Harvard Astronomers work on a broad variety of research areas ranging from the solar system to the edge of the observable Universe. You may read more details on a selected list of these research areas by clicking on the items on the left.
Imaging Black Holes" (Image credit: Avery Broderick, Avi Loeb)
Description of Research
The study of compact stellar remnants -- white dwarfs, neutron stars,
black holes -- and their larger cousins, supermassive black holes, is
a major area of research in modern astrophysics. Conditions are
extreme in the vicinity of these objects and lead to a variety of
unusual phenomena such as high energy X-ray and gamma-ray radiation,
high frequency oscillations, and relativistic jets. The objects are
often extraordinarily luminous and affect their surroundings to a much
greater extent than one might guess from their small sizes.
At the same time, compact objects are of interest in their own
right. The density inside a neutron star is greater than nuclear
density, and the magnetic field is far greater than anything we can
generate on Earth. A black hole is even more extreme. Within
classical physics, the density technically goes to infinity inside a
singularity. In addition, everything in the vicinity of the black hole
Event Horizon is ruled by strong gravitational effects associated with
Einstein's General Theory of Relativity.
Faculty in the Astronomy Department carry out research in diverse
topics in this field. A brief list includes: 1. Measuring the masses
and spins of stellar-mass and supermassive black holes. 2. Verifying
the reality of the mysterious Event Horizon. 3. Studying accretion
disks around white dwarfs, neutron stars and black holes, and
investigating how these disks cause relativistic jets. 4. Exploring
the formation of neutron stars and stellar-mass black holes in
supernova explosions, and the birth of supermassive black holes during
galaxy formation. 5. Investigating the extreme properties of quasars,
blazars and other active galactic nuclei and the evolution of these
populations as a function of cosmic time. 6. Studying energy and
momentum feedback from supermassive black holes and the enormous
effect these have on galaxy evolution. 7. Comparing and contrasting
the supermassive black hole in the center of our Milky Way Galaxy with
those in other galaxies.
Faculty Working in this Area:
Knowledge of black hole spin is essential for understanding such empirical issues as how gamma-ray bursts are powered and how black holes launch jets and other outflows that inject energy into the surrounding medium and affect structure formation on the scale of galaxies and even clusters of galaxies. During the past several years, we have established an accurate method for measuring the spins of stellar-mass black holes located in X-ray binary systems. This has allowed us to completely describe a dozen of these black holes by measuring both their spins and masses.
At the same time, given our deep knowledge of how these particular black holes behave, we now find ourselves at an exciting jumping-off place. For example, during this past year we published the first direct evidence for a relationship between jet power and black hole spin. Beyond astrophysics, our aspiration is to use secure measurements of black hole spin as a basis for making a compelling experimental test of the no-hair theorem.
Not only is astronomy the oldest science with a rich and instructive history, but many of its most important observations are available only in archival data (such as the HCO plate stacks of nearly 500,000 glass plate photographs) or in historical records. The Wolbach Library at CfA is especially complete and is part of the world's largest university library, which includes an unusually fine collection of rare astronomy classics. From time to time a historical lecture is presented as the Weekly Colloquium. The history of astronomy provides insights into the development and nature of science itself.
The CfA's Science Education Department provides the home for several National Science Foundation funded projects designed to improve the teaching of science in U.S. Schools and universities. Within these projects teachers collaborate with CfA scientists to develop hands-on activities, computer simulations and hardware, and text materials for the teaching of earth science, astronomy, and physics. Opportunities exist for involvement by graduate students, teachers, and scientists through sabbaticals, fellowships and summer institute programs.
Associated Professors and Lecturers
Associated Web Pages
Faculty Working in this Area:
This image compares the first Earth-size exoplanets found around a Sun-like star to planets in our own solar system, Earth and Venus. NASA's Kepler mission discovered the newfound planets, called Kepler-20e and Kepler-20f. Kepler-20e is slightly smaller than Venus with a radius .87 times that of Earth. Kepler-20f is a bit larger than Earth at 1.03 times the radius of Earth. The paper presenting the discovery was led by Francois Fressin of Harvard University.
Description of Research
One of the greatest scientific questions is whether or not there exist habitable worlds other than our own. This question has been posed for millennia, yet, remarkably, the time is at hand in which we can aspire to answer this age-old question. The study of exoplanets has proceeded at a breakneck pace from the detection 20 years ago of the first planets outside the Solar system to the recent discovery of the first Earth-sized worlds orbiting a Sun-like star. A major milestone was reached in 2012, when the Kepler Mission announced 2,324 exoplanet candidates, most of which are intermediate in size between Earth and Neptune.
The recent progress motivates several profound scientific questions: Can we develop the technology required both to determine the masses and hence densities of these Earth-sized worlds, and to undertake a survey of the nearby stars to find our neighboring exo-Earths? Can we understand the physical structures and atmospheres of these worlds, and by inference their formation history and the likelihood that they possess water oceans? Can we anticipate the chemical signature of life that might be observable remotely?
