jueves, 31 de mayo de 2012

Cosmic calculations: Advance will help astrophysicists explore where stars are born

A University of Delaware-led research team reports an advance in the June 1 issue of Science that may help astrophysicists more accurately analyze the vast molecular clouds of gas and dust where stars are born.
Krzysztof Szalewicz, professor of physics and astronomy at UD, was the principal investigator on the National Science Foundation funded research project, which solved equations of  to more precisely describe the interactions between molecules of hydrogen and carbon monoxide, the two most abundant gases in space.
Such calculations are important to , the science that identifies atoms or molecules by the color of light they absorb or emit.  discovered that sunlight shining through a prism would separate into a rainbow of colors. Today, spectroscopy is essential to fields ranging from medical diagnostics to airport security.
In , spectrometers attached to telescopes orbiting in space measure light across the visible, infrared, and microwave spectrum to detect and quantify the abundance of  and molecules, as well as their temperatures and densities, in places such as the vast , a celestial maternity ward crowded with , some 1,500  away.
Whereas carbon monoxide — the second-most abundant molecule in space — is easily detected by spectrometers, such is not the case for hydrogen. Despite ranking as the most abundant molecule in space, hydrogen emits and absorbs very little light in the spectral ranges that can be observed. Thus, researchers must deduce information about molecular hydrogen from its weak interactions with carbon monoxide in the interstellar medium (the stuff between the stars).
"The hydrogen spectra get lost on the way, but carbon monoxide is like a lighthouse — its spectra are observed more often than those of any other molecule," Szalewicz says. "You can indirectly tell what the density of hydrogen is from the carbon monoxide spectra."
Szalewicz and co-authors Piotr Jankowski, a former UD postdoctoral researcher who is now on the chemistry faculty at Nicolaus Copernicus University in Torun, Poland, and A. Robert W. McKellar, from the National Research Council in Ottawa, Canada, wanted to revisit the spectra of the hydrogen and  complex. The first time such a calculation was done was 14 years ago by Szalewicz and Jankowski, parallel to an accurate measurement by McKellar.
In their computational model, the scientists needed to determine first how electrons move around nuclei. To this end, they included simultaneous excitations of up to four electrons at a time. The energy levels produced by the rotations and vibrations of the nuclei then were computed and used to build a theoretical spectrum that could be compared with the measured one.
The team's calculations, accomplished with the high-powered kolos computing cluster at UD, have resulted in theoretical spectra 100 times more accurate than those published 14 years ago. The theoretical and experimental spectra are now in near-perfect agreement, which allowed the team to "assign" the spectrum, that is, to determine how each spectral feature is related to the underlying motion of the nuclei, Szalewicz says.
The combined theoretical and experimental knowledge about this molecular complex now can be used to analyze recent results from satellite observatories to search for its direct spectral signal. Even more importantly, this knowledge can be used to get better information about the hydrogen molecule in space from indirect observations, Szalewicz notes.
"Spectroscopy provides the most precise information about matter that is available," he says. "I am pleased that our computations have untangled such a complex problem."
Szalewicz's expertise is in numerically solving the equations for the motions of electrons resulting in molecules attracting or repelling each other and then using these interactions to look at different properties of clusters and condensed phases of matter.
His research has unveiled hidden properties of water and found a missing state in the beryllium dimer, both results previously reported in Science, and his findings about helium may lead to more accurate standards for measuring temperature and pressure.

Journal reference: Science
Source: PhysOrg.com

Astronomers probe 'evaporating' planet around nearby star with Hobby-Eberly telescope

Astronomers probe 'evaporating' planet around nearby star with Hobby-Eberly telescope
Astronomers from The University of Texas at Austin and Wesleyan University have used the Hobby-Eberly Telescope at UT Austin’s McDonald Observatory to confirm that a Jupiter-size planet in a nearby solar system is dissolving, albeit excruciatingly slowly, because of interactions with its parent star. Their findings could help astronomers better understand star-planet interactions in other star systems that might involve life.

The work will be published in the June 1 edition of The Astrophysical Journal in a paper led by Wesleyan University postdoctoral researcher Adam Jensen. The team includes University of Texas  Michael Endl and Bill Cochran, as well as Wesleyan professor Seth Redfield.
The star, HD 189733, lies about 63 light-years away in the constellation Vulpecula, the little fox.
In 2010 another team studied this star in ultraviolet light with the Hubble Space Telescope and discovered that its planet (called HD 189733b) is discharging hydrogen into space.
 The Texas-Wesleyan study finds that this streaming hydrogen gas — studied in a different wavelength range by one of the world's largest ground-based telescopes — is much hotter than anyone knew. This temperature is important: It indicates that the violent flares this star is throwing out are interacting with the planet's atmosphere.
 While this planet is not thought to be a home for life, such studies could help astronomers understand how interactions between "parent" stars and their "children" might affect life that could arise in other star systems.

