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Areas of Research
Our understanding of the cosmos has improved dramatically in recent years, thanks to parallel progress in theory, computation and observation. For example, we've gone from arguing about whether the age of our universe is 10 or 20 billion years to whether it's 13.7 or 13.8. Yet further improved measurements are on their way, and there's no shortage of pressing questions to tackle.
What's the nature of the data matter and dark energy that constitute 96% of the cosmic density?
What can we say about the ultimate origins and fate of our universe?
Multiple efforts to tackle such questions are underway at the MKI, lead by Edmund Bertschinger, Enectali (Tali) Figueroa-Feliciano, Jacqueline Hewitt and Max Tegmark, developing experimental, analytical, computational, and statistical tools to improve our understanding of gravitation and cosmology. Our main research topics include:
- Dark matter: experimental direct detection, improving our understanding of how it clusters to form galaxies and larger structures, investigating its detectability in the cosmos and laboratory
- Dark energy: phenomenology of theories of dark energy and their cosmological tests
- Cosmic origins: exploring and testing models of cosmological inflation
- Cosmic first-light: probing the epoch of cosmic dawn using novel radio telescopes
- Testing general relativity, especially in cosmology
- Developing consistent modified gravity theories and developing observational tests of them
- Other topics in theoretical physics and cosmology, e.g. cosmological perturbation theory, scalar fields and neutrinos in cosmology, parallel computation
For millenia, people have wondered whether other stars have planets, and whether those planets might harbor life. Within the last few decades, it has become possible to make progress on these timeless questions. Exoplanetary science --- the study of planets around other stars --- is one of the newest and most rapidly growing branches of astrophysics.
The MIT exoplanet community takes a comprehensive approach, by developing new space missions, pursuing ground-based observations, and advancing the theory of exoplanets. A particular focus is the study of transiting planets: those that eclipse their parent stars. Professor Joshua Winn's group studies orbital dynamics and planet formation with creative new observations using Magellan and other telescopes. Professor Sara Seager pioneered the theory of exoplanet atmospheres and leads several innovative space missions to find and study Earth-like planets. Winn and Seager are both part of the ongoing NASA Kepler mission. Dr. George Ricker is Principal Investigator of TESS, a proposed NASA mission to find transiting planets around the nearest and brightest stars in the sky. Professor Kerri Cahoy (Aero/Astro) develops new technologies for direct imaging of exoplanetary systems. Professor Nevin Weinberg studies the theory of tidal interactions between planets and stars. Biweekly meetings bring together our group of students, postdocs, faculty and research scientists who share a common interest in exploring other worlds.
Several researchers at MKI study extragalactic astrophysics, a broad category of research that includes observational studies of phenomena outside our own Milky Way Galaxy. Among the active topics of research are clusters of galaxies; composed of hundreds to thousands of galaxies and containing large amounts of hot gas and dark matter, these are the largest gravitationally bound structures in the universe. As such, they serve as rich targets to study astrophysical processes in the universe, including the formation of structure, chemical enrichment and evolution, and galaxy formation, evolution, and feedback. Since galaxy clusters form primarily through gravitational processes, the mass distribution of clusters as a function of redshift (distance) places useful constraints on cosmology. Understanding the astrophysics of clusters is crucial to eliminate biases due to non-gravitational processes.
Scientists at MKI are engaged in a variety of research projects targeting the astrophysics of galaxy clusters. These projects heavily use instruments with direct MKI involvement, such as the Chandra X-ray Observatory, the Suzaku X-ray Observatory, and the Magellan telescopes. Members of MKI are also engaged in work with the South Pole Telescope collaboration and researchers at other institutions in the US and abroad.
FIRST STARS/REIONIZATION, COSMIC STRUCTURE
MKI scientists are deeply engaged in searching for the first populations of stars which formed in the early universe. These sources ushered in the end of the cosmic dark age, a period which began around 300 million years after the Big Bang and lasted for 300-500 Million years thereafter. During this time before the first stars, the universe was composed of dark matter, mixed with hydrogen and helium gas, with no stars, galaxies or heavier elements. Theories of how the very first stars form - which remain as-yet untested - suggest that these objects may have looked very different from the familiar ones we see in the sky today. These distant ancestors would have been on average much brighter and more massive, containing a primordial chemical mixture. Their photons would bring into definition the location of early galaxies, and ionize the universe, ushering in the modern era of stars and galaxies.
