast electronics, more than 100 sources of very-high-energy gamma rays have been identified over the past three decades. The H.E..S.S. (High Energy Stereoscopic System) observatory in Namibia represents the latest generation of such telescope arrays. It is operated by scientists from 42 institutions in 12 countries, with major contributions by MPIK Heidelberg, Germany, CEA and CNRS, France.

Today we know that cosmic rays with energies up to approximately 100 teraelectronvolts (TeV)1 are produced in our galaxy, by objects such as supernova remnants and pulsar wind nebulae. Theoretical arguments and direct measurements of cosmic rays reaching the Earth indicate, however, that the cosmic-ray factories in our galaxy should be able to provide particles up to one petaelectronvolt (PeV)2 at least. While many multi-TeV accelerators have been discovered in recent years, so far the search for the sources of the highest energy Galactic cosmic rays has, so far, been unsuccessful.

Detailed observations of the Galactic centre region, made by H.E.S.S. over the past ten years, and published today in the journal Nature, finally provide direct indications for such PeV cosmic-ray acceleration. During the first three years of observations, H.E.S.S. uncovered a very powerful point source of gamma rays in the galactic-centre region, as well as diffuse gamma-ray emission from the giant molecular clouds that surround it in a region approximately 500 light years across. These molecular clouds are bombarded by cosmic rays moving at close to the speed of light, which produce gamma rays through their interactions with the matter in the clouds. A remarkably good spatial coincidence between the observed gamma rays and the density of material in the clouds indicated the presence of one or more accelerators of cosmic rays in that region. However, the nature of the source remained a mystery.

Deeper observations obtained by H.E.S.S. between 2004 and 2013 shed new light on the processes powering the cosmic rays in this region. According to Aion Viana (MPIK, Heidelberg), "the unprecedented amount of data and progress made in analysis methodologies enables us to measure simultaneously the spatial distribution and the energy of the cosmic rays." With these unique measurements, H.E.S.S. scientists are for the first time able to pinpoint the source of these particles: "Somewhere within the central 33 light years of the Milky Way there is an astrophysical source capable of accelerating protons to energies of about one petaelectronvolt, continuously for at least 1,000 years," says Emmanuel Moulin (CEA, Saclay). In analogy to the "Tevatron," the first human-built accelerator that reached energies of 1 TeV, this new class of cosmic accelerator has been dubbed a "Pevatron." "With H.E.S.S. we are now able to trace the propagation of PeV protons in the central region of the Galaxy," adds Stefano Gabici (CNRS, Paris).

The centre of our galaxy is home to many objects capable of producing cosmic rays of high energy, including, in particular, a supernova remnant, a pulsar wind nebula, and a compact cluster of massive stars. However, "the supermassive black hole located at the centre of the Galaxy, called Sgr A*, is the most plausible source of the PeV protons," says Felix Aharonian (MPIK, Heidelberg and DIAS, Dublin), adding that, "several possible acceleration regions can be considered, either in the immediate vicinity of the black hole, or further away, where a fraction of the material falling into the black hole is ejected back into the environment, thereby initiating the acceleration of particles."

The H.E.S.S. measurement of the gamma-ray emission can be used to infer the spectrum of the protons that have been accelerated by the central black hole -- revealing that Sgr A* is very likely accelerating protons to PeV energies. Currently, these protons cannot account for the total flux of cosmic rays detected at the Earth. "If, however, our central black hole was more active in the past," the scientists argue, "then it could indeed be responsible for the bulk of the Galactic cosmic rays that are observed today at the Earth." If true, this would dramatically influence the century old debate concerning the origin of these enigmatic particles.

[astroblogs]

Zwart gat in centrum van de Melkweg lijkt petadeeltjesversneller

Een artistieke impressie van de krachtige kosmische peta-elektronvoltversneller die een internationaal team van wetenschappers heeft ontdekt in het centrum van onze Melkweg. Credit: Dr. Mark A. Garlick & H.E.S.S. Collaboration

Een internationaal team van wetenschappers heeft een galactische deeltjesversneller ontdekt die met nog nooit vertoonde energie kosmische straling de ruimte in slingert. De onderzoekers vermoeden dat het zwarte gat in het centrum van onze Melkweg verantwoordelijk is. De wetenschappers, verenigd in het H.E.S.S.-consortium, publiceren hun bevindingen woensdagavond in Nature.

