NASA Marshall
Compte certifié @NASA_Marshall
2 mars
Using data from @NASA's @chandraxray, researchers have identified a fourth ultraluminous X-ray source as being a neutron star, and found new clues about how these objects can shine so brightly! LEARN MORE >>
http://go.nasa.gov/2oK2qFnMarch 2, 2018
Beaming with the Light of Millions of Suns
In the 1980s, scientists started discovering a new class of extremely bright sources of X-rays in galaxies. These sources were a surprise, as they were clearly located away from the supermassive black holes found in the center of galaxies. At first, researchers thought that many of these ultraluminous X-ray sources, or ULXs, were black holes containing masses between about a hundred and a hundred thousand times that of the sun. Later work has shown some of them may be stellar-mass black holes, containing up to a few tens of times the mass of the sun.
In 2014, observations with NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) and Chandra X-ray Observatory showed that a few ULXs, which glow with X-ray light equal in luminosity to the total output at all wavelengths of millions of suns, are even less massive objects called neutron stars. These are the burnt-out cores of massive stars that exploded. Neutron stars typically contain only about 1.5 times the mass of the sun. Three such ULXs were identified as neutron stars in the last few years. Scientists discovered regular variations, or "pulsations," in the X-ray emission from ULXs, behavior that is exhibited by neutron stars but not black holes.
Now, researchers using data from NASA's Chandra X-ray Observatory have identified a fourth ULX as being a neutron star, and found new clues about how these objects can shine so brightly. The newly characterized ULX is located in the Whirlpool galaxy, also known as M51. This composite image of the Whirlpool contains X-rays from Chandra (purple) and optical data from the Hubble Space Telescope (red, green, and blue). The ULX is marked with a circle.
Neutron stars are extremely dense objects — a teaspoon would weigh more than a billion tons, as much as a mountain. The intense gravity of the neutron stars pulls surrounding material away from companion stars, and as this material falls toward the neutron star, it heats up and glows with X-rays. As more and more matter falls onto the neutron star, there comes a time when the pressure from the resulting X-ray light becomes so intense that it pushes the matter away. Astronomers call this point — when the objects typically cannot accumulate matter any faster and give off any more X-rays — the Eddington limit. The new result shows this ULX is surpassing the Eddington limit for a neutron star.
The scientists analyzed archival X-ray data taken by Chandra and discovered an unusual dip in the ULX's X-ray spectrum, which is the intensity of X-rays measured at different wavelengths. After ruling out other possibilities, they concluded that the dip was likely from a process called cyclotron resonance scattering, which occurs when charged particles — either positively charged protons or negatively charged electrons — circle around in a magnetic field. The size of the dip in the X-ray spectrum, called a cyclotron line, implies magnetic field strengths that are at least 10,000 times greater than those associated with matter spiraling into a stellar-mass black hole, but are within the range observed for neutron stars. This provides strong evidence that this ULX is a neutron star rather than a black hole, and is the first such identification that did not involve the detection of X-ray pulsations.
An accurate determination of the magnetic field strength depends on whether the cause of the cyclotron line, either protons or electrons, is known. If the line is from protons, then the magnetic fields around the neutron star are extremely strong, comparable to the strongest magnetic fields produced by neutron stars, and may in fact be helping to break the Eddington limit. Such strong magnetic fields could reduce the pressure from a ULX's X-rays — the pressure that normally pushes away matter — allowing the neutron star to consume more matter than expected.
If the cyclotron line is from circling electrons, by contrast, then the magnetic field strength around the neutron star would be about 10,000 times less strong, and thus not powerful enough for the flow onto this neutron star to break the Eddington limit.
The researchers currently don't have a spectrum of the new ULX with enough detail to determine the cyclotron line's origin. To further address this mystery, the researchers are planning to acquire more X-ray data on the ULX in M51 and look for cyclotron lines in other ULXs.
