Astronomy & Science

Hubble encuentra pistas del nacimiento de los agujeros negros supermasivos

Ciencia Kanija -

Artículo publicado el 24 de mayo de 2016 en Hubble News

Los astrofísicos han dado un gran paso adelante en la comprensión de cómo se formaron los agujeros negros supermasivos. Usando datos procedentes de Hubble y de otros dos telescopios espaciales, investigadores italianos han encontrado la mejor prueba hasta el momento de las semillas que finalmente hacen crecer a estos gigantes cósmicos.

Durante años, los astrónomos han debatido sobre cómo se formó la primera generación de agujeros negros supermasivos tan rápidamente, relativamente hablando, tras el Big Bang. Ahora, un equipo italiano ha identificado dos objetos del joven Universo que parecen ser el origen de estos agujeros negros supermasivos primigenios. Los dos objetos representan los candidatos a semillas de agujeros negros más prometedores hallados hasta la fecha.

Impresión artística de una semilla de agujero negro supermasivo

Impresión artística de una semilla de agujero negro supermasivo Crédito: NASA/CXC/M. Weiss

El grupo usó modelos por computador y aplicaron un nuevo método de análisis a datos procedentes del Observatorio de Rayos-X Chandra de la NASA, el Telescopio Espacial Hubble de NASA/ESA, y el Telescopio Espacial Spitzer de NASA para encontrar e identificar los dos objetos. Los dos candidatos a semilla de agujero negro recientemente descubiertos parecen haberse creado menos de 1000 millones de años tras el Big Bang, y tienen una masa inicial de unas 100 000 veces la del Sol.

“Nuestro descubrimiento, de confirmarse, explicaría cómo nacen estos monstruosos agujeros negros”, comenta Fabio Pacucci, autor principal del estudio, de la Scuola Normale Superiore en Pisa, Italia.

Este nuevo resultado ayuda a explicar por qué vemos agujeros negros supermasivos en un periodo de menos de 1000 millones de años tras el Big Bang.

Existen dos teorías principales sobre la formación de los agujeros negros supermasivos en los inicios del universo. Una supone que las semillas a partir de las que crecen los agujeros negros tienen una masa de entre decenas a centenas de veces la del Sol, como se esperaría del colapso de una estrella masiva. La semilla del agujero negro crece entonces a partir de fusiones con otros pequeños agujeros negros, y atrayendo gas procedentes de sus alrededores. Sin embargo, tienen que crecer a una velocidad inusualmente alta para alcanzar la masa de lo agujeros negros supermasivos ya descubiertos en los primeros 1000 millones de años del universo.

Los nuevos hallazgos apoyan otro escenario donde, al menos algunas semillas de agujeros negros muy masivos con 100 000 veces la masa del Sol, se formaron directamente cuando colapsó una masiva nube de gas. En este caso, el crecimiento de los agujeros negros se inició y procedió con mayor rapidez.

“Existe una gran controversia sobre qué camino toman estos agujeros negros”, dice el coautor Andrea Ferrara también de la Scuola Normale Superiore. “Nuestro trabajo sugiere que estamos convergiendo hacia una respuesta, donde los agujeros negros empiezan con un gran tamaño y crecen a una velocidad normal, en lugar de empezar siendo pequeños y crecer muy rápidamente”.

Andrea Grazian, coautor del Instituto Nacional para Astrofísica de Italia explica: “Es extremadamente difícil encontrar y confirmar la detección de las semillas de agujeros negros. Sin embargo, creemos que nuestra investigación ha descubierto los dos mejores candidatos hasta la fecha”.

Incluso aunque ambas candidatas a semillas de agujeros negros encajan con las predicciones teóricas, se necesitan más observaciones para confirmar su auténtica naturaleza. Para distinguir completamente entre las dos teorías de formación también será necesario encontrar más candidatos.

El equipo planea llevar a cabo observaciones de seguimiento en el rango de los rayos-X y el infrarrojo para comprobar si los dos objetos tienen más de las propiedades esperadas para las semillas de agujeros negros. Futuros observatorios, como el Telescopio Espacial James Webb de NASA/ESA/CSA  y el European Extremely Large Telescope ciertamente marcarán un antes y un después en este campo, detectando agujeros negros más pequeños a mayores distancias.

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The Kavli Foundation Q&A: How Did Nature’s Heaviest Elements Form?

Sky&Telescope -

A unique galaxy loaded with hard-to-produce heavy elements sheds light on stellar histories and galactic evolution. The Kavli Foundation hosted a Q&A with three astronomers to probe this discovery.

Neutron stars colliding

An artist's impression of two neutron stars colliding.
Dana Berry / Skyworks Digital, Inc.

Researchers have solved a 60-year-old mystery regarding the origin of the heaviest elements in nature, conveyed in the faint starlight from a distant dwarf galaxy.

Most of the chemical elements, composing everything from planets to paramecia, are forged by the nuclear furnaces in stars like the Sun. But the cosmic wellspring for a certain set of heavy, often valuable elements like gold, silver, lead and uranium, has long evaded scientists.

Astronomers studying a galaxy called Reticulum II have just discovered that its stars contain whopping amounts of these metals — collectively known as "r-process" elements. (See "What is the R-Process?") Of the 10 dwarf galaxies that have been similarly studied so far, only Reticulum II bears such strong chemical signatures. The finding suggests some unusual event took place billions of years ago that created ample amounts of heavy elements and then strew them throughout the galaxy's reservoir of gas and dust. This r-process-enriched material then went on to form Reticulum II's standout stars.

Based on a new study, from a team of researchers at the Kavli Institute at the Massachusetts Institute of Technology, the unusual event in Reticulum II was likely the collision of two, ultra-dense objects called neutron stars. Scientists have hypothesized for decades that these collisions could serve as a primary source for r-process elements, yet the idea had lacked solid observational evidence. Now armed with this information, scientists can further hope to retrace the histories of galaxies based on the contents of their stars, in effect conducting "stellar archeology."

Courtesy of The Kavli Foundation, Sky & Telescope is featuring an in-depth Q&A with three astrophysicists on how this discovery can unlock clues to galactic evolution. The participants were:

  • Alexander Ji – is a graduate student in physics at the Massachusetts Institute of Technology (MIT) and a member of the MIT Kavli Institute for Astrophysics and Space Research (MKI). He is lead author of a paper in Nature describing this discovery.
  • Anna Frebel – is the Silverman Family Career Development Assistant Professor in the Department of Physics at MIT and also a member of MKI. Frebel is Ji's advisor and coauthored the Nature paper. Her work delves into the chemical and physical conditions of the early universe as conveyed by the oldest stars.
  • Enrico Ramirez-Ruiz – is a Professor of Astronomy and Astrophysics at the University of California, Santa Cruz. His research explores violent events in the universe, including the mergers of neutron stars and their role in generating r-process elements.

The following is an edited transcript of The Kavli Foundation's roundtable discussion with these three astronomers. The participants have been provided the opportunity to amend or edit their remarks.

THE KAVLI FOUNDATION: What was your reaction to discovering an abundance of heavy elements in the stars in the galaxy called Reticulum II?

