Astrophysics & Cosmology
Like the Universe itself, the cosmology and astrophysics program at Brown is expanding. Cosmology is the study of the origin, evolution and fate of the Universe. Astrophysics, on the other hand, seeks to understand the physics of objects in the Universe, such as stars, black holes, nebulae and galaxies. The research programs at Brown are active in both of these areas, with a healthy mix of theoretical, observational and experimental programs spanning the entire scale of size from the behavior of elementary particles to the largest scales of the Universe, the whole distance scale from the Solar system to the most distant light detectable, and the wavelength spectrum, from TeV gamma-rays to 21cm radio emission. We have four faculty members (Dell'Antonio, Gaitskell, Koushiappas, and Tucker) directly involved in cosmology and astrophysics. In addition, several faculty and students in other disciplines are working on projects of astrophysical application, from the development of advanced X-ray detectors (Seidel), to solar neutrino spectral measurements (Lanou, Maris & Seidel), to the mathematical properties of black holes (Lowe). A healthy contact between theorists, experimentalists and observers is maintained through a weekly astrophysics journal club and other meetings on areas of overlapping research. The different astro/cosmology groups are involved in a wide variety of research areas:
Ian Dell'Antonio’s group studies the distribution of matter in the universe and the evolution of gravitational clustering, as well as the star formation histories of galaxies, time-variable astrophysics and the nature of Dark Energy. One of the primary techniques used to study the distribution of matter is weak gravitational lensing. Light from distant galaxies is bent when it passes by a foreground mass distribution. By studying the distorted shapes of these distant galaxies, the distribution of matter in the foreground mass is inferred. The clustering properties of matter on various scales can be used to study both the nature of the dark matter and the geometry of the universe. By studying the clustering of matter on relatively small scales, such as individual galaxies or the centers of clusters of galaxies, we seek to differentiate between different types of candidate dark matter particles. By studying the distribution of matter on the largest scales, measuring how the clustering evolves with redshift, and especially comparing the clustering with the pattern of distortions found in the CMB, we can determine what sort of universe we live in. In particular, the weak lensing signal can be used to measure the rate of acceleration of the Universe (and its time evolution). Dell’Antonio’s group is involved in both ground-based and space-based missions to measure the Dark Energy.
Of course, other methods are available to measure the evolution of clustering. Dell’Antonio’s group has been using galaxy velocities (via the Tully-Fisher relation), infrared imaging with the Spitzer Space Telescope, and X-ray observations of clusters of galaxies to make complementary measurements of the distribution of matter. The same observations that are used for weak lensing (very deep, high quality imaging, photometric and spectroscopic redshifts, multiple exposures over a long time baseline) yield a wealth of astrophysical information. Dell’Antonio’s group has been using the data for a variety of projects ranging from Kuiper-belt object detection to galaxy collisions and compact groups of galaxies. In addition, we are also using other tracers, such as the distribution and velocities of galaxies and X-ray luminous clusters of galaxies in the distant universe, to study the evolution of structure. Learn more…
A wealth of observations in the last 70 years strongly support the view that more than 80% of the matter in the Universe is in the form of cold, dark matter, which so far can only be detected via its gravitational interaction with nearby objects. The leading candidate for dark matter is known as Weakly Interacting Massive Particles (WIMPs), which should be present in the halo of our own Milky Way and could potentially be observed by their interactions with terrestrial-based detectors. Current supersymmetry (SUSY) models in particle physics predict WIMP interaction rates that may be in a range of 1 evt/kg/day to as low as 1 evt/100kg/year, and possibly lower. The detection of WIMPs on Earth would have profound consequences for contemporary physics by solving some of the most fundamental problems in cosmology and particle physics.
Professor Gaitskell's group is trying to directly detect these theoretical rare interactions between WIMPs and ordinary matter by employing a novel detector technology, which uses liquified xenon as a target. Gaitskell's group was formerly a contributor to XENON10, a successful experiment that placed the most stringent limit on the WIMP-nucleon scattering cross-section to date, and is now focusing its efforts on the Large Underground Xenon (LUX) experiment, in which Gaitskell serves as the co-spokesperson. LUX is a time projection chamber (TPC) that employs 300 kg of liquified xenon to measure the energy and nature of particle interactions in its active volume. Gaitskell's group is primarily responsible for PMT testing and calibration, data acquisition, hardware/software development and integration, background simulations and WIMP search data analysis. LUX, the leading experiment at the new Sanford Lab in South Dakota, is an exciting experimental endeavor, as it promises to be the most sensitive dark matter detector in the world, and will be scaled up to a much larger version upon completion. Learn more…
Prof. Savvas Koushiappas
Savvas Koushiappas is trying to understand the nature of dark matter from a theoretical perspective. In particular, he is interested in the coupling of the physics of the dark matter particle to the clustering properties that are observed in numerical simulations as well as empirical observations. Large scale cosmological surveys indicate that the distribution of larger scale structure (positions and velocities of galaxies) in the Universe contains a wealth of information on the nature of dark matter. But structure is not only evident in large scales. The structure of the local group, such as the Milky Way, and its nearest neighbor, the Andromeda galaxy, as well as satellite galaxies orbiting the Milky Way, all contain a wealth of information about the nature of the dark matter particle. The distribution of dark matter in the Universe from the largest scales, to the smallest that are observed, point out to the need for new physics, beyond the standard model of particle physics, a very exciting endeavour! Koushiappas and his group are involved in theoretically interpreting the latest results from a diverse group of present and future large scale experiments, such as the LHC at CERN (particle physics), GLAST & VERITAS (gamma rays), as well as CDMS, XENON 10 and LUX (direct detection) and IceCUBE (neutrinos).
