Si tratta di una collaborazione internazionale che coinvolge più di 200 astronomi di oltre 40 istituti sparsi sul globo. Denominata MaNGA, che sta per Mapping Nearby Galaxies at Apache Point Observatory, questa nuova survey del cielo permetterà di espandere le nostre conoscenze sulle galassie, inclusa la Via Lattea, grazie ad una nuova tecnologia attraverso la quale sarà possibile studiare la struttura e la composizione di un campione di 10.000 galassie, con una precisione statistica che non è stata mai raggiunta prima. Continua a leggere MaNGA, una survey delle galassie vicine
Dopo gli ottimi risultati già ottenuti nel corso della sua prima stagione, è già iniziato il secondo anno della missione spaziale denominata Dark Energy Survey (DES), che avrà come obiettivo la survey del cielo meridionale con una accuratezza senza precedenti. Grazie alla risoluzione di 570 megapixel della Dark Energy Camera (DECAM), montata presso il telescopio Victor M. Blanco in Cile (post), gli scienziati avranno la possibilità di monitorare il cielo nel corso di cinque anni, sperando così di svelare i segreti dell’energia scura ed il suo impatto che essa avrà per l’evoluzione futura del nostro Universo. Inoltre, queste osservazioni permetteranno di realizzare tutta una serie di immagini spettacolari del profondo cielo senza precedenti.
Dark Energy Survey’s first season images
Dark Energy Detectives, the survey’s photo blog
DECam Interactive to see what the Dark Energy Camera sees
Il fatto che non esistano tante galassie nane distribuite come uno sciame d’api attorno a quelle più grandi ma che invece “danzino”, per così dire, su orbite ordinate a forma di disco rappresenta una sfida alle nostre conoscenze su come si è formato ed evoluto il nostro Universo. Oggi, un gruppo internazionale di astronomi, che include tra gli altri Geraint Lewis dell’University of Sydney’s School of Physics, hanno pubblicato i risultati di uno studio che sembra, però, contraddire il modello cosmologico standard.
Le prime immagini realizzate dalla survey denominata Dark Energy Survey (DES) hanno permesso di rivelare un oggetto esotico, ossia una supernova ‘superluminosa’ esplosa in una galassia 7,8 miliardi di anni fa. Denominata con la sigla DES13S2cmm, la sua luminosità supera quella di intere galassie e con ogni probabilità potrà essere osservata ancora tra 6 mesi circa, cioè alla fine del primo dei cinque anni previsti dalla survey. Continua a leggere DES rivela una supernova ‘super luminosa’
The SKA PAthfinder Radio Continuum Survey (SPARCS) Working Group was established in 2010 with the following goals:
1) To coordinate developments of techniques, to avoid duplication of effort and ensure that each project has access to best practice.
2) To hold cross-project discussions of the specific science goals, to ensure cross-fertilisation of ideas and optimum survey strategies.
3) To coordinate the surveys in their choice of area, depth, location on the sky, and other survey parameters, to maximise the science return from the surveys.
4) To distil the SKA pathfinder experiences into input to the SKA
La survey del cielo denominata Baryon Oscillation Spectroscopic Survey (BOSS), che rappresenta la parte più grande della terza survey Sloan Digital Sky Survey (SDSS-III), ha osservato i quasar distanti per realizzare una mappatura delle variazioni di densità del gas intergalattico a redshift elevati permettendo così di tracciare la struttura dell’Universo primordiale. BOSS ci fornisce da un lato una carta temporale della storia evolutiva dell’Universo al fine di avere maggiori indizi sulla natura dell’energia scura e dall’altro ci permette di realizzare nuove misure della struttura su larga scala, le più precise mai ottenute sull’espansione cosmica sin dall’epoca in cui si sono formate le prime galassie.
La più grande ‘caccia’ alle supernovae sta per iniziare il prossimo mese di Agosto. Per cinque anni, il programma scientifico denominato Dark Energy Survey avrà lo scopo di esplorare le esplosioni stellari cosmiche che saranno utilizzate come ‘candele standard’ per misurare con una precisione sempre più elevata l’espansione dell’Universo. Lo scopo della survey è quello di ottenere nuovi dati per comprendere gli effetti dell’energia scura, quella enigmatica componente che sta determinando una espansione accelerata del cosmo.