ALEX JI: I had spent some time looking at stars in other galaxies like this, and in every one of those, the content of this type of element – which we call r-process elements – was very low. So we went into this whole project thinking we would get very low detections as well with this galaxy. When we read off the r-process content of that first star in our telescope, it just looked wrong, like it could not have come out of this galaxy! I spent a long time making sure the telescope was pointed at the right star. Then I called Anna — actually, I had to wake her up, it was 3 a.m. — and we started doing instrument checks to make sure we were looking at the right thing. It turns out we were.

ANNA FREBEL: It was quite funny, because usually when I get a call in the middle of the night from someone at the telescope, it means something really bad has happened! [Laughter] In this case, we were all super-excited because Alex had found something in the data that was really unexpected and also was a smoking gun. We pretty quickly confirmed that at least that first star he was looking at really had all these heavy elements in rather large quantities.

Then another star showed the same kind of signature. I was like, "Oh my god—we've hit the lottery . . . twice!" We would have been happy walking away with just one awesome star, and then it turned into two, then into three, and four, five and so forth. The universe had thrown us a really big bone!

ENRICO RAMIREZ-RUIZ: I've been working on neutron star mergers for a while, so I was extremely excited to see Alex and Anna's results. Their study is indeed a smoking gun that exotic neutron star mergers were occurring very early in the history of this particular dwarf galaxy, and for that matter likely in many other small galaxies. Neutron star mergers are therefore probably responsible for the bulk of the precious substances we call r-process elements throughout the universe.

Supernova forging heavy elements

An artist's conception of a supernova forging heavy elements.
Supernova illustration: Akihiro Ikeshita; Particle CG: Naotsugu Mikami (NAOJ)

What Is the R-Process?

The r-process stands for "rapid neutron-capture process." This phenomenon, first theoretically described by nuclear physicists in 1957, creates elements in nature that are heavier than iron. In the supernova explosions of massive stars and in neutron star collisions, tremendous numbers of freely moving neutrons bind with iron atoms. As more and more neutrons pile up in the atom's nucleus, the neutrons undergo a radioactive decay, turning into protons. Accordingly, new, heavier elements are formed, because elements are differentiated by the number of protons in their nucleus. As its name implies, this process must occur rapidly in order to build up to very heavy, neutron-rich nuclei that then decay into heavy elements, such as uranium, which has 92 protons compared to iron's 26. While a theoretical understanding of the r-process is sound, scientists have debated over the astrophysical conditions and sites where the process can actually occur.

TKF: Why has the provenance of these elements been such a tough nut to crack?

FREBEL: The question of the cosmic origin of all of the elements has been a longstanding problem. The precursor question was, “Why do stars shine?” Scientists tackled that in the early part of the last century and solved the mystery only around 1950. We found out that stars do nuclear fusion in their cores, generating heat and light, and as part of that process, heavier elements are created. That led to a phase where a lot of people worked on figuring out how all the elements are made.

Understanding how heavy, r-process elements, are formed is one of hardest problems in nuclear physics. The production of these really heavy elements takes so much energy that it's nearly impossible to make them experimentally, even with current particle accelerators and apparatuses. The process for making them just doesn't work on Earth. So we have had to use the stars and the objects in the cosmos as our lab.

JI: As Anna just mentioned, we have been mostly stuck with astronomy, trying to measure what could have made all of these elements out in the stars. But it's also very difficult to find stars that give you any information about the r-process.

RAMIREZ-RUIZ: Right, it is very difficult to see these elements shine when they're created in the universe because they are very rare. For example, gold is only one part in a billion in the Sun. So even though the necessary physical conditions needed to make these elements were clear to physicists more than 50 years ago, it was a mystery as to what sort of objects and astrophysics would provide these conditions, because we couldn't see r-process elements being produced in explosion remnants in our own galaxy.

Two competing theories did emerge, which are that these elements are produced by supernovae and neutron star mergers. These phenomena are very different in terms of how often they should happen and in the amount of these elements they should theoretically produce. Just to give you an example, the explosion of a star with more than eight times the mass of the Sun is thought to produce about a Moon's mass-worth of gold. A neutron star merger, however, is thought to produce a Jupiter's mass-worth of gold. That's over 25,000 times more! So just one neutron star merger can provide the gold we would expect to find in about six million to 10 million stars.

Alex and Anna's observations are so unbelievably useful because they really show that the phenomenon which created these elements is something rare, but that produces a lot of these elements, as a neutron star merger should.

FREBEL: It took 60-something years of work to figure this out, and a variety of astronomers — observers as well as theorists — have all put in their share. That's exactly what we and Enrico are continuing to do.

TKF: Enrico, you study the ionized gas called plasma that composes stars. How is the material in neutron stars different than the plasma in run-of-the-mill stars like the Sun, and how does this provide the raw ingredients for making r-process elements?

RAMIREZ-RUIZ: Neutron stars are only about the size of San Francisco Bay, which I live close by, yet they pack in as much mass as the Sun — about 330,000 times the mass of the Earth. Neutron stars are the densest objects in the universe. A neutron star the size of a Starbucks cup would weigh as much as Mount Everest! We call them neutron stars because they are neutron-rich, and that's a key aspect for making r-process elements, as I'll let Alex and Anna explain.

JI: So the nuclear fusion in stars can only make the elements up to iron. That's because iron is the most stable nucleus. If you try to fuse two things to make elements heavier than iron, it actually takes more energy than the fusion reaction itself releases. A neutron that gets close enough to this dense iron nucleus can join it thanks to one of the fundamental forces of nature, the strong force, which binds protons and neutrons together.

You can keep increasing the size of this nucleus by adding more neutrons, but there’s a trade-off. That nucleus will undergo a radioactive decay called a beta decay. Specifically, one of those added neutrons will spontaneously release some energy and turn into a proton. The r-process is what happens when you capture neutrons faster than the beta decays happen, and in that way you can build up to heavier nuclei.

FREBEL: This process can only happen when you have lots and lots of free neutrons outside of an atomic nucleus, and that's actually a difficult thing to do, because neutrons only survive for about 15 minutes before they decay into a proton. In other words, almost as soon as you have free neutrons, they just disappear. So it's really hard to find places where there are even free neutrons to undergo this neutron capture. As far back as the 1930s, neutron stars had been postulated as something that could exist, and it wasn't until the late 1960s that we knew they were real.

RAMIREZ-RUIZ: As we learned more about neutron stars, we found out that about two percent of them have companion stars, and a very small fraction have another neutron star orbiting around them. If the neutron stars are close enough, they will merge within several billion years or less because they produce gravitational waves as they spin around each other. These waves simply carry off energy and angular momentum, so the stars get closer and closer, and eventually they touch each other.

"Neutron stars are the densest objects in the universe. A neutron star the size of a Starbucks cup would weigh as much as Mount Everest!"  — Enrico Ramirez-Ruiz

TKF: What happens to these heavy elements once two neutron stars collide? 

RAMIREZ-RUIZ: As these neutron stars come together, the stars eject some material in their tidal tails into space at very close to the speed of light. So the atoms of these elements are moving very fast when they are first formed. By the time the ambient gas and dust in the galaxy is able to slow these elements down, they have probably mixed with about a thousand Sun-masses worth of material, enriching it atom-by-atom.