Because early universe studies probe very faint and distant sources, scientific advancement depends on the development of novel observational techniques and new instrumentation. MKI has supported the construction of new wide-field radio telescopes designed to image neutral hydrogen structures from the time during and before First Light (J. Hewitt, M. Tegmark), and MKI also delivered the FIRE infrared spectrometer to the Magellan telescopes, enabling the direct observation of galaxies and quasars at >95% lookback time to the Big Bang (R. Simcoe). New surveys of the Milky Way's halo are yielding stars of very low chemical abundance that offer glimpses into how stars form in chemically pristine environments (A. Frebel). And new computational simulations are tying together these observational threads into a coherent early picture of how galaxies first assembled.
MKI scientists are studying the solar wind from its origin at the Sun to the boundaries of the solar system. They have instruments operating on two current spacecraft, the Wind spacecraft which observes the solar wind just upstream of Earth and the Voyager 2 spacecraft which is over 100 AU from the Sun and near the outer boundary of the heliosphere. They also participate in development of two future missions. DISCOVR will make fast solar wind measurements upstream of Earth and Solar Probe Plus will make the first observations close to the Sun.
STRONG GRAVITY & GRAVITATIONAL RADIATION
Gravity is the weakest of the four fundamental forces, and as such has only been carefully tested in weak fields, such as near the earth or in our solar system. All such tests have been consistent with the expectation that Einstein's theory of general relativity describes gravity, at least so far. Strong-gravity astrophysical systems, such as black holes and neutron stars, open up the possibility of testing gravity more stringently and seeing whether Einstein's relativity remains our best description of gravity, or whether something more exotic is needed to describe these objects. Strong-gravity objects are also the engines for some of the energetic processes in our universe; studying them gives us insight into the dynamics of these important astrophysical processes.
MKI researchers are leading several efforts to use upcoming astronomical observations to study strong-gravity objects. Gravitational waves are generated by the formation and dynamics of black holes and neutron stars. Scott Hughes' research group is pursuing several projects to model the gravitational waves generated by such compact objects in binary systems, to understand how to use them to test the nature of gravity, and to use them as probes of astronomy. The LIGO observatory leads the worldwide efforts to directly measure gravitational waves. We expect that coming data from the advanced LIGO detectors, in concert with theoretical modeling of the waves that come from strong-gravity sources, will be a new and powerful probe of strong gravity and strong gravity systems.
SUPERNOVAE, NEUTRON STARS & BLACK HOLES
The image below is an example of an "accretion-powered millisecond pulsar", a class of objects that is extensively studied by Deepto Chakrabarty's group at MKI.
This image (below) of the debris of an exploded star - known as supernova remnant 1E 0102.2-7219, or "E0102" for short - features data from NASA's Chandra X-ray Observatory. E0102 is located about 190,000 light years away in the Small Magellanic Cloud, one of the nearest galaxies to the Milky Way. It was created when a star that was much more massive than the Sun exploded, an event that would have been visible from the Southern Hemisphere of the Earth over 1000 years ago.
Chandra first observed E0102 shortly after its launch in 1999. New X-ray data have now been used to create this spectacular image and help celebrate the ten-year anniversary of Chandra's launch on July 23, 1999. In this latest image of E0102, the lowest-energy X-rays are colored orange, the intermediate range of X-rays is cyan, and the highest-energy X-rays Chandra detected are blue. The Chandra image shows the outer blast wave produced by the supernova (blue), and an inner ring of cooler (red-orange) material. This inner ring is probably expanding ejecta from the explosion that is being heated by a shock wave traveling backwards into the ejecta.
Listen to a NASA's Chandra X-ray Observatory podcast about E0102.
GRAVITATIONAL WAVE DETECTION
HIGH ENERGY ASTROPHYSICS
High-energy astrophysics studies X-ray and gamma-ray photons, which are produced in some of the most extreme conditions in the universe: temperatures of millions of degrees, high magnetic fields, extreme gravity, or massive explosions. MKI has a long successful history of high-energy astrophysics research spanning a wide range of topics and scales from planets to stars to the largest cluster of galaxies.