Astronomers probe 'evaporating' planet around nearby star with Hobby-Eberly telescope
 "One day we will use similar techniques to probe the atmosphere of smaller, Earth-like planets," The University of Texas' Endl said. "I think the pace of progress is stunning, to say the least. Twenty years ago we didn't really know of any exoplanets, and now we probe and study their atmospheres."
 The planet HD 189733b is not like Earth — it's a gas giant 20 percent heavier than Jupiter that orbits 10 times as close to its parent star as Mercury does to our sun, an exotic type of planet astronomers have dubbed a "hot Jupiter."
 To date, astronomers have discovered nearly 700 planets orbiting stars in our galaxy (with billions suspected), but they have probed the atmospheres of only a handful,using space telescopes and the largest ground-based telescopes such as the Hobby-Eberly Telescope (HET).
Studies of this planet's atmosphere are possible because it passes in front of its parent star as seen from Earth.
 “Each time the planet passes in front of the star,” Redfield said, “the planet blocks some of the star’s light. If the planet has no atmosphere, it will block the same amount of light at all wavelengths. However, if the planet has an atmosphere, gasses in its atmosphere will absorb some additional light.” The passages are called transits.
 In 2007 as a postdoctoral researcher at the McDonald Observatory, Redfield announced he had found sodium in this planet's atmosphere. That announcement was based on hundreds of HET observations spread out over a year, taken both with the planet in front of the star ("in-transit") and when the planet was not. Subtracting the latter from the former provided the planet's "transmission spectrum."
 Astronomers determine the spectrum of a star or planet when spreading out the telescope-collected light into its component wavelengths — a more sophisticated version of passing light through a prism to produce a rainbow. The spectrum is like a bar code that astronomers can read to determine the object's chemical composition, temperature, speed and direction of motion.
 Today, Redfield's postdoctoral fellow, Adam Jensen, is studying that same set of telescope observations and many more added by Endl in the intervening years.
 Just determining the spectrum of a transiting planet, let alone being able to decode it, is a difficult feat. As this planet passes in front of its , it blocks only 2.5 percent of the star’s total light, plus another 0.3 percent for the planet’s atmosphere. Teasing out that 0.3 percent and decoding it is the goal.
Journal reference: Astrophysical Journal
Source: PhysOrg.com

Hubble shows Milky Way is destined for head-on collision with Andromeda galaxy

Hubble shows Milky Way is destined for head-on collision
This illustration shows the collision paths of our Milky Way galaxy and the Andromeda galaxy. The galaxies are moving toward each other under the inexorable pull of gravity between them. Also shown is a smaller galaxy, Triangulum, which may be part of the smashup. (Credit: NASA; ESA; A. Feild and R. van der Marel, STScI)

NASA astronomers announced Thursday they can now predict with certainty the next major cosmic event to affect our galaxy, sun, and solar system: the titanic collision of our Milky Way galaxy with the neighboring Andromeda galaxy.

The Milky Way is destined to get a major makeover during the encounter, which is predicted to happen four billion years from now. It is likely the sun will be flung into a new region of our galaxy, but our Earth and solar system are in no danger of being destroyed.
"Our findings are statistically consistent with a head-on collision between the and our ," said Roeland van der Marel of the Space Telescope Science Institute (STScI) in Baltimore.

The solution came through painstaking  measurements of the motion of Andromeda, which also is known as M31. The galaxy is now 2.5 million light-years away, but it is inexorably falling toward the Milky Way under the mutual pull of gravity between the two  and the invisible dark matter that surrounds them both.

"After nearly a century of speculation about the future destiny of Andromeda and our Milky Way, we at last have a clear picture of how events will unfold over the coming billions of years," said Sangmo Tony Sohn of STScI.
The scenario is like a baseball batter watching an oncoming fastball. Although Andromeda is approaching us more than 2,000 times faster, it will take 4 billion years before the strike.
Computer simulations derived from Hubble's data show that it will take an additional two billion years after the encounter for the interacting galaxies to completely merge under the tug of gravity and reshape into a single elliptical galaxy similar to the kind commonly seen in the local universe.
Although the galaxies will plow into each other, stars inside each galaxy are so far apart that they will not collide with other stars during the encounter. However, the stars will be thrown into different orbits around the new galactic center. Simulations show that our  will probably be tossed much farther from the galactic core than it is today.

This illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. In this image, representing Earth's night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull. (Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger)

To make matters more complicated, M31's small companion, the Triangulum galaxy, M33, will join in the collision and perhaps later merge with the M31/Milky Way pair. There is a small chance that M33 will hit the Milky Way first.
The universe is expanding and accelerating, and collisions between galaxies in close proximity to each other still happen because they are bound by the gravity of the dark matter surrounding them. The Hubble Space Telescope's deep views of the universe show such encounters between galaxies were more common in the past when the universe was smaller.
A century ago astronomers did not realize that M31 was a separate galaxy far beyond the stars of the Milky Way. Edwin Hubble measured its vast distance by uncovering a variable star that served as a "milepost marker."
Hubble went on to discover the expanding universe where galaxies are rushing away from us, but it has long been known that M31 is moving toward the Milky Way at about 250,000 miles per hour. That is fast enough to travel from here to the moon in one hour. The measurement was made using the Doppler effect, which is a change in frequency and wavelength of waves produced by a moving source relative to an observer, to measure how starlight in the galaxy has been compressed by Andromeda's motion toward us.
Previously, it was unknown whether the far-future encounter will be a miss, glancing blow, or head-on smashup. This depends on M31’s tangential motion. Until now, astronomers had not been able to measure M31's sideways motion in the sky, despite attempts dating back more than a century. The Hubble Space Telescope team, led by van der Marel, conducted extraordinarily precise observations of the sideways motion of M31 that remove any doubt that it is destined to collide and merge with the Milky Way.
"This was accomplished by repeatedly observing select regions of the galaxy over a five- to seven-year period," said Jay Anderson of STScI.
"In the worst-case-scenario simulation, M31 slams into the Milky Way head-on and the stars are all scattered into different orbits," said Gurtina Besla of Columbia University in New York, N.Y. "The stellar populations of both galaxies are jostled, and the Milky Way loses its flattened pancake shape with most of the stars on nearly circular orbits. The galaxies' cores merge, and the stars settle into randomized orbits to create an elliptical-shaped galaxy."
The space shuttle servicing missions to Hubble upgraded it with ever more-powerful cameras, which have given astronomers a long-enough time baseline to make the critical measurements needed to nail down M31's motion. The Hubble observations and the consequences of the merger are reported in three papers that will appear in an upcoming issue of the Astrophysical Journal.
Journal reference: Astrophysical Journal
Provided by JPL/NASA
Source: PhysOrg.com

Science nugget: Catching solar particles infiltrating Earth's atmosphere

Science nugget: Catching solar particles infiltrating Earth's atmosphere
This graph shows the neutrons detected by a neutron detector at the University of Oulu in Finland from May 16 through May 18, 2012. The peak on May 17 represents an increase in the number of neutrons detected, a phenomenon dubbed a ground level enhancement or GLE. This was the first GLE since December of 2006. Credit: University of Oulu/NASA's Integrated Space Weather Analysis System

On May 17, 2012 an M-class flare exploded from the sun. The eruption also shot out a burst of solar particles traveling at nearly the speed of light that reached Earth about 20 minutes after the light from the flare. An M-class flare is considered a "moderate" flare, at least ten times less powerful than the largest X-class flares, but the particles sent out on May 17 were so fast and energetic that when they collided with atoms in Earth's atmosphere, they caused a shower of particles to cascade down toward Earth's surface. The shower created what's called a ground level enhancement (GLE).

GLEs are quite rare – fewer than 100 events have been observed in the last 70 years, since instruments were first able to detect them. Moreover, this was the first GLE of the current solar cycle--a sure sign that the sun's regular 11-year cycle is ramping up toward solar maximum.
This GLE has scientists excited for another reason, too. The joint Russian/Italian mission PAMELA, short for Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics, simultaneously measured the particles from the  that caused the GLE.  have been measured before, but PAMELA is sensitive to the very high-energy particles that reach ground level at . The data may help scientists understand the details of what causes this space weather phenomenon, and help them tease out why a relatively small flare was capable of producing the high-speed particles needed to cause a GLE.
"Usually we would expect this kind of ground level enhancement from a giant coronal mass ejection or a big X-class flare," says Georgia de Nolfo, a space scientist who studies high speed solar particles at NASA's Goddard Space Flight Center in Greenbelt, Md. "So not only are we really excited that we were able to observe these particularly high energy particles from space, but we also have a scientific puzzle to solve."

