IL FUTURO DELL’ASTROFISICA E DELLA FISICA

Il 2016 che ci attende

Un breve escursus su cosa accadrà nel 2016, sia dal punto della fisica che dell’astrofisica: si va dalla ricerca della materia oscura alle nuove missioni per Marte e Giove, senza dimenticare le onde gravitazonali

Mappa 3D della distribuzione su larga scala della materia oscura ricostruita da misure di lente gravitazionale debole utilizzando il telescopio spaziale Hubble

Cosa ci attende nel 2016? Secondo Nature e Science potrebbe essere l’anno della materia oscura e delle onde gravitazionali, ma sarà anche l’anno dell’esplorazione di Marte e di Giove.

Si comincia con l’insediamento di Fabiola Gianotti, che dal primo gennaio entrerà in carica come direttore del Cern, e le particelle sfuggenti di materia oscura, la materia invisibile e misteriosa che occupa circa il 25% dell’universo, potrebbero essere generate dalle collisioni del più grande acceleratore del mondo, il Large Hadron Collider (Lhc) del Cern, riattivato nel 2015 e che lavorerà ad una energia decisamente più elevata.  A caccia di materia oscura ci sono anche il rivelatore Ams (Alpha Magnetic Spectrometer), in funzione all’esterno della Stazione Spaziale, e la sonda cinese Dampe (Dark Matter Particle Explorer).

Ancora la fisica è ai primi posti nelle attese per il 2016: sia Nature che Science indicano la possibilità di poter vedere le onde gravitazionali, ossia le vibrazioni dello spazio-tempo provocate da eventi drammatici, come l’esplosione di supernovae, collisioni di buchi neri o il Big Bang.

L’Europa dello spazio aspetta la primavera, con il lancio della missione ExoMars, destinata nel 2016 a dimostrare la sua capacità di far atterrare un rover sul pianeta rosso e, nel 2018, a perforare il suolo marziano fino alla profondità di due metri. Sempre in tema di spazio, molto ci si attende dalla missione della NASA Juno, lanciata nel 2011 il suo arrivo nel sistema gioviano è previsto per la metà del 2016.

IL prossimo anno inizierà la costruzione di quello che sarà il più grande telescopio del mondo, l’E-ELT, telescopio ottico con “vista” italiana. Infatti concluse le opere di urbanizzazione inizia la fase realizzativa del telescopio vero e proprio che dovrebbe avere la sua prima luce nel 2024.

Al via anche la costruzione del Cherenkov Array Telescope Sud. L’osservatorio CTA sarà costituito da una batteria di telescopi destinati a studiare le sorgenti celesti di radiazione gamma e, una volta realizzato, sarà il più potente e sensibile osservatorio per i raggi gamma mai costruito. CTA sarà composto da circa 100 telescopi nell’emisfero Sud e circa 20 telescopi nell’emisfero Nord.

Coisas estranhas e inexplicáveis da ciência: a estrela que viveu antes do Big Bang

Publicado em 15.05.2015

A estrela é composta 75% de hidrogênio, 25% de hélio, e possui apenas 0,00007% de elementos mais pesadosA estranha estrela é composta de 75% hidrogênio, 25% hélio, e possui apenas 0,00007% de elementos mais pesados

 

Ela não tem um nome muito cativante, mas a estrela SDSS J102915 + 17297 tem uma história única e enraizada nas suas origens inexplicáveis e um tanto misteriosas.

Localizada na constelação Leo, a estrela em questão, conhecida como estrela de Caffau, foi formada em torno de 13 bilhões de anos atrás, tornando-se uma das mais antigas de nosso universo conhecido. No entanto, os astrônomos ainda estão confusos sobre a forma como ela nasceu e tem sobrevivido todo esse tempo.

Descoberta uma sobrevivente

A estrela foi avistada pela primeira através do Very Large Telescope (“Telescópio Muito Grande”, em tradução livre), do Chile. O nome “Estrela do Caffau” foi dado em homenagem à Elisabetta Caffau, do Centro de Astronomia na Universidade de Heidelberg e do Observatório de Paris. Ela também foi o principal autora de um dos primeiros artigos sobre a tal estrela.