Al ruim dertig jaar brengt een consortium van 42 instituten in 12 landen (waaronder onderzoekers van de Universiteit van Amsterdam) de gammastraling in kaart die uit de buurt van het centrum van onze Melkweg komt. Nu hebben de onderzoekers voor het eerst de precieze bron van deze kosmische straling aangewezen: het superzware zwarte gat in het galactisch centrum.

Voor wetenschappers was het al een eeuw een raadsel waar de deeltjes vandaan komen die met hoge energie op de aardse atmosfeer botsen. Van de meeste van deze deeltjes is het namelijk gewoonweg onmogelijk om de bron te herleiden. De deeltjes, zoals protonen, elektronen en atoomkernen, zijn namelijk elektrisch geladen en worden daardoor afgebogen door de magnetische velden die ze op hun weg door de ruimte tegenkomen.

Gelukkig is er ook gammastraling. Die reist in een rechte lijn en trekt zich niks aan van magneetvelden op de route. De gammastraling is dus wél te herleiden tot hun bron. En dat is nu, na intensief speurwerk, gebeurd.

De onderzoekers van het High Energy Stereoscopic System-consortium (H.E.S.S.-consortium) gebruikten daarvoor een groep van gekoppelde telescopen in Namibië. Tien jaar geleden hadden de onderzoekers al door dat er ergens rond het centrum van onze Melkweg een of meer gammastralingsbronnen moesten zijn, maar wat en hoe precies, dat was lastig te zeggen. Mogelijke ‘daders’ waren onder andere supernova-resten, clusters van zware sterren en het zwarte gat in het centrum van de Melkweg.

Door stug doormeten, konden de onderzoekers het zwarte gat in de kern van onze Melkweg als verantwoordelijke aanwijzen. De galactische versneller is ongeveer 100 keer zo krachtig als de LHC-versneller van CERN die ‘slechts’ 13 teraelektronvolt haalt. Het zwarte gat is daarmee de eerste peta-elektronvoltversneller ooit ontdekt.

De wetenschappers publiceren hun bevindingen op 16 maart in Nature. Vanuit Nederland waren Jacco Vink en David Berge (beiden Universiteit van Amsterdam) betrokken bij het onderzoek. Berge is coördinator van het galactische onderzoek met H.E.S.S: “Het is super dat we met elkaar, dankzij jarenlang meten en modelleren, nu eindelijk de bron van gammastraling hebben getraceerd.” Bron: Astronomie.nl.

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Astroblogs: http://www.astroblogs.nl/2016/03/17/zwart-gat-centrum-van-de-melkweg-lijkt-petadeeltjesversneller/

[astroblogs]

Drie bijzondere objecten ontdekt in nabij sterrenstelsel

Een internationaal team van wetenschappers heeft drie bijzondere objecten ontdekt in een van de buurstelsels van onze Melkweg. In dat sterrenstelsel, de 170.000 lichtjaar verre Grote Magelhaense Wolk, zijn een superbubbel, een pulsarwindnevel en de restanten van een supernova opgespoord (Science, 23 januari).

De superbubbel is nog wel de grootste verrassing van de drie ontdekkingen. Het is een enorm gebied waar veel sterren ontstaan en exploderen. Sterwinden en explosies blazen het aanwezige gas weg. Daardoor ontstaat een ijl gebied: een bubbel. ‘Volgens sommige theorieën is deze omgeving ideaal om deeltjes te versnellen tot zeer hoge energieën. Het feit dat we nu voor het eerst hoge-energie gammastraling waarnemen uit zo’n bubbel, lijkt die theorieën te bevestigen,’ aldus teamlid dr. Jacco Vink van de Universiteit van Amsterdam.

Bij elke nieuwe exploderende ster in de bubbel ontstaat een schokgolf die duizenden jaren met duizenden kilometers per seconde voortraast. In 30 Dor C, de naam van de superbubbel, is de schokgolf inmiddels 150 lichtjaar groot.

De nieuw ontdekte pulsarwindnevel N 157B lijkt in veel opzichten een tweelingzusje van de Krabnevel in onze eigen Melkweg. Een groot verschil is dat de nieuwe nevel zo’n tien keer meer gammastraling uitzendt. Dat komt waarschijnlijk onder andere doordat dicht bij de nieuwe nevel de afgelopen vier miljoen jaar zo’n duizend sterren zijn ontstaan die veel licht geven. De deeltjes in de pulsarwindnevel zetten dit licht om in gammastraling.

