Thirty Supernovas Per Second in the Universe --Is Red Giant Betelgeuse Next?

 

Betelgeuse, one of the brightest stars in the sky, could burst into its supernova phase and become as bright as a full moon -- and last for as long as a year. The massive star is visible in the winter sky over most of the world as a bright, reddish star, could explode as a supernova anytime within the next 100,000 years.

Some astronomers believe that one of the plausible reasons we have yet to detect intelligent life in the universe may due to the deadly effects of local supernova explosions that wipe out all life in a given region of a galaxy.

While there is, on average, only one supernova per galaxy per century, there is something on the order of 100 billion galaxies in the observable Universe. Taking 10 billion years for the age of the Universe (it's actually 13.7 billion, but stars didn't form for the first few hundred million), Dr. Richard Mushotzky of the NASA Goddard Space Flight Center, derived a figure of 1 billion supernovae per year, or 30 supernovae per second in the observable Universe!

The red giant Betelgeuse, once so large it would reach out to Jupiter's orbit if placed in our own solar system, has shrunk by 15 percent over the past decade in a half, although it's just as bright as it's ever been.

"To see this change is very striking," said retired Berkeley physics professor Charles Townes, who won the 1964 Nobel Prize for inventing the laser. "We will be watching it carefully over the next few years to see if it will keep contracting or will go back up in size."

Betelgeuse, whose name derives from Arabic, is easily visible in the constellation Orion. It gave Michael Keaton's character his name in the movie "Beetlejuice" and was the home system of Galactic President Zaphod Beeblebrox in "The Hitchhiker's Guide to the Galaxy."

Red giant stars are thought to have short, complicated and violent lifespans. Lasting at most a few million years, they quickly burn out their hydrogen fuel and then switch to helium, carbon and other elements in a series of partial collapses, refuelings and restarts.

Betelgeuse, which is thought to be reaching the end of its lifespan, may be experiencing one of those collapses as it switches from one element to another as nuclear-fusion fuel.

"We do not know why the star is shrinking," said Townes' Berkeley colleague Edward Wishnow. "Considering all that we know about galaxies and the distant Universe, there are still lots of things we don't know about stars, including what happens as red giants near the ends of their lives."

If Betelgeuse goes nova, it could offer Earth's astronomers an up close look at how supernovae evolve and the physics that governs how they work. The problem is that it is not clear when that will happen. While stories have been circulating that the star could explode in 2012, the odds of that are actually quite small. Betelgeuse may explode tomorrow night, or it may not go nova until the year 100,000 A.D. It's impossible to know.

Betelgeuse is beyond the death beam distance -- somewhere within 30 light years range -- where it could do ultimate damage to Earth. The explosion won't do the Earth any harm, as a star has to be relatively close -- on the order of 25 light years -- to do that. Betelgeuse is about 600 light years distant.

Betelgeuse, one of the most luminous stars known and ten times the size of the Sun, is thought to be only 10 million years old. The more massive a star is the shorter its lifespan, which is why astronomers think it has an outside chance of exploding relatively soon.

Late in 2009, astronomers witnessed the largest explosion ever recorded: a super giant star two hundred times bigger than the sun utterly obliterated by runaway thermonuclear reactions triggered by gamma ray-driven antimatter production. The resulting blast was visible for months because it unleashed a cloud of radioactive material over fifty times the size of our own star, giving off a nuclear fission glow visible from galaxies away.

The super-supernova SN2007bi is an example of a "pair-instability" breakdown, and that's like calling an atomic bomb a "plutonium-pressing" device. At sizes of around four megayottagrams (that's thirty-two zeros) giant stars are supported against gravitational collapse by gamma ray pressure. The hotter the core, the higher the energy of these gamma rays -- but if they get too energetic, these gamma rays can begin pair production: creating an electron-positron matter-antimatter pair out of pure energy as they pass an atom. Yes, this does mean that the entire stellar core acts as a gigantic particle accelerator.

