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In the news this month: record-breaking galaxy

The Hubble Ultra Deep Field
The Hubble Ultra Deep Field, the deepest image of the Universe ever taken, in near-infrared light. CREDIT: NASA/ESA

The most distant object in the known universe is a highly luminous gamma ray burst, a single explosion discovered near maximum light, at a redshift of 8.2, a time when the universe was only 630 million years old, less than 5 percent of its current age. The most distant known galaxy lies at a redshift of 6.96, the light we see now left the galaxy just 750 million years after the Big Bang. However, both these records have now been broken by a galaxy discovered by the Hubble Space Telescope which has a redshift of 8.56 and an estimated distance of 87 Gpc, making it the most distant object currently known.

First seen in the Hubble Ultra Deep Field, the deepest single image ever taken in near-infrared light, the galaxy (known as UDFy-38135539) was initially classified as a candidate high redshift object based on its colours. Now, a team led by Matthew Lehnert at the Observatoire de Paris in France, has used spectroscopic observations to confirm that the object is the most distant galaxy so far detected.

Since the universe is expanding, the further away an object is, the faster it appears to be moving away from us. This results in a shift in wavelength of the light emitted from an object (known as redshift) with the size of the shift relating to the distance between us and the object. (This is similar to the shift in pitch you hear when a police car travels past at high speed.) This effect allows distances to be calculated by measuring the shift in spectral lines from known chemicals. Lehnert's team used a sensitive spectrograph on the Very Large Telescope located in Chile to observe the spectrum of this galaxy and found an emission line which is likely to be caused by hydrogen shifted to redder wavelengths by the relative motion between the galaxy and us.

This is an exciting discovery because it is the first galaxy discovered in the so-called epoch of reionisation, the period in the history of the universe where the neutral material between the newly formed galaxies was being ionised - the light from young, hot stars stripped electrons from hydrogen atoms. The authors used the measured light from the galaxy to calculate the size of the region of surrounding gas which the galaxy should have been able to ionise on its own and found that, in order to explain the size of the ionised bubble which is consistent with the observations, there must be other sources of radiation. One suggestion is that dwarf galaxies clustering around larger, more easily observed galaxies, may be responsible for this additional radiation, but there are other explanations.

While observations such as these are difficult with current ground-based telescopes due to the faint nature of these distant sources, the planned next generation of larger and more sensitive ground- and space-based instruments should make observations of such sources much easier.

This blog post is a news story from the Jodcast, aired in the November 2010 edition.

Lehnert, M., Nesvadba, N., Cuby, J., Swinbank, A., Morris, S., Clément, B., Evans, C., Bremer, M., & Basa, S. (2010). Spectroscopic confirmation of a galaxy at redshift z = 8.6 Nature, 467 (7318), 940-942 DOI: 10.1038/nature09462

Posted by Megan on Tuesday 30th Nov 2010 (05:31 UTC) | Add a comment | Permalink

In the news this month: latest results from LCROSS

LCROSS imapcted the Moon on October 9th
Artists impression of the impact of the LCROSS spacecraft on the Moon back on October 9th CREDIT: NASA

Small lumps of rock hit the Moon quite regularly, but in 2009 two artificial projectiles impacted on the lunar surface in an experiment designed to search for water in the permanent shadows of a crater near the lunar south pole. Hints of subsurface water on the Moon had already been found in 1999 when NASA's Lunar Prospector spacecraft detected signatures of concentrated hydrogen, the "H" in "H2O", near the lunar poles. The Lunar CRater Observation and Sensing Satellite, or LCROSS, was a low-cost mission launched together with the Lunar Reconnaissance Orbiter in June 2009. The mission consisted of the Centaur upper stage of the Atlas-V launch vehicle, and a shepherding spacecraft equipped with various cameras and sensors. Moving at a speed of 1.5 miles per second, the Centaur stage impacted the lunar surface on October 9th 2009, sending up a plume of material from the permanently shadowed floor of the crater Cabeus. The LCROSS spacecraft observed the impact before flying through the plume to impact the surface some four minutes later. In the October 22nd issue of Science magazine, several teams working on data from the impact publish their findings.

Cabeus crater was chosen for the experiment as it contains an area which is permanently in shadow, due to its location close to the lunar south pole. The low temperatures, combined with the movement of soil (regolith) by micrometeorite impacts (known as "impact gardening") which buries accumulated material, makes such craters ideal places to search for volatiles - chemicals which are solid only at very low temperatures.

