{"419851":{"#nid":"419851","#data":{"type":"news","title":"The Universe May be Less Crowded than We Think","body":[{"value":"\u003Cp\u003EThere may be far fewer galaxies further out in the universe than might be expected, suggests a new study based on simulations conducted on the Blue Waters supercomputer at the National Center for Supercomputing Applications and supported by the Georgia Institute of Technology.\u003C\/p\u003E\u003Cp\u003EThe study, which was published July 1 in \u003Ca href=\u0022http:\/\/iopscience.iop.org\/2041-8205\/807\/1\/L12\/\u0022\u003EAstrophysical Journal Letters\u003C\/a\u003E and led by Michigan State University, shows the first results from the Renaissance Simulations, a suite of extremely high-resolution adaptive mesh refinement (AMR) calculations of \u003Ca href=\u0022http:\/\/earthsky.org\/astronomy-essentials\/what-is-a-redshift\u0022\u003Ehigh redshift galaxy formation\u003C\/a\u003E.\u003C\/p\u003E\u003Cp\u003EThe simulations show hundreds of well-resolved galaxies, allowing researchers to make several novel and verifiable predictions ahead of the October 2018 launch of the \u003Ca href=\u0022http:\/\/www.jwst.nasa.gov\/\u0022\u003EJames Webb Space Telescope (JWST)\u003C\/a\u003E, a new space observatory that succeeds the \u003Ca href=\u0022http:\/\/hubblesite.org\/\u0022\u003EHubble Space Telescope\u003C\/a\u003E.\u003C\/p\u003E\u003Cp\u003E\u201cThe Hubble Space Telescope can only see what we might call the tip of the iceberg when it comes to taking inventory of the most distant galaxies,\u201d said San Diego Supercomputer Center (SDSC) Director Michael Norman, who was part of the study\u2019s research team. \u201cA key question is how many galaxies are too faint to see. By analyzing these new, ultra-detailed simulations, we find that there are 10 to 100 times fewer galaxies than a simple extrapolation would predict.\u201d\u003C\/p\u003E\u003Cp\u003E\u201cOur work suggests that there are far fewer faint galaxies than one could previously infer,\u201d said principal investigator and lead author Brian O\u2019Shea, an associate professor at Michigan State. \u201cObservations of high redshift galaxies provide poor constraints on the low-luminosity end of the galaxy luminosity function, and thus make it challenging to accurately account for the full budget of ionizing photons during that epoch.\u201d\u003C\/p\u003E\u003Cp\u003EGeorgia Tech Assistant Professor John Wise wrote the code that made the simulations possible on Blue Waters. He also interpreted the data to make predictions for the JWST, serving as a \u201csimulation architect\u201d by setting the simulation parameters.\u003C\/p\u003E\u003Cp\u003EWise and his fellow researchers found that the ultraviolet luminosity function of the simulated galaxies is consistent with observations of redshift galaxy populations at the bright end of the luminosity function and essentially flat rather than rising steeply at lower luminosities.\u003C\/p\u003E\u003Cp\u003E\u201cThe flattening at lower luminosities is a key finding in the study and significant to researchers\u2019 understanding of the reionization of the universe, when the gas in the universe changed from being mostly neutral to mostly ionized,\u201d said Wise, Dunn Family Assistant Professor in Georgia Tech\u2019s School of Physics.\u003C\/p\u003E\u003Cp\u003EThe term \u2018reionized\u2019 is used because the universe was ionized immediately after the fiery Big Bang. During that time, ordinary matter consisted mostly of hydrogen atoms with positively charged protons stripped of their negatively charged electrons. Eventually, the universe cooled enough for electrons and protons to combine and form neutral hydrogen. They didn\u2019t give off any optical or UV light, and without that light astrophysicists aren\u2019t able to see traces of how the cosmos evolved during these dark ages using conventional telescopes. The light returned when reionization began.\u003C\/p\u003E\u003Cp\u003EBecause these simulations are so costly to generate, the team moved the entire output of the Renaissance Simulations to SDSC Cloud\u2013 some 100 terabytes of data, or the equivalent of about 150,000 audio compact discs. \u201cA data access portal is being set up so that others can investigate their properties in more detail,\u201d added Norman, also a distinguished professor of physics at UC San Diego and a faculty member with the Center for Astrophysics \u0026amp; Space Sciences at the university.