203 research outputs found
Pericenter passage of the gas cloud G2 in the Galactic Center
We have further followed the evolution of the orbital and physical properties
of G2, the object currently falling toward the massive black hole in the
Galactic Center on a near-radial orbit. New, very sensitive data were taken in
April 2013 with NACO and SINFONI at the ESO VLT . The 'head' of G2 continues to
be stretched ever further along the orbit in position-velocity space. A
fraction of its emission appears to be already emerging on the blue-shifted
side of the orbit, past pericenter approach. Ionized gas in the head is now
stretched over more than 15,000 Schwarzschild radii RS around the pericenter of
the orbit, at ~ 2000 RS ~ 20 light hours from the black hole. The pericenter
passage of G2 will be a process stretching over a period of at least one year.
The Brackett-{\gamma} luminosity of the head has been constant over the past 9
years, to within +- 25%, as have the line ratios Brackett-{\gamma} /
Paschen-{\alpha} and Brackett-{\gamma} / Helium-I. We do not see any
significant evidence for deviations of G2's dynamical evolution, due to
hydrodynamical interactions with the hot gas around the black hole, from a
ballistic orbit of an initially compact cloud with moderate velocity
dispersion. The constant luminosity and the increasingly stretched appearance
of the head of G2 in the position-velocity plane, without a central peak, is
not consistent with several proposed models with continuous gas release from an
initially bound zone around a faint star on the same orbit as G2.Comment: 10 figures, submitted to Ap
Revealing the Morning Transition in the Mountain Boundary Layer Using Fiber-Optic Distributed Temperature Sensing
Tsirelson's problem and Kirchberg's conjecture
Tsirelson's problem asks whether the set of nonlocal quantum correlations
with a tensor product structure for the Hilbert space coincides with the one
where only commutativity between observables located at different sites is
assumed. Here it is shown that Kirchberg's QWEP conjecture on tensor products
of C*-algebras would imply a positive answer to this question for all bipartite
scenarios. This remains true also if one considers not only spatial
correlations, but also spatiotemporal correlations, where each party is allowed
to apply their measurements in temporal succession; we provide an example of a
state together with observables such that ordinary spatial correlations are
local, while the spatiotemporal correlations reveal nonlocality. Moreover, we
find an extended version of Tsirelson's problem which, for each nontrivial Bell
scenario, is equivalent to the QWEP conjecture. This extended version can be
conveniently formulated in terms of steering the system of a third party.
Finally, a comprehensive mathematical appendix offers background material on
complete positivity, tensor products of C*-algebras, group C*-algebras, and
some simple reformulations of the QWEP conjecture.Comment: 57 pages, to appear in Rev. Math. Phy
A Detection of Sgr A* in the far infrared
We report the first detection of the Galactic Centre massive black hole,
Sgr~A*, in the far infrared. Our measurements were obtained with PACS on board
the \emph{Herschel} satellite at and .
While the warm dust in the Galactic Centre is too bright to allow for a direct
detection of Sgr~A*, we measure a significant and simultaneous variation of its
flux of and during one observation. The significance level of
the band variability is and the corresponding
band variability is significant at . We find
no example of an equally significant false positive detection. Conservatively
assuming a variability of in the FIR, we can provide upper limits to the
flux. Comparing the latter with theoretical models we find that 1D RIAF models
have difficulties explaining the observed faintness. However, the upper limits
are consistent with modern ALMA and VLA observations. Our upper limits provide
further evidence for a spectral peak at and
constrain the number density of electrons in the accretion
disk and or outflow.Comment: accepted for publication in AP
The Proper Motion Field Along the Magellanic Bridge: a New Probe of the LMC-SMC Interaction
We present the first detailed kinematic analysis of the proper motions (PMs)
of stars in the Magellanic Bridge, from both the \textit{Gaia} Data Release 2
catalog and from \textit{Hubble Space Telescope} Advanced Camera for Surveys
data. For the \textit{Gaia} data, we identify and select two populations of
stars in the Bridge region, young main sequence (MS) and red giant stars. The
spatial locations of the stars are compared against the known H {\small I} gas
structure, finding a correlation between the MS stars and the H {\small I} gas.
In the \textit{Hubble Space Telescope} fields our signal comes mainly from an
older MS and turn-off population, and the proper motion baselines range between
and 13 years. The PMs of these different populations are found to be
consistent with each other, as well as across the two telescopes. When the
absolute motion of the Small Magellanic Cloud is subtracted out, the residual
Bridge motions display a general pattern of pointing away from the Small
Magellanic Cloud towards the Large Magellanic Cloud. We compare in detail the
kinematics of the stellar samples against numerical simulations of the
interactions between the Small and Large Magellanic Clouds, and find general
agreement between the kinematics of the observed populations and a simulation
in which the Clouds have undergone a recent direct collision.Comment: 13 pages, 10 figures, 2 tables, submitted to ApJ, accepted February
8th, 201
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