Previous results from a neutron spectrometer aboard the Lunar Prospector spacecraft suggested that ice could make up between half and one percent of the soil near the lunar poles, and further results from a neutron detector on the Lunar Reconnaissance Orbiter showed a strong hydrogen signal, originally thought to be from water ice. But observations of the LCROSS plume, made with another instrument (LAMP, an ultraviolet spectrograph) on-board LRO, showed that as much of the hydrogen signal comes from molecular hydrogen as it does from water. Water is thought to have accumulated from cometary impacts, distributing water across the lunar surface in the ejecta, but it is far from certain where the molecular hydrogen originated.

The results from the nine instruments on-board the LCROSS shepherding spacecraft, reported in Science on October 22nd, show signatures of numerous different chemicals, including water vapour, water ice and hydroxyl radicals, a common result of the breaking up of water molecules. Using the spectra obtained, the LCROSS team calculated that the maximum amount of water vapour and ice visible in the field of view of the instruments was 155 kilograms. By estimating the amount of material that was excavated by the Centaur impact and became observable by reaching sunlight, they calculated that the concentration of water in the lunar regolith at the impact site was 5.6 percent. They also found that the observed abundances of other volatile compounds, such as ammonia, sulphur dioxide and carbon monoxide, were far higher than the abundances found in comets, suggesting that molecule formation may be going on in these shadowed regions on the surfaces of cold dust grains.

This blog post is a news story from the Jodcast, aired in the November 2010 edition.

Colaprete, A., Schultz, P., Heldmann, J., Wooden, D., Shirley, M., Ennico, K., Hermalyn, B., Marshall, W., Ricco, A., Elphic, R., Goldstein, D., Summy, D., Bart, G., Asphaug, E., Korycansky, D., Landis, D., & Sollitt, L. (2010). Detection of Water in the LCROSS Ejecta Plume Science, 330 (6003), 463-468 DOI: 10.1126/science.1186986

Schultz, P., Hermalyn, B., Colaprete, A., Ennico, K., Shirley, M., & Marshall, W. (2010). The LCROSS Cratering Experiment Science, 330 (6003), 468-472 DOI: 10.1126/science.1187454

Gladstone, G., Hurley, D., Retherford, K., Feldman, P., Pryor, W., Chaufray, J., Versteeg, M., Greathouse, T., Steffl, A., Throop, H., Parker, J., Kaufmann, D., Egan, A., Davis, M., Slater, D., Mukherjee, J., Miles, P., Hendrix, A., Colaprete, A., & Stern, S. (2010). LRO-LAMP Observations of the LCROSS Impact Plume Science, 330 (6003), 472-476 DOI: 10.1126/science.1186474

Hayne, P., Greenhagen, B., Foote, M., Siegler, M., Vasavada, A., & Paige, D. (2010). Diviner Lunar Radiometer Observations of the LCROSS Impact Science, 330 (6003), 477-479 DOI: 10.1126/science.1197135

Paige, D., Siegler, M., Zhang, J., Hayne, P., Foote, E., Bennett, K., Vasavada, A., Greenhagen, B., Schofield, J., McCleese, D., Foote, M., DeJong, E., Bills, B., Hartford, W., Murray, B., Allen, C., Snook, K., Soderblom, L., Calcutt, S., Taylor, F., Bowles, N., Bandfield, J., Elphic, R., Ghent, R., Glotch, T., Wyatt, M., & Lucey, P. (2010). Diviner Lunar Radiometer Observations of Cold Traps in the Moon's South Polar Region Science, 330 (6003), 479-482 DOI: 10.1126/science.1187726

Mitrofanov, I., Sanin, A., Boynton, W., Chin, G., Garvin, J., Golovin, D., Evans, L., Harshman, K., Kozyrev, A., Litvak, M., Malakhov, A., Mazarico, E., McClanahan, T., Milikh, G., Mokrousov, M., Nandikotkur, G., Neumann, G., Nuzhdin, I., Sagdeev, R., Shevchenko, V., Shvetsov, V., Smith, D., Starr, R., Tretyakov, V., Trombka, J., Usikov, D., Varenikov, A., Vostrukhin, A., & Zuber, M. (2010). Hydrogen Mapping of the Lunar South Pole Using the LRO Neutron Detector Experiment LEND Science, 330 (6003), 483-486 DOI: 10.1126/science.1185696

Posted by Megan on Tuesday 30th Nov 2010 (02:10 UTC) | Add a comment | Permalink

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