Category Archives: Dark Matter

Materia oscura

¿Oscuro y vacío destino final?

Proponen un nuevo modelo de energía oscura que predice un Cosmos futuro aún más vacío y aburrido que lo que se asumía.

Simulación a gran escala del Universo en la que se ven los filamentos de materia oscura. Fuente: John Wise, Tom Abel, Ralf Kaehler, Universidad de Stanford.

La idea que tenían en el medioevo sobre el Universo era muy distinta de la que tenemos ahora. Incluso a principios del Siglo XX desconocían muchas cosas que conocemos nosotros en este nuevo siglo. Incluso el gran divulgador de la Astrofísica que fue Carl Sagan se murió sin saber de la existencia de la energía oscura, concepto que ha cambiado radicalmente la visión que tenemos sobre el Cosmos.

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Científicos españoles analizan las posibilidades del LHC en 2015

El nuevo arranque del gran colisionador de hadrones del CERN durante el año que viene, los experimentos sobre neutrinos, el observatorio de rayos gamma CTA y la presencia de investigadores españoles en el laboratorio de física nuclear FAIR serán algunos de los temas que trataron los cerca de 200 investigadores que asisten en Sevilla a la reunión anual del Centro Nacional de Física de Partículas, Astropartículas y Nuclear. La divulgación científica y la transferencia tecnologica también estarán presentes en las jornadas.

Expertos españoles en la física del Gran Colisionador de Hadrones (LHC), la investigación de la estructura nuclear y los experimentos para descubrir el 95% del universo ‘invisible’ se reúnen la semana próxima en Sevilla en las VI Jornadas del Centro Nacional de Física de Partículas, Astropartículas y Nuclear (CPAN). Este congreso, que se celebra por primera vez en la capital hispalense, congrega a 200 investigadores en estos ámbitos de la física, que discutirán sobre los principales avances en sus respectivos campos.

Entre los principales temas a tratar está el programa de investigación previsto para el LHC, el mayor acelerador de partículas del mundo operado por el CERN, que se vuelve a poner en marcha a principios de 2015 tras una larga parada de mantenimiento. Después de descubrir el bosón de Higgs en 2012 con solo dos años de funcionamiento, aparecen nuevos retos como la búsqueda de la supersimetría o la detección de materia oscura. Doscientos investigadores y técnicos españoles participan en el LHC y sus experimentos, con el apoyo del CPAN.
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¿Posible prueba sobre la materia oscura?

Encuentran un exceso de rayos gamma procedente del centro galáctico que atribuyen a la presencia de materia oscura.

At left is a map of gamma rays with energies between 1 and 3.16 GeV detected in the galactic center by Fermi's LAT; red indicates the greatest number. Prominent pulsars are labeled. Removing all known gamma-ray sources (right) reveals excess emission that may arise from dark matter annihilations. Image Credit: T. Linden, Univ. of Chicago

At left is a map of gamma rays with energies between 1 and 3.16 GeV detected in the galactic center by Fermi’s LAT; red indicates the greatest number. Prominent pulsars are labeled. Removing all known gamma-ray sources (right) reveals excess emission that may arise from dark matter annihilations.
Image Credit: T. Linden, Univ. of Chicago

El asunto de la materia oscura probablemente es uno de los más frustrantes de la ciencia moderna. Pese a las décadas transcurridas desde que se propuso su existencia, todavía no se ha conseguido detectar directamente esta esquiva materia. Aunque falsas alarmas ha habido unas cuantas.

 

Known dwarf spheroidal satellite galaxies of the Milky Way overlaid on a Hammer-Aitoff projection of a 4-year LAT counts map (E>1??GeV). The 15 dwarf galaxies included in the combined analysis are shown as filled circles, while additional dwarf galaxies are shown as open circles.

Known dwarf spheroidal satellite galaxies of the Milky Way overlaid on a Hammer-Aitoff projection of a 4-year LAT counts map (E>1??GeV). The 15 dwarf galaxies included in the combined analysis are shown as filled circles, while additional dwarf galaxies are shown as open circles.

