Jardim Botânico do Rio de Janeiro
sexta-feira, 10 de julho de 2009
Primeiras estrelas do universo podem ter 'nascido gêmeas', diz estudo
A observação foi possível graças a uma simulação por computador. (Foto: Cortesia de Ralf Kaehler, Matthew Turk e Tom Abel )
Um estudo realizado nos Estados Unidos e publicado na quinta-feira (9) na revista científica "Science Express" indica que muitas das primeiras estrelas do universo se formaram como gêmeas.
A observação foi possível graças a uma simulação por computador do que seria o universo em suas origens, e permitiu que astrofísicos da Universidade de Michigan e da Universidade de Stanford conseguissem uma compreensão mais detalhada do fenômeno da formação das estrelas.
"Acreditava-se que essas primeiras estrelas se formaram como astros únicos, mas agora vemos que muitas tinham 'irmãs'", disse Matthew Turk, do Laboratório Nacional de Aceleração de Stanford, que presta serviços aos de Departamento de Energia americano, e um dos autores do estudo.
"Acreditava-se que essas primeiras estrelas se formaram como astros únicos, mas agora vemos que muitas tinham 'irmãs'", disse Matthew Turk, do Laboratório Nacional de Aceleração de Stanford, que presta serviços aos de Departamento de Energia americano, e um dos autores do estudo.
"Essas estrelas foram as sementes da geração seguinte de estrelas, então, ao entendê-las melhor, podemos compreender como outras estrelas e galáxias se formaram."
Universo virtual
Na simulação computadorizada, os pesquisadores criaram um universo virtual, no qual pulverizaram gás primordial e matéria escura, substâncias presentes logo após o chamado Big Bang, com radiação cósmica de fundo cujas variações refletem a origem de todas os corpos celestes.
Conforme o universo simulado se desenvolvia, ondas de gás e matéria escura giravam no cenário quente e denso.
À medida que o universo ia então se resfriando, os cientistas observaram que a gravidade começava a unir blocos de material. Em áreas ricas em matéria escura, foram registradas as formações de estrelas.
Em uma das cinco simulações realizadas, uma única nuvem de poeira e matéria escura se transformou em estrelas gêmeas: uma com massa 10 vezes maior do que o nosso Sol e outra 6,3 vezes maior.
Ambos os astros ainda estavam crescendo ao final da simulação, e estariam aumentando ainda se a experiência tivesse continuado.
"Esta descoberta abre um novo domínio de possibilidades de pesquisa. Essas estrelas podem ter evoluído para formar dois buracos negros, que por sua vez poderiam ter criado ondas gravitacionais", explicou Tom Abel, também do Laboratório de Aceleração.
Segundo os cientistas, a compreensão da formação e da evolução dos corpos celestes podem explicar como se formaram átomos presentes na Terra e até no corpo humano.
BBC
Previsão do Tempo - BRASIL
Condições do Tempo
Máximas
Mínimas
Pancadas de chuva entre SC, PR, e sul de SP e de MS.
Nesta sexta-feira (10/07) , a frente fria se mantém praticamente estacionária entre o MS, oeste do PR, SC e Atlântico.
Este sistema dará condições para ocorrência de pancadas de chuva entre o norte do RS, SC, PR, e centro-sul de SP e de MS, além de muita nebulosidade.
Áreas de instabilidade atingirão o norte e nordeste de SP, provocando pancadas de chuva no período da tarde.
Entre o PR, sul de MS e sul de SP, ocorrerão chuvas fortes, acompanhas de descargas elétricas, rajadas de vento e eventual queda de granizo.
No centro-sul do RS a nebulosidade diminui, e as temperaturas mínimas estarão baixas, com chances de geada na Região da Campanha.
Pancadas de chuva também deverão ocorrer entre o AM, RR, RO, AC, centro-norte do PA, e norte da Região Nordeste, devido principalmente aos altos valores de temperatura e umidade do ar.
Tempo instável no leste do Nordeste e com possibilidade de pancadas de chuva entre o leste do RN e da PB.
O dia será de predomínio de sol entre o centro-leste de MT, norte de GO, DF, TO, oeste da BA, sul do PI e do MA, e sudeste do PA.
Nas demais áreas do país, sol entre poucas nuvens.
.
Obs: Texto referente ao dia 09/07/2009-18h19
--
Postado por Lucimary Vargas no RADIO LATINA FM em 7/10/2009 02:14:00 AM
Análise da Imagem de Satélite - Previsão do Tempo
Análise da Imagem de Satélite.
Na imagem de satélite de hoje (09/07) das 21:00h (horário de Brasília), observam-se muitas nuvens entre SC, PR e áreas de SP devido a propagação de um cavado.