Science nugget: Catching solar particles infiltrating Earth's atmosphere

An artist's concept of the shower of particles produced when Earth's atmosphere is struck by ultra-high-energy cosmic rays. Credit: Simon Swordy/University of Chicago, NASA

The path to this observation began on Saturday, May 5, when a large sunspot rotated into view on the left side of the sun. The sunspot was as big as about 15 Earths, a fairly sizable , though by no means as big as some of the largest sunspots that have been observed on the sun. Dubbed Active Region 1476, the sunspots had already shown activity on the back side of the sun—as seen by a NASA mission called the Solar Terrestrial Relations Observatory (STEREO) -- so scientists were on alert for more. Scientists who study high-energy particles from the sun had been keeping their eye out for just such an active region because they had seen no GLEs since December of 2006.

In addition, they had high hopes that the PAMELA mission, which had focused on cosmic rays from outside our galaxy could now be used to observe solar particles. Such "solar cosmic rays" are the most energetic particles that can be accelerated at or near the sun.
But there was a hitch: the satellite carrying the PAMELA instruments were not currently usable since they were in calibration mode. Scientists including de Nolfo and another Goddard researcher, Eric Christian, let the PAMELA collaboration know that this might be the chance they had been waiting for and they convinced the Russian team in charge of the mission to turn the instruments back on to science mode.
"And then the active region pretty much did nothing for two weeks," says Christian. "But just before it disappeared over the right side of the sun, it finally erupted with an M-class flare."
Bingo. Neutron monitors all over the world detected the shower of neutrons that represent a GLE. Most of the time the showers are not the solar energetic particles themselves, but the resultant debris of super-fast particles slamming into  in Earth’s . The elevated levels of neutrons lasted for an hour.
Simultaneously, PAMELA recorded the incoming solar particles up in space, providing one of the first in-situ measurements of the stream of  that initiated a GLE. Only the early data has been seen so far, but scientists have high hopes that as more observations are relayed down to Earth, they will be able to learn more about the May 17 onslaught of solar protons, and figure out why this event triggered a GLE when earlier bursts of solar protons in January and March, 2012 didn't.
PAMELA is a space-borne experiment of the WiZard collaboration, which is an international collaboration between Italian (I.N.F.N. – Istituto Nazionale di Fisica Nucleare), Russian, German and Swedish institutes, realized with the main support of the Italian (ASI) and Russian (Roscosmos) Space Agencies.
Provided by JPL/NASA
Source: PhysOrg.com

El telescopio ALMA demuestra potencia con una imagen detallada de la Centaurus A

This New Image Of Centaurus A Combines ALMA And Near-Infrared Observations Of Th

El telescopio ALMA (Atacama Large Millimeter/submillimeter Array) el Observatorio Europeo Austral (ESO) permitirá a los astrónomos ver con "una calidad sin precedentes" tal y como ha demostrado con una de sus primeras imágenes en la que muestra de manera detallada el centro de la galaxia Centaurus A.

Según ha indicado la ESO, ALMA aún está en su fase de construcción pero "ya es el telescopio más poderoso de su tipo", a pesar de encontrarse actualmente en una fase de observaciones denominada de "ciencia temprana" (Early Science).

Centaurus A es una radiogalaxia elíptica masiva -que emite ondas de radio- y es la radiogalaxia más destacada del cielo, además de la más cercana. Centaurus A ha sido observada con numerosos telescopios y su luminoso centro alberga un agujero negro supermasivo con una masa de alrededor de cien millones de veces la masa del Sol.

En luz visible, una de las características de esta galaxia es la banda que oscurece su centro. Este camino de polvo alberga grandes cantidades de gas, polvo y estrellas jóvenes. Estas características, junto con la fuerte emisión en ondas de radio, son evidencias de que Centaurus A es el resultado de una colisión entre una galaxia elíptica gigante y una galaxia espiral de menor tamaño cuyos restos forman la banda polvorienta.

Para poder ver a través del polvo que oscurece la zona central, los astrónomos necesitan observar utilizando las longitudes de onda más largas de la luz. Esta nueva imagen de Centaurus A combina observaciones en longitudes de onda de alrededor de un milímetro, llevadas a cabo por ALMA, y observaciones en el rango del infrarrojo cercano. Des este modo, atravesando el polvo, se ha obtenido una clara visión del luminoso centro de la galaxia.

