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Hubble Helps Find Smallest Known Galaxy Containing a Supermassive Black Hole

Hubble Helps Find Smallest Known Galaxy Containing a Supermassive Black Hole | Tout est relatant |
Astronomers using data from NASA’s Hubble Space Telescope and ground observation have found an unlikely object in an improbable place — a monster black hole lurking inside one of the tiniest galaxies ever known.

The black hole is five times the mass of the one at the center of our Milky Way galaxy. It is inside one of the densest galaxies known to date — the M60-UCD1 dwarf galaxy that crams 140 million stars within a diameter of about 300 light-years, which is only 1/500th of our galaxy’s diameter.

If you lived inside this dwarf galaxy, the night sky would dazzle with at least 1 million stars visible to the naked eye. Our nighttime sky as seen from Earth’s surface shows 4,000 stars.

The finding implies there are many other compact galaxies in the universe that contain supermassive black holes. The observation also suggests dwarf galaxies may actually be the stripped remnants of larger galaxies that were torn apart during collisions with other galaxies rather than small islands of stars born in isolation.

“We don’t know of any other way you could make a black hole so big in an object this small,” said University of Utah astronomer Anil Seth, lead author of an international study of the dwarf galaxy published in Thursday’s issue of the journal Nature.

Seth’s team of astronomers used the Hubble Space Telescope and the Gemini North 8-meter optical and infrared telescope on Hawaii’s Mauna Kea to observe M60-UCD1 and measure the black hole’s mass. The sharp Hubble images provide information about the galaxy’s diameter and stellar density. Gemini measures the stellar motions as affected by the black hole’s pull. These data are used to calculate the mass of the black hole.

Black holes are gravitationally collapsed, ultra-compact objects that have a gravitational pull so strong that even light cannot escape. Supermassive black holes — those with the mass of at least one million stars like our sun — are thought to be at the centers of many galaxies.

The black hole at the center of our Milky Way galaxy has the mass of four million suns. As heavy as that is, it is less than 0.01 percent of the Milky Way’s total mass. By comparison, the supermassive black hole at the center of M60-UCD1, which has the mass of 21 million suns, is a stunning 15 percent of the small galaxy’s total mass.

“That is pretty amazing, given that the Milky Way is 500 times larger and more than 1,000 times heavier than the dwarf galaxy M60-UCD1,” Seth said.
One explanation is that M60-UCD1 was once a large galaxy containing 10 billion stars, but then it passed very close to the center of an even larger galaxy, M60, and in that process all the stars and dark matter in the outer part of the galaxy were torn away and became part of M60.

The team believes that M60-UCD1 may eventually be pulled to fully merge with M60, which has its own monster black hole that weighs a whopping 4.5 billion solar masses, or more than 1,000 times bigger than the black hole in our galaxy. When that happens, the black holes in both galaxies also likely will merge. Both galaxies are 50 million light-years away.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.
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Un "frère" perdu du Soleil retrouvé par des astronomes

Un "frère" perdu du Soleil retrouvé par des astronomes | Tout est relatant |
Des astronomes ont identifié un "frère" du Soleil : une étoile qui est probablement née du même nuage de gaz et de poussière que notre étoile.

En pointant une lunette astronomique bon marché en direction de la constellation d'Hercule, il vous sera possible d'y apercevoir l'un des « frères" de notre Soleil, non loin de l'étoile Vega. Baptisée HD 162826, cette étoile est en effet très probablement née dans la même nébuleuse de gaz de poussière que notre Soleil, il y a quelques 4,6 milliards d'années.

Détectée par une équipe d'astronomes emmenée par Ivan Ramirez (Université du Texas, États-Unis), l'étoile HD 162826 est située à 110 années-lumière de la Terre, et possède une masse supérieure de 15% à celle de notre Soleil.

L'étoile HD 162826 fait partie d'un groupe de 30 étoiles qui étaient étudiées depuis plusieurs années par les astronomes, car présentant des caractéristiques suggérant qu'elles pouvaient provenir du même nuage de gaz et de poussière que notre Soleil. Et c'est en passant au crible ces différentes caractéristiques à l'aide du télescope Harlan J. Smith de l'observatoire McDonald (Fort Davis, Etats-Unis), comme l'analyse de leur trajectoire orbitale au sein de notre galaxie ou l'étude de leur composition chimique, que l'astronome Ivan Ramirez et ses collègues sont parvenus à la conclusion que, parmi toutes ces candidates, l'étoile HD 162826 était manifestement l'un des "frères" perdus du Soleil.

Selon Ivan Ramirez, il n'est pas interdit de penser que les étoiles qui sont issues de la même nébuleuse de gaz et de poussière que notre Soleil, comme l'étoile HD 162826, ont une (petite) probabilité d'acceuillir des planètes abritant la vie. En effet, lorsque le Soleil et ses "frères" étaient en train de se former au sein de cette nébuleuse, des fragments rocheux portant potentiellement en leur sein des ingrédients nécessaires à la vie pourraient avoir voyagé d'une étoile à l'autre (et parmi elles, notre Soleil). Par conséquent, il est possible d'émettre l'hypothèse que ces ingrédients nécessaires à la vie, qui ont ensemencé la Terre, se sont également répandu au sein de ces autres étoiles nées avec le Soleil, et donc aussi au sein de leurs planètes.

Cette étude sera prochainement publiée dans la revue Astrophysical Journal sous le titre "Elemental Abundances of Solar Sibling Candidates". Ses références sont pour l'instant consultables sur le serveur de prépublication ArXiv : "Elemental Abundances of Solar Sibling Candidates".