Como essa estrela foi descoberta?

Um censo detalhado do universo estava sendo feito quando cientistas notaram algo diferente sobre a composição dessa estrela específica.

Estrelas são feitas principalmente de hidrogênio e hélio com uma pequena quantidade de elementos mais pesados (metais). Estranhamente, a estrela de Caffau tem 20 mil vezes menos metais em comparação a estrelas típicas.

O pesquisador Hans-Günter Ludwig, que participou do estudo desta grande descoberta, acredita que a falta de lítio é particularmente “intrigante”. Ele sugere que a estrela pode apenas ser diferente, uma excentricidade do universo.

O que é normal

É normal para as estrelas terem composições diferentes no que diz respeito a quantidades de metais. Estrelas como o nosso sol, por exemplo, classificadas como “População I”, são relativamente jovens. Elas geralmente têm cerca de 4,5 bilhões de anos e são compostas por algo em torno de 2 a 3% de metais.

Já as estrelas mais velhas, classificadas como “População II”, têm algo entre 0,01% e 0,1% de metais. Estas estrelas representam os dois tipos que somos capazes de observar.

Há uma outra população de estrelas, no entanto, da qual nós nunca vimos nenhuma e (provavelmente) nunca veremos. As estrelas que não possuem estes metais em sua composição são classificadas como “População III”. No entanto, como mencionado anteriormente, isso é apenas uma teoria, porque elas nunca foram observadas.

Mas porque elas nunca foram observadas?

Bem, porque viveram há MUITO tempo. Por causa do enorme tamanho que os pesquisadores acreditam que elas têm, elas teriam queimado rapidamente quando o universo estava apenas começando.

Assim, se a estrela de Caffau é de fato uma estrela da População III, os astrônomos não têm ideia de como ela poderia ter sobrevivido tanto tempo.

Formação da estrela de Caffau

O Big Bang resultou na criação dos primeiros elementos que (eventualmente) formaram todo o universo. Hidrogênio, hélio e lítio foram os principais e, como resultado, estes são o que compuseram as primeiras estrelas.

As estrelas queimaram rapidamente e a sua pressão e calor intenso resultou na formação de elementos tais como carbono e oxigênio. De acordo com o período de tempo em que os cientistas acreditam que a estrela de Caffau se formou, esses metais teriam sido necessários para resfriar as nuvens moleculares, já que estrelas não devem ser capazes de se formar sem estes materiais.

No entanto, não há nenhum carbono ou oxigênio presente na estrela de Caffau. Além disso, o lítio, um elemento conhecido por ser abundante no universo nesse momento, também está faltando na fotosfera da estrela, o que é incomum.

Existe uma resposta possível?

Um estudante na Universidade Estadual da Pensilvânia, nos Estados Unidos, pode ter resolvido o mistério estrelar. Nick Rufo e seu professor, Timothy Lawlor, sugerem que a estrela não se encaixa em nenhuma das populações estrelares anteriormente consideradas.

Em vez disso, ela estaria na fase subgigante da evolução e, portanto, seria muito maior do que o inicialmente observado.

Quando uma estrela esgota seu hidrogênio do núcleo e começa a queimar hidrogênio em um escudo em torno de um núcleo de hélio crescente, ela ilumina, se expande e se torna uma “subgigante”. Isso é algo que normalmente acontece no caminho para uma estrela se tornar uma gigante vermelha.

Rufo suspeita que, para a composição observada de lítio corresponder, a estrela teria de ser significativamente menor em massa, o que não era provável com base na temperatura em que se encontrava.

Além destas observações, os pesquisadores também consideram outras variáveis, tais como a dos efeitos do assentamento gravitacional, elemento de difusão e força radiativa. Estes teriam um impacto significativo sobre a falta de metais presentes na estrela de Caffau.

Importância

A existência da estrela de Caffau apoia uma ideia interessante: talvez o Big Bang não seja um evento tão extraordinário assim.

