Un trou noir surpris dans un homicide stellaire

                                             Photo NASA

Des chercheurs utilisant le telescope GALEX de NASA et l'observatoire Pan-STARRS a Hawaii decouvrirent la rupture d'une etoile par un supermassif trou noir. Cette etoile passait trop proche du trou noir. Ils utiliserent les donnees de Chandra pour ecarter la theorie d'un noyau actif galactique. La galaxie ou cet acte violent survint s'appelle PS1-10jh et est localisee a 2.7 billions d'annees-lumiere de la Terre.

L'image simulee a l'aide d'un computer montre l'eruption de gaz d'une etoile demantelee par des raz-de-marees de forces tandis qu'elle est absorbee par le trou noir. Une partie du gaz est aussi ejectee a grande vitesse dans l'espace.

.Utilisant des observations de telescopes dans l'espace et sur le terrain lea astronautes ont obtenu l'evidence la plus directe de ce violent processus: un supermassif trou noir detruisant une etoile qui voyageait trop pres. L'appareil orbitant GALEX de NASA et le telescope Pan-STARRS1 sur le sommet de Haleakala a Hawaii etaient utilises pour aider a identifier les restes de l'etoile.  
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Une fusee eclairante ultraviolette et de la lumiere optique montraient du gas tombant dans le trou noir aussi bien que du gaz riche en helium s'evacuant du systeme. Lors du demantelement de l'etoile une partie tombe dans le trou noir tandis que le reste se desagrege a grandes vitesses. La fusee eclairante et ses proprietes permettent une demonstration de ce scenario et fournissent des details inconnus a propos de la victime stellaire. 

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Pour ecarter la possibilite d'un noyau actif s'eclairant dans la galaxie au lieu de la destruction d'une etoile, l'equipe utilisait l'observatoire a rayons X Chandra de NASA pour etudier le gaz chaud. Chandrs montrait que les caracteristiques du gaz ne correspondaient pas a celles d'un noyau actif galactique.

La galaxie ou le supermassif trou noir detruisit l'etoile passante est connue comme etant PS1-10jh et est localisee a environ 2.7 billions d'annees-lumiere de la terre. Les astronautes estiment que le trou noir dans PS1-10jh a une masse de plusieurs millions de soleils, ce qui est comparable au supermassif trou noir de la voie lactee, notre propre galaxie.

 http://chandra.harvard.edu/photo/2012/ps1/

Ignoring 500 billion galaxies: Mathematics vs Common sense in the debate about the probability of Extraterrestrial life

Carl Sagan said that "extraordinary claims, require extraordinary evidence." In a stunning display of mathematical logic vs common sense, David Spiegel of Princeton University and Edwin Turner from the University of Tokyo published a paper last summer that turns the Drake equation upside down using Bayesian reasoning to show that just because we evolved on Earth, doesn’t mean that the same occurrence would necessarily happen elsewhere; "using evidence of our own existence doesn’t show anything" they argue, "other than that we are here."

What Bayesian reasoning overlooks, of course, is the inconvenient fact that there are some one trillion galaxies in the known universe and some 50 billion planets estimated to exist in the Milky Way alone and some 500,000,000 predicted to exist in a habitable zone.
Spiegel and Turner point out that basing our expectations of life existing on other planets, for no better reason that it exists here, is really only proof that were are more than capable of deceiving ourselves into thinking that things are much more likely than they really are.
They argue that other unknown factors exist that could have contributed to us being here that we don’t yet understand. So, they conclude that, deriving numbers from an equation such as that put forth by Drake, only serves to underscore our belief in the existence of other alien life forms, rather than the actual chances of it being so.
We think evidence will be discovered in the next 20 years: The Kepler mission has discovered 1,235 exoplanets that revolve around a sun, in an area that represents around 1/400th of the Milky Way. By extrapolating these numbers, the Kepler team has estimated that there are at least 50 billion exoplanets in our galaxy — 500 million of which sit inside the habitable "Goldilocks" zones of their suns, the area that it is neither too hot nor too cold to support life.
Astronomers estimate that there are 100 billion galaxies in the universe. If you want to extrapolate those numbers, that means there are around 50,000,000,000,000,000,000 (50 quintillion) potentially habitable planets in the universe.
As Arthur C. Clarke, physicist and author of 2001: A Space Odyssey wrote, "The idea that we are the only intelligent creatures in a cosmos of a hundred billion galaxies is so preposterous that there are very few astronomers today who would take it seriously. It is safest to assume therefore, that they are out there and to consider the manner in which this may impinge upon human society."To an objectivist, empirical view, the rules of Bayesian statistics can be justified by requirements of rationality and consistency and interpreted as an extension of logic. Using a subjectivist view, however, the state of knowledge measures a "personal belief".
More information: "Life might be rare despite its early emergence on Earth: a Bayesian analysis of the probability of abiogenesis" http://arxiv.org/abs/1107.3835 and physorg.com