Las nuevas observaciones de ALMA, mostradas en un rango de verdes, amarillos y anaranjados, revelan la posición y el movimiento de las nubes de gas en la galaxia. Son las observaciones de este tipo más precisas y de mayor sensibilidad realizadas hasta el momento, ha precisado ESO.

ALMA fue puesto a punto para detectar señales en una longitud de onda de alrededor de 1,3 milímetros, emitidas por las moléculas del gas de monóxido de carbono. El movimiento del gas en la galaxia causa pequeños cambios en esta longitud de onda, debido al efecto Doppler. El movimiento se muestra en esta imagen como cambios en el color.

Las observaciones de ALMA están superpuestas a una imagen de Centaurus A obtenida en el infrarrojo cercano por el instrumento SOFI, instalado en el telescopio de ESO New Technology Telescope (NTT). La imagen fue procesada utilizando una técnica innovadora que elimina el efecto de emisión producido por el polvo.

La construcción de ALMA, en el llano de Chajnantor, en el norte de Chile, se completará en el año 2013, cuando las 66 antenas de alta precisión estén totalmente operativas. Ya se han instalado la mitad de las antenas. Las observaciones de ciencia temprana con parte del conjunto de antenas empezaron en el año 2011, y ya están produciendo resultados destacados. Estas observaciones de Centaurus A llevadas a cabo por ALMA fueron tomadas durante tiempo destinado a la puesta a punto y verificación científica del telescopio.

Fuente: Europa Press

X-ray 'echoes' map a supermassive black hole's environs

X-ray 'echoes' map a supermassive black hole's environs
The galaxy NGC 4151 is located about 45 million light-years away toward the constellation Canes Venatici. Activity powered by its central black hole makes NGC 4151 one of the brightest active galaxies in X-rays. Credit: David W. Hogg, Michael R. Blanton, and the Sloan Digital Sky Survey Collaboration

An international team of astronomers using data from the European Space Agency's (ESA) XMM-Newton satellite has identified a long-sought X-ray "echo" that promises a new way to probe supersized black holes in distant galaxies.

Most big galaxies host a big central black hole containing millions of times the sun's mass. When matter streams toward one of these supermassive black holes, the galaxy's center lights up, emitting billions of times more energy than the sun. For years, astronomers have been monitoring such "active galactic nuclei" (AGN) to better understand what happens on the brink of a monster black hole.
"Our analysis allows us to probe black holes through a different window. It confirms some long-held ideas about AGN and gives us a sense of what we can expect when a new generation of space-based X-ray telescopes eventually becomes available," said Abderahmen Zoghbi, a postdoctoral research associate at the University of Maryland at College Park (UMCP) and the study's lead author.
One of the most important tools for astronomers studying AGN is an X-ray feature known as the broad iron line, now regarded as the signature of a rotating black hole. Excited iron atoms produce characteristic X-rays with energies around 6,000 to 7,000 electron volts -- several thousand times the energy in visible light – and this emission is known as the iron K line.

Matter falling toward a black hole collects into a rotating accretion disk, where it becomes compressed and heated before eventually spilling over the black hole's event horizon, the point beyond which nothing can escape and astronomers cannot observe. A mysterious and intense X-ray source near the black hole shines onto the disk's surface layers, causing iron atoms to radiate K-line emission. The inner part of the disk is orbiting the black hole so rapidly that the effects of Einstein's relativity come into play -- most notably, how time slows down close to the black hole. These relativistic effects skew or broaden the signal in a distinctive way.

Astronomers predicted that when the X-ray source near the black hole flared, the broad iron K line would brighten after a delay corresponding to how long the X-rays took to reach and illuminate the accretion disk. Astronomers call the process relativistic reverberation. With each flare from the X-ray source, a light echo sweeps across the disk and the iron line brightens accordingly.

