Cosmology with Gamma-Ray Bursts

Lorenzo Amati

INAF – IASF Bologna

torek, 29. 5. 2012, ob 14h v F5

Given their huge isotropic-equivalent luminosities, up to more than 10^54 erg/s, and their redshift distribution extending up to more than z=8, Gamma-Ray Bursts (GRB) are in principle a powerful tool for measuring the geometry and expansion rate of the Universe. However, they are not standard candles, given that their luminosities span several orders of magnitude, even when considering possible collimation angles.

In the recent years, several attempts to exploit the correlation between the photon energy at which the nu*F_nu spectrum peaks (”peak energy”) and the radiated energy (or luminosity) for “standardizing” GRBs and using them as tools, complementary to other probes like SN Ia, BAO and the CMB, for the estimate of cosmological parameters have been made. These studies show that already with the present data GRBs can provide a significant and independent confirmation of Ω_M~0.3 for a flat ΛCDM universe and that the measurements expected from present and next GRB experiments (e.g. Swift, Fermi/GBM, SVOM) will allow us to constrain Ω_M, Ω_Λ and, in particular, to get clues on dark energy properties and evolution.

The impact of, and evidence for, stellar migration in disk galaxies

Ponedeljkov fizikalni kolokvij

v ponedeljek 28. maja 2012, ob 16:15 v predavalnici F1

Pred predavanjem so vsi udeleženci vabljeni na čaj!

The impact of, and evidence for, stellar migration in disk galaxies

Dr. Victor Debattista, Jeremiah Horrocks Institute, University of Central Lancashire, UK

Until recently it was thought that stars remain at the same radius at which they are born all their lives. The realisation that spiral arms can move stars around in radius, without appreciably heating the disks, changed all that. This result is driving a paradigm shift in our understanding of disk galaxies and how they are assembled. Stellar migration complicates efforts at galactic archaeology, which is one of the principal goals of many large upcoming surveys, such as LSST and Gaia.
Migration has important consequences for interpreting the implied gas accretion rate, the Galactic orbit of the Sun, the fossil evidence of stellar accretion, and the Galactic “habitable zone”. Thus assessing to what extent stellar migration has affected the Milky Way’s disc is vitally important if we are to understand galaxy formation.

Interdisciplinary Science in Astronomy: A review

Ponedeljkov fizikalni kolokvij

IZJEMOMA v torek 22. maja 2012, ob 16:15 v predavalnici F1

Pred predavanjem so vsi udeleženci vabljeni na čaj!

Interdisciplinary Science in Astronomy: A review

Dr. Pavlos Protopapas, Harvard-Smithsonian Center for Astrophysics, Harvard University, Cambridge, USA

Are we ready to let machines do the work so we can now concentrate on the science questions? Have we reached the point where statistical and machine learning methods have become useful tools rather than a nuisance and the practice of the few? We will present four examples where significant progress has been made and the interdisciplinary practices have brought fruitful results. These include automatic classification, Bayesian parameter inferences, event detection and anomaly detection, and design of surveys and followups.

Ultraluminous X-ray Sources: The most extreme X-ray binaries

Luca Zampieri

INAF – OAPD

petek, 11. 5. 2012, ob 11h v F7 (*)

Despite the impressive advancements occurred in recent years, the existence of Ultraluminous X-ray sources (ULXs) represents still a theoretical challenge in modern Astrophysics. Likely the majority of them are the most extreme version of an X-ray binary, with a Black Hole in a mass range or in an accretion regime so far unexplored.

Here I will review our present understanding of ULXs, discuss some potential pathways to their formation and summarize possible future observational and theoretical prospects.

(*) POZOR: sprememba dneva/ure/predavalnice!

Architecture and Tomography of Galaxy Clusters

Mario Nonino

INAF – OATS

ponedeljek, 7. 5. 2012, ob 13h v F4 (*)

CLASH (Cluster Lensing And Supernova survey with Hubble), is one of the three selected Hubble Space Telescope Multi-Cycle Treasury Program. The main aim of CLASH is to place new constraints on the fundamental components of the cosmos, namely baryons, dark matter, and dark energy, via HST ACS/WFC3 multiband imaging of a selected sample of clusters of galaxies.

After introducing its goals, and current observational status, I will present the most recent results and potential application.

(*) POZOR: sprememba dneva/ure/predavalnice!

Najnovejše rezultate, o katerih bo govora v predavanju, si lahko preberete v članku na arhivih astro-ph.

