Big Bang, black holes and gravity waves
RIT scientists look into the nature of the universe
Editors note: Astrophysics research at RIT moves in two directions. One group of scientists focus on theoretical work. Another group, the observational astronomers and instrumentalists, is involved in experimental astrophysical research.
The following story takes a look at the work of the theory group. The fall issue of the magazine will feature the work of the observational astronomers and instrumentalists.
Scientists at RIT’s Center for Computational Relativity and Gravitation (CCRG) are producing groundbreaking research in computational astrophysics and numerical relativity, a research field that uses supercomputers to solve the complex equations in Einstein’s theory of general relativity.
The center was created in January 2007 when Manuela Campanelli and Carlos Lousto joined RIT’s School of Mathematical Sciences with post-doctoral fellow Yosef Zlochower (now an assistant professor in the School of Mathematical Sciences) and Hiroyuki Nakano. Also affiliated is David Merritt, a preeminent theorist.
Alessia Gualandris, also a post-doctoral fellow at the center, works closely with Merritt. Josh Faber, an expert in neutron stars and black holes from the University of Chicago, joined the team in December 2007.
Campanelli, director of CCRG and professor in the School of Mathematical Sciences, caused an international stir in 2005 when she, Lousto and Zlochower, simulated the merging of two black holes on a supercomputer following Einstein’s theory of general relativity. The team had spent three years working on the 10 interrelated equations for strong field gravity that comprise Einstein’s famous theory connecting matter, space and time.
The ability to simulate gravity waves has hinged for decades on a fresh approach to solving Einstein’s equations – and the development of sufficient computer power to simulate these waves. Einstein predicted that the collision of huge masses, such as black holes or neutron stars, would produce gravity waves.
Campanelli’s team, then at the University of Texas at Brownsville, was one of two independent groups of scientists to solve the equations in the same year. In fact, both groups presented their findings at the same academic conference. Their success thrust Campanelli’s team to the forefront of their field and helped to revive interest in the study of general relativity.
For some astrophysicists, the quest to observe gravity waves is akin to the fabled pursuit of the Holy Grail. This is because gravitational waves pass through matter that blocks light, or electro-magnetic radiation, and that is very interesting to scientists. Tracing gravity waves back in time might lead them to the other side of the Big Bang.
“We can look at the origin of the universe with gravitational waves and extract information that is otherwise blocked to electro-magnetic radiation,” explains Lousto. “Gravitational waves can also detect unexpected objects – things beyond the imagination of theoretical physicists and mathematicians, and maybe even science fiction writers. Many times it happens in science that when you develop a new technique, you discover unexpected objects.”
Searching for gravity
Scientists expect to measure actual gravity waves for the first time within the next decade. Astrophysicists will compare real waves coming from space with simulated ones such as those generated by research produced by Campanelli’s team.
Scientists from California Institute of Technology and MIT designed the ground-based detector known as the Laser Interferometer Gravitational Wave Observatory (LIGO) to measure the detailed form of gravitational waves. The National Science Foundation-funded project consists of two separate observatories that work in unison – one located in Livingston, La., and the other near Richland, Wash. The observatories became operational full-time in November 2005.
LIGO could identify gravity waves from the merger of two black holes in space as soon as 2013. When Advanced LIGO, the next phase, begins operation in 2012, the instrument’s vision will extend from 3 million to 300 million years into the past. (The Big Bang is thought to have occurred 13.7 billion years ago.)
A complementary gravity-wave seeking initiative in space is the upcoming NASA/European Space Agency space mission Laser Interferometer Space Antenna (LISA) that will fish the universe for gravity waves. LISA is expected to launch in 2015.
“In order to confirm the detection of gravitational waves, scientists need the modeling of gravitational waves coming from space,” Campanelli says. “They need to know what to look for in the data they acquire, otherwise it will look like just noise. If you know what to look for, you can confirm the existence of gravitational waves. That’s why they need all these theoretical predictions.”
Research at the center will support both LIGO and LISA initiatives, placing RIT among some 50 institutions in the LIGO Scientific Collaboration. In a November 2007 interview with Discover magazine, Kip Thorne, the Feynman Professor of Theoretical Physics at Caltech, author of Black Holes and Time Warps and a driving force behind LIGO, points to Campanelli and Lousto’s black-hole simulations as some of the most exciting research taking place.
Others agree. The June 2007 issue of New Scientist featured an article about the orbital spin of black holes that RIT scientists Campanelli, Lousto, Merritt and Zlochower had produced.
About the same time Discover published its interview with Thorne, Campanelli’s team simulated three black holes evolving, orbiting and eventually colliding, another computational feat never before done. The simulation of multiple black holes tested the formalism initially built for two masses and confirmed a robust computer code free of limitations. The results revealed the distinct gravitational signature three black holes might produce. This simulation was processed using the center’s new super computer cluster named “newHorizons.”