The antimatter annihilates with its opposite, as antimatter is wont to do, but the problem is that the speed of antimatter explosion -- which is pretty damn fast -- is still a critical delay in the gamma-pressure holding up the star. The outer layers sag in, compressing the core more, raising the temperature, making more energetic gamma rays even more likely to make antimatter, and suddenly the whole star is a runaway nuclear reactor beyond the scale of the imagination. The entire thermonuclear core detonates at once, an atomic warhead that's not just bigger than the Sun -- it's bigger than the Sun plus the mass of another ten close-by stars.

The entire star explodes. No neutron star, no black hole, nothing left behind but an expanding cloud of newly radioactive material and empty space where once was the most massive item you can actually have without ripping space. The explosion alone triggers alchemy on a suprasolar scale, converting stars' worth of matter into new radioactive elements.

And we saw this. This really happened. Someday, somewhere, another massive explosion will occur and no one will be left to tweet it.

Certain rare stars --real killers, type 11 stars -- are core-collapse hypernova that generate deadly gamma ray bursts (GRBs). These long burst objects release 1000 times the non-neutrino energy release of an ordinary "core-collapse" supernova. Concrete proof of the core-collapse GRB model came in 2003.

It was made possible in part to a fortuitously "nearby" burst whose location was distributed to astronomers by the Gamma-ray Burst Coordinates Network (GCN). On March 29, 2003, a burst went off close enough that the follow-up observations were decisive in solving the gamma-ray burst mystery. The optical spectrum of the afterglow was nearly identical to that of supernova SN1998bw. In addition, observations from x-ray satellites showed the same characteristic signature of "shocked" and "heated" oxygen that's also present in supernovae. Thus, astronomers were able to determine the "afterglow" light of a relatively close gamma-ray burst (located "just" 2 billion light years away) resembled a supernova.

It isn't known if every hypernova is associated with a GRB. However, astronomers estimate only about one out of 100,000 supernovae produce a hypernova. This works out to about one gamma-ray burst per day, which is in fact what is observed.

What is almost certain is that the core of the star involved in a given hypernova is massive enough to collapse into a black hole (rather than a neutron star). So every GRB detected is also the "birth cry" of a new black hole.

Scientists agree that new observations of T Pyxidis in the constellation Pyxis (the compass) using the International Ultraviolet Explorer satellite, indicate the white dwarf is part of a close binary system with a sun, and the pair are 3,260 light-years from Earth and much closer than the previous estimate of 6,000 light-years.

The white dwarf in the T Pyxidis system is a recurrent nova, which means it undergoes nova (thermonuclear) eruptions around every 20 years. The most recent known events were in 1967, 1944, 1920, 1902, and 1890. These explosions are nova rather than supernova events, and do not destroy the star, and have no effect on Earth. The astronomers do not know why the there has been a longer than usual interval since the last nova eruption.

Astronomers believe the nova explosions are the result of an increase of mass as the dwarf siphons off hydrogen-rich gases from its stellar companion. When the mass reaches a certain limit a nova is triggered. It is unknown whether there is a net gain or loss of mass during the siphoning/explosion cycle, but if the mass does build up the so-called Chandrasekhar Limit could be reached, and the dwarf would then become a Type 1a supernova. In this event the dwarf would collapse and detonate a massive explosion resulting in its total destruction. This type of supernova releases 10 million times the energy of a nova.

Observations of the white dwarf during the nova eruptions suggest its mass is increasing, and pictures from the Hubble telescope of shells of material expelled during the previous explosions support the view. Models estimate the white dwarf's mass could reach the Chandrasekhar Limit in around 10 million years or less.

According to the scientists the supernova would result in gamma radiation with an energy equivalent to 1,000 solar flares simultaneously -- enough to threaten Earth by production of nitrous oxides that would damage and perhaps destroy the ozone layer. The supernova would be as bright as all the other stars in the Milky Way put together. One of the astronomers, Dr. Edward Sion, from Villanova University in Pennsylvania, said the supernova could occur "soon" on the timescales familiar to astronomers and geologists, but this is a long time in the future, in human terms.

Astronomers think supernova explosions closer than 100 light years from Earth would be catastrophic, but the effects of events further away are unclear and would depend on how powerful the supernova is. The research team postulate it could be close enough and powerful enough to damage Earth, possibly severely, although other researchers, such as Professor Fillipenko of the Berkeley Astronomy Department, disagree with the calculations and believe the supernova, if it occurred, would be unlikely to damage the planet.