The Harvard-Smithsonian Center for Astrophysics is leading many exciting developments at the forefront of exoplanet research. In addition to active leadership of many activities of the Kepler Mission, CfA scientists are developing new tools and observatories devoted to discovering and characterizing Earth-like worlds; these facilities include the MEarth Observatory, the newly commissioned HARPS spectrograph, and the GCLEF instrument for the Giant Magellan Telescope. The exoplanet group at the CfA consists of 40 individuals with an emphasis on the mentorship of the next generation of leaders on the rapidly developing field.
Faculty Working in this Area:
|The Bullet Cluster, observed with Chandra in X-rays (pink) combined with a dark matter map (blue, derived from weak lensing), along with the optical image shows a supersonic merger taking place in the plane of the sky. The offset between the baryons (X-ray map) and mass (weak lensing map), is a direct proof of the existence of dark matter.|
Description of Research
High Energy Astrophysics explores energetic events in the Universe with energies extending from the far UV through the keV X-rays and into the ϒ-ray band. Scientific investigations of objects range from the Sun to distant active galactic nuclei. Research includes studies of the largest scales through wide area surveys. The resources for exploring High Energy Astrophysics at CfA are vast. The two largest areas of investigation exploit the Chandra X-ray Observatory, now in its 13th year and operated by SAO for NASA and a suite of Solar orbital and suborbital missions.
While many projects focus on high energy phenomena, the research is necessarily interdisciplinary, uniting observations across the electromagnetic spectrum along with theoretical calculations and simulations, as well as collaborations with research groups around the world. Examples of recent and ongoing investigations include:
Edo Berger, Martin Elvis, Douglas Finkbeiner, William Forman, Josh Grindlay, Christine Jones, Julia Lee, Avi Loeb, Jeffrey McClintock, Ramesh Narayan, Aneta Siemiginowska, Patrick Slane, Alicia Soderberg, Alexey Vikhlinin
Several Harvard Department of Astronomy faculty have active programs for development of cutting-edge new telescopes and instruments that provide numerous opportunities for students (and postdocs) to carry out research projects that will enable them fill the pressing need for future researchers and faculty with these skills. Astrophysics is a data-driven science, and new discoveries are usually strongly coupled with advances in both telescope and instrument design.
We are interested in answering some of the biggest and most exciting questions about the nature of the Universe. What was the Universe like at the beginning of time? What physical processes drove the origin of our Universe, and how can these explain its present-day structure and composition? Through precision measurements of the Cosmic Microwave Background (CMB), we directly explore the Universe as it was shortly after the Big Bang, and hope to solve some of most compelling questions of cosmology that are accessible to observations today.
The Keck Array is a suite of telescopes designed to measure the Cosmic Microwave Background polarization at high precision in search of the B-mode signature of inflation. Each Keck telescope duplicates the BICEP2 detector and optical design inside a compact, pulse tube cooled cryostat. This design allows up to five identical telescopes to be deployed on the DASI mount, located at the Martin A. Pomerantz Observatory at Amundsen-Scott South Pole Station. The Keck Array was successfully deployed during the austral summer of 2010-2011. Three receivers are currently observing, all at 150 GHz. Two more receivers are scheduled for deployment in 2011-2012 and will operate through 2015, measuring CMB B-mode polarization to fundamental background limits at multiple frequencies.
Surveys for accreting black holes in binaries or active galactic nuclei, as well as high energy transients and Gamma-ray Bursts, are best carried out with wide-field hard X-ray (~5 – 600 keV) telescopes. Unlike focusing X-ray telescopes (e.g. Chandra) which image by grazing incidence optics over a small (~10arcmin) field of view, coded aperture telescopes (e.g. Swift/BAT) can image over a ~70 degree FoV, though with reduced sensitivity due to higher backgrounds. We have developed a series of ever more sophisticated telescopes and finely pixelated imaging detector arrays that are tested, and conduct science, on high altitude (~39km) balloon flights under our NASA grants. The Oct. 2009 ProtoEXIST1 flight (see below) was very successful and will be followed by a Sept. 2012 ProtoEXIST2 flight with the highest spatial/spectral resolution, ~4X finer than Swift/BAT. The telescope/detector is a prototype for 4 such telescopes that may be launched in 2016 on a Brazil satellite (MIRAX-HXI) for a full southern-sky Time Domain Astrophysics survey mission in the era of LSST and Advanced LIGO.
Branden Allen, Jonathan E. Grindlay, Jaesub Hong
Instrument Group, led by Daniel Fabricant, designs, develops and operates instruments for the 6.5 m MMT and Magellan Telescopes, as well as the 1.2 and 1.5 meter telescopes on Mt. Hopkins. These include optical and near-infrared cameras and spectrographs that support a broad range of research from exoplanets to cosmology. The group has recently developed conceptual designs for wide-field near-infrared and precision radial velocity spectrographs for the 25m Giant Magellan Telescope (GMT).