De derde vondst, de overblijfselen van supernova N 132D, plaatst de onderzoekers voor een nieuw raadsel. De ster is duizenden jaren geleden al ontploft, maar straalt nog steeds gammastraling van hoge energie uit. Normaal gesproken doen oude supernovaresten dat niet.

De drie objecten zijn ontdekt met de High Energy Stereoscopic System afgekort H.E.S.S.. Dat is een opstelling van telescopen die speciaal voor de detectie van gammastraling is gemaakt. De telescopen staan in de woestijn van Namibië.

Bron: Nederlandse Onderzoekschool voor Astronomie

Astroblogs: https://www.astroblogs.nl/2015/01/23/drie-bijzondere-objecten-ontdekt-nabij-sterrenstelsel/

[astrohap]

H.E.S.S. II first light and furthest source ever seen for H.E.S.S. I

On July, 26 2012, scientists of the H.E.S.S. collaboration announced that the H.E.S.S. II telescope has started operation in Namibia. Meanwhile H.E.S.S I observed the currently most distant source of very high energy gamma rays. Read more...

(picture credit: H.E.S.S collaboration / F. van Greunen) 

[spaceplasma]

Exploring the Universe with gamma rays

The last decade has witnessed the birth of a new field of astronomy – Very High Energy (VHE) gamma ray astronomy – expanding wavelength coverage of astronomical instruments by another 10 octaves towards the highest energy radiation. These gamma rays are produced when high energy cosmic rays bump into interstellar gas, creating a bunch of elementary particles. Unlike charged cosmic rays, the gamma rays travel on a straight path and point back to the point in the sky where they were produced. Apart from serving as tracers of cosmic rays, speculation is that some VHE 6.2 Exploring the Universe with gamma rays gamma rays may result from decays of relic particles with have survived since the Big Bang, such as the mysterious dark matter particles; detection of such gamma rays would give first hints towards the nature of dark matter.

Very High Energy gamma rays are absorbed in the Earth’s atmosphere, creating a cascade of secondary elementary particles, most of which never reach the ground. Satellite instruments such as AGILE and Fermi (the former GLAST), now in orbit, detect gamma-rays before they enter the atmosphere, but their size is too small to capture enough of the highest-energy gamma rays.

After long development, a ground-based detection technique pioneered by the American Whipple telescope and perfected by the European-led H.E.S.S. and MAGIC instruments has brought a break-through: Imaging Atmospheric Cherenkov telescopes. These telescopes collect and image the bluish light emitted by the particle cascades created by a VHE gamma ray in the atmosphere. Light from a single VHE gamma ray illuminates a “light pool” of about 150 m radius on the ground, hence a single telescope will detect gamma rays incident upon an area of a few 10000 m2, compared to the sub-m2 area of satellite detectors. Latest generation Cherenkov telescope systems use multiple telescopes to provide stereoscopic viewing of gamma-ray induced particle cascades, for improved determination of impact direction and energy of a gamma-ray.

VHE gamma-ray astronomy is becoming part of mainstream astronomy, with surveys of the Galaxy revealing dozens of VHE gamma-ray emitting cosmic-ray accelerators. Objects discovered include supernova remnants, binary systems, pulsars, stellar associations and different species of active galaxies, hosting super-massive black holes at their centres.

[astrohap]

H.E.S.S. is a system of Imaging Atmospheric Cherenkov Telescopes that investigates very high energy (VHE) cosmic gamma-rays in the 100 GeV to 100 TeV energy range.

The name H.E.S.S. stands for High Energy Stereoscopic System, and is also intended to pay tribute to Victor Hess, who received the Nobel Prize in Physics in 1936 for the discovery of cosmic radiation. H.E.S.S. is located in Namibia, near the Gamsberg mountain, an area well known for its excellent optical quality.

The first four telescopes of Phase I of the H.E.S.S. project were all operational in December 2003. The second phase of the detector was completed in mid-November 2011 by installing a steel structure of 600 m2. Mirrors and camera will be installed in the first half of 2012.

        Source: mpi-hd.mpg.de 

Note that the H.E.S.S. II telescope is located in between (and not in front of!) the two H.E.S.S. I telescopes.

more about cosmic rays here more about the H.E.S.S. telescopes here