\u003C\/p\u003E\u003Cp\u003EThe results are detailed in the paper, titled Probing the Ultraviolet Luminosity Function of the Earliest Galaxies with the Renaissance Simulations.\u003C\/p\u003E\u003Cp\u003E\u003Ca href=\u0022http:\/\/www.news.gatech.edu\/2014\/07\/07\/small-plentiful-how-faintest-galaxies-illuminated-early-universe\u0022\u003EIn an earlier paper\u003C\/a\u003E, simulations conducted by two researchers who were part of this new study concluded that about 300 million years after the \u201cBig Bang,\u201d the universe was 20 percent ionized, 50 percent ionized at 550 million years, and fully ionized at 860 million years after its creation.\u0026nbsp;\u003C\/p\u003E\u003Cp\u003EWhile the James Webb Space Telescope will give cosmic researchers the ability to view and record substantial numbers of galaxies, the telescope has a relatively small field of view, according to the researchers. As a result, interpretation of any JWST survey must by necessity take into account cosmic variance \u2013 the statistical variation in the number of galaxies from place to place. A deeper understanding based on theory may be necessary to correctly interpret high redshift survey results.\u003C\/p\u003E\u003Cp\u003EThe simulations were done on the National Science Foundation-funded Blue Waters supercomputer, one of the largest academic supercomputers in the world.\u003C\/p\u003E\u003Cp\u003EThe research team also included Hao Xu, a postdoctoral research associate with the Center for Astrophysics \u0026amp; Space Sciences, at the University of California, San Diego. The research was funded by the National Science Foundation and NASA.\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003E\u0026nbsp;\u003C\/em\u003E\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":[{"value":"Study suggests there are fewer faint galaxies than expected"}],"field_summary":[{"value":"\u003Cp\u003ESimulations show hundreds of well-resolved galaxies, allowing researchers to make several novel and verifiable predictions ahead of the October 2018 launch of the \u003Ca href=\u0022http:\/\/www.jwst.nasa.gov\/\u0022\u003EJames Webb Space Telescope (JWST)\u003C\/a\u003E, a new space observatory that succeeds the \u003Ca href=\u0022http:\/\/hubblesite.org\/\u0022\u003EHubble Space Telescope\u003C\/a\u003E.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"There may be far fewer galaxies further out in the universe than might be expected."}],"uid":"27560","created_gmt":"2015-07-01 11:35:47","changed_gmt":"2016-10-08 03:18:52","author":"Jason Maderer","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2015-07-01T00:00:00-04:00","iso_date":"2015-07-01T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"419861":{"id":"419861","type":"image","title":"Renaissance simulations","body":null,"created":"1449254269","gmt_created":"2015-12-04 18:37:49","changed":"1475895157","gmt_changed":"2016-10-08 02:52:37","alt":"Renaissance simulations","file":{"fid":"202610","name":"oshea15-image.jpg","image_path":"\/sites\/default\/files\/images\/oshea15-image_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/oshea15-image_0.jpg","mime":"image\/jpeg","size":407223,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/oshea15-image_0.jpg?itok=RvB-Cc9b"}}},"media_ids":["419861"],"related_links":[{"url":"http:\/\/iopscience.iop.org\/2041-8205\/807\/1\/L12\/","title":"Read the study"}],"groups":[{"id":"1183","name":"Home"}],"categories":[{"id":"135","name":"Research"}],"keywords":[{"id":"97331","name":"Galaxies"},{"id":"12044","name":"John Wise"},{"id":"166937","name":"School of Physics"},{"id":"25211","name":"universe"}],"core_research_areas":[{"id":"39541","name":"Systems"}],"news_room_topics":[{"id":"71881","name":"Science and Technology"}],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003EJason Maderer\u003Cbr \/\u003ENational Media Relations\u003Cbr \/\u003E\u003Ca href=\u0022mailto:maderer@gatech.edu\u0022\u003Emaderer@gatech.edu\u003C\/a\u003E\u003Cbr \/\u003E404-385-2926\u003C\/p\u003E","format":"limited_html"}],"email":["maderer@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}