Tag Archives: dark matter

Materia oscura

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.”


Scientists to map universe in 3-D HD

La energía oscura se oculta

Entre las muchas teorías que tratan de explicar la naturaleza de la energía oscura se encuentran la quintaesencia y los campos fantasmas, dos hipótesis formuladas a partir de los datos de satélites como Planck y WMAP. Ahora investigadores de Barcelona y Atenas plantean que ambas posibilidades son solo un espejismo en las observaciones y es el vacío cuántico el que podría estar detrás de esa energía que mueve nuestro universo.

Los cosmólogos consideran que unas tres cuartas partes del universo están constituidas por una misteriosa energía oscura que explicaría su expansión acelerada. La verdad es que no saben lo que puede ser, así que plantean posibles soluciones.

Una es que exista la quintaesencia, un agente invisible gravitatorio que en lugar de atraer, repele y acelera la expansión del cosmos. Desde el mundo clásico hasta la Edad Media, ese término hacía referencia al éter o quinto elemento de la naturaleza, junto a la  tierra, el agua, el fuego y el aire.
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Dark Matters

The winter conference season is well under way, and what better way to fill my first blog post than with a report from one of the premier conferences in particle and astroparticle physics: the Rencontres de Moriond.

One of the nice things I like about attending a conference is that it lets me step away from my day-to-day work and think again about the wider context of what we do as physicists. In this conference, it was the progress being made in our understanding of dark matter that best seemed to bring together work from many different areas of investigation. (Note that some of the results I will mention were already included in Jessica Levêque’s post No Matter How Hard You Try… Standard Is Standard).

Artist’s impression of dark matter (in blue) surrounding the Milky Way. Credit: ESO/L. Calçada

Artist’s impression of dark matter (in blue) surrounding the Milky Way. Credit: ESO/L. Calçada

Dark matter is the material that holds galaxies and clusters of galaxies together – the evidence for its existence from astronomical measurements is overwhelming. The problem: no one knows what dark matter actually is. None of the particles we know will do the job, not even the elusive neutrinos. All we do know is that it must be electrically neutral, very weakly interacting, and stable over billions of years. But that’s pretty much it.

What to do? Well, we could try to detect collisions between dark matter particles and ordinary atoms. At the conference, the LUX and CDMS collaborations reported their searches to detect this mysterious substance. Neither group saw any evidence of a signal, more or less ruling out potential hints seen by other groups over the last few years. In addition, several searches for dark matter production in the ATLAS and CMS experiments were reported, also with null results.

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¿Está compuesta la materia oscura por neutrinos?

Un par de trabajos sugieren que los neutrinos tienen mayor masa de lo pensado y tendrían una gran contribución a la materia oscura.

A estas alturas todos conocemos el problema de materia oscura, esa masa que no vemos y que altera la rotación de las galaxias o contribuye al fenómeno de lentes gravitatorias. Normalmente se propone la existencia de partículas exóticas que den cuenta de esa masa, que es mucho mayor que la masa de la materia visible.
A veces se ha propuesto que sean los neutrinos los que hagan la materia oscura, al fin ya la cabo no interactúan prácticamente con la materia ordinaria. Para poder detectar alguno de los millones de neutrinos que nos atraviesan constantemente se usan miles de números de Avogadro de átomos corrientes y se espera a alguna interacción en un sitio aislado de la radiación natural. Esta baja interacción se debe a que los neutrinos sólo interaccionan con la materia ordinaria a través de la fuerza nuclear débil o la gravedad (que es la más débil de todas las fuerzas).
Hay tres tipos o “sabores” de neutrinos, cada uno asociado al electrón, al muón y al tau. Además, desde hace un tiempo, se ha propuesto la existencia de un cuarto neutrino que no interaccionaría con la materia ordinaria ni siquiera a través de la fuerza nuclear débil, sino que sólo interaccionaría con el resto de los neutrinos y con la gravedad. Tampoco sería capaz de cambiar su sabor. Los neutrinos estériles son un concepto puramente teórico, a diferencia de los otros tres tradicionales, que sí se han observado.
En un principio se creía que los tres neutrinos tradicionales carecían de masa, pero el descubrimiento de las oscilaciones de neutrinos que hace que unos tipos se transformen en otros (y que resuelve el problema de la paradoja de los neutrinos solares) nos dice que tienen alguna masa. Esta masa es muy pequeña, con una cota inferior es de 0,06 eV. Pero nadie sabe su masa real. Si tuvieran una masa pequeña, pero muy por encima de esa cota, entonces podrían dar cuenta de la materia oscura, pues la cantidad de neutrinos (principalmente primordiales) es inmensa. Por el contrario, si tuvieran una masa un poco superior a esos 0,06 eV, entonces su contribución a la materia oscura sería despreciable.
Una manera de medir la materia oscura es analizando el fondo cósmico de microondas (FCM), que se corresponde a la luz emitida al cabo 380.000 años tras del Big Bang. El FCM contiene pequeñas irregularidades que dan cuenta de varios aspectos del Universo y que permiten testar los distintos modelos cosmológicos. También permite determinar la cantidad de materia oscura.

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CERN&ESA: Origins 2013

The cosmic microwave background as observed by the European Space Agency’s Planck satellite (Image: ESA)
Come to CERN on Friday 27 September to celebrate European researchers’ night with ORIGINS2013.

Sign up for a speed-date with some of the researchers who discovered the Higgs boson or with researchers who study the big bang with the Planck telescope.

Can’t make it to CERN? The event will be webcast live from CERN at 7.30pm CET on 27 September.



The Enigma of the Dark Matter

Artículo publicado en Contemporary Physics 43 (2002) 51-62
¿De qué está hecho el Universo? (De las partículas elementales a la materia oscura)
Artículo publicado en el libro XIII Ciclo de Conferencias de Humanidades, Ingeniería y Arquitectura (2010), Ed. Universidad Politécnica de Madrid.

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Ponente: Carlos Muñoz Lopez
Ciclo: XIII Ciclo de Conferencias de Humanidades, Ingeniería y Arquitectura. Universidad Politécnica de Madrid
Descripción: Carlos Muñoz explica las ideas que se tienen sobre la composición del universo.

Solo entendemos la composición del universo si conocemos las partículas que lo constituyen y sus interacciones, para ello hay que hacer una lista de las partículas y de sus interacciones previamente para así saber cuáles son. Las observaciones astrofísicas implican que en el universo hay más materia de la que vemos.

No se sabe muy bien determinar de qué está hecha la materia oscura, para determinarlo se suelen plantean una serie de hipótesis y mediante la detección se confirman dichas hipótesis.