Em vez disso, pode haver múltiplas explosões médias que ocorrem periodicamente.

Portanto, a estrela de Caffau pode ter existido antes da explosão que deu origem a muitos dos objetos em nosso universo conhecido. Isso explicaria por que sua composição não combina muito bem com as estrelas que conhecemos e seria o ponto de partida para um raciocínio extremamente intrigante.

No entanto, outra evidência parece refutar essa ideia.

Alguns pesquisadores acreditam que houve apenas um Big Bang (no nosso universo observável, pelo menos). Essa explosão ocupou todos os lugares ao mesmo tempo, porque a evidência que vemos é que tudo no universo (em grandes escalas de distância) está se afastando de todo o resto. No caso de múltiplos Big Bangs, então, presumivelmente, a gente veria algumas galáxias distantes se movendo uma em direção a outra, ou, pelo menos, uma relação mais complexa entre a distância de objetos que vemos nas velocidades em que elas parecem estar se afastando de nós.

Desde a descoberta da estrela do Caffau, os astrônomos localizaram outras estrelas semelhantes, o que os forçaram a repensar o cenário de formação estelar.

Conforme os estudos dessas estrelas continuam, mais peças sobre universo e suas origens provavelmente vão aparecer pelo caminho. [fromquarkstoquasars]

Strange & Unexplained Things in Science: The Star that “Should not Exist” ?

It doesn’t have a very catchy name, but star SDSS J102915+17297 has a unique story rooted in its unexplained and somewhat mysterious origins. Located in the constellation Leo, the star in question, also known as Caffau’s star, was formed around 13 billion years ago, making it one of the oldest stars in our known universe. […]


It doesn’t have a very catchy name, but star SDSS J102915+17297 has a unique story rooted in its unexplained and somewhat mysterious origins.

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Located in the constellation Leo, the star in question, also known as Caffau’s star, was formed around 13 billion years ago, making it one of the oldest stars in our known universe. However, astronomers are still baffled as to how it was formed, and how it has survived this long.

Discovery and Survival

The star was first sighted using the Very Large Telescope (yes, that’s its real title) in Chile. The name “Caffau’s Star” comes from Elisabetta Caffau, of the Center for Astronomy at the University of Heidelberg and the Paris Observatory. She was also the lead author of a one of the first articles on the star.

A detailed census of the universe was being conducted by the Sloan Digital Sky Survey when they noticed something off about the star’s composition…

SDSS J102915+172927 composition

Time for some star science! Stars are composed of mainly hydrogen and helium with a small amount of heavier elements (metals). Strangely, Caffau’s star has almost none. It has a staggering 20,000 times less metals than typical stars.

Caffau’s colleague and co-author, Hans-Gunter Ludwig, finds the lack of lithium particularly “puzzling.” He believes that the star may just be unique, an oddity, or, in his words “nature has more than one way of skinning a cat.”

Of course, it’s normal for stars to be composed of different amounts of metals. Population I stars, like our sun, are relatively young. They are generally around 4.5 billion years old and composed of 2-3% metals. Older stars, or Population II stars, have between 0.01% and 0.1% of metals making up their structure. These stars are the two types that we are able to observe. There is another population of stars; however, we’ve never seen any stars from this grouping and we (likely) never will.

Stars that lack these metals are classified as Population III stars. However, as previously mentioned, that’s just a theory, as they have never been observed because they lived so long ago. Additionally, because of their assumed huge size, they would have burned out quickly, when the universe was just starting out.

So, if Caffau’s star is indeed a Population III star, astronomers have no idea how it could have survived this long.

Formation

The Big Bang resulted in the creation of the first elements that would (eventually) create everything in the universe. Hydrogen, helium, and lithium were the main elements and, as a result, these are what comprised the earliest stars. These stars burned rapidly, and their intense heat and pressure resulted in the formation of elements such as carbon and oxygen. According to the time-period at which we think Caffau’s star formed, these metals would have been the ones necessary to cool the molecular clouds so that formation could be successful. Stars shouldn’t be able to form without these materials.