FREBEL: Everything gets nicely mixed, like dough. And from that mixed material, the next generation of stars then forms. This stellar generation contains many, little, low-mass stars that have very long life times. It's these low-mass, long-lived stars that we observed today in Reticulum II for this study.

TKF: Anna, you published a book last year called "Searching for the Oldest Stars: Ancient Relics from the Early Universe." How do these results demonstrate what you call “stellar archeology?”

FREBEL: Finding these elements at Reticulum II thoroughly illustrates the concept of stellar archaeology. The idea is that we can use the composition of individual stars to trace the processes that created the elements in the early universe. Because the elements that we observe in our stars today were made prior to the stars' birth — the stars inherited these heavy elements like "cosmic genes" — we have this incredible opportunity to look back in time to study the early chemical and physical processes that ushered in stars and galaxy formation soon after the Big Bang.

Reticulum II is actually a perfect example of what we now call dwarf galaxy archaeology. It's pretty much the same thing I just described, but now we are able to add other dimensions by not just using individual stars, but the entire dwarf galaxy and all the information that comes with it. We can use galactic environmental conditions and the star formation history to trace what happened very early on in that galaxy that provided the various elements we see today.

It's very nice that despite all the progress we have made in this field, there is more to come. I really think these findings have opened a new door for studying galaxy formation with individual stars and to some extent individual elements. We are seriously connecting the really small scales of stars with the really big scales of galaxies. I'm very excited to see what else we find. I don’t think we'll find another galaxy like Reticulum II anytime soon, but hey, we're going to keep looking!

JI: The way I like to think about this is, imagine if you were an actual archaeologist and you wandered around on the surface of the Earth picking up artifacts whenever you found them. You'd find a collection of random artifacts from different periods and places, and you wouldn't be sure how to associate them. In contrast, looking at galaxies like Reticulum II is like digging into a coherent, subterranean layer and finding a collection of artifacts that are all telling the same story . . .

FREBEL: Like Pompeii!

JI: Yeah, like Pompeii!

TKF: Ah yes, the Roman town, and its residents, who were completely buried under volcanic ash. That was not a very nice outcome . . .

FREBEL: Not for the people, no.

RAMIREZ-RUIZ: But the archeological evidence did remain pristine . . .

"One of the things that I think attracts people to astronomy is understanding the origin of everything around us." — Alex Ji

TKF: Bad for Pompeians, but good for archeologists. Shifting gears here, what tools do you need to dig even deeper, if you will, into how elements like gold and silver originate, and otherwise find more cosmic archeological clues?

Reticulum II galaxy

A Dark Energy Survey image of Reticulum II. The nine stars, described in a recent study, are circled in red, seven of which have high r-process element abundances.
Alex Ji; Background image: Fermilab / Dark Energy Survey)

JI: There are two types of things that we need. First, we have to find dwarf galaxies and that requires very large sky surveys like the Dark Energy Survey—which discovered Reticulum II—as well as surveys conducted by the Large Synoptic Survey Telescope, which will start operations in the 2020s. The second thing is we have to look at the stars in those galaxies. The problem with galaxies is that they are far away, so we need pretty large telescopes to do that.

FREBEL: The stars that Alex has been observing are actually really, really faint. We had to work very hard to squeeze out whatever information we could about them. It was only because these stars had such a strong signal of r-process elements that we could see those signals in their light, very little of which we're actually able to capture with current telescopes.

So that really shows why we need larger telescopes. Multiple telescope projects are underway and are scheduled to open in the 2020s. They will have mirrors more than twice as big as today's best ground-based telescopes. These include the Giant Magellan Telescope, the Thirty Meter Telescope and the European Extremely Large Telescope. They promise more light per unit of time hour, which means we can observe fainter stars, but we can also go back to brighter stars and get insanely high quality data. That is what we need for these r-process stars because there is so much information in their light. I think the next five to 10 years will be very exciting in this regard.

RAMIREZ-RUIZ: I want to make a plug for the Laser Interferometer Gravitational-Wave Observatory, or LIGO. The ultimate dream of mine would be to detect the gravitational wave signal of a neutron-neutron star merger. When we have multiple gravitational wave observatories in operation, such as when LIGO India is built next decade, we will be able to pinpoint the location of these rare events. We can then use our conventional, light-based telescopes to look at the transient light signals from the merged neutron star, which we actually think will be powered by the decay of these precious elements. That would be the ultimate direct evidence that these mergers are indeed producing all of these elements.

FREBEL: Pinpointing the location of neutron star mergers might become possible for events in the nearby universe. But I don't think we'll go back far enough in space, and therefore time, to see a merger like in Reticulum II that went off billions of years ago. I agree with Enrico, though, it would be really great to have a nearby example that shows us, right in front of our eyes, how this really all works.

RAMIREZ-RUIZ: Anna's absolutely right. We won't see the r-process enrichment events that took place at the time when a galaxy like Reticulum II was being formed, but hopefully we'll see the newly synthesized gold closer to home! [Laughter]

"We are seriously connecting the really small scales of stars with the really big scales of galaxies." — Anna Frebel

TKF: Let's take a moment to consider that most of the gold, silver and platinum in our valuable jewelry, as well as the uranium in our nuclear reactors, was created when mind- bogglingly dense neutron stars crushed into each other at incredible speeds. As you're doing your research, does this sort of notion ever stop you in your tracks?

JI: It does stop you in your tracks, right? Definitely one of the things that I think attracts people to astronomy is understanding the origin of everything around us. The other part of it for me is these neutron stars mergers are happening on really small scales, but these events are explosive enough to affect a whole galaxy! Imagining that event, then zooming out to the whole galactic scale, then zooming back down to us on Earth—I think it's pretty cool to be able to follow the consequences of the production of these elements from beginning to end.

RAMIREZ-RUIZ: Something to think about is that all the gold originally here on Earth sank into the planet's center because the early Earth was molten. So all the gold we have today on or near the surface is from asteroid impacts!

FREBEL: As we've been saying, the gold wasn't made in the asteroids, it was probably made in a neutron star merger. It then mixed into the cloud of gas and dust in which all the asteroids and planets formed. That gold was then transported to us on Earth as a special delivery. [Laughter]

RAMIREZ-RUIZ: We have some gold atoms in our bodies, too. If we were to "talk" to one of these atoms, it would tell us a story how it was formed in billions of degrees, how it flew through space. Because just one of these neutron star mergers produced so much gold, probably all of the gold atoms that are in the four of us in this roundtable discussion came from the same event. So we're not only linked by genetics, but by these exotic phenomena that happen in the universe.

The post The Kavli Foundation Q&A: How Did Nature’s Heaviest Elements Form? appeared first on Sky & Telescope.

4 Things to Know About the 2017 Solar Eclipse

Sky&Telescope -

What is a total solar eclipse?

A total solar eclipse occurs when the Moon covers the face of the Sun as seen from Earth. The complete coverage allows us to see the day as if it were night, and it reveals the solar corona's ghostly whisps. The next total solar eclipse will occur on August 21, 2016, and the eclipse path will cross the continental United States.

Start planning now for the 2017 total solar eclipse: enter your email to download your FREE guide to watching the eclipse from locations across the continental U.S. You'll also be subscribed to Sky & Telescope's free e-newsletter that will keep you up to date with the latest astronomy and observing news.

