About

Professor Charles R. Alcock is the Donald H. Menzel Professor of Astrophysics at the Center for Astrophysics | Harvard & Smithsonian. His research interests include the determination of the composition of cosmic dark matter, innovative surveys of the outer solar system, massive compact halo objects, comets, and asteroids. He was educated at the University of Auckland, New Zealand, and at the California Institute of Technology. Throughout his career, he has held positions at the Institute for Advanced Study, Massachusetts Institute of Technology, Lawrence Livermore National Laboratory, and the University of Pennsylvania. He served as the Director of the Center for Astrophysics from 2004 to 2023 and was Acting Undersecretary for Science for the Smithsonian from 2008 to 2009. Professor Alcock has received numerous awards, including the Department of Energy’s Ernest O. Lawrence Award for Physics in 1996 and the Beatrice M. Tinsley Award of the American Astronomical Society in 2000. He was elected to the National Academy of Sciences in 2001 and to the American Academy of Arts & Sciences in 2006.

Research topics

• Astrophysics
• Physics
• Quantum mechanics
• Mathematics
• Astronomy
• Nuclear physics
• Computational physics
• Geometry

Selected publications

• Probing Plasma Composition with the Next Generation Event Horizon Telescope (ngEHT)

  Galaxies · 2023 · 9 citations

  • Physics
  • Astrophysics
  • Computational physics

  We explore the plasma matter content in the innermost accretion disk/jet in M87* as relevant for an enthusiastic search for the signatures of anti-matter in the next generation of the Event Horizon Telescope (ngEHT). We model the impact of non-zero positron-to-electron ratio using different emission models, including a constant electron to magnetic pressure (constant βe model) with a population of non-thermal electrons as well as an R-beta model populated with thermal electrons. In the former case, we pick a semi-analytic fit to the force-free region of a general relativistic magnetohydrodynamic (GRMHD) simulation, while in the latter case, we analyze the GRMHD simulations directly. In both cases, positrons are being added at the post-processing level. We generate polarized images and spectra for some of these models and find out that at the radio frequencies, both of the linear and the circular polarizations are enhanced with every pair added. On the contrary, we show that, at higher frequencies, a substantial positron fraction washes out the circular polarization. We report strong degeneracies between different emission models and the positron fraction, though our non-thermal models show more sensitivities to the pair fraction than the thermal models. We conclude that a large theoretical image library is indeed required to fully understand the trends probed in this study, and to place them in the context of a large set of parameters which also affect polarimetric images, such as magnetic field strength, black hole spin, and detailed aspects of the electron temperature and the distribution function.

  PublisherOA PDFDOI

• Morphological Types of DM Halos in Milky Way-like Galaxies in the TNG50 Simulation: Simple, Twisted, or Stretched

  The Astrophysical Journal · 2021 · 4 citations

  • Physics
  • Astrophysics
  • Astronomy

  Abstract We present a comprehensive analysis of the shape of dark matter (DM) halos in a sample of 25 Milky Way-like galaxies in TNG50 simulation. Using an enclosed volume iterative method, we infer an oblate-to-triaxial shape for the DM halo with median T ≃ 0.24. We group DM halos into three different categories. Simple halos (32% of the population) establish principal axes whose ordering in magnitude does not change with radius and whose orientations are almost fixed throughout the halo. Twisted halos (32%) experience levels of gradual rotations throughout their radial profiles. Finally, stretched halos (36%) demonstrate a stretching in the lengths of their principal axes where the ordering of different eigenvalues changes with radius. Subsequently, the halo experiences a “rotation” of ∼90° where the stretching occurs. Visualizing the 3D ellipsoid of each halo, for the first time, we report signs of a reorienting ellipsoid in twisted and stretched halos. We examine the impact of baryonic physics on DM halo shape through a comparison to dark matter only (DMO) simulations. This suggests a triaxial (prolate) halo. We analyze the impacts of substructure on DM halo shape in both hydrodynamical and DMO simulations and confirm that they are subdominant. We study the distribution of satellites in our sample. In simple and twisted halos, the angle between satellites’ angular momentum and the galaxy’s angular momentum grows with radius. However, stretched halos show a flat distribution of angles. Overlaying our theoretical outcome on the observational results presented in the literature establishes a fair agreement.