This illustration compares the environment around NGC 4151's supermassive black hole with the orbits of the planets in our solar system; the planets themselves are not shown to scale. Echoes of X-ray flares detected in XMM-Newton data demonstrate that the X-ray source (blue sphere, center) is located above the black hole's accretion disk. The time lag between flares in the source and their reflection in the accretion disk places the X-ray source about four times Earth's distance from the sun. Credit: NASA's Goddard Space Flight Center

Unfortunately, neither ESA's XMM-Newton satellite nor NASA's Chandra X-ray Observatory possess telescopes powerful enough to spot reverberations from individual flares.
The team reasoned that detecting the combined echoes from multiple flares might be possible if a sufficiently large amount of data from the right object could be analyzed. The object turned out to be the galaxy NGC 4151, which is located about 45 million light-years away in the constellation Canes Venatici. As one of the brightest AGN in X-rays, NGC 4151 has been observed extensively by XMM-Newton. Astronomers think that the galaxy's active nucleus is powered by a black hole weighing 50 million solar masses, which suggested the presence of a large accretion disk capable of producing especially long-lived and easily detectable echoes.
Since 2000, XMM-Newton has observed the galaxy with an accumulated exposure of about four days. By analyzing this data, the researchers uncovered numerous X-ray echoes, demonstrating for the first time the reality of relativistic reverberation. The findings appear in the May 8 issue of Monthly Notices of the Royal Astronomical Society.
The team found that echoes lagged behind the AGN flares by a little more than 30 minutes. Moving at the speed of light, the  associated with the echo must have traveled an additional 400 million miles -- equivalent to about four times Earth's average distance from the sun -- than those that came to us directly from the flare.
"This tells us that the mysterious X-ray source in AGN hovers at some height above the accretion disk," said co-author Chris Reynolds, a professor of astronomy at UMCP and Zoghbi's adviser. Jets of accelerated particles often are associated with AGN, and this finding meshes with recent suggestions that the X-ray source may be located near the bases of these jets.
"The data show that the earliest echo comes from the most broadened iron line emission. This originates from closest to the black hole and fits well with expectations," said co-author Andy Fabian, an astrophysicist at the University of Cambridge in England.
Amazingly, the extreme environment at the heart of NGC 4151 is built on a scale comparable to our own solar system. If we replaced the sun with the black hole, the event horizon would extend less than halfway to Earth if the black hole spins rapidly; slower spin would result in a larger horizon. The X-ray source would hover above the black hole and its  at a distance similar to that between the sun and the middle of the asteroid belt.
"Teasing out the echo of X-ray light in NGC 4151 is a remarkable achievement. This work propels the science of AGN into a fundamental new area of mapping the neighborhoods of ," said Kimberly Weaver, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md., who was not involved in the study. NASA Goddard hosts the  Guest Observer Facility, which supports U.S. astronomers who request observing time on the satellite.
The detection of X-ray echoes in AGN provides a new way of studying black holes and their accretion disks. Astronomers envision the next generation of X-ray telescopes with collecting areas large enough to detect the echo of a single AGN flare in many different objects, thereby providing astronomers with a new tool for testing relativity and probing the immediate surroundings of massive 
More information: Paper: Relativistic iron K X-ray reverberation in NGC 4151http://onlinelibra … 7.x/abstract
Provided by JPL/NASA
Source: PhysOrg.com 

Astrónomos logran identificar ecos de rayos X provenientes de un agujero negro supermasivo

Detectan ecos de rayos X provenientes de agueros negros supermasivos
Detectan ecos de rayos X provenientes de agueros negros supermasivos

Un equipo de astrónomos internacionales ha detectado por primera vez unos ecos de rayos X provenientes de los alrededores de un agujero negro super masivo, hallazgo que promete una nueva manera de investigar estos agujeros negros gigantes en galaxias lejanas. Para este descubrimientos, los científicos han usado los datos del satélite de la Agencia Espacial Europea (ESA) XMM Newton.
Las galaxias más grandes albergan un agujero negro supermasivo que contiene millones de veces la masa del sol. Durante años, los astrónomos han estado observando los AGN (núcleos activos de las galaxias) para entender mejor lo que sucede en el borde de estos agujeros negros monstruosos. Una de las herramientas más importantes para los astrónomos que estudian estos fenómenos es precisamente el haz de rayos X.
Estos rayos están producidos por átomos de hierro, con energías varios miles de veces superiores a la energía de la luz visible. Esta emisión se conoce como la 'línea de hierro K'
Fuente: teinteresa.es

Enceladus plume is a new kind of plasma laboratory

Enceladus plume is a new kind of plasma laboratory
Cassini imaging scientists used views like this one to help them identify the source locations for individual jets spurting ice particles, water vapor and trace organic compounds from the surface of Saturn's moon Enceladus. Image credit: NASA/JPL/Space Science Institute

Recent findings from NASA's Cassini mission reveal that Saturn's geyser moon Enceladus provides a special laboratory for watching unusual behavior of plasma, or hot ionized gas. In these recent findings, some Cassini scientists think they have observed "dusty plasma," a condition theorized but not previously observed on site, near Enceladus.