Há um sistema frontal em SC e sudoeste de MS, áreas onde há significativa nebulosidade. Algumas nuvens baixas estão localizadas no centro-leste de MG e no ES, área com influência dos ventos úmido do oceano.
Algumas nuvens de trovoadas são observadas no noroeste, nordeste e oeste do AM, associadas ao calor e umidade.
O mesmo pode ser visto no sul do AP e nordeste do PA de forma bem mais localizada.
Atualizado: 09/07/2009 - 23:25
Atualizado: 09/07/2009 - 23:25
--
Postado por Lucimary Vargas no RADIO LATINA FM em 7/10/2009 02:09:00 AM
ATENÇÃO - Alerta Meteorológico - Chuva forte em parte do Sul e Sudeste e frio intenso no Sul
Chuva forte em parte do Sul e Sudeste e frio intenso no Sul
.
Estado de Atenção
Estado de Atenção
.
Nesta sexta-feira (10/07) , as chuvas fortes deverão se concentrar no PR, oeste, centro-sul, cone leste e nordeste de SP, centro-sul e leste de MS e no extremo sul de MG, podendo atingir o extremo sul do RJ.
Em algumas localidades do PR são esperados acumulados diários de chuva próximos a 100 mm. As temperaturas mínimas declinarão significativamente no centro-sul do RS, onde são esperadas geadas no sudoeste (campanha) desse Estado.
No sábado (11/07) , as chuvas intensas se concentrarão sobre PR e sul e leste de SP.
Nesse dia poderão ocorrer acumulados diários de chuva superiores a 100 mm no PR e no extremo sul de SP.
O frio continuará na Região Sul com possibilidade de queda de neve nas serras gaúcha e catarinense e geada no oeste/sudoeste do RS.
Em situações de risco consulte a Defesa Civil.
--
Postado por Lucimary Vargas no RADIO LATINA FM em 7/10/2009 01:43:00 AM
Nebulosa da Trífida
Uma beleza indiscritível e gradientes inimagináveis podem ser encontrados na Nebulosa da Trífida. Também conhecida como M20, esta nebulosa fotogénica é visível com binóculos na direcção da constelação de Sagitário. O processo energético da formação de estrelas cria não apenas cores, mas também caos. O gás vermelho resulta de radiação que atravessa o hidrogénio interestelar. Os filamentos de poeira escura que se entrelaçam por M20 foram criados nas atmosferas de estrelas gigantes frias, no remanescente de explosões de supernovas. Quais são as estrelas que iluminam a nebulosa de reflexão azul é um dos temas que ainda está em investigação. A luz de M20 que vemos hoje terá abandonado a nebulosa há cerca de 3,000 anos, embora a distância exacta à mesma ainda não tenha sido determinada. A luz demora cerca de 20 anos para atravessar M20.
A bolha cósmica misteriosa
 Alguns meses atrás, saiu aqui mesmo no G1 uma reportagem sobre uma bolha misteriosa que foi encontrada a vários bilhões de anos-luz de distância daqui. Esse tipo de objeto já era conhecido (mas não entendido) já havia pelo menos uma década. Essas bolhas, chamadas de "bolhas de Lyman alfa" por causa de sua emissão de hidrogênio, são encontradas desde que o Universo tinha uns 2 bilhões de idade, ou apenas 15% de sua idade atual. Ninguém conseguiu explicar (até agora) como essas bolhas surgiram e, pior, qual a fonte de energia que as faz brilhar. Agora, com certa pompa até, observações com o telescópio de raios-X Chandra conseguiram desvendar esses mistérios. Em uma conferência alardeada coma a que revelaria mistérios do início do Universo, J. Geach, da Universidade de Durham, conseguiu mostrar que as bolhas não passam de um dos estágios de formação de galáxias ocorridos no início do Cosmos. De acordo com os modelos, as galáxias se formam quando o gás é atraído pela ação da gravidade e acaba esfriando ao emitir radiação. Este processo para quando o gás que está em queda ainda é aquecido pela radiação da própria galáxia e dos buracos negros que nela se formam. A suspeita até agora era que essas bolhas representassem um desses estágios, o de captura de matéria ou o de repulsão do gás. Beleza – mas entre um estágio e outro a diferença é de meros bilhões de anos. Baseados nos novos dados do Chandra e com alguns argumentos teóricos, Geach e seus colaboradores mostraram que o aquecimento do gás causado por buracos negros supermaciços em processo de crescimento, ou pelos surtos de formação estelar na galáxia, consegue energizar as bolhas. A partir disso, a hipótese mais provável é a de que as bolhas de gás representam o estágio quando as galáxias interrompem seu processo de rápido crescimento por acréscimo de matéria, justamente por causa desse aquecimento interno. Este é um estágio crucial na evolução das galáxias e representa o limite final de acúmulo de matéria, quando tanto as galáxias quanto os buracos negros param de crescer a altas taxas e acabam por repelir a matéria circundante e dando origem às misteriosas bolhas. Isso é mostrado na figura acima, onde à esquerda está a bolha mais distante (que foi observada pelo Subaru), junto com imagens do Hubble, do Spitzer e do Chandra. À direita, temos uma ilustração para entender o processo de como a radiação interna excita a nuvem de gás circundante. Somente a imagem do Chandra levou 4 dias e 15 horas para ser adquirida.. Mas, comparando isso aos mais de dez anos de mistério, foi um investimento baixíssimo PS. Quanto ao "novo" Hubble, nenhuma notícia, que eu saiba. Perguntei a um colega que trabalha na ESA, mas até agora ele não me respondeu. A caracterização e integração de tantos instrumentos novos deve mesmo levar algum tempo. O negócio é esperar! Fonte da notícia:http://colunas.g1.com.br/observatoriog1 |
Anéis e montanhas
Postado por Cássio Barbosa |
A "Briny Deep" Inside Enceladus?