The new image below shows that the giant star's atmosphere extends out to five times the size of its visual surface. It reveals two hot spots within the outer atmosphere and a faint arc of cool gas even farther out beyond the radio surface of the star.

The hot spots are separated by roughly half the visual diameter of the star and have a temperature of about 4,000-5,000 Kelvin, much higher than the average temperature of the radio surface of the star and even higher than the visual surface. The arc of cool gas lies almost 7.4 billion km away from the star – about the same distance as the farthest Pluto gets from the Sun. It is estimated to have a mass almost two thirds that of the Earth and a temperature of about 150 Kelvin.

“It was not yet clear why the hot spots are so hot. One possibility is that shock waves, caused either by the star pulsating or by convection in its outer layers, are compressing and heating the gas. Another is that the outer atmosphere is patchy and we are seeing through to hotter regions within. The arc of cool gas is thought to be the result of a period of increased mass loss from the star at some point in the last century but its relationship to structures like the hot spots, which lie much closer in, within the star’s outer atmosphere, is unknown,” explained Dr Anita Richards of the University of Manchester, lead author of a paper published in the journal Monthly Notices of the Royal Astronomical Society (arXiv.org version).

The mechanism by which supergiant stars like Betelgeuse lose matter into space is not well understood despite its key role in the lifecycle of matter, enriching the interstellar material from which future stars and planets will form. Detailed high-resolution studies of the regions around massive stars like the ones presented here are essential to improving our understanding.

“Betelgeuse produces a wind equivalent to losing the mass of the Earth every three years, enriched with the chemicals that will go into the next generation of star and planet formation. The full detail of how these cool, evolved stars launch their winds is one of the remaining big questions in stellar astronomy,” Dr Richards said.

“This is the first direct image showing hot spots so far from the center of the star. We are continuing radio and microwave observations to help decide which mechanisms are most important in driving the stellar wind and producing these hot spots. This won’t just tell us how the elements that form the building blocks of life are being returned to space, it will also help determine how long it is before Betelgeuse explodes as a supernova.”

Future observations planned with e-MERLIN and other arrays, including ALMA and VLA, will test whether the hot spots vary in concert due to pulsation, or show more complex variability due to convection. If it is possible to measure a rotation speed this will identify in which layer of the star they originate.

Bibliographic information: A. M. S. Richards et al. e-MERLIN resolves Betelgeuse at λ 5 cm: hotspots at 5 R. MNRAS, published online April 23, 2013; doi: 10.1093/mnrasl/slt036

Image Credits: APOD/Xavier Haubois (Observatoire de Paris) et al.

Source: The Daily Galaxy via Nature and SpaceRef

Una nueva y extraña binaria nos permite poner a prueba la teoría de la gravedad de Einstein.

 

Una nueva y extraña binaria nos permite poner a prueba la teoría de la gravedad de Einstein

Los astrónomos han utilizado el telescopio VLT (Very Large Telescope) de ESO, junto con otros radiotelescopios de todo el mundo, para encontrar y estudiar una estrambótica pareja de estrellas formada por la estrella de neutrones más masiva encontrada hasta el momento, orbitada por una estrella enana blanca. Esta nueva y extraña binaria nos permite poner a prueba la teoría de la gravedad de Einstein — la relatividad general — de una forma imposible hasta el momento. Hasta ahora, las nuevas observaciones encajan exactamente con las predicciones de la relatividad general y son inconsistentes con algunas teorías alternativas. Los resultados aparecen en la revista Science del 26 de abril del 2013.

Un equipo internacional ha descubierto un exótico objeto doble formado por una pequeña, pero inusualmente pesada, estrella de neutrones que gira 25 veces por segundo sobre sí misma, orbitada por una estrella enana blanca que tarda dos horas y media en hacer una órbita completa. La estrella de neutrones es un púlsar que emite ondas de radio que pueden ser captadas desde la Tierra por los radiotelescopios. Al margen del interés que esta pareja genera por sí misma, se trata además de un laboratorio único para poner a prueba los límites de las teorías físicas.