The star that should not exist

Paolo Molaro

INAF – OATS

ponedeljek, 23. 4. 2012, ob 13h v F4 (*)

Extreme metal-poor stars are records of the chemical composition of the young Galaxy and provide information on the early chemical evolution in the Universe and on the type of the first stars. They are very rare and current theories predict the existence of a threshold in metallicity to form low mass stars that could be observed today.

We developed an automatic procedure to select metal poor candidates from the Sloan Digital Sky Survey. Some of these were observed during the GTO of the spectrograph X-Shooter and their metallicity confirmed. We also succeeded in finding out a record metal-poor star. Some of the implications of this discovery will be discussed.

(*) POZOR: sprememba dneva/ure/predavalnice!

Numerical relativity and the formation of black holes

Jerome Novak

Laboratoire Universe et Théories, CNRS (France)

torek, 6. 3. 2012, ob 14h v F3

Stellar-type black holes (of the order of 10 solar masses) are supposed to be born during the collapse of very massive stars. As even an approximate limit on mass and metalicity of main-sequence progenitors, discriminating between neutron star and black hole formation, is poorly known, it is very important to perform numerical simulations in order to understand the physical processes at work during the stellar core-collapse: hydrodynamics, relativistic gravity, neutrino transport, nuclear matter properties, … In this talk, I shall present a ongoing project to simulate these events. I shall start with a general overview of the core-collapse context, introducing then the general-relativistic formalism to compute the gravitational field and to simulate black holes, before giving some numerical tools (in particular spectral methods) for the solution of partial differential equations arising within this model.

The cluster origin of the solar system

Prof. Dr. Susanne Pfalzner

Max-Planck-Institute für Radioastronomie, Bonn, Germany

torek, 28. 2. 2012, ob 14h v F5

The solar system was not born in a such sparse environment as it is located in today but as part of a relatively dense star cluster. It will be shown how one comes to that conclusion and how this shapes our knowledge about the early history of the solar system. This cluster environment influenced various properties of the solar system like its composition, size and the orbital parameters of some of its constituting bodies. Recently it has been demonstrated that in the Milky Way such massive clusters as that of the solar birth cluster clusters only form in two forms – starburst clusters and leaky clusters. Here it will be investigated how likely it is that our own Solar System has formed in one of these two cluster environments and how this gives us a much more precise picture of the first 20 Myr of our solar system.

Predavanje “Ultraluminous X-ray Sources” odpade

Predavanje prof. Zampierija iz Padove zaradi težav odpade. Prosimo za razumevanje.

Topla temna snov in nelinearne kozmološke strukture

Katarina Markovič

Univerzitetni Observatorij München

ponedeljek, 16. 1. 2012, ob 11h v F6

(POZOR! neobičajen termin)

Meritve iz fizike delcev še vedno ne izključujejo okolice nekaj kiloelektronvoltov za maso delcev temne snovi. Takšna masa bi pomenila, da termični učinek teh delcev na porazdelitev mase v zgodnjem vesolju ni zanemarljiv! Temno snov, ki lahko zatre perturbacije gostote na majhnih razdaljah, imenujemo topla temna snov (angl. Warm Dark Matter – WDM). Nerelativistične delce hladne temne snovi (angl. Cold Dark Matter ali CDM) ločimo od tople temne snovi po njihovi porazdelitvi hitrosti v zgodnjem vesolju. Učinek tople temne snovi je razviden kot zmanjšanje spektra moči perturbacij na majhnih skalah. Na žalost pa se ta “odtis” močno zmanjša med nelinearno evolucijo porazdelitve mase v vesolju. Modeliranje nelinearnih struktur dandanes je že v “hladnem” scenariju nepopolno, v “toplem” scenariju pa je še v povojih. Vendar pa vstop v dobo kozmologije visoke natančnosti zahteva izpopolnitev teorij, če se želimo izogniti omejitvam sistematičnih napak iz teorije in slediti natančnosti eksperimentov.

Was the “Christmas Star” a gamma-ray burst?

Drejc Kopač

FMF, Univerza v Ljubljani

torek, 20. 12. 2011, ob 12h v F3
(POZOR! sprememba ure in predavalnice)

We will discuss an unusual gamma-ray burst GRB 101225A, which was detected on the Christmas Day 2010. After presenting the observations and the obtained data, we will focus on two different theoretical interpretations for this event, published in the December 2011 issue of the Nature journal (Thöne et al. 2011 and Campana et al. 2011). The “dual personality” of this gamma-ray burst is clearly a signature that many phenomena in high-energy astrophysics are not yet explained, but more (strange) events will help us advance in the field.

