02 febbraio 2012

LOFAR il radiotelescopio "diffuso" che ascolta l'FM

Inizierà il suo lavoro con una mappatura completa del cielo a frequenze normalmente inaccessibili ai normali radiotelescopi, lunghezze d'onda comprese tra i 2 e 10 metri, quelle che normalmente interessano tutti noi. Si parla infatti di frequenze che partono dal limite estremo delle onde corte e arrivano fino alla banda III televisiva o del DAB, dove i radioastronomi e gli studiosi di cosmologia possono studiare - grazie all'interazione tra particelle cosmiche e molecole dei primi strati atmosferici - i primordi dell'universo, le giovani galassie, le pulsar. Sarà possibile anche scoprire nuovi pianeti extrasolari "ascoltando" le loro aurore boreali.
Partono così le attività del LOFAR Low Frequency Array, un progetto olandese (ne ho già parlato quattro anni fa, quando era stato lanciato ufficialmente) che sfrutta decine di migliaia di economiche antenne a bassa (30-80 Mhz) e alta (100-240 MHz) in location sparse in Olanda (36 stazioni), Germania, Francia, Svezia, Regno Unito e in futuro Polonia, tutte unite tra loro da una rete in fibra ottica. L'obiettivo è andare a pieno regime entro la fine dell'anno. La mappa "total sky" sarà la prima di questo tipo e verrà tracciata con l'aiuto di sofisticati algoritmi che coordinano una ricezione "parcellizzata" ricostruendo i segnali di tutte quelle antenne via software, ma anche correggendo le informazioni raccolto tenendo conto dell'effetto delle interferenze terrestri e della variabilità della ionosfera. L'equivalente di un radiotelescopio del diametro di 12 campi di calcio, con una risoluzione impensabile.

International LOFAR radio telescope kicks off all-sky survey

World's most complex radio telescope begins its first low frequency survey of the sky, as it prepares to open its doors to the international astronomy community this year.
Scientists from the International LOFAR Telescope (ILT) today announced the kick-off of the project's first all-sky survey at low radio frequencies and its first open call for observing proposals from the international astronomical community. LOFAR, the Low Frequency Array, is an innovative radio telescope built in the Netherlands and across northern Europe. LOFAR will make the still largely unexplored low-frequency radio sky accessible to astronomers for the first time. It will search for the first stars and black holes in the universe, hunt for cosmic radio bursts, pulsars, and ultra-high energy cosmic particles, study the sun and planets, and explore cosmic magnetic fields.
The project will complete its hardware construction phase in 2012 and open its doors for researchers from all over the world. Early science results from the commissioning phase of LOFAR were presented at the American Astronomical Society meeting in Austin, Texas.
The first major observing project of LOFAR will be the Multi-frequency Snapshot Sky Survey (MSSS). The survey will ultimately yield the most accurate catalogue of radio sources ever produced at these very long radio wavelengths. Designed to observe light at radio wavelengths from 2 to 20 meters, LOFAR can observe multiple, large areas of the sky simultaneously. This means it can survey the radio sky faster. "With LOFAR, we can systematically explore the low-frequency radio sky like never before and see, for example, powerful black holes throughout the entire universe." says MSSS Project Leader, Dr. George Heald. This initial survey is expected to take several months to complete, although final processing of the data will likely take longer. Much deeper, follow-up surveys are also planned.
When it opens later this year to the science community, LOFAR will already offer some unique capabilities to radio astronomers. LOFAR is a fully digital radio telescope that uses fiber optic cables to connect more than 20,000 low-cost antennas via the internet into a single large telescope. These antennas are grouped together into 48 separate stations distributed over the northeastern part of the Netherlands as well as in Germany, France, the UK, and Sweden. Funding for additional stations has also recently been approved in Poland. Signals from these stations are combined using an IBM BlueGene/P supercomputer to create a telescope with a collecting area of 12 football fields and a resolution equivalent to a telescope 1,000 km in diameter. The combination of many antennas and large effective size gives LOFAR unprecedented sensitivity and resolving power at long radio wavelengths.
The first science team within the LOFAR project counting on this increased sensitivity to achieve their scientific goals is the Epoch of Reionization (EoR) project, led by Prof. Ger de Bruyn. The EoR team hopes to detect extremely feeble signals from the highly redshifted neutral hydrogen 21cm emission line produced during the earliest phase of the Universe before the first stars and galaxies formed. LOFAR's large collecting area makes it uniquely suited to detect these extremely faint signals. According to Prof. de Bruyn, "Detection of signals from highly redshifted neutral hydrogen, emitted during the childhood years of the Universe, would be a watershed moment in cosmology." If the EoR observation detection proves successful, the results will reveal detailed information on the first stars and galaxies born in the universe. Several pilot observations by the EoR team have already yielded some of the deepest LOFAR images yet, and the most sensitive ever at these wavelengths. Even deeper observations are planned for the coming year to push closer to the required detection sensitivity of the EoR signal itself.
Low-frequency radio imaging is particularly challenging due to the Earth's variable ionosphere and interference from man-made radio transmitters, such as FM radio stations. "The first phase of commissioning has demonstrated that a fully digital telescope can overcome these obstacles, which have plagued low-frequency astronomy for so long.", says Heino Falcke, chair of the International LOFAR Telescope (ILT). "After ten years of hard work on this project, it is fantastic to see that it actually works."
LOFAR's unique capabilities are already proving useful for researchers studying pulsars, the highly magnetized and rapidly rotating neutron stars formed during the gravitational collapse of a massive star following a supernova. Many of these objects give off brief but intense bursts of radio emission lasting in some cases only millionths of a second. LOFARs sensitivity and highly accurate clocks make it possible to study pulsars over the lowest 4 octaves of the observable radio spectrum all at once. When combined with data from other radio telescopes operating at shorter wavelengths, LOFAR observations can isolate the origin of pulsar's radio emission to within 100km above the magnetic poles of the star. LOFAR's large field of view will also be used to perform efficient surveys to study known pulsars and detect new ones.
LOFAR will offer its unique scientific capabilities to the astronomical community starting in May with the announcement of its first open call for observing projects. A fraction of the available observing time for the coming year will be allocated to a number of Key Science Projects with the remaining time available for open-sky observing projects. "LOFAR really is the most versatile radio telescope in the world. When we open the doors in May, this amazing new facility will be available to any scientist in the world to use.", said LOFAR Project Scientist, Dr. Michael Wise.
International LOFAR Telescope Operations are coordinated by ASTRON, the Netherlands Institute for Radio Astronomy, on behalf of a consortium consisting of the Netherlands, Germany, France, the UK, and Sweden. Many of the technological solutions developed for LOFAR, in particular the calibration of phased-arrays as well as large-scale data transport and processing, will be highly relevant for future radio telescope projects such as the Square Kilometer Array (SKA). The SKA is a 1.5 billion euro, global science project to build the world's largest and most sensitive radio telescope over the next decade. LOFAR represents the first of several SKA technology pathfinder projects to come online.

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