News 2016

Jan 07, 2016
Recent change in the optical and gamma-ray polarization observed in the center of the Crab Nebula

The Crab Nebula, thought for decades to be a "standard candle", has recently seen this status challenged by the observation of intense high-energy gamma rays flares. An Irish and French team (centre for Astronomy of the Université of Galway and Service d’Astrophysique from CEA–Irfu ) has stressed this finding by observing for the first time a change of polarization in visible and gamma-ray light in the central region of the nebula from 2005 to 2012. This results from a programme combining observations made at the Mount Palomar 5 meter telescope with the GASP polarimeter from the University of Galway, by the astronomical gamma-ray satellite Integral and archival data from the Hubble Space Telescope. The polarization changes could be related according to the researchers to a rearrangement process of the magnetic field and effects induced on energetic particles in a region near the central pulsar. This work is published in the journal Monthly Notices of the Royal Astronomical Society and object of the Picture Of the Month (POM) from the European Space Agency (ESA).

Sep 28, 2016
The deepest millimetric observations of the young Universe

An international team of astronomers used the Atacama Large  (Sub) Millimeter Array (ALMA) to explore the farthest part of the universe revealed by the Ultra Deep Field of the Hubble satellite (HUDF). These new observations from ALMA are significantly deeper and more resolved than previous surveys in the millimeter range. They clearly demonstrate the existence of a close relationship between the star formation rate in young galaxies and their total stellar mass. They also reveal the abundance and spatial distribution of the gas from which stars are born, providing new insight into this "Golden Age" of galactic formation dated some 10 billion years.

New observational results from ALMA will be published in
a series of articles in press in the Astrophysical Journal and the Monthly Notices of the Royal Astronomical Society. They are also unveiled at the conference "Five Years ALMA : Half a Decade of ALMA: Cosmic Dawns Transformed", held this week in Palm Springs, California, USA.


For more information : see the French version

Jul 06, 2016
Instabilities and shocks disrupt the atmosphere of exoplanets

In collaboration with the Observatory of Bordeaux and the University of Bern in Switzerland, a researcher of the Astrophysics Departement-Laboratory AIM at CEA-IRFU has demonstrated the existence of significant instabilities in supersonic winds at the surface of giant planets very close to their star, described as "hot Jupiters". Using idealized 3D hydrodynamic simulations at high spatial resolution, the team showed that violent equatorial winds of the hot Jupiters are destabilized by instabilities called Kelvin-Helmholtz, well known in laboratory hydrodynamics. These instabilities cause oscillations of the wind trajectory around the equator and could be responsible for the appearance of shocks in the upper layers of the atmosphere. These phenomena may significantly affect the infrared emission and the atmospheric chemistry of these planets. These results are published in the journal Astronomy & Astrophysics

Jun 06, 2016
Star formation in the filamentary Aquila and Taurus molecular clouds

Based on observations of nearby molecular clouds with the Herschel space observatory, recently large samples of future stars were detected in the form of dense cores. The properties of these compact seeds and their connection with interstellar filaments reveal us the earliest key stages of stars and the way of low-mass star formation.

Among several cloud complexes along the Gould Belt (see image below) the Aquila and Taurus regions were targeted. While the star formation in Aquila was relatively unexplored until recently, the Taurus cloud with its main filaments is well known. The Aquila Rift lies above the Galactic plane at the distance of about 260 parsec (approximately 850 light-years from the Sun). The Taurus region is more nearby, it seems to sit in the wall of the Local Bubble - a cavity, surrounding the Solar System- at 140 parsec (or 450 light-years) from us. 

Jun 23, 2016
An instability to trigger the initial rotation of a neutron star.

The birth spin of a neutron star is a key parameter to better understand the nature of its progenitor as well as the dynamical processes at play during the collapse of a massive star. However, the distribution of initial pulsar spins is poorly known. A study led by R. Kazeroni from SAP/CEA and his collaborators, using numerical simulations, emphasized the efficiency of a hydrodynamic instability named “SASI” to impart a rotational velocity to the neutron star. Surprisingly, the simulations show that, in some cases, the direction of rotation of the compact object is opposite to the perturbation which triggers the rotation. These results are published in the journal Monthly Notices of the Royal Astronomical Society.

Jun 13, 2016
A laboratory scale-model of accretion column onto a highly magnetized dense star

Scientists from a large international collaboration (Oxford, AWE, CEA, LULI, Observatoire de Paris, University of Michigan, University of York and STFC Rutherford Appleton Laboratory) have succeeded for the first time in generating a laboratory analogue of a strong shock that is produced when matter falls at very high speed on the surface of extremely dense stars called white dwarfs.  Understanding the physics of these astrophysical objects is crucial because they are considered as the possible progenitors of thermonuclear supernovae. These supernovae are used in cosmology to measure the acceleration of the universe expansion that is linked to dark energy. To perform this spectacular astrophysics experiment, the scientists made use of the powerful Orion Laser Facility at Aldermaston (UK) to evaporate a millimetre size target and produce a hot plasma flow for an extremely short duration (less than 100 nanoseconds) [1].
Recent theoretical work has shown that, by using adapted scaling laws, this tiny size experiment can be scaled to its cosmic counterpart making it a valid replicate. Powerful lasers can therefore be used as microscopes to explore, during few nanoseconds, the high-energy radiation processes occurring in astrophysical objects from regions largely unresolved by the most powerful telescopes. The Orion experiment which is the first academic experiment on this facility, confirms that these accretion shocks, which could not be studied in laboratory a few years ago at exact scale, can now be produced commonly in laboratory. These results are published in Nature Communications, June 13th, 2016.


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