In addition as part of a large collaboration let by Los Alamos National Laboratory scientists, he is involved in the analysis of very large cosmological simulations that model theoretical predictions of the distribution of dark matter. Such studies not only probe the nature of dark matter, but they also contain phenomenological tests of the nature of dark energy, the mysterious energy density that is responsible for the accelerated expansion of the Universe, one of the greatest discoveries of the 20th century. Koushiappas and his collaborators are developing theoretical tools that can be used to extract information about dark energy in future ambitious experiments.
Koushiappas also maintains interest in the astrophysical field of galaxy formation. The assembly of a galaxy is governed by complex processes that take place in the potential centers of dark matter halos. This complex "baryonic" physics is responsible for all the light we see in the Universe, whether it is originating from individual stars and interstellar gas clouds, or whether it is originating from the cumulative distribution of both of these sources in far galaxies at the edge of the Universe. Such processes include star formation, the origin of cosmic rays and the early formation of supermassive black holes in the centers of galaxies, whose origin is a mystery.
Greg Tucker's group studies cosmology and the formation of
galaxies and stars. The cosmic microwave background (CMB) provides a snapshot of the universe 380,000 years
after the Big Bang. Accurate measurements of the spatial variations in temperature of this light provides information on
the physics that occurred in the early universe. Measurements of the polarization of this light should reveal the imprint
of gravitational waves on the CMB from the epoch of inflation 10-35 seconds after the Big Bang, a
regime not accessible by direct observation. Greg Tucker's group explores the CMB by making observations of the
CMB using ground-based experiments
(MBI-4 and QUBIC) and balloon-borne instruments and is involved with the Wilkinson Microwave Anisotropy Probe
(WMAP) satellite.
Tucker's group is also looking at the very first galaxies to form in the universe with the Balloon-borne Large Aperture Submillimeter Telescope (BLAST). The galaxies are brightest at submillimeter wavelengths. These observations have helped us understand how galaxies and structures of galaxies formed. BLAST has identified the dust-enshrouded galaxies that hide about half of the cosmic starlight. Star formation takes place in clouds composed of hydrogen gas and a small amount of dust. The dust absorbs the starlight from young, hot stars, heating the clouds to 30 K. The light is re-emitted at much longer infrared and submillimeter wavelengths. Thus, as much as 50% of the Universe's light energy is infrared light from young, forming galaxies. While those familiar optical images of the night sky contain many fascinating and beautiful objects, they are missing half of the picture describing the cosmic history of star formation.
BLAST has been flown three times since 2003 and is now being modified to make it polarization sensitive. The new BLAST experiment will make observations of star formation regions in our own galaxy to help us better understand star formation. Thesis students typically help design and build an experiment and/or make observations and analyze the resulting data. Learn more…
Prof. Robert Lanou, Prof. Humphrey Maris, Prof. George Seidel
The particle astrophysics effort of Robert Lanou, Humphrey Maris, and George Seidel focuses on high rate measurements of neutrinos produced in the Sun. They are developing a new technique in the HERON experiment which uses superfluid helium as the target. Helium at superfluid temperatures (~50 mK) provides a completely radioactivity-free and compact target. This technique will distinguish the flux and spectra of neutrinos produced in p-p and Be7 reactions in the Sun. Unlike other current detectors for low energy neutrinos, the superfluid helium detector is sensitive to all neutrino types, not just electron neutrinos.
In addition, this group is developing low temperature
calorimeters
that are providing the sensitivity necessary to make a number
of experiments in astrophysics possible. They are focussing
on the development of devices that use the measurement of
the magnetization of paramagnetic ions to detect the absorption
of single x-rays with very high energy resolution.
Selected Recent PhD Dissertations
2010
| Luiz de Viveiros | "Optimization of Signal versus Background in Liquid Xe Detectors Used for Dark Matter Direct Detection Experiments" | (Prof. R. Gaitskell) |
2008
| Peter Sorensen | "A position-sensitive Liguid Xenon Time-Projection Chamber for Direct Detection of Dark Matter: The XENON10 Experiment" | (Prof. R. Gaitskell) |
2007
| Thorsten Battefeld | "Cosmological Perturbations in the Early Universe " | (Prof. R. Brandenberger) |
| Hossein Khiabanian | "A new method for weak lensing mass reconstructions" | (Prof. I. Dell’Antonio) |
| Matthew Truch | "The Balloon-borne Large Aperture Submillimeter Telescope" | (Prof. G. Tucker) |
2006
| Mike Attisha | "Cryogenic Dark Matter Search (CDMS II) - Application of Neural Networks and Wavelets to Event Analysis" | (Prof. R. Gaitskell) | Jeff Kubo | "Searching for Strong galaxy-galaxy lensing in the Deep Lens Survey" | (Prof. I. Dell'Antonio) |
2005
| Jaiseung Kim | "The Millimeter-wave Bolometric Interferometer (MBI) for the Cosmic Microwave Background Polarization Observation" | (Prof. G. Tucker) |
Facilities:
Ladd Observatory
Rooftop Observatory
Other Links:
| Courses | Concentration Info | Astrophysics Journal Club | arXiv.org |
| American Astronomical Society | Clear Sky Clock | USNO Sun and Moon data | Physics Department Undergraduate Group |