However, there is barely any carbon or oxygen present in Caffau’s star. In addition, Lithium, an element known to be abundant in the universe at that time, is also lacking in the star’s photosphere, which is unusual.

A Possible Answer?

A student at Penn State may have solved the mystery of our star. Nick Rufo and his professor, Timothy Lawlor, suggest that the star doesn’t fit into any of the star populations previously considered. Instead, it would actually be in the subgiant phase of evolution—and thus much larger than initially observed.  When a star exhausts its core hydrogen, and begins to burn hydrogen in a shell around a growing helium core, it brightens and expands and becomes a “subgiant.” It’s something that usually happens on the way to becoming a red giant.

 

Lawlor explained that Rufo suspected that “for the observed composition of lithium to match, the star would have to be significantly less massive, which was not likely based on the temperature.” In addition to these observations, they also considered other variables, such as the effects of gravitational settling, element diffusion, and radiative force. These would both have a significant impact on the lack of metals present in Caffau’s star.

Importance and Further Study

The existence of Caffau’s star supports an interesting idea. Perhaps the Big Bang was not some extraordinary event. Instead, there may have been multiple Medium Bangs, if you will, that occurred periodically. Therefore, Caffau’s star may have existed prior to the explosion that gave rise to many of the objects in our known universe. This would explain why its composition doesn’t quite match the starting point at which we are placing it.

However, other evidence seems to refute this idea. As Cornell notes,

We think there was only one Big Bang (in our observable universe, at least) taking placeeverywhere simultaneously because the evidence we see is that everything in the universe (on large distance scales) is moving away from everything else. If there were multiple Big Bangs, then presumably you would see some faraway galaxies moving towards each other, or at least a more complicated relationship between the distance of objects we see and the speeds at which they appear to be moving away from us.

Since the discovery of Caffau’s star, astronomers have located other similar stars, forcing them to rethink the star-formation scenario. As the studies of these stars continue, more pieces of the universe and its origins will likely emerge.

Water on Alien Worlds: Ganymede

Written By

Science Editorial TeamFuturism8 months ago

 

We know Enceledus has liquid water by its cryovolcanoes. There are other ways we can tell if a moon has a water interior, but one of the more interesting methods is to look at a moon’s aurora. This approach was recently used to show that Jupiter’s moon Ganymede has more liquid water than Earth. You might […]


water in Ganymede

We know Enceledus has liquid water by its cryovolcanoes. There are other ways we can tell if a moon has a water interior, but one of the more interesting methods is to look at a moon’s aurora. This approach was recently used to show that Jupiter’s moon Ganymede has more liquid water than Earth.

You might have seen an aurora on Earth when there has been a rise in solar activity. On Earth, the aurora (or northern lights) are caused by charged particles emitted by solar flares that interact with Earth’s magnetic field. When a charge enters Earth’s magnetic field, the magnetic field causes the charge to spiral along the magnetic field. For this reason magnetic fields tend to trap charges along their field lines. The charges generally stay trapped unless they collide with each other (not likely in interstellar space) or interact with something else, such as our atmosphere. Where the particles strike our atmosphere depends upon the energy of the charged particles, and thus the activity level of the Sun. As the activity level of the Sun varies, the latitude at which aurora are most prominent can vary.

Aurora have been observed on other planets, as well as moons such as Ganymede. The difference is that the aurora of Ganymede are driven by the interaction with Jupiter’s magnetic field rather than the Sun. The process is much the same as aurora on Earth, but the latitude at which they are observed depends upon fluctuations of Jupiter’s magnetic activity. This has been known for a while, but in this new work the team demonstrated that the latitude variations of Ganymede’s aurora can be used to study the moon’s interior.