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North American viewers off the eclipse path will still see a partial solar eclipse.

Read more about viewing the Sun safely.

When is the next solar eclipse going to happen?

The eclipse beings on August 21, 2017, at 16:48:33 Universal Time (UT), when the shadow touches down on the Pacific Ocean and the Moon takes its first small bite out of the Sun. Totality begins at 18:24:11.9 UT.

To find the precise start and end times calculated for your location, as well as eclipse maps and other tables, visit NASA's Eclipse website.

Where's the best place to watch the eclipse?

The best location to watch the total eclipse will along the eclipse path that crosses the United States from Oregon to South Carolina. This total eclipse is on the shorter side, with a maximum duration of 2 minutes and 40.1 seconds. Canada, Mexico, and continental America off the path of totality will see a partial solar eclipse.

When's the next solar eclipse?

The next total solar eclipse will occur on June 2, 2019, when the eclipse path will fall largely over the Pacific Ocean. Some viewers on land in Chile and Argentina will spot totality at sunset. Find more information at NASA's eclipse site.

 

The post 4 Things to Know About the 2017 Solar Eclipse appeared first on Sky & Telescope.

¿Superllamaradas solares desencadenaron la vida en la Tierra?

Ciencia Kanija -

Artículo publicado por Tushna Commisariat el 24 de mayo de 2016 en physicsworld.com

Un agitado y joven Sol pudo haber proporcionado a la Tierra los ingredientes, y el clima, necesarios para dar inicio a la vida. Esto es lo que afirman científicos de la NASA, que dicen que potentes erupciones solares pudieron haber calentado la Tierra en una época en la que el Sol era relativamente frío. También dicen que el suministro de nitrógeno que dio lugar a la vida en la Tierra fue sintetizado a partir de partículas energéticas procedentes del Sol.

Tener una clara idea de las condiciones necesarias para que surja la vida en la Tierra es un objetivo científico clave – tanto para rastrear nuestros orígenes como para evaluar mejor cuál de los muchos miles de exoplanetas conocidos puede albergar vida. Un escollo concreto en el desarrollo de una clara descripción de la evolución temprana en la Tierra era que, hace 4000 millones de años, cuando se estaban desarrollando las condiciones adecuadas para la vida, el joven Sol no eran lo bastante luminoso como para calentar nuestro planeta. A pesar de su agitación, el Sol era un 30% más tenue de lo que es actualmente.

Llamarada solar

Llamarada solar

Frío y agitado

“Por entonces, la Tierra recibía apenas un 70% de la energía que recibe en la actualidad procedente del Sol”, señala el científico solar Vladimir Airapetian del Centro de Vuelo Espacial Goddard de la NASA en Maryland. “Esto significa que la Tierra debería haber sido una bola de hielo. En lugar de esto, las pruebas geológicas dicen que era un orbe cálido con agua líquida. A esto lo llamamos la paradoja del joven Sol”.

Otro problema es el hecho de que un componente clave para los bloques básicos de la vida es el nitrógeno (N) – pero en esa época sólo estaba presente en la atmósfera el nitrógeno molecular no reactivo (N2). Habría sido necesario un proceso muy energético para romper las moléculas de nitrógeno molecular en nitrógeno atómico, permitiendo que se recombinase en formas más adecuadas para la biología. En la última investigación, Airapetian y sus colegas demuestran que las partículas cargadas procedentes de las tormentas solares podrían haber descompuesto el nitrógeno y proporcionado el calor requerido para la vida.

Para obtener pistas de cómo se habría comportado el joven Sol, los científicos estudiaron estrellas similares en nuestra galaxia en distintas etapas de su ciclo vital. Aparte de conformar que el joven Sol habría sido relativamente tenue, los estudios también demuestran que las estrellas jóvenes producen frecuentes y potentes llamaradas. Enormes estallidos de luz y otras radiaciones que son similares a las llamaradas que vemos en el Sol actualmente. Tales llamaradas a menudo vienen acompañadas de enormes nubes de material solar, conocidas como eyecciones de masa coronal (CMEs), que se lanzan al espacio.

Lluvias de superllamaradas

La misión Kepler de la NASA ha encontrado jóvenes estrellas similares al Sol, y se ha observado en muchas de ellas la producción de “superllamaradas” – enormes explosiones que son tan raras en la actualidad que experimentamos una cada 100 años, aproximadamente. Pero los datos de Kepler demuestran que estas jóvenes estrellas producen casi 10 superllamaradas al día. Basándose en estas observaciones, Airapetian y sus colegas dicen que las nubes de partículas cargadas eyectadas debido a un estallido en el joven Sol disparó los cambios en la química de la atmósfera de la Tierra.

El equipo simuló cómo las superllamaradas interactuarían con nuestro planeta, y encontraron que habrían distorsionado el campo magnético de la Tierra – que también era más débil en esa época – creando grandes huecos alrededor de los polos. Estos huecos proporcionaron puertas para que las energéticas partículas solares penetrasen en la atmósfera. “Nuestros cálculos demuestran que se verían regularmente auroras hasta Carolina del Sur”, comenta Airapetian.

Calentándose

Las partículas cargadas viajarían a través de las líneas de campo magnético y colisionarían con el nitrógeno molecular, así como con el dióxido de carbono, que se dividiría en monóxido de carbono y oxígeno. Los átomos libres de nitrógeno y oxígeno se combinarían entonces para formar óxido nitroso (N2O) – un potente gas invernadero – y ácido cianhídrico (HCN). Es más, el óxido nitroso es 300 veces más potente calentando la atmósfera que el dióxido de carbono. Según demostraron los cálculos del equipo, incluso si sólo un 1% del dióxido de carbono en la atmósfera se convirtiese en N2O, sería suficiente para calentar la superficie de la Tierra a una temperatura que podría albergar agua líquida, así como los inicios de la vida. “Si cambias la química de la atmósfera resulta que todo cambia para la vida en la Tierra”, señala Airapetian.

Los investigadores también creen que el HCN podría haber proporcionado una fuente de nitrógeno para las moléculas biológicas, tales como los aminoácidos. De hecho, la dosis diaria de partículas solares puede también haber proporcionado la enorme cantidad de energía necesaria para crear las moléculas complejas. tales como el ARN y el ADN, que finalmente sembraron la vida.

Al mismo tiempo, la constante radiación y lluvias solares podrían haber sido perjudiciales. El ataque magnético podría incluso arrancar la atmósfera del planeta si la magnetosfera es demasiado débil. Determinar dónde está el equilibrio nos ayudará a determinar qué sistemas extrasolares podrían, potencialmente, albergar vida. “Queremos recopilar toda esta información – lo cerca que está un planeta de su estrella, cuán energética es, lo fuerte que es la magnetosfera de un planeta – para ayudar a la búsqueda de planetas habitables alrededor de estrellas cercanas a la nuestra y en toda la galaxia”, comenta el miembro del equipo William Danchi. Trabajando con otros compañeros en campos relacionados, los investigadores esperamos llegar a una “robusta descripción de cómo podrían haber sido los primeros días de nuestro planeta – y dónde podría existir la vida en otros lugares”.

El trabajo se publica en la revista Nature Geoscience.