| Mercury may have its volcanic plains, Mars its buried glaciers, and the Kuiper Belt its dwarf planets — but arguably there's no more exciting place in the solar system right now than the Saturnian moon Enceladus. It's drawn the attention of planetary dynamicists, geophysicists, volcanologists, glaciologists, oceanographers, astrobiologists, and plasma physicists — not bad for a modest moon that's barely 300 miles (490 km) across.  A false-color view of geysers jetting from near the south pole of Enceladus, as recorded by Cassini in 2005. NASA / JPL / Space Science Inst. The heat to power all this activity — an astounding 15 gigawatts, based on the latest Cassini estimates — must be due to a tidal interaction with Saturn that's causing the icy crust to flex rhythmically during each orbit. This causes frictional heat to build up inside the icy moon. On paper, the heat must have created a subsurface global ocean at some depth, the "lubricant" that decouples the flexing crust from the moon's deeper interior.  The tortured surface of Saturn's moon Enceladus exhibits five distinct terrain types, including four rifts near its south pole that are the source of its gas-and-particle plumes. Blue tints in this false-color view from Cassini indicate an icy surface covered with coarse grains and boulders. Click on the image for a larger view. NASA / JPL / Space Science Inst. A few weeks ago, at a meeting of geophysicists in Toronto, a trio of dynamicists led by James Roberts (Applied Physics Laboratory) explained there almost has to be a layer of liquid water down there somewhere — it's the only physically plausible way to channel so much heat out of the interior. But they also emphasized that Enceladus can't possibly remain warm-hearted indefinitely — and consequently, given the current orbital arrangement, a subterranean water ocean is "likely to freeze on a geologically short timescale." So if a hidden ocean exists, what's it like? Initially, the Cassini team envisioned a body of water so close to the icy surface that rivulets can escape upward along fractures and rush into space after explosively decompressing into vapor. Not everyone agrees with this "Cold Faithful" geyser model. Others have speculated that an ocean might not be needed at all. Instead, frozen water-based compounds called clathrates, which lock up volatile molecules like methane, carbon dioxide, or nitrogen, are decomposing into the jets of gas and ice..  A closeup of the four 80-mile-long rifts near Enceladus's south pole (white cross). These "tiger stripes"are the source of its gas-and-particle plumes. Blue tints in this false-color view from Cassini indicate an icy surface covered with coarse grains and boulders. NASA / JPL / Space Science Inst. Two new results, published today in Nature, offer glimpses into the jets' true origin. In one, Frank Postberg (Max Planck Institute for Nuclear Physics) and others reveal that about 6% of the tiny particles in Saturn's E ring are quite salty, containing up to 1½% sodium chloride (NaCl). This makes sense if the ocean inside Enceladus has been in contact with deep-seated rocks for millions of years, long enough for sodium and other elements to leach into the water. Postberg's team concludes that the moon's ocean might be as salty as terrestrial seawater (6 to 20 grams of NaCl per kilogram). But an extensive effort to detect sodium in the plumes spectroscopically from Earth has come up empty. Even a trace should have been evident — atomic sodium has very strong emissions in yellow light. Nicholas Schneider (University of Colorado), who headed the observing team, concludes that the lack of sodium in the plume vapor rules out the near-surface geyser model, because in such an explosive getaway both the gas and particles should mimic each other's composition. Instead, Schneider believes the saltless spectra imply that the gas is slowly evaporating in deep caverns below the surface — just like water escaping as vapor from the top of Earth's oceans. The gas collects in pressurized pockets until it can jet to space through fissures. "This idea of slow evaporation from a deep cavernous ocean is not the dramatic idea that we imagined before," Schneider notes in a press release. He adds that other explanations are possible, including warm clathrate-rich ice decomposing and escaping to space — or liquid water created from the friction and heat when tidal flexure causes slabs of ice to rub against each other. "These are all hypotheses, but we can't verify any one with the results so far," said Schneider. "We have to take them all with, well, a grain of salt." Cute turn of phrase, Nick. But seriously, folks, Enceladus in exciting because its putative ocean is rapidly emerging as one of the places in the solar system most conducive to the development of life. As Cassini investigator John Spencer (Southwest Research Institute) notes in his accompanying Nature perspective, this little hotbed of activity appears to have all three of the basic ingredients: a source of heat, a suitable chemical mix, and liquid water. Fonte da notícia:http://www.skyandtelescope.com/news/49027426.html |
