March 30-31, 2009
Technological Institute, Northwestern University
The search for Gravitational Waves is currently one of the most active research areas of astrophysics, as technological advances have made possible the construction of interferometric detectors, capable of performing on the desired sensitivity levels (the two ground-based LIGO detectors are shown on the bottom left corner, along with the upcoming space-based LISA detector). The detection of Gravitational Waves will not only be an excellent test of Eintein's General Relativity, allowing astrophysicists to probe our understanding of basic physic's principles, but will also teach us a great deal about the sources of Gravitational Waves. One such promising category of sources is the collision of Super Massive Black Holes (Black Holes with masses of millions to billions that of the mass of our Sun. The upper left corner of the photo shows a sequence of galaxies about to or already merging with each other). Every galaxy in our universe is believed to harbor such a Super Massive Black Hole in their center. When galaxies collide (a procedure often called "Galactic Cannibalism"), their central Black Holes are doomed to merge as well, following a wild dance around each other, during which, Gravitational Waves are being emitted. The detection and mostly the interpretation of those Gravitational Waves here on Earth, depends crucially on our understanding of their properties. To guide the search for Gravitational Waves, astrophysicists all over the world (including the theoretical astrophysics group at NU) build, with the help of supercomputers (upper right: the NU theoretical astrophysics cluster, FUGU), template databases (i.e., theoretical models of Gravitational Waves; bottom right in the picture) as well as search algorithms, that are used in order to 'fish out' the real Gravitational Wave signal from the noise of the detectors and furthermore to interpret the characteristics of the sources (masses, type of object, distance, etc.).
The picture summarizes some of the tools used by the theoretical Astrophysics Group at Northwestern University to study stars. A computer cluster named Fugu (middle left) is utilized for theoretical calculations (middle right) that describe the evolution of stars. To represent the state of a star, from birth to destruction, the most commonly used graph is the H-R diagram (lower right). Visualization softwares (e.g. Shake, in the middle) allow to use outputs of numerical simulations and create movies of stellar evolution. Two snapshots from a movie about the evolution of a star ten times more massive than the sun are also shown. On the upper left is a snapshot from the red giant phase when the star is about 220 times bigger than the sun. On the lower left is a snapshot of the neutron star left at the end of the life of the star.