Wednesday, November 24, 2010

Nov. 24 - Dark energy on firmer footing‏

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Dark energy on firmer footing

Geometric test supports the existence of a key thread in the fabric of the Universe.

galaxiesThe distribution of pairs of galaxies that orbit one another has verified key elements of the standard model of cosmology — suggesting the presence of dark energy.NASA/ESA

The claim that mysterious dark energy is accelerating the Universe's expansion has been placed on firmer ground, with the successful application of a quirky geometric test proposed more than 30 years ago.

The accelerating expansion was first detected in 1998. Astronomers studying Type 1a supernovae, stellar explosions called "standard candles" because of their predictable luminosity, made the incredible discovery that the most distant of these supernovae appear dimmer than would be expected if the Universe were expanding at a constant rate.1 This suggested that some unknown force - subsequently dubbed dark energy - must be working against gravity to blow the universe apart.

Since that time, studies comparing variations in the cosmic microwave background radiation — an echo from the Big Bang — with the distribution of galaxies today have allowed cosmologists to trace how the Universe has expanded, supporting the idea of dark energy. They have also suggested that the Universe is 'flat' — that is, it contains just enough matter to keep it delicately poised between collapsing in on itself and expanding forever2.

“It's a very clever idea, it's unexpected, and it's going to take a while to determine whether it's accepted or not.”

Charles Alcock
Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts

These two assumptions have become a fundamental part of cosmologists' understanding of the Universe. Now Christian Marinoni and Adeline Buzzi of the Centre for Theoretical Physics at the University of Provence in Marseilles, France, have independently checked these ideas by analysing the geometry of orbiting pairs of galaxies. Their study is published this week in Nature3.

The researchers used a version of the Alcock–Paczynski test, which relies on identifying symmetrical objects in space and using them as 'standard spheres'. Any distortions in space caused by the expansion of the cosmos would cause the most distant standard spheres to appear asymmetrical. "This provides a similar level of accuracy to supernovae," says Marinoni. "It's a direct proof of dark energy."

Object lessons

For example, if the universe is expanding outwards due to dark energy, distant objects will appear elongated along the line of sight from Earth, because Earth and the objects are being propelled away from one another along that direction.

Several groups have tried to apply the test, for example by considering clusters of galaxies as the standard spheres, but largely failed because they could not measure distant objects with sufficient accuracy.

To get round this, Marinoni and Buzzi instead studied the distribution in orientations of pairs of galaxies that orbit each other. In a Universe without dark energy, that distribution is expected to be spherically symmetrical — in other words, the number of galaxy pairs oriented in any particular direction should be the same.

The researchers found that the farther away the galaxy pairs were, the more asymmetrical the distribution was, with more galaxy pairs oriented along the line of sight from Earth. The pattern matched what would be expected in a flat Universe expanding due to dark energy.

The reliability of the test depends on the assumption that the distribution in orientations of galaxy pairs doesn't change depending on their distance from Earth — an idea that is largely untested. But researchers are still excited by the result.


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"It's a very clever idea, it's unexpected, and it's going to take a while to determine whether it's accepted or not," says Charles Alcock, director of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and co-proposer, in 1979, of the test Marinoni and Buzzi used4.

"This is a cool new tool. It's another indication that everything is consistent," says Anthony Tyson, who studies cosmology at the University of California, Davis. Tyson adds that he is sceptical about some of the assumptions underlying theories of dark energy, so he finds independent efforts to confirm its presence extremely valuable. "For those of us who are doubters, it's making us think twice," he says.

Future surveys of distant objects are planned, for example using the European Space Agency's planned Euclid space telescope, and the Wide Field Infrared Survey Telescope, a proposed mission that was the top recommendation of the US National Academy of Sciences Decadal Survey of Astronomy and Astrophysics. Marinoni says he hopes these will find further remote pairs of galaxies that can be analysed to pin down the nature of dark energy, perhaps even enough to overtake the accuracy offered by studies of type Ia supernovae.

  • References

    1. Riess, A. G. Astron. J. 116, 1009 (1998).
    2. Spergel, D. N. et al. Astrophys. J. Suppl. Ser. 170, 377-408 (2007).
    3. Marinoni, C. & Buzzi, A. Nature 468, 539-541 (2010).
    4. Alcock, C. & Paczynski, B. Nature 281, 358-359 (1979).

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How to Digitally Record/Video a UFO sighting:

Como registar digitalmente ou gravar um vídeo de um avistamento de um UFO:

Stabilize the camera on a tripod. If there is no tripod, then set it on top of a stable, flat surface. If that is not possible lean against a wall to stabilize your body and prevent the camera from filming in a shaky, unsteady manner.