Este pulsar se llama PSR J0348+0432 y se trata de los restos de una explosión de supernova. Es dos veces más pesada que el Sol, pero tiene solo 20 kilómetros de tamaño. La gravedad en su superficie es más de 300.000 millones de veces más fuerte que la de la Tierra y, en su centro, cada volumen equivalente a un azucarillo cuadrado pesa más de mil millones de toneladas concentradas. Su compañera, la estrella enana blanca, solo es un poco menos exótica: es el brillante resto de una estrella mucho más ligera que ha perdido su atmósfera y se está enfriando lentamente.

“Estaba observando el sistema con el Very Large Telescope de ESO, buscando cambios en la luz emitida por la enana blanca causados por su movimiento alrededor del púlsar”, afirma John Antoniadis, un estudiante de doctorado del Instituto Max Planck de radioastronomía (MPIfR) en Bonn, y autor principal del artículo. “Un rápido análisis inmediato me hizo ver que el púlsar era muy pesado. Es el doble de la masa del Sol, lo que la convierte en la estrella de neutrones más masiva conocida hasta el momento y, al mismo tiempo, en un excelente laboratorio de física fundamental”.

La teoría de la relatividad general de Einstein, que explica la gravedad como una consecuencia de la curvatura del espacio-tiempo creada por la presencia de masa y energía, ha superado todas las pruebas desde que fue publicada por primera vez hace casi cien años. Pero no puede ser la explicación definitiva y en última instancia acabará siendo sustituida.

Los físicos han concebido otras teorías de la gravedad que hacen predicciones diferentes a las que plantea la relatividad general. Para algunas de estas alternativas, esas diferencias solo se mostrarían en campos gravitatorios extremadamente fuertes que no pueden encontrarse en el Sistema Solar. En términos de gravedad, PSR J0348+0432 es un objeto verdaderamente extremo, incluso comparado con los otros púlsares que han sido utilizados en pruebas de alta precisión de la relatividad general de Einstein. En este tipo de campos gravitatorios tan fuertes, pequeños aumentos en la masa pueden desencadenar grandes cambios en el espacio-tiempo que rodea a estos objetos. Hasta ahora, los astrónomos no tenían ni idea de qué podría pasar en presencia de estrellas de neutrones tan masivas como PSR J0348+0432, por lo que se trata de una oportunidad única para llevar a cabo pruebas en campos inexplorados.

El equipo combinó observaciones de la estrella enana blanca llevadas a cabo con el Very Large Telescope con medidas muy precisas del púlsar obtenidas con radiotelescopios. Una pareja tan cercana entre sí emite ondas gravitacionales y pierde energía. Esto hace que el periodo orbital cambie ligeramente y las predicciones de este cambio hechas por la relatividad general y otras teorías competidoras son diferentes.

“Nuestras observaciones en radio eran tan precisas que ya hemos podido medir un cambio en el periodo orbital de 8 millonésimas de segundo por año, exactamente lo que predice la teoría de Einstein”, afirma Paulo Freire, otro miembro del equipo.

Esto es solo el principio de un estudio detallado de estos objetos únicos y los astrónomos los utilizarán para poner a prueba la teoría de la relatividad general en busca de una mayor precisión a medida que pase el tiempo.

Fuente: Noticias de Ciencia - ESO

Extreme Galaxy! Observed Forming Stars 100 Times Rate of Milky Way.

The tiny red spot in the image above is one of the most efficient star-making galaxies ever observed, converting gas into stars at the maximum possible rate. The galaxy is shown here in an image from NASA's Wide-field Infrared Survey Explorer (WISE), which first spotted the rare galaxy in infrared light. Visible-light observations from NASA's Hubble Space Telescope (inset) reveal that the starlight in this galaxy is extraordinarily compact, with most of the light emitted by a region just a fraction of the size of the Milky Way galaxy. Within that tiny region, stars are forming at a rate hundreds of times that of our galaxy.

The galaxy, called SDSSJ1506+54, jumped out at the researchers when they looked at it using data from WISE's all-sky infrared survey. Infrared light is pouring out of the galaxy, equivalent to more than a thousand billion times the energy of our sun.

"Galaxies burn gas like a car engine burns fuel. Most galaxies have fairly inefficient engines, meaning they form stars from their stellar fuel tanks far below the maximum theoretical rate," said Jim Geach of McGill University, lead author of a new study appearing in the Astrophysical Journal Letters. "This galaxy is like a highly tuned sports car, converting gas to stars at the most efficient rate thought to be possible," he said.