Data from Cassini's fields and particles instruments also show that the usual "heavy" and "light" species of charged particles in normal  are actually reversed near the plume spraying from the moon's . The findings are discussed in two recent papers in the Journal of Geophysical Research.
"These are truly exciting discoveries for plasma science," said Tamas Gombosi, Cassini fields and particles interdisciplinary scientist based at the University of Michigan, Ann Arbor. "Cassini is providing us with a new plasma physics laboratory."
Ninety-nine percent of the matter in the universe is thought to be in the form of plasma, so scientists have been using Saturn as a site other than Earth to observe the behavior of this cloud of ions and electrons directly. Scientists want to study the way the sun sends energy into Saturn's plasma environment, since that jolt of energy drives processes such as weather and the behavior of . They can use these data to understand how Saturn's plasma environment is similar to and different from that of Earth and other planets.
The small, icy  is a major source of ionized material filling the huge around Saturn. About 200 pounds (about 100 kilograms) of water vapor per second - about as much as an active comet - spray out from long cracks in the south polar region known as "tiger stripes." The ejected matter forms the Enceladus plume - a complex structure of icy grains and neutral gas that is mainly water vapor. The plume gets converted into charged particles interacting with the plasma that fills Saturn's magnetosphere.
The nature of this unique gas-dust-plasma mixture has been revealed over the course of the mission with data from multiple instruments, including the Cassini plasma spectrometer, magnetometer, magnetospheric imaging instrument, and the radio and plasma wave science instrument. What scientists found most interesting is that the grains range continuously in size from small water clusters (a few water molecules) to thousandths of an inch (100 micrometers). They also saw that a large fraction of these grains trap electrons on their surface. Up to 90 percent of the electrons from the plume appear to be stuck on large, heavy grains.
In this environment, Cassini has now seen positively charged ions become the small, "light" plasma species and the negatively charged grains become the "heavy" component. This is just the opposite of "normal" plasmas, where the negative electrons are thousands of times lighter than the positive ions.
In a paper published in the December issue of the journal, a team of Swedish and U.S. scientists on the  examined radio and plasma wave science instrument observations from four flybys of Enceladus during 2008. They found a high plasma density (both ions and electrons) within the Enceladus plume region, although the electron densities are usually much lower than the ion densities in the plumes and in the E ring. The team concluded that dust particles a hundred millionth to a hundred thousandth of an inch (a nanometer to micrometer) in size are sweeping up the negatively charged electrons. The mass of the observed "nanograins" ranges from a few hundred to a few tens of thousands of atomic mass units (proton masses), and must therefore contain tens to thousands of water molecules bound together. At least half of the negatively charged electrons are attached to the dust, and their interaction with the positively charged particles causes the ions to be decelerated. Because the dust is charged and behaves as part of the plasma cloud, this paper distinguishes this state of matter from dust that just happens to be in plasma.
"Such strong coupling indicates the possible presence of so-called 'dusty plasma', rather than the 'dust in a plasma' conditions which are common in interplanetary space," said Michiko Morooka from the Swedish Institute of Space Physics, lead author of the paper and a Cassini radio and plasma wave science co-investigator. "Except for measurements in Earth's upper atmosphere, there have previously been no in-situ observations of dusty plasma in space."
In a dusty plasma, conditions are just right for the dust to also participate in the plasma's collective behavior. This increases the complexity of the plasma, changes its properties and produces totally new collective behavior. Dusty plasma are thought to exist in comet tails and dust rings around the sun, but scientists rarely have the opportunity to fly through the dusty plasma and directly measure its characteristics in place.
A separate analysis, based on data obtained by the Cassini plasma spectrometer, revealed the presence of nanograins having an electric charge corresponding to a single excess electron. "The Cassini plasma spectrometer has enabled us to discover and analyze new classes of charged particles that were wholly unanticipated when the instrument was designed and built in the 1980s and 90s," said Tom Hill, the study's lead author and a co-investigator based at Rice University in Houston.
The nature of the Enceladus plume has been revealed over time due to the synergistic nature of the fields and particles instruments on Cassini, which has been in residence in Saturn's magnetosphere since 2004. Following the original detection of the plume based on magnetometer measurements, Sven Simon from the University of Cologne, Germany, and Hendrik Kriegel from the University of Braunschweig, Germany, found that the observed perturbation of Saturn's magnetic field required the presence of negatively charged dust grains in the plume. These findings were reported in the April and October 2011 issues of  Space Physics. Previous data obtained by the ion and neutral mass spectrometer revealed the complex composition of the plume gas, and the cosmic dust analyzer revealed that the plume grains were rich in sodium salts. Because this scenario can only arise if the plume originated from liquid water, it provides compelling evidence for a subsurface ocean.
Cassini will continue to study the complex nature of the plume region in the three planned additional flybys of Enceladus. 