Estabilize a camera com um tripé. Se não tiver um tripé, então coloque-a em cima de uma superfície estável. Se não for possível, então encoste-se a uma parede para estabilizar o corpo e evitar que a camera registe de maneira tremida e instável.

Provide visual reference points for comparison. This includes the horizon, treetops, lampposts, houses, and geographical landmarks (i.e., Horsetooth Reservoir, Mt. Adams, etc.) Provide this in the video whenever is appropriate and doesn’t detract from what your focus is, the UFO.

Forneça pontos visuais de referência para comparação. Isso inclui o horizonte, cimo das árvores, postes de iluminação, pontos de referência geográficos (como o Reservatório de Horsetooth, Mone Adams, etc) Forneça esses pontos no vídeo sempre que for apropriado e não se distraia do que é o seu foco, o UFO/a Nave.

Narrate your videotape. Provide details of the date, time, location, and direction (N,S,E,W) you are looking in. Provide your observations on the weather, including approximate temperature, windspeed, any visible cloud cover or noticeable weather anomalies or events. Narrate on the shape, size, color, movements, approximate altitude of the UFO, etc and what it appears to be doing. Also include any unusual physical, psychological or emotional sensations you might have. Narrate any visual reference points on camera so they correlate with what the viewer will see, and thereby will be better able to understand.

Faça a narração do vídeo. Forneça pormenores sobre a data, hora, local e direcção (Norte, Sul, Este, Oeste) que está a observar. Faça observações sobre as condições atmosféricas, incluindo a temperatura aproximada, velocidade do vento, quantidade de nuvens, anomalias ou acontecimentos meteorológicos evidentes. Descreva a forma, o tamanho, a cor, os movimentos, a altitude aproximada onde se encontra o UFO/nave, etc e o que aparenta estar a fazer. Inclua também quaisquer aspectos pouco habituais de sensações físicas, psicológicas ou emocionais que possa ter. Faça a narração de todos os pontos de referência visual que o espectador irá ver e que, deste modo, será capaz de compreender melhor.

Be persistent and consistent. Return to the scene to videotape and record at this same location. If you have been successful once, the UFO sightings may be occurring in this region regularly, perhaps for specific reasons unknown, and you may be successful again. You may also wish to return to the same location at a different time of day (daylight hours) for better orientation and reference. Film just a minute or two under “normal” circumstances for comparison. Write down what you remember immediately after. As soon as you are done recording the experience/event, immediately write down your impressions, memories, thoughts, emotions, etc. so it is on the record in writing. If there were other witnesses, have them independently record their own impressions, thoughts, etc. Include in this exercise any drawings, sketches, or diagrams. Make sure you date and sign your documentation.

Seja persistente e não contraditório. Volte ao local da cena e registe o mesmo local. Se foi bem sucedido uma vez, pode ser que nessa região ocorram avistamentos de UFOs/naves com regularidade, talvez por razões específicas desconhecidas, e talvez possa ser novamente bem sucedido. Pode também desejar voltar ao mesmo lugar a horas diferentes do dia (durante as horas de luz)para ter uma orientação e referência melhor. Filme apenas um ,inuto ou dois em circunstâncias “normais” para ter um termo de comparação. Escreva tudo o que viu imediatamente após o acontecimento. Logo após ter feito o registo da experiência/acontecimento, escreva imediatamente as impressões, memórias, pensamentos, emoções, etc para que fiquem registadas por escrito. Se houver outras testemunhas, peça-lhes para registar independentemente as suas próprias impressões, pensamentos, etc. Inclua quaisquer desenhos, esbolos, diagramas. Certifique-se que data e assina o seu documento/testemunho.

Always be prepared. Have a digital camera or better yet a video camera with you, charged and ready to go, at all times. Make sure you know how to use your camera (and your cell phone video/photo camera) quickly and properly. These events can occur suddenly, unexpectedly, and often quite randomly, so you will need to be prepared.

Esteja sempre preparado, Tenha sempre uma camera digital, melhor ainda, uma camera vídeo consigo, carregada e pronta a usar sempre que necessário. Certifique-se que sabe como lidar com a sua camera (ou com o seu celular/camera fotográfica) rápida e adequadamente. Esses acontecimentos podem acontecer súbita e inesperadamente e, por vezes, acidentalmente, por isso, necessita estar preparado.

Look up. Be prepared. Report. Share.

Olhe para cima, Esteja preparado, Relate, Partilhe.



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