Maruša Bradač

 
 
Studying dark matter...
One of the most important outstanding quests in cosmology is the understanding of the formation and evolution of galaxies and galaxy clusters. In particular, we seek to answer what the dark matter is and what are its properties, and how it shapes galaxies and galaxy clusters through cosmic time. Whereas the currently accepted 
paradigm for galaxy formation works well in general, some discrepancies between model predictions and observations (such as the abundance of substructure in halos, and dark matter profile shapes) still remain. 

The principal objective of my research is to study the dark matter and its properties over a variety of scales and environments. With accurate mass measurements of gravitational lensing by clusters and galaxies I will be able to constrain their dark matter profile and distribution. Following the pioneering example of the ``bullet'' cluster 1E0657-56 I  am studying more merging clusters; these are ideal laboratories for distinguishing between CDM and other scenarios (warm dark matter, self-interacting dark matter, modified gravity, etc.) that have been proposed to resolve the CDM crises or to eliminate the need for dark matter altogether. 

``Science is a collaborative effort, between us and the universe. We propose ideas, the universe smacks them down -- or occasionally agrees (S. Caroll).''




Studying dark matter continues...

How do we find more Bullet-like clusters? I wish it was as easy as this:

















But with a bit more hard work we now have not only two colliding clusters of galaxies, but four that are all telling us the same story. Dark matter is all around us and it is weird.  We have recently discovered second system where two clusters of galaxies have collided, making visible (ordinary, regular, baryonic) matter separate from the dark matter component, allowing us to study the properties of the later...



Read more about it here. Or follow  links in wikipedia...

Read the article published in ApJ here.
 

The color composite of the bullet cluster. The two clusters (their galaxies are predominantly  the yellowish ones in this image) have smashed through each other with 15 million kilometers per hour (10 million miles per hour). The dominant mass component (dark matter, blue) has separated from the dominant luminous material (hot gas, red).  Credit: NASA Press Release; X-ray NASA/CXC/CfA Optical: NASA/STScI; Magellan/U.Arizona; [Clowe et al 2006, Bradač et al 2006]

You can see a cool movie from John Wise and read much more on this at SLAC and NASA webpage.

and highest redshift Universe...
Galaxy clusters are not only useful to study dark matter. among other fantastic research one can do, clusters also act as gigantic magnifying glasses, again due to the gravitational lensing effect. Therefore we can observe fainter and more distant sources than would otherwise be possible. I use massive clusters as cosmic telescopes to explore the Universe in its infancy, by studying the sources responsible for reionization; an era  in which  the Universe should go from highly
neutral to highly ionized. After that period the universe becomes transparent for visible light and we mark it as the end of Dark Ages. We currently lack a full understanding of the exact properties of the sources responsible for this process,  to observe these sources we need to look very far back, at the time when the Universe was only about 400 million years old. I am currently studying these extremely faint sources, a task made possible through magnifying power of massive clusters through gravitational lensing effect. 
            
http://www.nasa.gov/mission_pages/chandra/news/08-111.htmlhttp://en.wikipedia.org/wiki/MACS_J0025.4-1222http://www.physics.ucsb.edu/~marusa/Papers/MACSJ0025.pdfhttp://www.slac.stanford.edu/~marusa/Work/clowe.pdfhttp://www.slac.stanford.edu/~marusa/Work/bradac_strong_weak_III.pdfhttp://www.slac.stanford.edu/~jwise/research/movies/HiResBullet.movhttp://home.slac.stanford.edu/pressreleases/2006/20060821.htmhttp://chandra.harvard.edu/press/06_releases/press_082106.htmlshapeimage_1_link_0shapeimage_1_link_1shapeimage_1_link_2shapeimage_1_link_3shapeimage_1_link_4shapeimage_1_link_5shapeimage_1_link_6shapeimage_1_link_7
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Department of Physics, University of California Davis

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Davis, CA 95616

U.S.A.

Phone: 1-(530) 752-6762

Fax:     1-(530) 752-4717

Email: marusa at physics.ucdavis.edu