Artículos Relacionados

This Week’s Sky at a Glance, May 27 – June 4

Sky&Telescope -

Mars, Saturn, Antares at dusk, late May - early June 2016

All week Mars, Saturn, and Antares draw the eye southeast at nightfall. . .

Jupiter under Leo, late May - early June, 2016

. . .while Jupiter, similarly bright, shines under Leo in the southwest.

Friday, May 27

• Have you been watching the triangle of Mars, Antares, and Saturn changing shape? Look southeast after dusk. The triangle is lengthening as bright Mars pulls westward away from the other two. This will continue until the end of June. Then Mars will start to slingshot back to fly right between Antares and Saturn in late August. Plan to watch this slow summer drama!

• Jupiter's Great Red Spot transits Jupiter's central meridian tonight around 2:02 a.m. Eastern Daylight Time; 11:02 p.m. Pacific Daylight Time. It's positioned in good view for about an hour before and after transiting.

Saturday, May 28

• Constellations seem to twist around fast as they pass the zenith, if you're comparing them to the direction "down." Just a week ago the Big Dipper floated horizontally in late twilight an hour after sunset (as seen from near 40° N latitude). Now the Dipper is strongly tilted an hour after sunset, bowl down. Another two weeks, and an hour after sunset it will hang straight down by its handle.

• Jupiter's Great Red Spot transits Jupiter's central meridian around 9:54 p.m. EDT.

Sunday, May 29

• Last-quarter Moon (exact at 8:12 a.m. EDT). Tonight the Moon doesn't rise until around 2 a.m., positioned between the dim spilling bucket of Aquarius and the equally dim Circlet of Pisces.

• With the Moon gone from the evening sky, hunt out the little-known galaxy bunches at the legs of Virgo using Sue French's Deep-Sky Wonders article, charts, and photos in the June Sky & Telescope, page 54.

Monday, May 30

• Mars is closest to Earth tonight (0.503 a.u.) and appears 18.6 arcseconds in diameter. For all practical purposes it remains this close for at least another week. You can watch a live telescopic feed from Slooh tonight from 9 to 10 p.m. EDT (1:00 to 2:00 May 31st UT).

• Just off Jupiter's eastern limb, Ganymede disappears into eclipse by Jupiter's shadow around 9:48 p.m. EDT, then re-emerges somewhat farther east of the planet around 12:59 a.m. EDT. During this interval, Jupiter's Great Red Spot transits the central meridian around 11:33 p.m. EDT, and Io reappears out of eclipse off the eastern limb at 12:27 a.m. EDT.

Tuesday, May 31

• As darkness arrives these evenings, look south about halfway between Jupiter and Mars. One star there stands out: Spica, in Virgo. High above it shines brighter Arcturus in Bootes. Half that far to Spica's lower right is the constellation Corvus, the Crow, eyeing Spica to steal it from Virgo's hand as she looks the other way.

Wednesday, June 1

• Is your sky dark enough for you to see the Coma Berenices star cluster naked-eye? As soon as twilight is completely over, look above Jupiter by about 25° (about two and a half fists at arm's length). The cluster is at least 5° wide, the size of a golf ball at arm's length. Its brightest stars, near its middle, form a sort of inverted Y shape. Binoculars bring it right out, though the loose, sparse cluster almost fills the view.

Thursday, June 2

• Now it's Saturn's turn at opposition. It's the second-brightest point in the southeast after dark, 16° to Mars's lower left.

Cassiopeia at its lowest

Cassiopeia inches along sideways low due north at dusk.

Friday, June 3

• In springtime at mid-northern latitudes, the Milky Way lies right down out of sight all around the horizon. But watch the east now. The rich Cepheus-Cygnus-Aquila Milky Way starts rising up all across the east late these nights; less late every week.

Saturday, June 4

• "Cassiopeia" usually means "Cold!" Late fall and winter are when this landmark constellation stands high overhead (seen from mid-northern latitudes). But even on hot June evenings, it still lurks low. After dark, look for it down near the north horizon: a wide, upright W, as shown here. The farther north you are the higher it'll appear, but even as far south as San Diego and Atlanta it's completely above the horizon.

• New Moon (exact at 11:00 p.m. EDT). A new lunar month begins.

_________________________

Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.

Pocket Sky Atlas, jumbo edition

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae. Shown above is the new Jumbo Edition for easier reading in the night. Click image for larger view.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or new Jumbo Edition), which shows stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5, nearly three times as many. The next up, once you know your way around, is the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger Night Sky Observer's Guide by Kepple and Sanner.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."

This Week's Planet Roundup Mars on April 19, 2016

Mars was 14.4 arcseconds wide on April 19th when Phil Miles of Queensland, Australia, took this image with a 20-inch reflector. South is up. Dark Sinus Sabaeus and Sinus Meridiani extend in from the left (preceding). The pointy peninsula a bit farther right is the Oxia Palus region. Lower right from there are big Niliacus Lacus and Mare Acidalium. The North Polar Cap has almost shrunken away in the northern-hemisphere summer. Clouds appear in the wintry far south and especially around the morning limb.

Jupiter on May 15, 2016

Jupiter as imaged by Christopher Go on May 15th with a 14-inch scope. South is up. The Great Red Spot remains vivid. Dark material lines the Red Spot Hollow like eye shadow.

Saturn on March 19, 2016. Damian Peach photo.

Saturn's rings are wide open this season, tipped 26° to our line of sight and extending above the planet's north and south poles. Damian Peach took this image with a 14-inch Schmidt-Cass on March 19th. South is up.

Mercury is hidden deep in the glow of sunrise.

Venus is lost behind the Sun.

Mars is closest to Earth in a decade all this week and next (exactly closest on May 30th). It's the bright yellow-orange thing (magnitude –2.0) shining low in the southeast during evening, near at the head of Scorpius. Mars was at opposition on May 22nd; it's getting a little higher each night. After dark, Mars burns just about as brightly as white Jupiter does in the southwest.

Look lower left of Mars at nightfall, by about 12°, for Saturn and (lower) orange Antares. The Mars-Saturn-Antares triangle stands highest in the south around midnight or 1 a.m. daylight-saving time, when the planets are likely to be sharpest in a telescope.

Mars appears 18.4 to 18.6 arcseconds in diameter this week and next, the biggest and best we'll see it until the summer of 2018. See our telescopic guide to Mars, with map, in the April Sky & Telescope, page 48, or the version online. And set our Mars Profiler for your time and date. If you're ambitious and have a big scope, now's the time to hunt Phobos and Deimos, the two tiny Martian moons, using the June Sky & Telescope, page 48.

Jupiter (magnitude –2.1, in southern Leo) stands high in the southwest during twilight and moves lower as the evening progresses. See our telescopic guide to Jupiter in the March Sky & Telescope, page 48.

Saturn (magnitude +0.1, in southern Ophiuchus) comes to opposition on the night of June 2nd. It shines lower left of Mars in the evening. Look to Saturn's lower right for Antares. See our telescopic guide to Saturn in the June Sky & Telescope, page 48.

Uranus is still veiled by the glow of dawn.

Neptune (magnitude 7.9, in Aquarius) is fairly well up in the southeast just before dawn begins.

__________________________

All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 hours.

__________________________

“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”

— Neil deGrasse Tyson

The post This Week’s Sky at a Glance, May 27 – June 4 appeared first on Sky & Telescope.

