Cosmic 'fog' produced by ancient starlight measured

 

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Agencies : Washington, Sat Nov 03 2012, 13:19 hrs

Astronomers have made the most accurate measurement of starlight in the universe and used it to establish the total amount of light from all of the stars that have ever shone.
Using NASA's Fermi Gamma-ray Space Telescope, scientists determined how many gamma rays should be emitted at different energies.
More distant blazars show fewer gamma rays at higher energies - especially above 25 GeV - thanks to absorption by the cosmic fog.
Researchers then determined the average gamma-ray attenuation across three distance ranges between 9.6 billion years ago and today.
From this measurement, the scientists were able to estimate the fog's thickness.
The average stellar density in the cosmos is about 1.4 stars per 100 billion cubic light-years, which means the average distance between stars in the universe is about 4,150 light-years.
"The Fermi result opens up the exciting possibility of constraining the earliest period of cosmic star formation, thus setting the stage for NASA's James Webb Space Telescope," said Volker Bromm, an astronomer at the University of Texas.
"In simple terms, Fermi is providing us with a shadow image of the first stars, whereas Webb will directly detect them," Bromm said in a NASA statement.
Measuring the extragalactic background light was one of the primary mission goals for Fermi.
"We're very excited about the prospect of extending this measurement even farther," said Julie McEnery, the mission's project scientist at NASA's Goddard Space Flight Center.
Gamma rays are the most energetic form of light. Since the Fermi's launch in 2008, its Large Area Telescope (LAT) observes the entire sky in high-energy gamma rays every three hours, creating the most detailed map of the universe ever known at these energies.

Mars --clues of lost atmosphere

Curiosity ingests Mars air and finds clues of lost atmosphere

 

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Agencies : Washington, Sat Nov 03 2012, 16:44 hrs

NASA’s Mars rover, Curiosity, has provided clues to changes in Martian atmosphere.
Learning what happened to the Martian atmosphere will help scientists assess whether the planet ever was habitable. The present atmosphere of Mars is 100 times thinner than Earth’s.
A set of instruments aboard the rover has ingested and analysed samples of the atmosphere collected near the “Rocknest” site in Gale Crater where the rover is stopped for research.
Findings from the Sample Analysis at Mars (SAM) instruments suggest that loss of a fraction of the atmosphere, resulting from a physical process favouring retention of heavier isotopes of certain elements, has been a significant factor in the evolution of the planet. Isotopes are variants of the same element with different atomic weights.
Initial SAM results show an increase of 5 percent in heavier isotopes of carbon in the atmospheric carbon dioxide compared to estimates of the isotopic ratios present when Mars formed. These enriched ratios of heavier isotopes to lighter ones suggest the top of the atmosphere may have been lost to interplanetary space.
Losses at the top of the atmosphere would deplete lighter isotopes. Isotopes of argon also show enrichment of the heavy isotope, matching previous estimates of atmosphere composition derived from studies of Martian meteorites on Earth.
Scientists theorize that in Mars’ distant past its environment may have been quite different, with persistent water and a thicker atmosphere. NASA’s Mars Atmosphere and Volatile Evolution, or MAVEN, mission will investigate possible losses from the upper atmosphere when it arrives at Mars in 2014.

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First mouse, now human, lab-grown eye tissue November 1, 2012

 

An embryonic eye derived from human embryonic stem cells. Credit: 2012 Elsevier Producing retinal tissue from human embryonic stem cells is now possible thanks to a team of researchers led by Yoshiki Sasai of the RIKEN Center for Developmental Biology in Kobe, Japan. Sasai and his colleagues have developed a novel cell culture method in which embryonic stem (ES) cells are grown in suspension instead of on a flat surface. ES cells grown under these conditions can organize themselves into complex three-dimensional structures when they are treated with the appropriate combination of growth factors. Last year, Sasai's team reported that mouse ES cells cultured in this way recapitulate developmental mechanisms and self-organize into a cupped, layered structure that resembles the embryonic eye and contains all the cell types found in the mature retina, including photoreceptor cells. In their latest study, the team repeated these experiments using human ES cells, and found major differences in how they form eye-like structures. The structures derived from human ES cells were substantially larger and thicker than those formed by mouse cells, reflecting the differences in size between the two species. And unlike the structures formed from mouse cells, the human-based structures also had a tendency to curve more at the edges. Importantly, the human ES cells took significantly longer to form embryonic eyes—more than 100 days compared to just 20 days for mouse cells, presumably reflecting the differences in normal gestation times. This made the experiments technically challenging, because it is difficult to maintain stable cell cultures for periods of longer several weeks. Sasai and his colleagues noticed, however, that the cell cultures that grew well during the first month tended to generate well-formed retinal tissue. To keep the cultures stable at this critical stage, they developed a novel cryonic preservation method for storing the tissue at this critical intermediate stage. The cryopreservation method involves cutting the retinal tissue from the cupped structures after 18 days in culture and then leaving it to continue growing in suspension for another 12 days. The tissue is then briefly cooled on ice before being submerged in liquid nitrogen. Crucially, the tissue can be stored in this state for long periods of time, but remains healthy and continues to grow when thawed later on. "We now plan to test the functionality by grafting these tissues into animal eyes," says Sasai. "The most straightforward application would be for transplantation to patients suffering from retinitis pigmentosa, in which photoreceptors gradually degenerate, leading to blindness." More information: Nakano, T., Ando, S., Takata, N., Kawada, M., Muguruma, K., Sekiguchi, K., Saito, K., Yonemura, S., Eiraku, M. & Sasai, Y. Self-formation of optic cups and storable stratified neural retina from human ESCs. Cell Stem Cell 10, 771–785 (2012). dx.doi.org/10.1016/j.stem.2012.05.009 Eiraku, M., Takata, N., Ishibashi, H., Kawada, M., Sakakura, E., Okuda, S., Sekiguchi, K., Adachi, T. & Sasai, Y. Self-organizing optic-cup morphogenesis in three-dimensional culture. Nature 472, 51–56 (2011). www.nature.com/nature/journal/v472/n7341/abs/nature09941.html Read more at: http://phys.org/news/2012-11-mouse-human-lab-grown-eye-tissue.html#jCp