Since Ganymede’s aurora are driven by the activity of Jupiter, the team could calculate the amount of variation one would expect given the strength of Ganymede’s magnetic field, giving a variation of about 6 degrees. However, the observed variation is only about two degrees. It would seem that something is dampening latitudinal oscillation of the aurora. One mechanism for this kind of dampening is an interior ocean of saline water. Salt water is a good conductor of electricity, so as Jupiter’s magnetic field varies, it induces a magnetic field in addition to Ganymede’s regular magnetic field. As a result, there are less latitudinal fluctuations in aurora.

ganymede

The team created a model of this interior ocean. They found that without an ocean there would be a fluctuation of about 6 degrees, but with an interior ocean the fluctuations are lessened. Given an observed fluctuation of about 2 degrees, the interior ocean would need to be about 100 kilometers thick, starting about 150 kilometers beneath the moon’s surface. That means Ganymede has about 70% more water than Earth.

Provided by Brian Koberlein at One Universe at a Time

Close Encounters: Andromeda May Be Arriving Ahead Of Schedule

Recent analysis of past observations made by the orbiting Hubble Space Telescope have found a massive halo of hot, heavy gas surrounding our neighboring galaxy, Andromeda. This expansive mass of material around Andromeda could mean that it will begin merging with the Milky Way ahead of schedule. Previously, we knew that the two galaxies were heading for […]


(Image by A. Feild via NASA and ESA)

Recent analysis of past observations made by the orbiting Hubble Space Telescope have found a massive halo of hot, heavy gas surrounding our neighboring galaxy, Andromeda. This expansive mass of material around Andromeda could mean that it will begin merging with the Milky Way ahead of schedule.

Previously, we knew that the two galaxies were heading for a fender bender in about 4 billions years. Ultimately, this event is the culmination of a collision course of intergalactic proportions (literally), and it’s an event that no one is going to be able to put the brakes on. But the million light-year halo discovered around Andromeda means wisps of that galaxy will be entering the Milky Way ahead of schedule. Indeed, it raises the possibility that the two galaxies may alreadybe in contact.

This last scenario may be a reality if the Milky Way also possesses a similar halo. If that’s the case, the currently estimated 2.5 million light-year gap between the galaxies could already have been covered by the respective galactic halos, which could even now be mingling at the edges.

The data on Andromeda was unearthed as scientists examined observations that were conducted of quasars over the course of the the last several years. Upon inspection, the researchers found a dip in the brightness of quasars where the light had to pass through the region that (we now understand) is covered by the galactic halo. Quasars along a line of sight outside that span exhibited no such dip in brightness.

Whirlpool Galaxy

By analyzing the range of the ultraviolet light that is absorbed by the halo, the researchers were able to determine that the gases composing the halo are heavier than hydrogen and helium. That means that the only likely source is a supernova, or several, which explode from with in the main disk of the galaxy and expel that material far beyond the central body of the galaxy.

Galactic halos have been observed previously, but Andromeda’s appears larger and more massive than any other detected so close to the Milky Way. In fact, Andromeda’s halo contains perhaps half of all mass generated by supernovae exploding within the galaxy since its formation. Unsurprisingly, it is around 1000 times more massive than previously estimated.

The scale suits Andromeda (also known as M31, for it’s Messier number): The galaxy is already the most massive in the Local Group of galaxies. Housing around one trillion stars in the last galactic census, Andromeda has more than double the number of stars that are in the Milky Way.

But with our impending merger accelerated, soon (well, within a few million years, anyway) we’ll be able to claim the glory of belonging to the largest Local Group galaxy along with any hypothetical Andromedaites out there.

NuSTAR Provides Explosive Evidence For Supernova Asymmetry

Written By

Science Editorial TeamFuturism8 months ago

 

New results from the NASA NuSTAR telescope show that a supernova close to our galaxy experienced a single-sided explosion. A team of scientists including Lawrence Livermore National Laboratory researchers found that X-ray emissions taken with the Nuclear Spectroscopic Telescope Array (NuSTAR) show that the Supernova 1987A explosion was highly asymmetric. The results appear in the […]


New results from the NASA NuSTAR telescope show that a supernova close to our galaxy experienced a single-sided explosion.

A team of scientists including Lawrence Livermore National Laboratory researchers found that X-ray emissions taken with the Nuclear Spectroscopic Telescope Array (NuSTAR) show that the Supernova 1987A explosion was highly asymmetric. The results appear in the May 8 edition of the journal, Science.