Galaxy Cluster Spotted in Early Universe

Sky&Telescope -

The newly discovered protocluster of galaxies located in the Bootes field of the NOAO Deep Wide-field Survey.  The green circles identify the confirmed cluster members. Density contours (white lines) emphasize the concentration of member galaxies toward the center of the image. The inset images highlight two example members that glow in the Ly-alpha line of atomic hydrogen.   Dr. Rui Xue, Purdue University

The newly discovered protocluster of galaxies located in the Bootes field of the NOAO Deep Wide-field Survey.
The green circles identify the confirmed cluster members. Density contours (white lines) emphasize the concentration of member galaxies toward the center of the image. The inset images highlight two example members that glow in the Ly-alpha line of atomic hydrogen.
Dr. Rui Xue (Purdue University)

Astronomers discover a vast collection of young galaxies from the early universe. 

Astronomers have discovered a collection of young galaxies, stretching more than 489 million by 244 million light-years whose light has taken 12 billion years to reach Earth, one of the most massive structures known at that distance. This “protocluster,” a precursor to giant galaxy clusters near us such as the Coma Cluster, exists in a universe only 1.7 billion years old.

Modern-day galaxy clusters may contain thousands of galaxies drawn together by gravity. But while nearby clusters can be studied in detail, their early history and formation is not well understood. With the discovery of 65 galaxies in this faraway protocluster, scientists can witness its formation directly.

Measurements put this baby cluster at a mass of a thousand trillion Suns — already gigantic. “The protocluster will very likely grow into a massive cluster of galaxies like the Coma cluster,” said Kyoung-Soo Lee (Purdue University), in a press release. Clusters this massive are extremely rare, with only a handful of candidates known at such a young age. And it’s not just that they’re difficult to observe — they’re rare even in cosmological simulations.

This system was the first to be confirmed using extensive spectroscopy. The team first obtained very deep images of a small patch of sky, about the size of two full Moons, using the Mayall telescope on Kitt Peak. Then they used the Keck II Telescope on Mauna Kea to measure the distance to the faint galaxies within the patch, to determine which galaxies live close to each other and which are chance alignments.

“Many of the faint galaxies in this patch lie at the same distance,” says Arjun Dey (National Optical Astronomy Observatory). “They are clumped together due to gravity and the evidence suggests that the cluster is in the process of forming.”

The team is now searching larger areas of the sky to uncover more examples of young and massive protoclusters. “The discovery and confirmation of one distant and massive protocluster is very exciting,” says Naveen Reddy (University of California at Riverside), “but it is important to find a large sample of these so we can understand the possibly varied formation history of the population as a whole.”

If astronomers can find even more clusters at these kinds of distances, their prevalence can help constrain the size and expansion history of the universe.

This discovery was reported in the Astrophysical Journal (full text here); also read more information in the NOAO press release.

The post Galaxy Cluster Spotted in Early Universe appeared first on Sky & Telescope.

Ecos de una antigua cosmología encontrados en un yacimiento de nativos americanos

Ciencia Kanija -

Artículo publicado por Tom Metcalfe el 19 de mayo de 2016 en SPACE.com

Un curioso yacimiento prehistórico en la cima de una colina en el norte de Ohio puede reflejar la cosmología espiritual de los antiguos cazadores-recolectores que construyeron el lugar hace unos 2300 años, de acuerdo con un nuevo estudio.

El conocido como yacimiento de Heckelman, situado cerca de la ciudad de Milan, en el Condado de Erie en Ohio, es un risco de cima plana sobre el río Hurón. Allí, una población del periodo “Silvícola temprano” de la prehistoria norteamericana, erigió altas pértigas sin apoyos como parte de las ceremonias sociales y religiosas del grupo.

El arqueólogo Brian Redmond, conservador del Museo de Historia Natural de Cleveland, dijo que la localización del yacimiento parecía un eco de la concepción del cosmos de muchas poblaciones nativas americanas.

Molde de poste

Molde de poste Crédito: Brian Redmond

“Sabemos que los nativos americanos, y otros muchos grupos tribales, tenían una visión muy específica del mundo en forma de un cosmos en tres capas: el mundo superior, el mundo intermedio, en el que vivimos los hombres, y el inframundo”, comenta Redmond, autor de un artículo de investigación sobre los primeros ocupantes del yacimiento de Heckelman, a Live Science.

Tres capas

El yacimiento está rodeado por agua la cual, según las antiguas poblaciones, podría haberse visto como un símbolo del inframundo, señala Redmond. Las pértigas de madera en el risco pudieron haber sido construidas para alcanzar el cielo, en la dirección del mundo superior, añade.

“Por tanto, esto podría haberse visto como un poderoso paisaje espiritual donde se conectaban los tres mundos, siendo las pértigas una especie de ‘axis mundi‘ (eje del mundo) o ‘árbol de la vida’, que es global en la forma en que las culturas antiguas apreciaban estas cosas”, señala Redmond.

El yacimiento de Heckelman es único entre los yacimientos silvícolas tempranos de la región debido a que no tiene señales de enterramientos humanos o preparaciones para enterramientos, explica Redmond. En lugar de esto, el yacimiento parece haberse usado para rituales o festivales asociados con la vida, más que con la muerte, comenta.

“A partir de todo lo que vemos, estamos seguros de que fue una especie de lugar ceremonial. El hecho es que no hemos encontrado enterramientos humanos, tratamientos mortuorios, ni ceremoniales mortuorios — este yacimiento destaca por no haberse encontrado ninguna prueba directa de estos elementos”, comenta Redmond. “Por lo que es un tipo de ceremonia distinta, un ritualismo relacionado con la vida — representa que esta población tenía una rica vida ceremonial, una vida religiosa que no sólo implicaba enterrar a personas”.

Lo que queda

El inusual yacimiento muestra dos zanjas paralelas que rodean la cima del risco, y una zanja oval que abarca una área plana de 8080 metros cuadrados, donde se erigieron las pértigas de madera.

No queda ninguna de las pértigas, pero puede determinarse su posición por lo que queda de los “moldes de los postes”, o agujeros, que se excavaron para mantener las pértigas verticales, dicen los investigadores. Juzgando a partir del tamaño de los agujeros, las pértigas se habrían erigido hasta una altura de 3 a 3,7 metros, señalan los investigadores.

“Al contrario que otros yacimientos donde tenemos moldes de postes, estos no representan los muros de una estructura, o una construcción específica. Parecen estar erguidos sin apoyo, verticales, lo cual indica que tenían un tipo de función distinta”, señala Redmond. “Cuando miras los datos y los mapas de distribución de estas pértigas, es un hábito intentar que formen una estructura, buscar rectángulos, círculos, o algo similar a un edificio, y estaba realmente frustrado por el hecho de que no podía lograrlo allí. Y entonces me di cuenta de que eran otra cosa”.

Se han identificado aproximadamente seis grupos de pértigas en el yacimiento por el momento. Cada grupo puede haber sido parte de ceremonias celebradas en el lugar en distintas épocas, o por distintos grupos de gente, explica Redmond.