Hubble's visible-light observations revealed that the galaxy is extremely compact, with most of its light emanating from a region just a few hundred light-years across.

"This galaxy is forming stars at a rate hundreds of times faster than our Milky Way galaxy, but the sharp vision of Hubble revealed that the majority of the galaxy's starlight is being emitted by a region just a few percent of the diameter of the Milky Way. This is star formation at its most extreme," said Geach.

The team then used the IRAM Plateau de Bure Interferometer to measure the amount of gas in the galaxy. The ground-based telescope detected millimeter-wave light coming from carbon monoxide, an indicator of the presence of hydrogen gas, which is fuel for stars. Combining the rate of star formation derived with WISE, and the gas mass measured by IRAM, the scientists get a measure of the star formation efficiency.

The results reveal that the star-forming efficiency of the galaxy is close to the theoretical maximum, called the Eddington limit. In regions of galaxies where new stars are forming, parts of gas clouds are collapsing due to gravity. When the gas is dense enough to squeeze atoms together and ignite nuclear fusion, a star is born. At the same time, winds and radiation from stars that have just formed can prevent the formation of new stars by exerting pressure on the surrounding gas, curtailing the collapse.

The Eddington limit is the point at which the force of gravity pulling gas together is balanced by the outward pressure from the stars. Above the Eddington limit, the gas clouds would be blown apart, halting star formation.

"We see some gas outflowing from this galaxy at millions of miles per hour, and this gas may have been blown away by the powerful radiation from the newly formed stars," said Ryan Hickox, an astrophysicist at Dartmouth College, Hanover, N.H., and a co-author on the study.

Why is SDSSJ1506+54 so unusual? Astronomers say they're catching the galaxy in a short-lived phase of evolution, possibly triggered by the merging of two galaxies into one. The star-formation is so ferocious that in a few tens of millions of years, the blink of an eye in a galaxy's life, the gas will be used up, and the galaxy will mature into a massive elliptical galaxy.

The scientists also used data from the Sloan Digital Sky Survey, the W.M. Keck Observatory on Mauna Kea, Hawaii and the MMT Observatory on Mount Hopkins, Arizona.

Astronomers have combined these star-formation and size measurements from WISE and Hubble, with a measurement of the amount of gas -- fuel for star formation -- from the IRAM Plateau de Bure interferometer to confirm that SDSSJ1504+54 is forming stars at the maximum theoretical rate. This is a case of star formation at its most extreme.

To access the article: http://iopscience.iop.org/2041-8205/767/1/L17

Image Credit: NASA/JPL-Caltech/STScI/IRAM

Source: The Daily Galaxy

El antiquísimo origen de parte del agua de los anillos y satélites de Saturno.

Recreación artística de un primer plano de partículas de los anillos de Saturno. El planeta se ve en el fondo de la imagen, en tonos amarillo y marrón. Las partículas, en color azul, están compuestas principalmente de hielo, aunque no son uniformes. (Imagen: NASA JPL / Universidad de Colorado)

Los datos del espectrómetro VIMS de la sonda espacial Cassini han revelado que el hielo de agua en el sistema de Saturno es bastante más abundante de lo que cabría esperar si el agua sólo hubiera sido depositada allí por cometas tiempo después de la formación del sistema, o por otros medios relativamente recientes.

A raíz de esa discrepancia, los científicos que han realizado el análisis deducen que el hielo de agua debió formarse casi al mismo tiempo que nacía el sistema solar como tal. Eso encaja con el hecho de que Saturno gira alrededor del Sol en una órbita situada por fuera de la así llamada "línea de nieve". Por fuera de esta línea, en regiones del sistema solar como la franja orbital por la que se mueve Saturno, el ambiente es propicio para preservar el hielo, como en una cámara congeladora. Por dentro de la línea de nieve del sistema solar, el ambiente es mucho más cálido debido a la mayor cercanía del Sol, y debido a esto, el hielo y otras sustancias volátiles se disipan con mayor facilidad.

