News 2008

Jan 23, 2008
A new look at early star births (23 January 2008)

An international team of astronomers lead by scientists of the Astrophysics Division of CEA-IRFU has discovered large molecular gas reservoirs - the combustible for forming new stars - hosted in ordinary massive galaxies in the young, distant Universe. The discovery has been made with the IRAM Plateau de Bure Interferometer located in the French Alps, observing at millimeter wavelengths. This finding indicates that massive galaxies built major fractions of their stars in a nearly continuous way, and not on very rapid bursts as thought before, and open new major possibilities for understanding galaxy formation at high redshifts. The results are published in the January 2008 issue of the Astrophysical Journal.

Image credits: MPIA Heidelberg (Hi_res 1.7Mo / Med_res 0.4Mo)

Nov 17, 2008
Dense electron clouds around neutron stars.

Neutron stars are the most magnetized objects in our Universe. Some of them, dubbed "Magnetars" have a record magnetic field of 1011 Tesla (T), which corresponds to one million of billions times that of the Sun during a quiescent phase. It's around this class of objects that an over-density of electrons has been discovered. These results, delivered by an international team of researchers that includes Diego Götz from the Service d'Astrophysique of CEA-Irfu, is the result of a careful analysis of the X-ray emission observed with the satellites of the European Space Agency (ESA) XMM-Newton and INTEGRAL. The enormous battery represented by the highly magnetized neutron stars provides its magnetosphere with electrons in a much efficient way, with respect to other neutron stars. These physical phenomena, completely inaccessible in laboratory experiments due to the enormous magnetic fields required, allow to better understand the behavior of matter in extreme conditions. This work has been published by The Astrophysical Journal, and has been the object of a press release by ESA.

Sep 29, 2008
No planets around Sirius ?

Sirius, the brightest star of the sky, is reported to have shown a change of colour, a possibility that has led some scientists to suspect a possible but yet undetected small companion.
Now using a specific mask and the modern technique of adaptive optics which allows to suppress most of the blurring of the atmosphere, Jean-Marc Bonnet-Bidaud and Eric Pantin of the C.E.A. Astrophysical Department have obtained the first and most sensitive image of the Sirius field, in the infrared domain. It is in this energy range that the smallest stars and even planets can be most easily detected.
The new image, despite its high spatial resolution (0,2 arcsecond) and superior contrast, does not reveal any other companion than the already known white dwarf Sirius-B. The limiting mass is that of a massive planet so that at least no big planets orbit Sirius.
The image also provides the first measurements of Sirius-B infrared fluxes and yields some surprise. It reveals a possible small infrared excess that may indicate the existence of circumstellar material around the white dwarf. Though still to be confirmed by further observations this may show that if planets exist around Sirius, it could be only planetary debris around Sirius-B, as already observed around other white dwarfs.
The results are published in the October issue of the Astronomy and Astrophysics Journal.

 

Images Images Audio Podcast J.M. Bonnet-Bidaud
  with Ciel&Espace Radio (in french)
Video Video-Animation
(fichier MOV 4.3 Mo)
Jan 10, 2008
INTEGRAL discovers a factory of positrons in the Milky Way (10 January 2008)

Surprisingly, an asymmetry in the distribution of antimatter in the central regions of our Galaxy has just been discovered. By adding all scientific data acquired since five years by the spectrometer SPI aboard the INTEGRAL satellite, a European research group, including scientists from the Service d'Astrophysique at CEA-IRFU , has observed a gamma-ray photon emission of an energy of 511 keV, which is characteristic for the annihilation of electrons and their antimatter particles, the positrons. The researchers could determine the morphology of the 511 keV emission in the central regions of our Galactic disk, which reveals to be asymmetric and very similar to the distribution of a certain type of X-ray binary sources. For some time already these objects are thought to be efficient factories for positron production, and could explain the origin of these antimatter particles in the central regions of our Galactic disk. This work has been published in the scientific journal Nature on January 10th, 2008.

 

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