“Es realmente muy distinto de lo que hemos visto antes”, añade. “Ves pértigas en algunos yacimientos de la cultura Adena, en el sur de Ohio, tales como las formaciones circulares de postes conocidos como ‘woodhenge‘ — a veces estas áreas se encuentran bajo los túmulos funerarios Adena, pero este tipo de patrón regular es algo que no vemos aquí”.

Una historia rica

El yacimiento de Heckelman, que toma su nombre de los propietarios del terreno, se conoce desde la década de 1950, gracias a un gran número de artefactos prehistóricos hallados allí por los propietarios y arqueólogos aficionados. Estos objetos incluyen cerámica, puntas de lanza, y hojas de cuchillos.

Las excavaciones durante las décadas de 1960 y 1970 hallaron una de las zanjas paralelas en un lado de la cima del risco, y un estudio geomagnético en 2008 reveló una segunda zanja y el recinto oval.

Arqueólogos del Museo de Historia Natural de Cleveland y el Centro de Investigación Arqueológica Firelands, en Amherst, Ohio, excavaron partes del lugar cada verano desde 2009 a 2014.

Además de las pruebas de las pértigas sin apoyo, los investigadores encontraron huecos llenos de restos de cerámica y rocas quemadas, que probablemente son los restos de alimentos que se habían preparado como parte de las ceremonias en el lugar, explica Redmond.

“Realizando analogías con grupos históricos de nativos americanos, y otros, parece que estas ceremonias también habrían implicado preparar alimentos y comidas comunales, o festines”, comenta.

Una comunidad antigua

Las poblaciones del silvícola temprano eran cazadores-recolectores que vivían en comunidades de pocas familias, y muchos de estos grupos probablemente usaron el yacimiento de Heckelman, comenta Redmond.

“Sus asentamientos se basaban en pequeños grupos de familias relacionadas, pero se congregaban en grupos mucho mayores para rituales o festivales estacionales”, señala Redmond. “Probablemente era algo muy social. ¿Se reunirían para intercambiar información, hablar sobre dónde lograr el mejor sílex, o dónde vieron gansos o patos la semana pasada?”.

Y puede haber otros beneficios sociales, también, añade.

“Necesitaban interactuar, reunirse y desarrollar organizaciones sociales y relaciones, y estos lugares probablemente se usaban para esto”, apunta Redmond. “Por lo que probablemente es por las interacciones sociales, no sólo por la religión, por lo que iban a estos lugares”.

Redmond dice que los descubrimientos en el yacimiento de Heckelman subrayan la importancia de conservar los recursos arqueológicos en los Estados Unidos. En muchos casos, hacer esto depende de los propietarios privados del terreno, explica.

“El padre e hijo que mantienen esta propiedad nos ayudan mucho en lo que hacemos. Incluso han ido más allá en algunos años, dejando de sembrar en partes de los campos en las que queríamos excavar”, comenta. “Por lo que realmente queremos extender el mensaje de que existen buenas pruebas de nuestro pasado por toda Norteamérica, y que es realmente importante conservar estos yacimientos”.

El estudio se publicó a principios de 2016 en la revista Midcontinental Journal of Archaeology.

Artículos Relacionados

How Dead Galaxies Stay Dead

Sky&Telescope -

A galaxy in the midst of a merger isn’t forming stars, even though it could. Astronomers think the galaxy’s central black hole might be the reason why.

galaxy merger

This image from the Sloan Digital Sky Survey shows the interacting galaxies Tetsuo (left) and Akira. Astronomers see signs of a gaseous outflow from Akira, which is a bulgy, red-and-dead galaxy. The image was taken through an r-band filter, which means it lets through light in and near the red part of the visible spectrum, in this case centered near 620 nm.
SDSS

Galaxies form stars from cold gas. The more gas a galaxy has, the more stars it could in principle create. But long ago astronomers discovered that something is stopping starbirth in many galaxies. Up to three-quarters of the old, “red-and-dead” galaxies still have enough gas to fuel star formation, yet only maybe 15% of them have stellar nurseries. What gives?

The short answer is, the gas is too warm. Warm gas won’t collapse into stars. But that raises the question, why is the gas warm? One popular idea is that the galaxy’s central black hole is to blame. If the black hole is scarfing down gas, it can shoot out jets, or winds can blow off the disk of material feeding it. The jets and winds would stir up gas in the galaxy and keep it from cooling.

Astronomers do see signs of this process in galaxies with the most enthusiastically gobbling black holes. But they’ve had trouble confirming this process is at work in more typical, quieter galaxies.

Edmond Cheung (University of Tokyo) and colleagues might now have done just that. The team studied about 700 galaxies observed with one of the latest iterations of the Sloan Digital Sky Survey, called Mapping Nearby Galaxies at Apache Point Observatory (MANGA). About 5% were of the red and dead variety, yet they seemed to have gas flowing out of them. That implies something is going on inside, whether it be stars dramatically sloughing off layers or a black hole bullying gas.

The team homed in on a single galaxy, which they nicknamed Akira. Akira is in the midst of merging with a much smaller galaxy (moniker Tetsuo) that’s about one-tenth as massive. (For the curious, these names come from characters in a manga comic.) Mergers often trigger bursts of starbirth. Yet, although observations show that Akira has gas, it’s not churning out stars.

The team argues in the May 26th Nature that that might be because of the black hole. The black hole is active — although not egregiously so: it doesn’t have big jets — and the researchers estimate that it could be putting out enough energy in small-scale jets or winds to literally stir up trouble for star formation and create the outflow they detect.

The connection is only “qualitative,” cautions Marc Sarzi (University of Hertfordshire, UK) in his opinion piece in Nature — there’s no smoking gun here. But Akira is one more puzzle piece in the picture we’re building of how supermassive black holes affect the galaxies they live in.

 

Reference: Edmond Cheung et al. “Suppressing star formation in quiescent galaxies with supermassive black hole winds.” Nature. May 26, 2016.

Read more about black holes in our free ebook.

The post How Dead Galaxies Stay Dead appeared first on Sky & Telescope.

Fair Lawn High School Planetarium

Sky&Telescope -

NAME

Fair Lawn High School Planetarium

ADDRESS

Fair Lawn Senior High School
14-00 Berdan Ave.
Fair Lawn
New Jersey 07410 USA

CONTACT

Mr. Andrew Temme, Planetarium Director

PHONE

201-794-5450 ext 1598

EMAIL

atemme@fairlawnschools.org

URL

http://flhs.org/index.php/flhs-planetarium

NUMBER OF MEMBERS OTHER INFORMATION

High School Astronomy Club, Bi Annual open house to public

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Se sugiere que la materia oscura podría ser agujeros negros primordiales

Ciencia Kanija -

Artículo publicado por Francis Reddy el 24 de mayo de 2014 en NASA

La materia oscura es una misteriosa sustancia que compone la mayor parte del material del universo, y que ahora, comúnmente, se piensa que es alguna forma de partícula exótica masiva. Una interesante alternativa es que la materia oscura está hecha de agujeros negros que se formaron durante el primer segundo de la existencia de nuestro universo, conocidos como agujeros negros primordiales. Ahora, un científico del Centro de Vuelo Espacial Goddard de la NASA en Greenbelt, Maryland, sugiere que esta interpretación se alinea con nuestro conocimiento del brillo de fondo cósmico en el infrarrojo y los rayos-X, y que puede explicar la masa inesperadamente alta de la fusión de agujeros negros detectada el año pasado.