Einstein's Gravity Protects Earth
| If the universe obeyed Newton's laws of gravity, there would be about a 60% chance that Mercury would head toward the Sun or Venus during the Sun's lifetime. But according to a new study, corrections to Newton's laws using Einstein's theory of gravity (general relativity) lower these chances to about 1%. That's good news, because if Mercury had a near miss with Venus or the Sun, it could wreak havoc on Earth.  Artist's concept of a collision between Venus and Earth. J. Vidal-Madjar / IMCCE / CNRS If that happens, Mercury would likely smash into Venus or the Sun, according to a new study by Jacques Laskar and Mickael Gastineau (Paris Observatory, France), published in the June 11th issue of Nature. For all of Jupiter's mass, sending Mercury farther out than Venus requires an "alignment of planets" of sorts — a near-perfect geometry that physicists call a resonance — allowing a small effect to build up over time. In the case of Jupiter and Mercury, the accidental matching is provided by the speed at which their elliptical orbits move around the Sun — the precession of their perihelia — which happens to be nearly synchronized. But the warping of space-time near the Sun predicted by general relativity introduces a slight mismatch, by speeding up Mercury's precession. So the resonance is less likely to happen. We can thank Einstein once more (and Laskar too) for informing us that Mercury has only a 1% chance of going out of whack. Laskar's estimate following Newtonian gravity was 60%. "[The Newtonian calculation] had to be wrong," says Jack Lissauer (NASA/Ames Research Center), arguing that, with such high probabilities, Mercury would already have hit Venus or the Sun during the past few billion years.  Example of long-term evolution of the planetary orbits: Mercury (white), Venus (green), Earth (blue), Mars (red). Time is indicated in thousands of years (kyr). (a) In the vicinity of the current state, the orbits become distorted under the influence of planetary perturbations, but without allowing close encounters or collisions. (b) In about 1% of cases, the orbit of Mercury may be distorted enough to allow a collision with Venus or the Sun in less than 5 billion years. (c) In one of the trajectories, the eccentricity of Mars increases sufficiently to allow for a close encounter or collision with Earth. (d) This leads to a destabilization of the terrestrial planets and collision between Venus and Earth. ASD / IMCCE / CNRS Mercury's demise brings little consequences for Earth, unless Venus tidally disrupts Mercury, sending fragments our way. "There would be a lot of these chunks, and they could hit Earth," says Lissauer. If Mercury goes haywire but misses Venus and the Sun on its new, highly eccentric trajectory, Mercury can perturb the orbits of Mars, Venus, or Earth; the more massive outer planets would remain unaffected. It's difficult to know whether this will happen, because the solar system is chaotic. "That the system is chaotic doesn't mean anything can happen," Laskar explains, but relates to the "butterfly effect.." All the planets and smaller bodies gravitationally influence each other, meaning that any imprecision on today's trajectory is multiplied by ten every 10 million years. Because of this chaos, astronomers will never be able to predict the positions of planets beyond a few hundred million years, and nobody can guarantee that Earth will even orbit the Sun so far in the future. "We can never overcome this limitation," says Laskar, even if the inaccuracy started out less than a trillionth of a trillionth of an inch. "If I jump in the air, Earth moves more than that," Laskar says. So instead of aiming for the unknown exact trajectory of Mercury, Laskar and Gastineau went for a random sampling of what might happen. Modifying Mercury's current position in steps of 0.38 millimeters, they created 2,501 trajectories. These tiny variations could be thought of as due to Laskar jumping up, an asteroid or star passing by, the influences of tides, or the finite size of the planets. We can't tell the 2,501 trajectories apart today, but as they diverge in the future, they provide a sample of the innumerable possible outcomes. The result is expressed in terms of probabilities, yielding the 1% for Mercury going haywire, and only a small fraction of this percent for it going haywire but missing Venus or the Sun. If it misses, Mercury can then send Mars or Venus hurling toward Earth, with dramatic consequences. Even without a direct hit, Earth's orbit can be enormously modified, Laskar says, "In all these cases, we have very strong climate change." Mercury may cause chaotic events in the future, says Renu Malhotra (University of Arizona), but it might even owe its current eccentricity, inclination, and high density to some previous collision. Maybe this isn't a coincidence after all… See a movie on Jacques Laskar's website. For an expert's opinion, read the News & Views in Nature by Greg Laughlin (University of California, Santa Cruz). Fonte da notícia: http://www.skyandtelescope.com/news/48552537.html |
