Colloquia

I will review some recent results about the molecular content of galaxies and its dynamics, obtained from CO lines, dense tracers (HCN,HCO+), or the dust continuum emission. New data to constrain the conversion factor XCO will be discussed. The molecular surface density is essential to determine the star formation efficiency in galaxies, and the resolved Kennicutt-Schmidt law will be presented as a function of surface density and galaxy type. Large progress has been made on galaxy at moderate and high redshifts, allowing to interprete the star formation history and star formation efficiency as a function of gas content, or galaxy evolution. In massive galaxies, the gas fraction was higher in the past, and galaxy disks were more unstable and more turbulent. ALMA observations will allow the study of more normal galaxies at high z with higher spatial resolution and sensitivity.

I will discuss how the acoustic oscillations that propagate in the photon-baryon fluid during the first million years of the Universe provide a robust method for measuring the cosmological distance scale. The distance that the sound can travel can be computed to high precision and creates a signature in the late-time clustering of matter that serves as a standard ruler. Galaxy clustering results from the Sloan Digital Sky Survey reveal this feature, giving a geometric distance to a redshift of 0.3 and an accurate measurement of Omega_matter. I will review our recent work on the theory and practice of the acoustic oscillation method and our latest cosmology results from SDSS-II. I will then present SDSS-III, which will use the acoustic method to produce 1% distance measurements in order to map the curvature and expansion history of the Universe and measure the evolution of dark energy.

Massive stars lose mass through powerful, radiatively driven stellar winds. Building on the original "CAK" model for steady, spherical winds driven by line-scattering, this talk will review recent research on the multi-faceted nature of such wind mass loss under varied conditions, for example due to rapid rotation, magnetic channeling, binary interaction, or a luminosity near the Eddington limit. An overall theme is that wind mass loss can in this way lead to a wide variety of astrophysical phenomena, including bipolar nebulae, massive star magnetospheres, colliding winds or compact companion accretion, and luminous blue variable eruption. The discussion here will summarize these with an emphasis on their varied observational signatures.

The Square Kilometre Array is intended to be the centimeter- and meter-wavelength telescope for the 21st Century. Originally proposed as the "hydrogen telescope," the science case is now recognized to be much broader, and the SKA will address fundamental questions in astrophysics, physics, and astrobiology. The international science community has developed a set of Key Science Programs: (1) Emerging from the Dark Ages and the Epoch of Reionization; (2) Galaxy Evolution, Cosmology, and Dark Energy; (3) The Origin and Evolution of Cosmic Magnetism; (4) Strong Field Tests of Gravity Using Pulsars and Black Holes; and (5) The Cradle of Life & Astrobiology. I highlight how the SKA's Key Science Programs will be an integral component of the multi-wavelength, multi-messenger frontiers for astronomy and how the science pathfinding for the SKA is beginning now.

In this talk I consider two questions. First, I investigate the formation of molecular clouds from diffuse interstellar gas. It has been argued that the midplane pressure controls the fraction of molecular hydrogen present, and thus the star formation rate. Alternatively, I and others have suggested that the gravitational instability of the disk controls both. I present numerical results demonstrating that the observed correlations between midplane pressure, molecular hydrogen fraction, and star formation rate can be explained within the gravitational instability picture. Second, I discuss how ionization affects the formation of massive stars. Although most distinctive observables of massive stars can be traced back to their ionizing radiation, it does not appear to have a strong effect on their actual formation. Rather, I present simulations suggesting that stars only ionize large volumes after their accretion has already been throttled by gravitational fragmentation in the accretion flow. At the same time these models can explain many aspects of the observations of ultracompact H II regions.

The massive black holes found at the centers of most nearby galaxies including our own, are believed to be the ashes of the fuel that powered quasars early in the history of the universe. I will briefly review the astronomical evidence for these objects and then describe some of the exotic dynamical phenomena that originate in their vicinity, including hypervelocity stars, resonant relaxation, and warped and lopsided stellar disks.

In his public talk, Prof. Narayan will summarize our knowledge of Black Holes in the universe. He will describe how Black Holes are discovered, how their properties are measured, and what the results mean. He will also discuss the many ways in which Black Holes influence their surroundings and the profound effect they have had on the evolution of the universe.

An astrophysical black hole is completely described with just two parameters: its mass and its dimensionless spin. A few dozen black holes have mass estimates, but until recently none had a reliable spin estimate. The first spins have now been measured for black holes in X-ray binaries. The talk will describe the method used to make these measurements and will discuss implications of the results obtained so far.

The Baryon Oscillation Spectroscopic Survey (BOSS) is a Stage III dark energy experiment on the Sloan Telescope. For the five years from 2009-2014, we are mapping 1.5 million galaxies at z<0.7. A simultaneous survey of 160,000 QSOs is mapping the hydrogen gas in absorption at redshifts 2 < z < 3. BOSS will provide the definitive measurement of the low redshift (z<0.7) BAO distance scale, and it will pioneer a powerful new method of measuring BAO at high redshift. BigBOSS is a proposed Stage IV dark energy experiment that will extend this map to 20 million galaxies over 14,000 deg² to z=1.7. I will describe this survey and its technical status.

En mi conferencia haré una introducción a la Física Cuántica y a continuación pasaré a discutir diferentes casos en los que los fenómenos cuánticos juegan un papel determinante en el trabajo de diferentes máquinas médicas. De hecho, los ejemplos que explicaré recorrerán la historia de la medicina moderna, la del siglo XX, desde el punto de vista de la terapia como de la inspección. Para todo ello tendré que echar mano, por ejemplo, del principio de incertidumbre de Heisenberg, del efecto túnel de la corriente eléctrica y del espín, de la resonancia atómica. Todo ello para explicar, entre otros casos, cómo se “ve” el corazón, cómo se detectan los pensamientos, porque el feto de la madre roba el oxígeno a la sangre de su madre para poder vivir.