Journal reference: Journal of Geophysical Research
Provided by JPL/NASA
Source: PhysOrg.com

Venus transit may boost hunt for other worlds

The transit of Venus before the Sun will not happen again for 105 years
The planet Venus transits in front of the Sun in 2004. Astronomers around the world will be using advanced telescopes to watch Venus cross in front of the Sun on June 5 and 6 in the hopes of finding clues in the hunt for other planets where life may exist.

Astronomers around the world will be using advanced telescopes to watch Venus cross in front of the Sun on June 5 and 6 in the hopes of finding clues in the hunt for other planets where life may exist.

By studying the  of a well-known planet in this once-in-a-lifetime event, scientists say they will learn more about how to decipher the atmospheres of  as they cross in front of their own stars.
"There are many, many of these events that are observed for . The thing is that stars are just points of light because we are so far away, so you can't actually see what is going on," Alan MacRobert,  and editor of Sky and magazine, told AFP.
However the , an event that will not happen again for another 105 years, or until 2117, offers a chance to practice decoding the atmosphere of a planet based on the impression it leaves on its star's light.
"The idea is some of that  skims through the atmosphere of the planet and the atmosphere leaves its imprint on that tiny, tiny little bit of a star's light," MacRobert said.
"If you can separate that from the rest of the star's light -- analyzing the light before, during and after the transit and looking for the difference -- you can actually tell something about the planet's atmosphere," he added.
"And this is absolutely at the cutting edge of present day technology."
The beginning of the transit will be visible in North America, Central America and the northern part of South America on the evening of June 5, as long as the skies stay clear. The end will not be seen in these regions due to sunset.
All of the transit will be visible in  and the Western Pacific.

Astronomers around the world will be using advanced telescopes to watch Venus cross in front of the Sun on June 5 and 6 in the hopes of finding clues in the hunt for other planets where life may exist.

Europe, the Middle East and  will get to see the end stages of the  as they go into sunrise on June 6.
However, due to the risk of blindness or painful, permanent eye damage, people should not look directly at the Sun without a proper solar filter to try and observe the tiny black dot crossing its surface.
Global astronomers are keenly searching the universe for hints of a rocky planet like Earth in the Goldilocks zone -- not too hot and not too cold -- with the right atmosphere and the existence of water to support life.
Experts believe the galaxy is teeming with billions of rocky planets that might be able to support life. Most have not yet been discovered by Earthlings, and are located so far away that they would be impossible to reach with modern technology.
The latest catalog released by NASA's Kepler space telescope team in March showed a total of 2,321 planet candidates transiting 1,790 stars.
Ten of the 46 planet candidates found in the habitable zone where liquid water could exist are close to the size of Earth, according to NASA. But in most cases, scientists lack details about these planets' atmospheres.
Even though Venus, the second planet from the Sun, is far too hot to be habitable and has a dense, C02 thick atmosphere, watching it transit the Sun is a valuable exercise for science.
"The fact that Venus is not in a habitable zone does not really matter," said Rick Feinberg of the American Astronomical Society.
"It gives us an opportunity to study in very great detail something we are observing very much further away and gives us more confidence in our ability to interpret the signals we are getting."
Feinberg added that the best times for scientists to watch the transit are the first and last 20 minutes, when sunlight filters through the Venus's atmosphere as it forms a fine shell around the planet.
The US National Solar Observatory in Tucson, Arizona, will use telescopes in Arizona, New Mexico, California, Hawaii, Australia and India to monitor the transit and collect data.
"This one will help us calibrate in several different instruments, and hunt for extrasolar planets with atmospheres," said Frank Hill, director of the NSO's Integrated Synoptic Program.
In the 18th and 19th centuries, astronomers used transits to measure the distance of the Earth to the Sun, he added.
"We have that number nailed down now, but transits are still useful."
Source: PhysOrg.com