New Candidates for Midsize Black Holes
| Long, long ago, when I was a college student, my profs taught me about stellar black holes, the remains of collapsed stars so dense and massive (3 to 15 Suns's worth) that not even light could escape from them. Then along came evidence for "supermassive black holes," hoarding millions or billions of times the Sun's mass, and by the 1990s it became clear that these behemoths must lurk at the center of most galaxies. Several years ago astronomers began to speculate about the existence of a third class of supercompact object that, heft-wise, lies somewhere in between. The evidence for these intermediate-mass black holes was largely circumstantial: an ultra-luminous stream of X rays coming from inside a galaxy — but not from its center. The candidates included sources in the famous globular cluster Omega Centauri and in Messier 81 (Bode's Galaxy). But no observer could make an ironclad case for an IMBH. Skeptics argued that these beacons could simply be stellar-mass black holes that are beaming X-ray jets at Earth, thus appearing more massive than they actually are. Or they could be massive white-dwarf stars gobbling matter from companions at a furious rate, belching copious X rays in the process. Or they could even be unrelated X-ray sources juxtaposed either directly in front or behind the candidate galaxy.  In this red-light image obtained with the Very Large Telescope, a yellow circle marks the location of a putative intermediate-mass black hole designated HLX-1. The black oval shows the positional uncertainty of a strong radio source coming from the host galaxy, whose extent is indicated by the gray oval. S. A. Farrell & others / Nature The first, reported in Nature for July 2nd, involves the edge-on spiral galaxy ESO 243-49 in the southern constellation Phoenix. Observers led by Sean Farrell (now at the University of Leicester) first identified it in a 2004 X-ray survey compiled by XMM-Newton, a European space observatory launched in 1999. When the researchers made a follow-up observation last November, they found that their target had dimmed and its X-ray spectrum had changed. Dubbed HLX-1 (for Hyper-Luminous X-rays), the source is offset from the galaxy's center by about 8 arcseconds. Farrell and his colleagues believe they've ruled out alternate explanations like X-ray beaming, a voracious white dwarf, or a binary neutron star. They can't completely dismiss a more distant X-ray beacon coincidentally aligned with the galaxy — there's a 1-in-11 chance of that.  Artist's impression of the X-ray beacon HLX-1 (starburst to upper left of the galactic bulge) in the edge-on spiral galaxy ESO 243-49. Astronomers believe HLX-1 is likely an intermediate-mass black hole weighing in at 500 Suns or more. Heidi Sagerud / Univ. of Leicester A second strong candidate has been identified by Rodrigo Ibata (University of Strasbourg) and others, who're making their claim in a paper submitted to Astrophysical Journal Letters. This time the host is a globular cluster, Messier 54, which is embedded in the Sagittarius dwarf galaxy. Ibata's team used the Very Large Telescope in Chile to measure the orbital velocities of stars whirling tightly around the cluster's densely packed core. The high speeds observed argue that they're circling something quite massive. But what is it? Ibata and his colleagues admit that one explanation is a central crush of stars in peculiar orbits. But if it's an IMBH, then its mass must be about 9,400 Suns. Observations with the Chandra X-ray Observatory, which found a bright source at the same location, appear to back up this claim. This estimated mass is strikingly similar to that of the candidate object at the center of Omega Centauri, a globular that astronomers suspect is what remains of a galaxy stripped of everything but its core. The same fate has been suggested for the Sagittarius dwarf galaxy. So might M54 be the core of a once-larger system, the decimated loser of an intergalactic fight? Fonte da notícia:http://www.skyandtelescope.com/news/49871412.html |
A Glowing Vision of the Early Universe
| Galaxy formation in the early universe just became a little less mysterious.  