Imagen de Spitzer en infrarrojo de una zona del cielo de Ursa Major

Imagen de Spitzer en infrarrojo de una zona del cielo de Ursa Major Crédito: NASA/JPL-Caltech/A. Kashlinsky (Goddard)

“Este estudio es un esfuerzo por unir un amplio conjunto de ideas y observaciones para poner a prueba lo bien que encajan, y encajan sorprendentemente bien”, comenta Alexander Kashlinsky, astrofísico en NASA Goddard. “Si esto es correcto, entonces todas las galaxias, incluyendo la nuestra, están incrustadas dentro de una vasta esfera de agujeros negros, cada uno con unas 30 veces la masa del Sol”.

En 2005, Kashlinsky dirigió a un equipo de astrónomos que usaron el Telescopio Espacial Spitzer de la NASA para explorar el brillo de fondo de la luz infrarroja en una parte del cielo. Los investigadores informaron de una excesiva irregularidad en el brillo, y concluyeron que, probablemente, estaba provocado por la luz agregada de las primeras fuentes que iluminaron el universo hace más de 13 mil millones de años. Los estudios de seguimiento confirmaron que este fondo cósmico infrarrojo (CIB) mostraba una inesperada estructura similar a la de otras partes del cielo.

En 2013, otro estudio comparó el fondo cósmico de rayos-X (CXB) detectado por el Observatorio de rayos-X Chandra de la NASA con el CIB en la misma área del cielo. Las primeras estrellas emitieron principalmente en luz óptica y ultravioleta, la cual hoy está estirada al infrarrojo por la expansión del universo, por lo que no contribuyen significativamente al CXB.

Aun así el irregular brillo de los rayos-X de baja energía en el CXB encajaba con la heterogeneidad del CIB bastante bien. El único objeto que sabemos que puede ser lo bastante luminoso a lo largo de un rango de energía tan amplio es un agujero negro. El equipo de investigación concluyó que los agujeros negros primordiales debían haber sido abundantes entre las primeras estrellas, formando, al menos, una de cada cinco fuentes que contribuyen al CIB.

La naturaleza de la materia oscura sigue siendo uno de los problemas más importantes por resolver en la astrofísica. Los científicos actualmente se decantan por los modelos teóricos que explican la materia oscura como una partícula masiva exótica pero, por el momento, las búsquedas no han logrado llegar a ninguna prueba de que realmente existan estas hipotéticas partículas. La NASA está actualmente investigando este problema como parte de sus misiones Alpha Magnetic Spectrometer y Fermi Gamma-ray Space Telescope.

“Estos estudios proporcionan resultados cada vez más sensibles, disminuyendo lentamente los parámetros en los que pueden ocultarse las partículas de materia oscura”, comenta Kashlinsky. “El hecho de no lograr encontrarlos ha llevado a un renovado interés por el estudio de lo bien que podrían funcionar los agujeros negros primordiales – agujeros negros que se formaron en la primera fracción de segundo del universo – como materia oscura”.

Los físicos han esbozado algunas vías en las que el caliente universo en rápida expansión pudo producir agujeros negros primordiales en las primeras milésimas de segundo tras el Big Bang. Cuanto antes tuvieron lugar estos mecanismos, de mayor tamaño pueden ser los agujeros negros. Y debido a que la ventana para crearlos duró apenas una fracción de segundo, los científicos esperan que los agujeros negros primordiales muestren un estrecho rango de masas.

El 14 de septiembre de 2015, las ondas gravitatorias producidas por la fusión de un par de agujeros negros a 1300 millones de años luz fueron captadas por las instalaciones de (LIGO) en Hanford, Washington, y Livingston, Louisiana. Este acontecimiento marcó la primera detección de ondas gravitatorias, así como la primera detección directa de agujeros negros. La señal proporcionó a los científicos de LIGO información sobre la masa individual de los agujeros negros, que fue de 29 y 36 veces la del Sol, con un margen de error de 4 masas solares. Estos valores eran inesperadamente grandes, y sorprendentemente similares.

“Dependiendo del mecanismo en funcionamiento, los agujeros negros primordiales podrían tener propiedades muy similares a los que detectó LIGO”, explica Kashlinsky. “Si suponemos que éste sea el caso, que LIGO captó la fusión de dos agujeros negros que se formaron en los inicios del universo, podemos apreciar las consecuencias que tiene esto para nuestra comprensión de cómo evolucionó finalmente el cosmos”.

En su nuevo artículo, publicado el 24 de mayo en la revista The Astrophysical Journal Letters, Kashlinsky analiza lo que podría suceder si la materia oscura consistiera en una población de agujeros negros similares a los detectados por LIGO. Los agujeros negros distorsionan la distribución de masa en los inicios del universo, añadiendo una pequeña fluctuación que tiene consecuencias cientos de millones de años más tarde, cuando empiezan a formarse las primeras estrellas.

Durante gran parte de los primeros 500 millones de años del universo, la materia normal estaba demasiado caliente como para agruparse y formar las primeras estrellas. La materia oscura no se vio afectada por esta alta temperatura dado que, sea cual sea su naturaleza, interactúa principalmente mediante la gravedad. Agregándose mediante atracción mutua, la primera materia oscura colapsó en cúmulos conocidos como minihalos, los cuales proporcionaron una semilla gravitatoria que permitió la acumulación de la materia normal. El gas caliente colapsó hacia estos minihalos, dando como resultado bolsas de gas lo bastante densas como para colapsar aún más por sí mismas para formar las primeras estrellas. Kashlinsky demuestra que, si los agujeros negros desempeñan la parte de la materia oscura, este proceso tiene lugar más rápidamente y produce con mayor facilidad la heterogeneidad del CIB detectada en los datos de Spitzer, incluso si sólo una pequeña fracción de minihalos logra producir estrellas.

Cuando el gas cósmico cae en los minihalos, los agujeros negros que lo constituyen capturan de forma natural parte de él también. La materia que cae hacia un agujero negro se calienta y, finalmente, produce rayos-X. Juntos, la luz infrarroja de las primeras estrellas y los rayos-X del gas que cae en los agujeros negros de materia oscura pueden explicar la concordancia observada entre la irregularidad del CIB y el CXB.

Ocasionalmente, algunos agujeros negros pasarán lo bastante cerca como para ser capturados gravitatoriamente en sistemas binarios. Los agujeros negros de cada uno de estos sistemas binarios emitirán, durante eones, radiación gravitatoria, perdiendo energía orbital y cayendo en una espiral hasta, finalmente, fusionarse en un agujero negro de mayor tamaño similar al observado por LIGO.

“Futuras observaciones de LIGO nos dirán mucho más sobre la población del universo de agujeros negros, y no pasará mucho tiempo antes de que sepamos si el escenario que aquí esbozamos se apoya o se descarta”, comenta Kashlinsky.

Kashlinsky dirige un equipo científico con sede en Goddard que participa en la misión Euclid de la Agencia Espacial Europea, que actualmente tiene previsto su lanzamiento para 2020. El proyecto, conocido como LIBRAE, permitirá al observatorio estudiar las poblaciones fuente en el CIB con una alta precisión, y determinar qué porción está producida por agujeros negros.

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