Instruments in operation include Megacam and MMIRS at the Magellan Clay Telescope and Hectospec, Hectochelle, and SWIRC at the MMT. Binospec, a powerful optical spectrograph, is scheduled for delivery at the MMT in early 2014.
Warren Brown is involved in the design of advanced infrared spectrographs and characterization of the performance of existing instruments, and leads the OIR Telescope Data Center. Nelson Caldwell leads the scientific operations for Hectospec and Hectochelle. Daniel Fabricant is leading the development of Binospec and the design study for the GMT wide-field infrared spectrograph. John Geary develops electronics to operate large optical and near infrared arrays, and is expert in the characteristics of these detectors. Brian McLeod is leading the development of the adaptive optics (AO) phasing camera for GMT and is actively involved with AO development for GMT, and infrared spectroscopy with current and future instruments. Andrew Szentgyorgyi is developing laser comb technology for calibration of ultra-precise radial velocity spectrographs, and new concepts for precision radial velocity instruments, including a GMT instrument.
Harvard faculty are active in observational cosmology, with interests including the study of inflation, dark energy, dark matter, and the large-scale structure of the Universe. Professors Kirshner and Stubbs lead groups using Type Ia supernovae to measure the acceleration of the expansion rate of the Universe. Professor Eisenstein is director of the Sloan Digital Sky Survey III and is an expert in the use of galaxy clustering to measure the cosmic distance scale with the baryon acoustic oscillation method. Professor Stubbs pursues dark energy by measuring the abundance of clusters detected in the Sunyaev-Zel'dovich effect with the South Pole Telescope. Professor Kovac builds state-of-the-art experiments to search for gravitational waves from inflation using cosmic microwave background polarization measured by telescopes sited at the South Pole. Professor Finkbeiner searches for dark matter annihilation signatures in the gamma-ray and microwave sky. Dr. Alexey Vikhlinin is an expert on cluster of galaxies. His group pioneered studies of dark energy with observations of the evolving cluster mass function. Dr. Vikhlinin leads several prominent long-term observing programs with the Chandra X-ray Observatory. In addition to using CfA telescope facilities, the CfA is a member of the PanStarrs survey, Sloan Digital Sky Survey III, BICEP-II, SPUD, and Polar collaborations, and the Murchison Wide Field Array. The CfA observational cosmology programs work in close collaborations with the Institute for Theory and Computation to build a close bond between theory and observation.
21-cm Map of the Reionization of the Universe" (Image credit: Jonathan Pritchard, Avi Loeb)
Simulating galaxy formation" (Image credit: Debora Sijacki, Mark Vogelsberger, Lars Hernquist)
Description of Research
Since the Universe is expanding, it must have been denser in the past. But even before we get all the way back to the Big Bang, there must have been a time when stars like our Sun or galaxies like our own Milky Way did not exist because the Universe was denser than these objects are. We therefore face the important question about our origins: how and when did the first stars and galaxies form? Harvard faculty study theoretically the formation of the first galaxies and their environmental impact in terms of the reionization of the intergalactic medium. State-of-the-art numerical simulations are used to predict the formation of stars and black holes within galaxies throughout cosmic history. These predictions will be tested over the upcoming decade through deep observations with the next generation of large-aperture infrared telescopes as well as low-frequency radio mapping of the 21-cm line of hydrogen.
Recent highlights include: (i) The discovery of gamma-ray bursts at redshift of 8-9.5, the most distant objects in the universe; (ii) the formation of relativistic jets and the breakout of shocks in supernovae; (iii) the discovery of the most luminous known supernovae, with an energy scale that requires new exotic explosion mechanisms; (iv) the first detection of the birth of a jet from the tidal destruction of a stray star by a supermassive black hole; (v) first results from century-long monitoring of the sky as part of the DASCH project; and (vi) refined measurement of the equation of state of dark energy using Type Ia supernovae (including the 2011 Nobel Prize in Physics awarded to two former Harvard graduate students!)
Harvard Astonomers study Star Formation, Stars and Stellar Evolution, and the Interstallar Medium (ISM).
A deep view of star formation in Perseus from Megacam, taken
by (then) Harvard Graduate Students Jonathan Foster and Jaime Pineda
Nearly all of the light we see from the Universe comes from stars and the interstellar material that forms them. Thus, understanding the processes which turn interstellar matter into stars is key to our understanding of the Universe and its evolution.
Groups within the Department study the interstellar medium and star formation across many scales, from the early Universe to high-redshift galaxies to local galaxies and the Milky Way. A range of diverse theoretical efforts, involving both analytic and numerical work are underway, as well as observational projects across the electromagnetic spectrum.
Many researchers at the CfA are interested in improving the conceptual picture of nearby star formation, and in using it to refine the more empirical view historically employed in models of how the ISM is converted to stars in distant, unresolved, galaxies. On small scales, other projects focus on sharpening our view of the disks that form around stars as interstellar matter coalesces, and on using the information about these circumstellar disks to learn how planets form.