A composite image of a black hole (blue) lighting up a lyman alpha blob (yellow) X-ray (NASA/CXC/Durham Univ./D.Alexander et al.); Optical (NASA/ESA/STScI/IoA/S.Chapman et al.); Lyman-alpha Optical (NAOJ/Subaru/Tohoku Univ./T.Hayashino et al.); Infrared (NASA/JPL-Caltech/Durham Univ./J.Geach et al.) But why did galaxies come out the size they did, rather than staying small or growing indefinitely huge? Astronomers have new insight on this question thanks to images obtained in 2007 by NASA's Chandra X-ray Observatory and released to the public today. Scientists have known for nearly 10 years about gassy objects in the early universe called "Lyman-alpha blobs.." They're named for their emission of ultraviolet light at the Lyman-alpha wavelength given off by hot hydrogen atoms. The energy to make the blobs light up must come from somewhere. In a paper to be published in the July 10th Astrophysical Journal, a team describes observing a region of Lyman-alpha blobs called SSA22 about a half million light-years in diameter.. They say they have found why the blobs shine and have also turned up a correlation between the blobs and active black holes at the center of galaxies within them. Massive black holes exist in most galaxies, but only some of the holes are consuming matter fast enough to light up brightly. Co-author Jim Geach (Durham University, UK) says 1% to 10% of galaxies in general have an active-black-hole nucleus, but the percentage is five times higher among the early galaxies with Lyman-alpha blobs surrounding them. These are large galaxies in the late stages of formation, seen when the universe was only about 15% of its present age. By then the holes in question had grown very massive, to roughly a billion solar masses. Apparently, when we see a Lyman-alpha blob we are seeing the blaze from these black holes (and perhaps from nascent stars) heating a galaxy's remaining gas and driving it off into intergalactic space, thereby preventing it from coalescing into new stars. In other words, we're seeing galaxies at the point when they shut off their own growth. Theorists modeling the early universe have been eager to observe this crucial "feedback" stage in galaxy evolution. The feedback mechanism explains the strong correlation between the mass of a galaxy's central bulge of old stars and the mass of its central black hole (the ratio is always about 700 to 1). The growing flood of radiation from the growing black hole blows remaining gas out of the galaxy — both preventing the galaxy from forming new stars and preventing the hole's further growth. (The gassy disk of a spiral galaxy, full of younger stars, would be the result of new material falling in later.) This transition stage should be brief in cosmic terms, which is why it has been hard to catch in progress. But the research team suspects that nearly all galaxies should go through it. More information is available in today's press release. Valerie Daum is an editorial intern at Sky & Telescope Fonte da notícia:http://www.skyandtelescope.com/news/49035521.html |
"First Light" for New Lunar Orbiter
| NASA's newest lunar orbiter arrived on the scene just a few days ago, but it's wasting little time building its portfolio of stunning Moon shots. Today members of the Lunar Reconnaissance Orbiter Camera (LROC) team released the instrument's first views of the crater-scarred terrain below.  Taken on June 30, 2009, this dramatic image from the Lunar Reconnaissance Orbiter Camera shows a swatch of crater-dotted about 3,000 feet (900 m) wide. The smallest details are only 10 feet (3 m) across. Click here for a larger, full-frame view. NASA / GSFC / Arizona State Univ. The view here, a region east of Hell E crater in the lunar highlands south of Mare Nubium, reveals details down to about 10 feet (3 meters) across. The deep shadowing suggests a craggy and inhospitable surface, explains LROC team leader Mark Robinson in a press release. But in reality, he notes, "the area is similar to the region where the Apollo 16 astronauts safely explored in 1972." Click here for additional details about the craft's first images of the lunar surface. Besides LROC, ground controllers have already activated two other instruments: the Lunar Exploration Neutron Detector, or LEND, designed to identify regions enriched in hydrogen (a tracer for deposits of water ice); and the Cosmic Ray Telescope for the Effects of Radiation (CRaTER). The remaining four will be switched on next week. Fonte da notícia: |
Galaxies Coming of Age in Cosmic Blobs
| Galaxies Coming of Age in Cosmic Blobs 06.23.09  Artist concept of a galaxy inside of a glowing hydrogen "blob." Image credit: NASA/CXC/M.Weiss The "coming of age" of galaxies and black holes has been pinpointed thanks to new data from NASA's Chandra X-ray Observatory and other telescopes. This discovery helps resolve the true nature of gigantic blobs of gas observed around very young galaxies. About a decade ago, astronomers discovered immense reservoirs of hydrogen gas -- which they named "blobs" – while conducting surveys of young distant galaxies. The blobs are glowing brightly in optical light, but the source of immense energy required to power this glow and the nature of these objects were unclear. A long observation from Chandra has identified the source of this energy for the first time. The X-ray data show that a significant source of power within these colossal structures is from growing supermassive black holes partially obscured by dense layers of dust and gas. The fireworks of star formation in galaxies are also seen to play an important role, thanks to Spitzer Space Telescope and ground- based observations. "For ten years the secrets of the blobs had been buried from view, but now we've uncovered their power source," said James Geach of Durham University in