“Gravity waves can also confirm the existence of black holes directly because they have a special signature,” Lousto says. “That’s what we’re simulating. We are predicting a very specific signature of black hole encounters. And so, if we check that, there’s a very strong evidence of the existence of black holes.”
“It’s very timely research because it’s on the verge of discovery,” Campanelli adds. “And what we do is critical for this discovery to happen. We expect this area to keep expanding because the detection of gravitational waves will be the birth of gravitational wave astronomy, a new kind of astronomy. There will be a lot of interest in the world.”
Campanelli anticipates the center expanding in the near future to include scientists specializing in LIGO analysis of gravitational waveforms. This area of research within the field of numerical relativity bridges the gap between simulation and experimentation. It makes connections between the waveforms Campanelli’s team models with real data, and provides a necessary link in the pursuit of gravity waves.
Black holes and galaxies
Also affiliated with the Center for Relativity and Gravitation, Merritt, a preeminent theorist at RIT, focuses on galaxies and the supermassive black holes typically found at their centers. While Campanelli and Lousto are concerned with space-time around black holes, Merritt is concerned with the interplay between black holes and the galaxies in which they live. Merritt, a professor of physics, collaborated with his CCRG colleagues on a paper published last year in Physical Review Letters predicting how fast a black hole can be thrown or “kicked” out of its galaxy.
Merritt studies the evolution of star clusters and galaxies with a dedicated computer known as a gravitySimulator. Now three years old, the supercomputer was one of the first in the world built to study how gravitational forces cause black holes to form in the densest regions in the universe. Merritt’s work was featured in the cover story about black hole research in the May 2006 issue of Astronomy.
Merritt and colleague Laura Ferrarese from the University of Victoria in Australia made what many consider to be a major discovery known as the M-Sigma relationship – a connection between the mass of supermassive black holes and the mass of their host galaxies. Their findings imply that black holes and galaxy growth are closely related. Merritt and Ferrarese suggest that the energy released by black holes might regulate the growth and evolution of their host galaxy – a result having potentially important cosmological consequences.
Merritt is also engaged in a long-term project called Virtual Galaxy to simulate the entire Milky Way galaxy, star by star.
“The astrophysics group is already unified,” Merritt says. “All of us are talking about the centers of galaxies where there are supermassive black holes from one point of view or another. There are lots of opportunities for cross-interaction.”
From RIT to TV
In 2003, Merritt contacted Hans-Peter Bischof, associate professor of computer science, to write software visualizing his research. Now, a member of the CCRG team, Bischof, an expert in framework design, specializes in bringing black holes into view through computer graphics and animated movies illustrating the team’s results.
Some of Bischof’s images of black holes simulated by Campanelli, Lousto, Zlochower and Merritt were used in the History Channel’s series The Universe: Cosmic Holes, which broadcast in December 2007.
“The science done at CCRG is very difficult to explain to the general public,” Bischof says. “A movie is one way to capture the essential information and let it speak
Big Bang and dark energy
Cosmology is another important area of astrophysics. It is the study of the entire universe and the behavior of its component parts. Currently, studies in theoretical cosmology fall to Manasse Mbonye, a relativistic astrophysicist who applies Einstein’s theory of general relativity to understanding space-time under extreme gravitational influences. Mbonye believes these properties can provide an understanding of the early universe and the nature of the Big Bang as well as the physics inside black holes.
“The interior of black holes may in some ways share attributes with the early universe,” he says.
Mbonye’s work in these areas is guided by his “cosmic equilibrium conjecture,” an idea maintaining that regions of infinite density and pressure known as singularities might not exist in space-time.
Mbonye’s conjecture implies that the early universe may not have started from a physical singularity and that black hole interiors may be singularity-free. Based on this space-time paradigm, Mbonye searches for possible connections between black hole interiors and the early universe.
Mbonye also studies cosmic dynamics, including the current dark-energy driven cosmic acceleration. Being the only cosmologist at RIT doesn’t bother Mbonye, who takes a holistic look at the pending graduate program.
“Everything is complementary,” he says. “Our job here is to try to equip our students with the knowledge and understanding that we have of the kind of universe we live in. Each of us contributes a chunk of knowledge, and when you add those chunks in a complementary way you can create in the mind of a student a picture that comes as close as we can make it to understanding our world, our universe.
“That’s how astrophysics works,” he continues. “That’s how science works. No one single area of physics can alone make you understand this reality.”
For more information about RIT’s Center for Computational Relativity and Gravitation, visit http://ccrg.rit.edu.