A paper describing this research, led by Murray Brightman of the California Institute of Technology, appears in the latest issue of Nature Astronomy. The other authors include F. Fürst of the European Space Astronomy Centre; M.J. Middleton of University of Southampton, United Kingdom; D.J. Walton and A.C. Fabian of University of Cambridge, United Kingdom; D. Stern of NASA's Jet Propulsion Laboratory; M. Heida of Caltech; D. Barret of France's Centre national de la recherche scientifique and University of Toulouse; and M. Bachetti of Italy's Istituto Nazionale di Astrofisica.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.
Image credit: X-ray: NASA/CXC/Caltech/M. Brightman et al.; Optical: NASA/STScI
Read More from NASA's Chandra X-ray Observatory.
For more Chandra images, multimedia and related materials, visit:
http://www.nasa.gov/chandraLast Updated: March 2, 2018
Editor: Lee Mohon
Tags: Chandra X-Ray Observatory, Galaxies, Stars, Universe
Feb. 15, 2018
Supermassive Black Holes Are Outgrowing Their Galaxies
The biggest black holes in the Universe are growing faster than the rate of stars being formed in their galaxies, according to two new studies using data from NASA’s Chandra X-ray Observatory and other telescopes.
Over many years, astronomers have gathered data on the formation of stars in galaxies and the growth of supermassive black holes (that is, those with millions or billions the mass of the Sun) in their centers. These data suggested that the black holes and the stars in their host galaxies grow in tandem with each other.
Now, findings from two independent groups of researchers indicate that the black holes in massive galaxies have grown much faster than in the less massive ones.
“We are trying to reconstruct a race that started billions of years ago,” said Guang Yang of Penn State who led one of the two studies. “We are using extraordinary data taken from different telescopes to figure out how this cosmic competition unfolded.”
Using large amounts of data from NASA's Chandra X-ray Observatory, the Hubble Space Telescope and other observatories, Yang and his colleagues studied the growth rate of black holes in galaxies at distances of 4.3 to 12.2 billion light years from Earth. The X-ray data included the Chandra Deep Field-South & North and the COSMOS-Legacy surveys.
The scientists calculated the ratio between a supermassive black hole's growth rate and the growth rate of stars in its host galaxy. A common idea is that this ratio is approximately constant for all galaxies.
Instead, Yang and colleagues found that this ratio is much higher for more massive galaxies. For galaxies containing about 100 billion solar masses worth of stars, the ratio is about ten times higher than it is for galaxies containing about 10 billion solar masses worth of stars.
“An obvious question is why?” said co-author Niel Brandt, also of Penn State. “Maybe massive galaxies are more effective at feeding cold gas to their central supermassive black holes than less massive ones.”
Another group of scientists independently found evidence that the most massive black holes’ growth has outstripped that of stars in their host galaxies. Mar Mezcua, of the Institut of Space Sciences in Spain, and her colleagues studied black holes in some of the brightest and most massive galaxies in the Universe. They studied 72 galaxies located at the center of galaxy clusters at distances ranging up to about 3.5 billion light years from Earth. The study used X-ray data from Chandra and radio data from the Australia Telescope Compact Array, the Karl G. Jansky Very Large Array and Very Long Baseline Array.
Mezcua and her colleagues estimated the masses of black holes in these galaxy clusters by using a well-known relationship that connects the mass of a black hole to the X-ray and radio emission associated with the black hole. The black hole masses were found to be about ten times larger than masses estimated by another method using the assumption that the black holes and galaxies grew in tandem.
“We found black holes that are far bigger than we expected,” said Mezcua. “Maybe they got a head start in this race to grow, or maybe they’ve had an edge in speed of growth that’s lasted billions of years.”
The researchers found that almost half of the black holes in their sample had masses estimated to be at least 10 billion times the mass of the Sun. This places them in an extreme weight category that some astronomers call “ultramassive” black holes.
