Research Activity

  1. Research Interests
  2. Projects for Students
  3. International Cooperations



Research Interests


Gravitational Physics/LIGO


Theoretical prediction of gravitational wave backgrounds motivated by LIGO/Advanced LIGO. EIRSA has strong ties with the LIGO collaboration (see the EGRG website for details).



The Quest for Dark Energy (DE)


The most puzzling aspect of modern cosmology is the presence of a force accelerating the expansion of the universe. We engage from theoretical models for DE to possibility of detection and data analysis. There are four primary means of detecting and constraining DE, baryonic oscillations, weak lensing, cluster number counts, and supernovae data. The upcoming Pan-STARRS survey at the University of Hawaii will be used to pursue all of these directions, our focus being on contributing on the first two possibilities.



Cosmic Microwave Background (CMB)


The study of the small fluctuations in the CMB has been one of the most fruitful of all areas of cosmology: our understanding and characterizing the presently popular "concordance model" hinges entirely on measurements of the CMB by the WMAP and other experiments. The future lies in studying the polarization, especially the B-mode polarization, which full provide further consistency checks on our models, as well as constraints on the tensor contribution to the fluctuations. The upcoming Planck survey especially motivates our research.



Virtual Observatories/Astronomical Databases


With exponential increase of astronomical data, the storage and retrieval of astronomical data sets is becoming a science in itself. Science questions, which in the past could only be answered by proposing large observational projects, now can be tackled using virtual observations in a large database. Organizing and correlating such archival data from multiple sources will yield interesting results, e.g. correlating galaxy counts from Pan-STARRS with Planck will constrain DE.



Analysis of large data sets


Contemporary data analysis tools are inadequate for future large data sets, even with the most powerful supercomputers existing or projected. A new approach to these problems consists of a powerful mixture of advanced computer science, statistics, and group theory. As an example, standard analysis of megapixel CMB maps from Planck would take a million years on hypothetical computers equipped with TeraBytes of memory. We are developing tools and techniques which allow the analysis of such large data sets on human time-scales using reasonable resources.



Cosmological Structure Formation


Over the last decade, a "standard model of cosmology" has emerged, in which the present expansion of the Universe is dominated by the dark energy and dark matter, and cosmic structures formed from the primordial density fluctuations that had a scale-invariant power spectrum. This model is supported by a long list of various measurements that probe the universe on large (approximately >10 Mpc) scales. However, cosmic structure formation in this model starts from the "bottom up", with the nonlinear collapse of perturbations on small scales. The model on these small scales is not directly supported by any observations. One of the frontiers of current cosmology is to study the epoch of first structure formation, and how predictions for this epoch can be confronted with future observations.



Supermassive Black Holes


One of the most exciting discoveries in Astronomy over the last decade is the existence of super-massive black holes. Black holes with 10^9 solar masses and larger are now known to exist at the centers of most nearby galaxies, and are also inferred to be present already in the early universe, powering the most distant quasars, discovered at the horizon of current astronomical telescopes. How these black holes formed, grew, and evolved, is currently, however, very poorly understood.




Projects for students 



  • Formation of Caustics in the Circumbinary Disk around a Binary Black Hole

Supermassive Black Holes (SMBHs) are now known to be present in most galactic nuclei. The mergers of distant galaxies are then expected to produce SMBH binaries that coalesce and emit gravity waves detectable by the proposed space interferometer LISA. Finding the electromagnetic counterpart of LISA sources would revolutionarize cosmology and astrophysics. Unfortunately, LISA's angular localization is poor, and the selection of the right counterpart is likely to be difficult. One possibility is to identify the counterpart as a variable source. We therefore would like to know whether the orbiting SMBH binary can lead to variable emission. Such variable emission may be produced as the circumbinary gas responds to the several 100 km/s recoil (or "kick") experienced by the binary at coalescence.




Lippai, Z., Frei, Z., and Haiman, Z. 2008, ApJL, 676, 5 (a mock N-body simulation of caustic-formation after the kick in two simple cases)

Milosavljevic, M., and MacFadyen, A. I 2007, astro-ph/0607467 (an existing hydro-simulation of the behaviour of the gas disk before coalescence)

Kocsis, B., Haiman, Z., Menou, K., and Frei, Z. 2007, Phys. Rev. D. 76, 022003 (for general motivation) 




  • The Proximity Effect in Quasar Spectra

The proximity effect refers to the "thinning" of the so--called Lyman alpha forest absorption near quasars, where the gas is exposed to an ionizing flux higher than the background, so it is more ionized than the mean IGM. Whereas this effect has been claimed to be seen in individiual quasar spectra, there is a recent claim by D. Tytler that there is no proximity effect, on average, in all quasar spectra. This may be naturally explained by the fact that both the IGM density and the abundance of galaxies are enhanced around quasars.




Bajtlik, Duncan, and Ostriker 1988, ApJ, 327, 570 (the original discussion of the proximity effect)

Dall'Aglio, A., Wisotzki, L. and Worseck, G. 2008, A&A, 480, 359 (and introduction therein; for recent data)




International Cooperations





EIRSA formed a group to join the Laser Interferometer Gravitywave Observatory 

(LIGO). Eötvös Gravity Research Group (EGRG) - named after Baron Roland von 

Eötvös, who was a Hungarian physicist and is remembered today for his 

experimental work on gravity, in particular his study of the equivalence of 

gravitational and inertial mass (the so-called weak equivalence principle) - has 

joined the LIGO Scientific Collaboration in March 2007. The first and largest group 

to do so in Hungary, including not only EIRSA core members, but also integrating 

external members from the Uniersity of Szeged and from the Institute of Nuclear 

Research of the Hungarian Academy of Sciences in Debrecen. 


EGRG participates in several LSC working groups, contributing to data analysis of burst signals, to detector characterization, and even to public outreach. Details can be fond at the dedicated EGRG website.





The Sloan Digital Sky Survey (SDSS) is one of the most ambitious and influential surveys in the history of astronomy. Over eight years of operations (SDSS-I, 2000-2005; SDSS-II, 2005-2008), it obtained deep, multi-color images covering more than a quarter of the sky and created 3-dimensional maps containing more than 930,000 galaxies and more than 120,000 quasars.


EIRSA member István Csabai and former member Gyula Szokoly are among the Builders of SDSS. 





 István Szapudi - Pan-STARRS





The goal of Hungarian Virtual Observatory (HVO) is to coordinate the efforts of Hungarian researchers who are working on VO development. HVO is developing services for the Virtual Observatory, mainly using the Web services technology. All of these services are very useful for astronomers: in the absence of services it would involve several steps to download data, convert to a given format, write programs to calculate the desired physical property, etc. All of these steps are hidden, everything is automatic. One of the recent development is the Spectrum and filter service (LINK), which will be extended by Photometric redshift estimation and Synthetic spectrum service in the future.


EIRSA member István Csabai is the leader of HVO.