Članke si oglejte preko povezav v povzetku predavanja (odebeljeni tekst).

Kaj se dogaja s plinom na obrobju jat galaksij?

Dunja Fabjan

CO Vesolje-SI in Univerza v Ljubljani

torek, 29. 11. 2011, ob 14h v F5

Najnovejša rentgenska opazovanja jate galaksij v Perzeju so pokazala, da bi naj bil delež mase plina na razdalji virialnega radija večji od pričakovanega (Simionescu et al. 2011). Simulacije jat galaksij (Nagai & Lau 2011) nazorno kažejo, da je vzrok v zgoščinah plina in da so le-te odvisne od fizikalnih procesov znotraj jate.
Ogledali si bomo rezultate, ki jih je pred kratkim objavila skupina astronomov (Eckert et al. 2011), ki je uporabila arhivske podatke nedavno “upokojenega” rentgenskega satelita ROSAT in jih primerjala s tremi različnimi serijami simulacij jat galaksij.

Članke si oglejte preko povezav v povzetku predavanja (odebeljeni tekst). Če nimate dostopa do revij (Full Refereed Journal Article) si lahko članek ogledate preko povezave na astro-ph arhive (arXiv e-print).

Accelerated Expansion of the Universe – 2011 Nobel prize in physics

Ponedeljkov fizikalni kolokvij

Vid Iršič in prof. Tomaž Zwitter

Fakulteta za matematiko in fiziko, Univerza v Ljubljani

ponedeljek, 14. 11. 2011, ob 16.15 v predavalnici F1

Pred predavanjem so vsi udeleženci vabljeni na čaj!

The fact that the Universe is expanding has been known ever since Edwin Hubble’s discovery in late 1920s that distant galaxies recede from each other at velocities proportional to distances between them. A shock to scientific community came in the late 1990s when two independent groups discovered that the Universe is not only expanding but is doing so at an ever increasing rate. Both groups were using distant supernovae as standard candles to measure distances that stretch billions of kilometers over space. The results were compatible with predictions of general theory of relativity with additional term, cosmological constant, which was postulated by Einstein himself which he later disregarded and dubbed it his greatest bundle. The discovery for which this year’s Nobel prize is awarded proved this bundle to be of a more brilliant type. However, even though the mathematical construction exists to explain this phenomena we are no closer to understand it in the framework of standard model of particle physics.

Klasifikacija z metodo Locally Linear Embedding

Gal Matijevič

Fakulteta za matematiko in Fiziko, Univerza v Ljubljani

torek, 8. 11. 2011, ob 14h v F5

Dandanes je količina podatkov v mnogih novih astronomskih bazah tolikšna, da je ročno pregledovanje takšnih baz skrajno nepraktično in pogosto povsem nemogoče. K sreči obstaja širok nabor računalniških metod, s katerimi je mogoče skrite zakonitosti v podatkih odkrivati preprosto in učinkovito. Ogledali si bomo relativno novo metodo z imenom Locally Linear Embedding – LLE, ki sta jo prva predstavila Roweis in Saul (2000), nedavno pa je bila uspešno uporabljena za klasifikacijo galaktičnih spektrov pregleda neba SDSS (Vanderplas in Connolly, 2009). Pokazali bomo še, kako je s to metodo mogoče razlikovati med spektri pregleda neba RAVE in kako jo uporabimo za klasifikacijo prekrivalnih dvojnic misije Kepler.

Članka si oglejte na povezavah v povzetku predavanja (odebeljeni tekst).

Astronomy in the Czech Republic

Petr Heinzel

Director of the Astronomical Institute (Czech Republic)

petek, 30. 9. 2011, ob 11h v F5

The Astronomical Institute in Ondřejov near Prague is one of the oldest scientific institutions in the Czech Republic and belongs to the Academy of Sciences. The informal talk will be about the research in astronomy covered by the Astronomical Institute. Currently the institute participates in ESO and ESA projects, as the Czech republic became a member state of these organisations in 2007 and 2008, respectively, and in the European Association of Solar Telescopes. Some brief information will also be given about the history of astronomy in the Czech Republic and about czech research institutes doing astronomy nowadays.