DES is operated by an international collaboration of researchers from 25 institutions and consortia, including six universities in the UK. It will use a massive new 570 Megapixel camera (DECam) installed on the four-meter diameter Blanco telescope, high in the mountains of Chile. The instrument was commissioned in September and October 2012, and this was followed by a period of science verification from November through February 2013. “Thanks to the extreme sensitivity of the camera and to the large area of sky that can be imaged through the telescope at once (about 15 times the size of the full moon), we expect DES to find more supernovae than any previous experiment. During the verification phase, we have already identified at least 200 good candidates“, said Chris D’Andrea, a researcher at the University of Portsmouth’s Institute of Cosmology and Gravitation. More than just numerous, these supernovae are very old, with the light from the most distant having travelled towards Earth for over 8 billion years. Of particular interest are Type Ia supernovae, which all have nearly the same luminosity when they reach their brightest phase.
By comparing the brightness of Type Ia supernovae, scientists in DES will be able to determine accurately the distance to the supernovae and measure how the Universe has expanded over time.
This method was used in the Nobel Prize-winning research that led to the discovery of the accelerated expansion of the universe 15 years ago. While those researchers used a few dozen supernovae in their study, DES will find over 3500 of these objects. This glut of data poses a challenge for the team to analyse. “Traditionally, astronomers have identified supernovae by analysing the spectrum of light from candidates. Because DES will give us so many candidates – we already have hundreds just from the commissioning phase – we don’t have the resources to do this for each individual candidate supernova. We need to use other techniques to confirm which of the objects we observe really are exploding stars“, said D’Andrea. An alternative method for identifying supernovae is to monitor changes in the brightness and colour of their light over time. However, the scientists also need to know how much the Universe has expanded since the star exploded. This information can be gathered by analysing the spectra of light from galaxies in which supernovae have occurred, unlike a supernova, a galaxy does not quickly fade away. “DES is a long-term survey – we may not know whether some of our candidates are ‘real’ supernovae until the end of the project. However, in collaboration with Australian researchers, our team has recently been awarded 100 nights of time on a telescope in Australia over the next five years. The Anglo-Australian Telescope has the ability to take spectra of nearly 400 galaxies at the same time. With the first of these nights scheduled for September, it won’t be that long before we can start to accurately classify the supernovae candidates discovered in DES“, concluded D’Andrea.
This school comes at a unique time in cosmology. Our understanding of the Universe has been revolutionized by observations of the cosmic microwave background (in particular Wilkinson Microwave Anisotropy Probe), the large-scale structure of the universe (Two-degree-Field Galaxy Redshift Survey and Sloan Digital Sky Survey), and distant supernovae. These studies have conclusively shown that we are living in a strange Universe: 96% of the present-day energy density of the universe is dominated by the so-called dark matter and dark energy. However, we do not know what dark matter and dark energy actually are. The data also suggest that it is likely that the Universe underwent a rapid accelerating expansion phase in the very early universe called the inflationary phase. However, we still do not know how inflation happened.
Now, we are about to have another revolution in cosmology because, during the next couple of years, we expect to see a further qualitative jump in our knowledge of the Universe. The Planck satellite collaboration, mostly funded by ESA, in particular, will publish the first cosmological results by early 2013 (post). Planck will provide an essentially complete view of temperature anisotropy of the Cosmic Microwave Background. A host of ground-based experiments measuring polarization of the cosmic microwave background (e.g., ACTpol, SPTpol, Polarbear, BICEP) will report their results soon. The next-generation galaxy surveys (BOSS, DES, HSC, HETDEX) will begin to yield data. These new data will undoubtedly address fundamental questions about the Universe: what is the nature of dark energy and dark matter? What powered the Big Bang? Did inflation occur? If it did, how did it occur? What is the mass of neutrinos? When and how were the first stars and galaxies formed? Now is an ideal time to organize a school focused on these subjects, as we enter a new revolution in cosmology.