"We know that black holes are extreme objects,” said co-author J. Hlavacek-Larrondo of the University of Montreal, “so it may not come as a surprise that the most extreme examples of them would break the rules we thought they should follow."
The work by Mezcua et al. was published in the February 2018 issue of Monthly Notices of the Royal Astronomical Society (MNRAS) and is available online (https://arxiv.org/abs/1710.10268). The paper by Yang et al. has been accepted and will appear in the April 2018 issue of the MNRAS (available online:
https://arxiv.org/abs/1710.09399).NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.
Read More from NASA's Chandra X-ray Observatory.
For more Chandra images, multimedia and related materials, visit:
http://www.nasa.gov/chandraMolly Porter
NASA Marshall Space Flight Center, Huntsville, Ala.
256-424-5158
molly.a.porter@nasa.govMegan Watzke
Chandra X-ray Center, Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.eduLast Updated: Feb. 15, 2018
Editor: Lee Mohon
Tags: Black Holes, Chandra X-Ray Observatory, Galaxies, Universe
ESA EarthObservation
Compte certifié @ESA_EO
4 hil y a 4 heures
At the beginning of #February Phil the groundhog predicted six more weeks of winter... From this recent pic of a freezing #Italy looks like the furry rodent was right!
http://bit.ly/2GQwwOY Title Snowbound Italy
Released 28/02/2018 4:10 pm
Copyright contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO
Description
Italy is usually associated with relatively warm weather, but this week it, too, has fallen victim to the cold snap nicknamed the Beast from the East.
Freezing temperatures carried on winds from Siberia have brought snow to much of Europe, causing widespread disruption. As this image captured on 27 February by the Copernicus Sentinel-3A satellite shows, Italy in southern Europe was not spared. Temperatures in Rome (bottom right of the image) are normally between 6°C and 14°C, but this week it has been down to –5°C during the night, and it is the first time the city has seen snowfall in six years. Naples also had its heaviest snowfall in decades.
Id 390765
http://www.esa.int/spaceinimages/Images/2018/02/Snowbound_ItalyTitre : Le secret de Polichinelle
Poète : Antoine-Vincent Arnault (1766-1834)
Recueil : Fables, Livre I (1812).
Fable VII, Livre I.
Qui découvre une vérité,
A dit un grave personnage,
La gardera pour soi, s'il est quelque peu sage
Et chérit sa tranquillité.
Socrate, Galilée, et gens de cette étoffe,
Ont méconnu ce dogme, et s'en sont mal trouvés.
Quels maux n'ont-ils pas éprouvés !
D'abord c'est Anitus qui crie au philosophe ;
Mélitus applaudit ; et mon sage, en prison,
Reconnaît, mais trop tard, le tort d'avoir raison :
Socrate y but la mort : mais quoi ! son infortune,
Qui n'a fait qu'assurer son immortalité,
Pourrait-elle étonner mon intrépidité ?
Ce qu'il osa cent fois, je ne l'oserais une !
Non, non, je veux combattre un préjugé reçu.
Dût l'Anitus du jour, aboyant au scandale,
Calomnier mes mœurs pour venger la morale,
Je rectifie un fait qu'on n'a jamais bien su ;
Des générations erreur héréditaire,
Erreur qu'avec Fréron partage aussi Voltaire ;
Polichinelle, amis, n'était pas né bossu.
L'histoire universelle affirme le contraire ;
Je le sais fort bien ; mais-qu'y faire ?
Ne pas lui céder sur ce point,
Ni sur cet autre encor : monsieur Polichinelle
Grasseyait bien un peu, mais ne bredouillait point,
Quoi qu'en ait dit aussi l'histoire universelle.
Du reste, en fait d'esprit, se croyant tout donné,
Pour avoir un peu de mémoire,
Monsieur Polichinelle, au théâtre adonné,
Fondait sur ce bel art sa fortune et sa gloire :
Il voulait l'une et l'autre. Assez mal à propos,
Un soir donc il débute en costume tragique,
Ignorant, l'idiot, qu'un habit héroïque
Veut une taille de héros.