La última propuesta parte, otra vez, de los datos tomados por el observatorio espacial Fermi. Según un grupo de científicos del Fermilab, del CfA, del MIT y de University of Chicago un supuesto exceso de energía en forma de rayos gamma registrada por Fermi y procedente del centro galáctico se puede explicar bien si por allí hay materia oscura. Han elaborado incluso un nuevo mapa de la zona.
La presencia de púlsares, la colisión de nubes de gas y otras posibles explicaciones no son suficientes según Dan Hooper y colaboradores para explicar el exceso de energía observado. Sin embargo, si se tiene en cuenta la aniquilación de partículas de materia oscura, entonces los datos encajan mejor.

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Keeping things awesome on the Dark Energy Survey

This article appeared in symmetry on May 1, 2014.

Scientists stay inspired in their sometimes tedious task of inspecting photographs taken in the Dark Energy Survey’s ambitious cataloging of one-eighth of the sky. Image courtesy of Dark Energy Survey

Scientists stay inspired in their sometimes tedious task of inspecting photographs taken in the Dark Energy Survey’s ambitious cataloging of one-eighth of the sky. Image courtesy of Dark Energy Survey

Physicists working on the Dark Energy Survey can expect to pull many an all-nighter. The international collaboration of more than 120 scientists aims to take about 100,000 photographs peering deep into the night sky. Scientists must personally review many of these photos to make sure the experiment is working well, and they’ve come up with ways to stay motivated while doing so.

DES scientists collected almost 14,000 photographs from August 2013 to February 2014, in the first of five seasons they plan to operate their sophisticated Dark Energy Camera. Even for those of us who aren’t trying to take the most detailed survey of the universe, it might not come as a surprise that complications can occur during operation. For example, the telescope may not always sync up with the natural movement of the night sky, and passing airplanes can create trails in the images. Software bugs can also cause issues.

Two of the DES researchers, Erin Sheldon of Brookhaven National Laboratory and Peter Melchior of The Ohio State University, created the DES Exposure Checker, an online gallery of images from the telescope. Team members use the photo repository as a way to spot imperfections and other issues with the images so they can fix problems as quickly as possible.

“These problems are easier for an actual person to see rather than some automated program,” Sheldon says. “And then we can create an inventory to help diagnose troubles that may occur with future images.”

When reviewing photos, DES scientists flag the ones that show symptoms of different problems, such as long streaks from satellites; unwanted reflections, called ghosts; or marks left by cosmic rays. But the process can get overwhelming with thousands of photos to look over. So the DES researchers decided to add a positive classification to the mix—an “Awesome!” category. When someone sees an incredible photo, they can mark it as such in the database.

Sheldon points out one of his favorite images, one that captured a passing comet. “It was just so serendipitous. We couldn’t find that if we pointed the telescope in the same place at any other time,” he says.

Steve Kent, Fermilab scientist and head of the experimental astrophysics group, says one of his favorite images from the survey shows a dying star. In the color photo, a bright blue oxygen haze surrounds the hot remnant of what was formerly a giant red star.

A second way to encourage team members classifying images is the leader board posted on the DES Exposure Checker website, honoring individuals who have categorized the most photos. Researchers compete to see their names at the top.

But more than friendly competition drives the DES team to categorize images. They’re also seeking answers to questions about the past and future of our universe such as: Has the density of dark energy changed over time? Why is the expansion of the universe speeding up?

“For me, it’s a mystery,” Sheldon says. “I have this question, and I have to find out the answer.”

Amanda Solliday

Scientists to map universe in 3-D HD

The Dark Energy Spectroscopic Instrument will create the clearest three-dimensional map yet of one-third of the sky.

Maps do more than tell us where we are. Rich with information elegantly arranged, they give us a way to assimilate our vast world. The clearer the map, the more confidently we set out to explore, looking for something it doesn’t show.

In a few years, scientists will come out with a new map of a third of the sky, one that will go deeper and bring that depth into sharper focus than any survey has yet achieved. It will pinpoint in three dimensions the locations of 25 million galaxies and quasars, pulling back the curtains on the history of the universe’s expansion over more than half of the age of the universe.