the United Kingdom, who led the study. "Now we can settle some important arguments about what role they played in the original construction of galaxies and black holes." Galaxies are believed to form when gas flows inwards under the pull of gravity and cools by emitting radiation. This process should stop when the gas is heated by radiation and outflows from galaxies and their black holes. Blobs could be a sign of this first stage, or of the second. Based on the new data and theoretical arguments, Geach and his colleagues show that heating of gas by growing supermassive black holes and bursts of star formation, rather than cooling of gas, most likely powers the blobs. The implication is that blobs represent a stage when the galaxies and black holes are just starting to switch off their rapid growth because of these heating processes. This is a crucial stage of the evolution of galaxies and black holes - known as "feedback" - and one that astronomers have long been trying to understand. "We're seeing signs that the galaxies and black holes inside these blobs are coming of age and are now pushing back on the infalling gas to prevent further growth," said coauthor Bret Lehmer, also of Durham. "Massive galaxies must go through a stage like this or they would form too many stars and so end up ridiculously large by the present day." Chandra and a collection of other telescopes including Spitzer have observed 29 blobs in one large field in the sky dubbed "SSA22." These blobs, which are several hundred thousand light years across, are seen when the Universe is only about two billion years old, or roughly 15% of its current age. In five of these blobs, the Chandra data revealed the telltale signature of growing supermassive black holes - a point-like source with luminous X-ray emission. These giant black holes are thought to reside at the centers of most galaxies today, including our own. Another three of the blobs in this field show possible evidence for such black holes. Based on further observations, including Spitzer data, the research team was able to determine that several of these galaxies are also dominated by remarkable levels of star formation. The radiation and powerful outflows from these black holes and bursts of star formation are, according to calculations, powerful enough to light up the hydrogen gas in the blobs they inhabit. In the cases where the signatures of these black holes were not detected, the blobs are generally fainter. The authors show that black holes bright enough to power these blobs would be too dim to be detected given the length of the Chandra observations. Besides explaining the power source of the blobs, these results help explain their future. Under the heating scenario, the gas in the blobs will not cool down to form stars but will add to the hot gas found between galaxies. SSA22 itself could evolve into a massive galaxy cluster. "In the beginning the blobs would have fed their galaxies, but what we see now are more like leftovers," said Geach. "This means we'll have to look even further back in time to catch galaxies and black holes in the act of forming from blobs." These results will appear in the July 10 issue of The Astrophysical Journal. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass. More information, including images and other multimedia, can be found at: Janet Anderson, 256-544-6162 Marshall Space Flight Center, Huntsville, Ala. Janet.L.Anderson@nasa.gov Megan Watzke 617-496-7998 Chandra X-ray Center, Cambridge, Mass. m.watzke@cfa.harvard.edu Fonte da notícia:http://www.nasa.gov/mission_pages/chandra/main/index.html |
First pictures from Lunar Reconnaissance Orbiter
| NASA PHOTO RELEASE Posted: July 2, 2009 NASA's Lunar Reconnaissance Orbiter has transmitted its first images since reaching the moon on June 23. The spacecraft's two cameras, collectively known as the Lunar Reconnaissance Orbiter Camera, or LROC, were activated June 30. The cameras are working well and have returned images of a region in the lunar highlands south of Mare Nubium (Sea of Clouds). As the moon rotates beneath LRO, LROC gradually will build up photographic maps of the lunar surface. "Our first images were taken along the moon's terminator -- the dividing line between day and night -- making us initially unsure of how they would turn out," said LROC Principal Investigator Mark Robinson of Arizona State University in Tempe. "Because of the deep shadowing, subtle topography is exaggerated, suggesting a craggy and inhospitable surface. In reality, the area is similar to the region where the Apollo 16 astronauts safely explored in 1972. While these are magnificent in their own right, the main message is that LROC is nearly ready to begin its mission." These images show cratered regions near the moon's Mare Nubium region, as photographed by the Lunar Reconnaissance Orbiter's LROC instrument. Each image shows a region 1,400 meters (0.87 miles) wide. the bottoms of both images face lunar north. The image below shows the location of these two images in relation to each other.