Aussi la pourpre et l'or dont mon vilain rayonne,
Font-ils voir aux plus étourdis
Ce qui, sous ses simples habits,
N'avait encor frappé personne ;
Son dos un peu trop arrondi,
Son ventre un peu trop rebondi,
Sa figure un peu trop vermeille.
De plus, si ce n'est trop de la plus douce voix
Pour dire ces beaux vers qui charment à la fois
L'esprit, et le cœur et l'oreille,
Imaginez-vous mon grivois
Psalmodiant Racine et grasseyant Corneille.
On n'y tint pas : il fut hué,
Siffle, bafoué, conspué.
Un autre en serait mort, ou de honte ou de rage.
Lui, plus sensé, n'en mourut pas ;
Et crut même de ce faux pas
Pouvoir tirer quelqu'avantage.
Mes défauts sont connus : pourquoi m'en affliger ?
Mieux vaudrait les mettre à la mode.
Je ne saurais les corriger,
Affichons-les ; c'est si commode !
Il est plusieurs célébrités,
Hommes de goût, gens à scrupules,
La vôtre est dans vos qualités,
La nôtre est dans nos ridicules.
Il dit, et sur son dos, qui n'était que voûté,
il ajuste une bosse énorme ;
Puis un ventre de même forme
À son gros ventre est ajouté.
Loin d'imiter ce Démosthènes,
Qui, bredouilleur ambitieux,
Devant les flots séditieux,
Image du peuple d'Athènes,
S'exerçait à briser les chaînes
De son organe vicieux,
Confiait aux vents la harangue
Où des Grecs il vengeait les droits,
Et, pour mieux triompher des rois,
S'efforçait à dompter sa langue,
Polichinelle croit qu'on peut encore charmer
Sans être plus intelligible
Que tel que je pourrais nommer,
Et met son art à se former
Un parlage un peu plus risible.
Puis, vêtu d'un habit de maint échantillon,
Il barbouille de vermillon
Sa face déjà rubiconde ;
Prend des manchettes, des sabots ;
Dit des sentences, des gros mots ;
Bref, n'omet rien pour plaire aux sots
Et plaît à presque tout le monde.
Quels succès, par les siens, ne sont pas effacés ?
Les Roussels passeront, les Janots sont passés !
Lui seul, toujours de mode, à Paris comme à Rome,
Peut se prodiguer sans s'user ;
Lui seul, toujours sûr d'amuser,
Pour les petits enfants est toujours un grand homme.
Ajoutons à ce que j'ai dit,
Que tel qui tout bas s'applaudit
De la faveur universelle,
Ne doit sa vogue et son crédit
Qu'au secret de Polichinelle.
Antoine-Vincent Arnault.
Ainsi,
CELA NOUS DONNE T'IL LE DROIT DU PIED DE NEZ EN DEVENANT
LE TYRAN SUR LA VICTIME ET L'ASSASSIN. LE SERVICE EST AINSI
UNE FORME DE REGARD SUR NOTRE SOCIÉTÉ ET LE DOSSIER EST
DE NOUS DIRE QUE DANS LE SURRÉALISME D'UN JUGE SE TROUVE
LES TERMES QUI INCITENT DES PERSONNES à VOULOIR
CONSTRUIRE DES SORTES DE FUNÉRAILLES DU TERRORISME:
CERTAINS TUENT COMME LES ANCIENS PARTAGEAIENT LE
CARNAGE ET L'INSENSIBILITÉ: CELA DOIT CHANGER, OUI, CHANGER !
SENTIMENTS ET DISCOURS DU
CITOYEN
TIGNARD YANIS
SUR LE PORTS DES ARMES AUX PORTÉES RÉELLES...
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