Armed with this detailed picture, scientists will be better equipped to search for something the map can’t show but whose effects will likely be all over it—dark energy. The researchers’ cartographic tool will be the Dark Energy Spectroscopic Instrument, or DESI.

“We have very precise measurements of positions and shapes of galaxies and galaxy clusters in the lateral dimensions, but the resolution in the distance away from us is much worse,” says Fermilab’s Brenna Flaugher, one of the leading scientists on DESI. “With DESI, you get the really fine measurements in depth. Your map of the universe suddenly gets clearer.”

The DESI project, managed at Lawrence Berkeley National Laboratory, is one of a number of surveys looking to get a handle on how dark energy operates.

“We’re going to try to understand what dark energy is,” says Berkeley Lab’s Michael Levi, DESI project director. “We don’t know if it’s something having to do with gravity that we don’t understand or some new form of energy that we just haven’t gotten our heads around yet.”

Whatever it is, it leaves its trace in the growth and structure of the universe.

DESI will model the universe’s expansion using two approaches. One is to precisely measure the spectra of the light coming from galaxies to determine their distance from us. The redder the light is, the farther away the galaxy.

The other approach is to measure the distances between galaxies. Galaxies arose from areas left dense with matter when the universe cooled down from the rapid expansion of the big bang. These peaks in density are known as baryon acoustic oscillations. Back when the peaks formed, they corresponded to a separation of about 490 million light-years. Since then the expansion of the universe has stretched them apart. Comparing the standard ruler against the distances between galaxies as the universe developed to its current state, scientists will be able to measure how space has stretched since the early times.

Together, the measurements will tell scientists how and how fast the universe is growing.

“Being able to make those two measurements at the same time—one about the expansion rate of the universe and the other about how structure is growing—allows you to test the theory of general relativity on this huge length and time scale,” says SLAC National Accelerator Laboratory’s Risa Wechsler, DESI co-spokesperson.

DESI will be the first survey to make measurements accurate to less than 1 percent of the expansion rate of the universe over the last 11 billion years.

The Dark Energy Spectrographic Instrument is designed to attach to the Mayall 4-Meter Telescope (pictured above) in Arizona. Once construction is completed, it will have 5000 fibers for collecting the spectra of galaxy light.

Using data from the Dark Energy Camera in Chile, which is currently focused on taking imaging data for the Dark Energy Survey, DESI will point each of those 5000 fibers at a galaxy. Once the fibers get what they need, they will move on to the next set of 5000 celestial objects.

“It’s like a big pincushion that wiggles at every image,” Flaugher says. “Every 20 minutes you take an image, and then you reposition each of these little fibers onto new targets.” It will keep doing that until it hits 25 million galaxies.

DESI grew out of two separate proposals to develop a spectroscopic instrument to explore dark energy. The DESI collaboration is made of 180 scientists from 45 institutions around the world, including five DOE laboratories.

Scientists expect to finish DESI’s construction in 2018. The experiment will then run for five years.

“The other cosmic surveys that are going on now and over the next 10 years—the Dark Energy Survey, LSST—are spectacular, and they’ll take images of a lot more galaxies than DESI will measure, but they’re making a 2- or 2.5-dimensional measurement of the universe.” Wechsler says.

“DESI is really making a 3-D map. You get a lot of additional power because you can say what the universe looks like in three dimensions over this long history.”

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Scientists to map universe in 3-D HD

Nuevas propuestas para detectores de WIMPs

Proponen dos nuevos sistemas para detectar las supuestas partículas que componen la materia oscura del Universo.

El ser humano lleva varias décadas intentando encontrar las partículas que forman la materia oscura sin mucho éxito. Se han instalado varios experimentos en minas profundas para así detectar estas hipotéticas partículas, a salvo de los rayos cósmicos que generarían tanto ruido en la señal que impediría reconocer la supuesta marca producida cuando muy raramente una de estas partículas interaccionan con la materia ordinaria. A estas partículas débilmente interactuantes de materia oscura se les ha denominado WIMP según sus siglas en inglés.

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