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Water Vapor Found on Neptune-size Alien Planet

Water Vapor Found on Neptune-size Alien Planet | Tout est relatant |

A Neptune-size planet beyond the solar system has telltale traces of water vapor in its atmosphere, making it the smallest exoplanet known to have the wet stuff yet, scientists say.

Several massive Jupiter-size giants have had the components of their atmosphere examined, but until now, the atmospheres of smaller planets have proved more elusive. In this new study, scientists discovered traces of water on the alien planet HAT-P-11b, which orbits a star 124 light-years from Earth in the constellation Cygnus.

"Water is the most cosmically abundant molecule that we can directly observe in exoplanets, and we expect it to be prevalent in the upper atmospheres of planets at these temperatures," lead author Jonathan Fraine said in an email interview. Fraine, a graduate student at the University of Maryland, worked with a team lead by Drake Deming, also of the University of Maryland. [10 Alien Planets That Might Support Life]


"Detecting it is both a confirmation of our theories and revealing for the bulk of the spectrum that we can observe," Fraine told

As a planet passes, or transits, between Earth and its sun, it blocks light from the star. The dip in light is how many exoplanets are first found. But these transits also allow astronomers to study the atmospheres of exoplanets. By observing the spectrum of light that passes through an exoplanet’s atmosphere, scientists can determine what it is made up of. [Quiz: Are You an Exoplanet Expert?]

For HAT-P-11b, a planet roughly four times the radius of Earth, that makeup is 90 percent hydrogen, with traces of water vapor. The Neptune-size planet orbits its sun every five days, at a distance that is only one-twentieth of the Earth-sun distance (which is 93 million miles, or 150 million kilometers). As a result, the temperature climbs higher on HAT P-11b than it does on gas giants in the solar system, reaching a sizzling 1,120 degrees Fahrenheit (605 degrees Celsius).

Scientists have been studying the atmospheres of Jupiter-like planets for years, but smaller planets produce a smaller signal that is more challenging to observe. For the new study, researchers examined the atmospheres of four other smaller exoplanets — two roughly the size of Neptune and two smaller super-Earths — but the results were disappointingly featureless.

"We do indeed have the technology — the resolution — to observe Neptune-size exoplanets, and even super-Earths," Fraine said.

But the chemical compositions of the other four planets were blocked by a familiar phenomenon — clouds.

"We've just been seeing a whole lot of nothing," Eliza Kempton, of Grinnell College in Iowa. Kempton models planetary atmospheres but was not involved in the research.

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Kilonova: Dead-Star Crashes May Spark Mysterious Cosmic Explosions

Kilonova: Dead-Star Crashes May Spark Mysterious Cosmic Explosions | Tout est relatant |

Cataclysmic crashes involving black holes and ultradense neutron stars may explain the briefest of the most powerful explosions in the universe, scientists say.


NASA scientists are calling the new type of short, but intense, cosmic collision and conflagration a "kilonova," an explosion so powerful it is 1,000 times stronger than a typical star explosion, called a nova. Such events have long been predicted by astronomers, but never seen until now, researchers said. The discovery could shed light on the origin of heavy elements such as gold and platinum, they added.


Gamma-ray bursts are the most intense outbursts ever detected, giving off as much energy in an instant as our sun will beam out during its entire 10-billion-year lifetime. A nearby burst directed at Earth could easily cause a mass extinction, researchers say. [See more photos of the "kilonova" gamma-ray-burst explosion]


There are two kinds of gamma-ray bursts — ones that are longer-lived, lasting more than two seconds, and less common short-lived ones, lasting about two seconds or less.


Scientists have suggested these brief gamma-ray bursts might be caused by cataclysmic mergers of incredibly dense cosmic bodies — either two neutron stars (the tiny remnants of exploded stars) or a neutron star and a black hole. However, they lacked evidence until now.





Astronomer Nial Tanvir at the University of Leicester in England and his colleagues analyzed the short gamma-ray burst GRB 130603B, which exploded about 4 billion light-years away on June 3. NASA's Swift satellite measured it as 0.18 seconds long, while NASA's Wind spacecraft determined that it lasted only 0.09 seconds.


The mergers of dense cosmic bodies that are thought to cause short gamma-ray bursts can also blast out neutron-rich gas that rapidly generates heavy elements such as gold and platinum, scientists say. These "r-process" elements can undergo radioactive decay and release an enormous amount of energy — 1,000 times or so that given off by stellar explosions such as novas. These powerful events are thus known as "kilonovas" ("kilo" means "thousand" in Greek).

NASA's Hubble Space Telescope revealed that the near-infrared afterglow that accompanied GRB 130603B was the kind one would expect from a kilonova. This is smoking-gun evidence that an explosive merger caused the gamma-ray burst, Tanvir told

"This is just the first example, and we will have to search for and study others to be completely sure, but it certainly looks right," Tanvir said.


It remains uncertain what kind of merger caused this kilonova and gamma-ray burst. The theoretical predictions for these mergers and the behavior of kilonovas "still have many uncertainties, so it is too early to try to distinguish these possibilities," Tanvir said.


In the future, the researchers aim to find other examples of kilonovas accompanying short gamma-ray bursts. Tanvir added that future research into kilonovas could shed light on the origin of r-process elements.


"The r-process elements are heavy elements whose origin we have long been uncertain about," Tanvir said. "They are not produced in normal stars, and astronomers have generally assumed they must be created in supernovae. However, the calculations suggest supernovae may not be good at creating those elements, so it is possible that kilonovae from merging compact objects may be the primary route in the universe to producing these elements."


The scientists detailed their findings online Aug. 3 in the journal Nature.

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