The satellite also has started to activate its six other instruments. The Lunar Exploration Neutron Detector will look for regions with enriched hydrogen that potentially could have water ice deposits. The Cosmic Ray Telescope for the Effects of Radiation is designed to measure the moon's radiation environment. Both were activated on June 19 and are functioning normally. Instruments expected to be activated during the next week and calibrated are the Lunar Orbiter Laser Altimeter, designed to build 3-D topographic maps of the moon's landscape; the Diviner Lunar Radiometer Experiment, which will make temperature maps of the lunar surface; and the Miniature Radio Frequency, or Mini-RF, an experimental radar and radio transmitter that will search for subsurface ice and create detailed images of permanently-shaded craters. The final instrument, the Lyman Alpha Mapping Project, will be activated after the other instruments have completed their calibrations, allowing more time for residual contaminants from the manufacture and launch of LRO to escape into the vacuum of space. This instrument is an ultraviolet-light imager that will use starlight to search for surface ice. It will take pictures of the permanently-shaded areas in deep craters at the lunar poles. "Accomplishing these significant milestones moves us closer to our goals of preparing for safe human return to the moon, mapping the moon in unprecedented detail, and searching for resources," said LRO Project Scientist Richard Vondrak of NASA's Goddard Space Flight Center in Greenbelt, Md. While its instruments are being activated and tested, the spacecraft is in a special elliptical commissioning orbit around the moon. The orbit takes less fuel to maintain than the mission's primary orbit. The commissioning orbit's closest point to the lunar surface is about 19 miles over the moon's south pole, and its farthest point is approximately 124 miles over the lunar north pole. After the spacecraft and instruments have completed their initial calibrations, the spacecraft will be directed into its primary mission orbit in August, a nearly-circular orbit about 31 miles above the lunar surface. Goddard built and manages LRO, a NASA mission with international participation from the Institute for Space Research in Moscow. Russia provides the neutron detector aboard the spacecraft. Fonte da notícia: http://spaceflightnow.com/atlas/av020/090702firstpix/ |
ESA to build its third deep space ground station in Argentina
Supernovae: Cosmic-Ray Superfactories
| Astronomers have had good reasons for quite a while to think that shock waves in supernova remnants create cosmic rays. These are charged particles that have been accelerated to very near light-speed; some of them have been boosted to energies far higher than the best particle accelerators can do on Earth.  X-ray emission from the supernova remnant RCW 86. The white box shows the region studied. ESA / Univ. of Utrecht / J.Vink et al. Yes, according to a new study published today in Science Express (Thursday, June 25th). Expanding supernova remnants could put half or more of their energy into cosmic-ray acceleration, accounting for all the "intermediate-energy" particle Earth receives. No one knew the process was so efficient. High and very-high energies Cosmic rays are the highest-energy particles in the universe. At the very highest-end, a single proton can pack as much kinetic energy as a well-served tennis ball (1020 electron-volts). These probably have extragalactic sources related to active galactic nuclei. Much more abundant are particles with millions of times less energy, but still much more than the best accelerators on Earth can impart. These are the ones in the new study, and they likely come from within our galaxy.  Composite image of X-ray and visible emission from part of supernova remnant RCW 86, 8,200 light-years away. The image is about 6 arc minutes across. ESO / E. Helder / NASA / Chandra Enrico Fermi even described a plausible mechanism in 1949. When a star explodes, says Vink, "the supernova ejecta material goes at a speed much larger than the speed of sound" (pressure waves) in the surrounding interstellar medium. So it forms a shock wave, in which particle density and magnetic field strengths vary wildly. Such a magnetic field can repeatedly send charged particles back and forth behind the shock front, where they can gain momentum -at the expense of the shock wave's speed- until they reach extremely high energies. The Missing Energy Three supernovae explode in the Milky Way on average per century. On paper, that's more than enough energy to accelerate all the cosmic rays we see. But is the process efficient enough actually to do it? "The only missing link now was: can they convert this energy into cosmic rays?" says Vink. "The answer seems to be: Yes!" "At least half the energy of the shock goes into cosmic rays," says lead author Eveline Helder (Astronomical Institute Utrecht, Netherlands). That, anyway, is the case for the part of the ejecta ring that Helder and collaborators studied in the young supernova remnant RCW 86, located 8,200 light-years away. Chinese (and even maybe Roman) records from 185 AD mention a corresponding nine-month-lived star. The scientists deduced the energy of the shock wave by comparing X-ray images three years apart, taken by NASA's Chandra X-Ray Observatory. The motion of the shock wave between the images amounted to approximately 6,000 km per second, or about 2 percent of the speed of light. Behind the shock, the scientists found the thin gas to be much less hot than expected: 30 million degrees centigrade instead of half a billion. To measure the temperature of the gas, the scientists used ESO's Very Large Telescope to observe visible light emitted by hydrogen atoms. The width of the hydrogen emission lines, created by the Doppler shift due to the random thermal motion of atoms, told the temperature.  The Paranal site, at 8,600ft in Chile, with the four 8..2-meter units making up the Very Large Telescope at the summit of the mountain, and ESO's famous Residencia hotel below, featured in the 22nd James Bond movie "Quantum of Solace". ESO This is more than a simple confirmation of previous results. "It's a much more sophisticated set of measurements," says Luke Drury (IAS Dublin, Ireland). "This one I think will generate much more interest from the community." The new result confirms that the cosmic-ray production process is remarkably efficient. "Everyone was a bit nervous about saying that, because it seemed so outlandish," says Drury. This research may also help in understanding similar acceleration processes occurring in gamma-ray bursts and radio jets, says Don Ellison (North Carolina State): "Supernova remnants offer the best laboratory to study the mechanism." Fonte da notícia: http://www.skyandtelescope.com/news/49089086.html |
Assinar:
Postagens (Atom)
LinkWithin