  PublisherDOI

• The TAOS Project Stellar Variability II. Detection of 15 Variable Stars

  OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2021-04-26

  articleOpen access

  Abstract not provided

  Publisher

• EBAI: Eclipsing Binaries with Artificial Intelligence

  Astrophysics Source Code Library · 2019-08-01

  article
  Publisher

• The Role of Small Telescopes in the Upcoming Era of the Giant Magellan Telescope and Other Extremely Large Telescopes (Abstract)

  Journal of the American Association of Variable Star Observers (JAAVSO) · 2017-06-01

  article1st authorCorresponding
  Publisher

• New Proper Motions of the Small Magellanic Cloud Using HST and Implications for Milky Way Mass

  Proceedings of the International Astronomical Union · 2017-07-01 · 2 citations

  articleSenior author

  Abstract As new work on the proper motions (PMs) of the Large Magellanic Cloud (LMC) has come out, our view of the history of the Magellanic Clouds has evolved. We now believe they are on their first infall into the Milky Way (MW), having been tidally bound at the start of infall (though not necessarily now). Combining these observations with initial PMs of the Small Magellanic Cloud (SMC) suggests a new formation mechanism of the Magellanic Stream through the stripping of material from the SMC. However, large uncertainties remain in the exact mass of the LMC. We present a measurement of the systemic proper motions of the SMC from astrometry with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST), covering a ~3 year baseline of 30 fields with background QSOs. We find these motions to be μ W = −0.82 ± 0.06 mas/yr and μ N = −1.23 ± 0.07 mas/yr. Combining these measurements with previous efforts in studying the Clouds will help constrain their interactions with each other and the MW, including the mass of the LMC and the MW, as well as provide new insight into the internal dynamics of the SMC.

  PublisherDOI

• Repetitive patterns in rapid optical variations in the nearby black-hole binary V404 Cygni

  Nature · 2016-01-01 · 87 citations

  articleOpen access
  PublisherOA PDFDOI

• The DEEP-SOUTH: Round-the-clock physical characterization of near-Earth objects in the Southern Hemisphere

  Asteroids, Comets, Meteors 2014 · 2014-07-01

  articleSenior author
  Publisher

• The Binarity of the Clouds and the Formation of the Magellanic Stream

  2013-08-03 · 2 citations

  articleSenior author

  Abstract. The HST proper motion (PM) measurements of the Clouds have severe implications for their interaction history with the Milky Way (MW) and with each other. The Clouds are likely on their first passage about the MW and the SMC’s orbit about the LMC is better described as quasi-periodic rather than circular. Binary L/SMC orbits that satisfy observational constraints on their mutual interaction history (e.g. the formation of the Magellanic Bridge during a collision between the Clouds ∼300 Myr ago) can be located within 1σ of the mean PMs. However, these binary orbits are not co-located with the Magellanic Stream (MS) when projected on the plane of the sky and the line-of-sight velocity gradient along the LMC’s orbit is significantly steeper than that along the MS. These combined results ultimately rule out a purely tidal origin for the MS: tides are ineffective without multiple pericentric passages and can neither decrease the velocity gradient nor explain the offset stream in a polar orbit configuration. Alternatively, ram pressure stripping of an extended gaseous disk may naturally explain the deviation. The offset also suggests that observations of the little-explored region between RA 21 h and 23 h are crucial for characterizing the full extent of the MS.

  Publisher

• Kepler and Kuiper (K&K): Addressing Key Questions in Astrophysics and Planetary Science

  2013-02-05

  article1st authorCorresponding

Recent grants

• Studies of Solar System Planetesimals and Extra-Solar Planets: Occultations and Transits enabled by novel fast CCD cameras

  NSF · $397k · 2004–2009

• SEI: Collaborative Research: Discovering Unexpected Planets and Other Astronomical Oddities

  NSF · $192k · 2007–2011

Frequent coauthors

• C. W. Stubbs

  396 shared

• K. Griest

  Laboratory for Atmospheric and Space Physics

  355 shared

• M. R. Pratt

  University of Utah

  284 shared

• D. P. Bennett

  260 shared

• K. C. Freeman

  North Carolina Central University

  257 shared

• M. J. Lehner

  255 shared

• B. A. Peterson

  Mount Stromlo Observatory

  252 shared

• D. R. Alves

  228 shared

Education

• Ph.D., Astronomy

  Harvard University

  1982

• B.A., Physics

  University of California, Berkeley

  1977

Awards & honors

• Department of Energy’s Ernest O. Lawrence Award for Physics…
• Beatrice M. Tinsley Award of the American Astronomical Socie…
• Elected to the National Academy of Sciences (2001)
• Elected to the American Academy of Arts & Sciences (2006)