MKI has been and continues to be involved in instrumentation for a variety of space-based high-energy astrophysics missions including the Advanced CCD imaging Spectrometer (ACIS) and High-Energy Transmission Grating Spectrometer (HETGS) on NASA's Chandra X-ray Observatory and the X-ray Imaging Spectrometer on the Japanese Suzaku spacecraft. MKI provides support to both the Chandra and Suzaku missions through instrument calibration, software development, and observer support. Continuing detector development from the CCD Lab promises to lead to improvements over current instruments, such as faster readouts and better radiation tolerance. Work on optics and diffraction gratings at the Space Nanotechnology Lab will provide much higher diffraction efficiency and spectral resolution than previous technology.
Radio astronomy research at MIT is currently focussed on the development of low-frequency radio arrays and techniques, with an emphasis on mapping neutral hydrogen throughout our Universe via its redshifted 21 cm line. This offers a unique opportunity to probe the cosmic “dark ages” and the formation of the first luminous objects (the Epoch of Reionization). Moreover, because it can map a much larger volume of our Universe, it has the potential to overtake the cosmic microwave background as the most sensitive cosmological probe of the epoch of reionization, inflation, dark matter, dark energy, and neutrino masses. Another topic being pursued with radio techniques at MIT is the detection and characterization of transient emission associated with compact objects and, possibly, gravitational wave sources.
The MIT Kavli Institute is a partner in the Murchison Widefield Array (MWA) project, a low frequency radio array under construction in Western Australia. The MWA is made up of 128 antenna "tiles," 4X4 arrays of crossed dipoles. Signals from all tiles are brought to a central location, enabling correlation interferometric imaging, as well as custom data processing for other applications. Detecting signatures of the Epoch of Reionization is a key science goal of the MWA.
In addition, the MIT Kavli Institute is developing a novel radio array design, the Omniscope, aimed at dramatically reducing the cost of the much larger future radio arrays required to take full advantage of the cosmological 21 cm signal. By arranging N small, cheap antennas in a hierarchical grid pattern, the signal processing cost can be cut from N2 to N log N and calibration can be fully automated using redundant baselines.
HIGH PERFORMANCE COMPUTING
High performance computing (HPC) is a necessary component of modern astrophysics research. MKI has used 3 HPC clusters over the past decade. The first cluster has been used by the Chandra space telescope for data analysis and modeling associated with the HETG instrument contract. It is still in use today.
The second cluster was used by the LIGO project, and was recently retired. As LIGO undergoes upgrades to Advanced LIGO sensitivity, the computing and analysis infrastructure will be completely overhauled.
The third cluster was originally built by Professors Edmund Bertschinger and Scott Hughes, and largely used by their research groups. It was significantly upgraded in 2008, replacing the original 32-bit compute nodes with 64-bit nodes. It has recently been further upgraded to use CentOS Enterprise Linus with the Rocks Cluster Suites, an open source cluster management package. The HPC cluster currently consists of 31 compute nodes and one master node, plus 2 storage servers providing researchers 248 CPU processors (cores) with 496 GB memory and 48 TB data storage. We also have recently added a Graphics Processing Unit (GPU) server providing nVidia's Tesla 2050 card with 448 GPU cores and 12GB memory.
Over the past several years, this cluster has become a major computing resource for many MKI research groups. The following groups have used the cluster for a variety of MKI research projects:
Scott Hughes Group
Modeling of gravitational-wave sources and their measurement by gravitational-wave detectors. Modeling sources requires solving the equations of generic relativity to high accuracy, which requires large, parallel, high-precision HPC simulations. Modeling gravitational-wave measurement requires large Monte-Carlo simulations in order to explore the parameter space of signals that nature might provide and to understand how well these signals can be distinguished from one another.
Edmund Bertschinger Group
Evolving with high precision and few approximations a system of N particles that interact through gravity.
Computing x-ray scattering from dust in the interstellar medium (ISM).
Computing exoplanet atmosphere models.
Leslie Rogers (thesis project)
Modeling the interior structure of super-Earth and sub-Neptune exoplanets, as a contribution to the Kepler Science Group.
Anna Frebel Group
Computing models of galactic haloes, and simulating galaxy formation. Galaxy formation is a complicated nonlinear process. Researchers run large-scale N-body simulations to compare their theoretically predicted galaxies to observed ones. Because these programs are computationally expensive and require lots of memory, Frebel's group uses the MKI HPC cluster to run and analyze these N-body simulations in order to gain intuition about the formation of galaxies.