Grazie ad una serie di osservazioni nella banda dell’infrarosso e dei raggi-X relative alla stessa porzione di cielo, realizzate con i telescopi spaziali Chandra e Spitzer, un gruppo di astronomi hanno rivelato la presenza di un numero significativo di buchi neri che esistevano già durante le fasi primordiali della storia cosmica, all’epoca cioè quando andavano formandosi le prime stelle. I ricercatori concludono che almeno una sorgente su cinque che contribuisce al fondo della radiazione infrarossa è associata ad un buco nero.
“Our results indicate black holes are responsible for at least 20 percent of the cosmic infrared background, which indicates intense activity from black holes feeding on gas during the epoch of the first stars“, said Alexander Kashlinsky, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Md. The cosmic infrared background (CIB) is the collective light from an epoch when structure first emerged in the Universe. Astronomers think it arose from clusters of massive suns in the Universe’s first stellar generations, as well as black holes, which produce vast amounts of energy as they accumulate gas. Even the most powerful telescopes cannot see the most distant stars and black holes as individual sources. But their combined glow, traveling across billions of light-years, allows astronomers to begin deciphering the relative contributions of the first generation of stars and black holes in the young cosmos. This was at a time when dwarf galaxies assembled, merged and grew into majestic objects like our own Milky Way galaxy. “We wanted to understand the nature of the sources in this era in more detail, so I suggested examining Chandra data to explore the possibility of X-ray emission associated with the lumpy glow of the CIB“, said Guenther Hasinger, director of the Institute for Astronomy at the University of Hawaii in Honolulu, and a member of the study team. Hasinger discussed the findings Tuesday at the 222nd meeting of the American Astronomical Society in Indianapolis. The work began in 2005, when Kashlinsky and his colleagues studying Spitzer observations first saw hints of a remnant glow. The glow became more obvious in further Spitzer studies by the same team in 2007 and 2012. The 2012 investigation examined a region known as the Extended Groth Strip, a single well-studied slice of sky in the constellation Bootes. In all cases, when the scientists carefully subtracted all known stars and galaxies from the data, what remained was a faint, irregular glow. There is no direct evidence this glow is extremely distant, but telltale characteristics lead researchers to conclude it represents the CIB. In 2007, Chandra took especially deep exposures of the Extended Groth Strip as part of a multiwavelength survey. Along a strip of sky slightly larger than the full moon, the deepest Chandra observations overlap with the deepest Spitzer observations. Using Chandra observations, lead researcher Nico Cappelluti, an astronomer with the National Institute of Astrophysics in Bologna, Italy, produced X-ray maps with all of the known sources removed in three wavelength bands. The result, paralleling the Spitzer studies, was a faint, diffuse X-ray glow that constitutes the cosmic X-ray background (CXB). Comparing these maps allowed the team to determine whether the irregularities of both backgrounds fluctuated independently or in concert. Their detailed study indicates fluctuations at the lowest X-ray energies are consistent with those in the infrared maps. “This measurement took us some five years to complete and the results came as a great surprise to us“, said Cappelluti, who also is affiliated with the University of Maryland, Baltimore County in Baltimore. The process is similar to standing in Los Angeles while looking for signs of fireworks in New York. The individual pyrotechnics would be too faint to see, but removing all intervening light sources would allow the detection of some unresolved light. Detecting smoke would strengthen the conclusion at least part of this signal came from fireworks. In the case of the CIB and CXB maps, portions of both infrared and X-ray light seem to come from the same regions of the sky. The team reports black holes are the only plausible sources that can produce both energies at the intensities required. Regular star-forming galaxies, even those that vigorously form stars, cannot do this. By teasing out additional information from this background light, the astronomers are providing the first census of sources at the dawn of structure in the Universe. “This is an exciting and surprising result that may provide a first look into the era of initial galaxy formation in the Universe“, said another contributor to the study, Harvey Moseley, a senior astrophysicist at Goddard. “It is essential that we continue this work and confirm it“.