La época en la que esa masa de agua antigua pasó a formar parte del sistema de Saturno se remonta a más de 4.000 millones de años atrás. En aquellos tiempos, los cuerpos planetarios de nuestro vecindario cósmico empezaron a formarse a partir de la nebulosa protoplanetaria, la nube de material que todavía giraba alrededor del Sol después de que éste se encendiera como estrella.

El análisis ha sido realizado por el equipo de Gianrico Filacchione, miembro del equipo de la Cassini y científico en el Instituto Nacional Italiano de Astrofísica, en Roma.

Fuente: Noticias de la Ciencia y la Tecnoligía

Origin of Jupiter's Water Solved --The Massive 1994 Comet Bombardment.

ESA's Herschel space observatory has solved a long-standing mystery as to the origin of water in the upper atmosphere of Jupiter, finding conclusive evidence that it was delivered by the dramatic impact of comet Shoemaker-Levy 9 in July 1994. During the spectacular week-long collision, a string of 21 comet fragments pounded into the southern hemisphere of Jupiter, leaving dark scars in the planet's atmosphere that persisted for several weeks.

The remarkable event was the first direct observation of an extraterrestrial collision in the Solar System. It was followed worldwide by amateur and professional astronomers with many ground-based telescopes and the NASA/ESA Hubble Space Telescope.

ESA's Infrared Space Observatory was launched in 1995 and was the first to detect and study water in Jupiter's upper atmosphere. It was widely speculated that comet Shoemaker-Levy 9 may have been the origin of this water, but direct proof was missing.

Scientists were able to exclude an internal source, such as water rising from deeper within the planet's atmosphere, because it is not possible for water vapour to pass through the 'cold trap' that separates the stratosphere from the visible cloud deck in the troposphere below.

Thus the water in Jupiter's stratosphere must have been delivered from outside. But determining its origin had to wait more than 15 years, until Herschel used its sensitive infrared eyes to map the vertical and horizontal distribution of water's chemical signature.

Herschel's observations found that there was 2–3 times more water in the southern hemisphere of Jupiter than in the northern hemisphere, with most of it concentrated around the sites of the 1994 comet impact. Additionally, it is only found at high altitudes.

"Only Herschel was able to provide the sensitive spectral imaging needed to find the missing link between Jupiter's water and the 1994 impact of comet Shoemaker-Levy 9," says Thibault Cavalié of the Laboratoire d'Astrophysique de Bordeaux, lead author of the paper published in Astronomy and Astrophysics.

"According to our models, as much as 95% of the water in the stratosphere is due to the comet impact."

The image below shows an abundance of water in Jupiter's stratosphere. The north-south asymmetry is clearly observed. The green and red areas correspond to the highest abundances. (Credit: Astronomy & Astrophysics, Cavalié et al. 2013, A&A, 553, A21).

Another possible source of water would be a steady rain of small interplanetary dust particles onto Jupiter. But, in this case, the water should be uniformly distributed across the whole planet and should have filtered down to lower altitudes.

Also, one of Jupiter's icy moons could deliver water to the planet via a giant vapour torus, as Herschel has seen from Saturn's moon Enceladus, but this too has been ruled out. None of Jupiter's large moons is in the right place to deliver water to the locations observed.

Finally, the scientists were able to rule out any significant contributions from recent small impacts spotted by amateur astronomers in 2009 and 2010, along with local variations in the temperature of Jupiter's atmosphere.

"All four giant planets in the outer Solar System have water in their atmospheres, but there may be four different scenarios for how they got it," says Dr Cavalié. "For Jupiter, it is clear that Shoemaker-Levy 9 is by far the dominant source, even if other external sources may contribute also."

"Thanks to Herschel's observations, we have now linked a unique comet impact – one that was followed in real time and which captured the public's imagination – to Jupiter's water, finally solving a mystery that has been open for nearly two decades," adds Göran Pilbratt, ESA's Herschel project scientist.

The observations made in this study foreshadow those planned for ESA's future Jupiter Icy moons Explorer mission launching towards the Jovian system in 2022, where it will map the distribution of Jupiter's atmospheric ingredients in even greater detail.