NuSTAR observations, including those of 1987A, provide strong and compelling observational evidence that supernovae are not symmetric. Supernova 1987A in the Large Magellanic Cloud provides a unique opportunity to study a nearby (170,000 light years) core collapse supernovaexplosion (CCSN) and its subsequent evolution into a supernova remnant.

Rendering of SN 1987A

SN1987A has validated some basic scientific assumptions about CCSNs. A neutrino flash confirmed that the overall explosion is driven by the collapse of the central core to a neutron star. Direct gamma-ray detection of cobalt isotopes and the correlation between the exponential decay of the optical light curve and lifetime of these isotopes confirmed that the light curve is powered by radioactive decay.

“Even with all we have previously learned about SN1987A, NuSTAR has taught us some new things,” said Michael Pivovaroff, one of the LLNL scientists and co-author of the paper. “Our observations confirmed the tremendous speeds at which the exploding material is moving and helped us constrain geometrical models that show just how lopsided the supernova explosion was.”

In core-collapse supernovae, an isotope of titanium (?? Ti) is produced in the innermost ejecta, in the layer of material directly on top of the newly formed remnant. The radioactive decay of this isotope provides a direct probe of the supernova engine. NuSTAR measurements confirm that heavy elements are moving at speeds of about 3,000 kilometers per second, several times higher than expected from spherically symmetric models.

There has been growing evidence for asymmetries in supernovae explosions over the past decades, including in SN1987A from the extensive evidence for mixing and polarized optical emission. NuSTAR observations of the spatial distribution of ?? Ti in the Cassiopeia Asupernova remnant shows direct evidence of asymmetry. And these observations indicate even more asymmetry for SN1987A.

Lopsided Supernova

Subsequent X-ray observations have revealed expanding, brightening ejecta (a supernova remnant). To date, there is no evidence yet for a compact central object that formed form the core of the exploding star.NuSTAR observed SN1987A for multiple periods between September 2012 and July 2014 with a total exposure of 2,283 kiloseconds (a kilosecond is 1,000 seconds).

(Source: NASA)

Astronomy Photo of the Day: 5/10/15 — NGC 2903 Revisited

Written By

Science Editorial TeamFuturism8 months ago

 

Meet NGC 2903: a beautiful and bustling galaxy found approximately 20 million light-years away from Earth in the Leo constellation. It’s about as easy as it comes to classify which group it belongs to: the spiral galaxies. Like all spiral galaxies, it has a large and bright central core, which is partially obscured by a large, dense wall […]


NGC 2903

Meet NGC 2903: a beautiful and bustling galaxy found approximately 20 million light-years away from Earth in the Leo constellation. It’s about as easy as it comes to classify which group it belongs to: the spiral galaxies.

Like all spiral galaxies, it has a large and bright central core, which is partially obscured by a large, dense wall of interstellar dust. Then, we see the spiral arms themselves, which contain dust as well, with high concentrations of gas present too. Of course, there isn’t enough of either to prevent starlight from seeping through. In fact, these regions continue to churn out a mind-boggling number of new stars—giving NGC 2903 an additional classification: a ‘starburst’ galaxy.

Its fantastic blue coloring comes from these energetic new stars, while shades of red come from a combination of HII regions, and much older populations of stars. To expand, HII regions are regions in which newly-formed stars energize the gas around them, ultimately stripping electrons from atoms; when the pair inevitably recombine, they glow brightly (astronomers call this ionization).

NGC 2903 is additionally known for the ring of hot spots that surround it; astronomers believe the galaxy’s ring is comprised of young globular clusters (the stars within them, which are independent of the galaxy itself, are pretty strange. The Milky Way’s globular clusters are extremely old—the oldest stars anywhere in our galaxy, even).

Despite the distance, NGC 2903 is one of the brightest galaxies visible from the northern hemisphere. Measuring in at around 80,000 light-years across, the galaxy is just a 20 percent smaller than the Milky Way.

See a larger image here.

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