Simona Vegetti (former MKI postdoctoral fellow)
Modeling a large sample of gravitational lens galaxies. The goal of this modeling is to determine the posterior probability density distribution of lens parameters, as well as the Bayesian evidence. This allows Vegetti to objectively compare models that allow for the presence of mass clumps in the lens galaxy versus models that assume a smooth mass distribution.
Modeling the complex polarized beam patterns of the MWA tiles for their different pointing directions.
The telescopes used by MIT's optical and IR astronomers are the direct descendants of Galileo's, but have almost a million times more light gathering power. And instead of using their eyes, they use huge arrays of detectors not unlike those in cell phones, but cooled to liquid nitrogen temperatures.
The vacuum of space is not so empty. Apart from the plethora of photons spanning from radio to gamma rays crossing interstellar and intergalactic space, there is a large variety of massive particles with cosmogenic origin. Particle Astrophysics studies the generation, evolution and properties of these particles, which include cosmic rays, neutrinos, and dark matter.
These particles can be studies directly with detectors in space, on the ground, or underground. They can also be studied by the products of their interactions, which can happen locally with the Earth or its atmosphere, or much farther away.
MKI is involved in the direct detection of dark matter through the Cryogenic Dark Matter Search, and with the AMS-II experiment (S. Ting).
PLANETARY REMOTE SENSING
Microwave: MKI supplied the PI for the Magellan Venus radar mapping mission (1990-94) and was responsible for the analysis of altimetry and radiometry data. This resulted in what are currently the most detailed topographic maps of Venus, with accompanying information on the global distribution of surface roughness and dielectric constant (related to the density and composition of surface material). MKI scientists are also active in the radar mapping of Titan from the Cassini Saturn orbiter and in proposals for sending orbiting radars and radiometers to Venus, Mars and the Moon.
LIDAR: MKI scientists participated in the LIDAR (Light Detection and Ranging) experiment (MOLA) aboard the Mars Global Surveyor (operative 1999-2001), concentrating on an analysis of the echoes from CO2 clouds in the polar night. The locations and times at which the clouds were found, and their relation to Martian surface features, seasons, dust storms, etc., yielded important information on the state of the polar atmosphere and its relation to the seasonal CO2 ice caps.
X-Ray: Numerous observations of X-rays from Jupiter and Saturn have been made by instruments aboard Earth-orbiting spacecraft: Chandra, XMM-Newton, and Suzaku. They have been analyzed by a team from MKI, UCL, SwRI, and MSFC. Spectra have been obtained of X-rays from the Jovian aurora and from Saturn's rings, and X-rays have been detected from Jupiter's moons Io and Europa and from the Io plasma torus. Combining these measurements with simultaneous optical observations from HST and ground-based telescopes has led to a deeper understanding of Jupiter's and Saturn's auroral regions and of Jupiter's extended magnetotail.
Theoretical astrophysicists use physical principals to develop models of the Universe and its constituents. These models provide a framework that allows us to interpret observations and, conversely, observations tell us which models are the most plausible. This interplay between theory and observations is an important component of astrophysics research and is highly valued at MKI.
Researchers at MKI work on a broad range of topics in theoretical astrophysics.
Ed Bertschinger group: formation of cosmic structure, the physics of dark matter, the physics of gravitation, and the processes governing matter and radiation close to black holes.
Alan Guth group: application of theoretical particle physics to the early universe, including the inflationary cosmological model.
Scott Hughes group: astrophysical general relativity, focusing in particular upon black holes and gravitational-wave sources.
Paul Joss group: theory of neutron stars, supernovae, and binary systems.
Saul Rappaport group: formation and evolution of binary systems containing collapsed stars — white dwarfs, neutron stars, and black holes.
Sara Seager group: atmospheric composition and the interior structure of exoplanets, with a focus on the new and growing data set of transiting exoplanets.
Max Tegmark group: precision cosmology, e.g., combining theoretical work with new measurements to place sharp constraints on cosmological models and their free parameters.
Nevin Weinberg group: compact objects, tides and binary evolution, stellar oscillations, and explosive thermonuclear burning.