For more information: "The spatial distribution of water in the stratosphere of Jupiter from Herschel-HIFI and –PACS observations," by T. Cavalié et al. is published in Astronomy & Astrophysics, 553, A21, May 2013. dx.doi.org/10.1051/0004-6361/201220797

Journal reference: Astronomy and Astrophysics Astronomy & Astrophysics 

Source: The Daily Galaxy via European Space Agency

La Luna y Vesta, blancos de impacto de una misma población de meteoritos.

La Luna, a la izquierda, y Vesta. (Fotos: Respectivamente, NASA JPL y NASA JPL, Caltech, UCLA, MPS, DLR, IDA)

Se ha descubierto que una parte considerable de los meteoritos que impactaron contra la Luna hace 4.000 millones de años, pertenecía a la misma población de proyectiles cósmicos de alta velocidad de la que formaron parte meteoritos que acabaron estrellándose contra el asteroide Vesta, y probablemente contra otros asteroides grandes.

La investigación, realizada por un equipo de especialistas del Instituto de Ciencia Lunar de la NASA (NLSI), en Moffett Field, California, revela un vínculo inesperado entre Vesta y la Luna, y proporciona nuevos medios para reconstruir la historia del gran bombardeo meteorítico de hace unos 4.000 millones de años en la zona interior del sistema solar.

Los resultados apoyan la teoría de que el cambio de posición de planetas gaseosos gigantes, como Júpiter y Saturno, desde sus órbitas originales a su ubicación actual, desestabilizó partes del cinturón de asteroides y provocó numerosas colisiones entre estos y contra otros astros, abarcando casi todo el sistema solar y causando en la Luna un cataclismo.

La investigación reduce el rango de fechas de inicio y la duración del cataclismo lunar, y demuestra que el mismo fenómeno, y hasta la misma población de proyectiles, afectaron severamente no sólo a los planetas más interiores del sistema solar, sino también al cinturón de asteroides.

Las rocas lunares traídas por los astronautas del programa Apolo han sido utilizadas muchas veces para estudiar la historia de aquel bombardeo meteorítico en el caso específico de la Luna. Ahora, las edades deducidas a partir del análisis de las muestras de meteoritos han permitido usar tales muestras para estudiar el mismo fenómeno pero para el caso específico de los principales miembros del cinturón de asteroides.

El equipo de Simone Marchi ha encontrado que la misma población de proyectiles cósmicos responsables de la formación de cráteres y cuencas de impacto en la Luna también golpeó, con velocidades muy altas, a Vesta.

Los análisis indican que la población de la que surgieron los proyectiles que golpearon a Vesta se caracterizaba, entre otras cosas, por seguir órbitas que también permitían a algunos objetos impactar contra la Luna a altas velocidades.

Fuente: Noticias de la Ciencia y la Tecnología

Supernova Powered Photons --The Long-Sought 'Mystery' Source of Cosmic Rays?

Supernovae are critical to life in the universe. They and their progenitor stars create most of the elements in the universe, and their explosive deaths disburse them into interstellar space where they can later be incorporated into new stars and planets. Supernovae are also active research topics because their bright emission enables them to be used as probes of the very distant universe. Not least, supernovae are astrophysical laboratories for the study of very high-velocity shocks and the physics of particles under extreme conditions.

Harvard-Smithsonian CfA astronomer John Raymond and seven colleagues, writing in the latest issue of Science magazine, investigate the links between supernova remnants and cosmic rays - the very rapidly moving nuclear particles that impact the earth from space. Cosmic rays can have energies millions of times larger than the most energetic particles produced in man-made particle accelerators, but astronomers are not sure where they come from or how they are accelerated to such fantastic energies. Supernovae have been a likely suspect for over fifty years because their powerful shocks were thought to be capable of accelerating subatomic particles to high energies.

In their new paper, the scientists used a new optical spectrometer to analyze in detail the shock activity at the outer edge of SN1006.They report finding gas motions of over five thousand kilometers per second and evidence for the presence of fast-moving protons (as well as for fast moving but much less massive electrons).

The team suggests that such protons may be the seed particles for cosmic rays once they are further accelerated by the shocks. The study with its new techniques offer powerful new evidence towards clarifying the role of supernova remnants in the production of the mystery cosmic rays.

Journal reference: Science

Source: The Daily Galaxy via Harvard-Smithsonian Center for Astrophysics