About

John E. Carlstrom is a Professor and the Subramanyan Chandrasekhar Distinguished Service Professor in the Departments of Astronomy and Astrophysics and Physics at The University of Chicago. He is associated with the Research Office ERC 341 and the Chair's Office ERC 599E. His research focuses on astrophysics, cosmology, and related fields, contributing to the understanding of fundamental physics. He has been recognized for his work, including the award of the 2020 Breakthrough Prize in Fundamental Physics to the Event Horizon Telescope.

Research topics

• Astrophysics
• Physics
• Astronomy
• Computer Science
• Optics
• Algorithm
• Statistics
• Particle physics
• Quantum mechanics
• Mathematics
• Remote sensing
• Computational physics
• Geology

Selected publications

• Millimeter-wave observations of Euclid Deep Field South using the South Pole Telescope

  Astronomy and Astrophysics · 2026-01-29 · 2 citations

  preprintOpen access

  Context . The South Pole Telescope third-generation camera (SPT-3G) has observed over 10 000 square degrees of sky at 95, 150, and 220 GHz (3.3, 2.0, 1.4 mm, respectively) and will significantly overlap the ongoing 14 000 square-degree Euclid Wide Survey. The Euclid collaboration recently released Euclid Deep Field South (EDF-S) observations of 23 square degrees at wide field depths in the first quick data release (Q1). Aims . With the goal of releasing complementary millimeter-wave data and encouraging legacy science, we performed dedicated observations of a 57-square-degree field overlapping the EDF-S. Methods . The observing time totaled 20 days, and we reached noise depths of 4.3, 3.8, and 13.2 μK-arcmin at 95, 150, and 220 GHz, respectively. Results . In this work we present the temperature maps and two catalogs constructed from these data. The emissive source catalog contains 601 objects (334 inside EDF-S) with 54% synchrotron-dominated sources and 46% thermal dust emission-dominated sources. The 5σ detection thresholds are 1.7, 2.0, and 6.5 mJy in the three bands. The cluster catalog contains 217 cluster candidates (121 inside EDF-S) with median mass M 500c = 2.12 × 10 14 M ⊙ /h 70 and median redshift z = 0.70, corresponding to an order-of-magnitude improvement in cluster density over previous tSZ-selected catalogs in this region (3.81 clusters per square degree). Conclusions . The overlap between SPT and Euclid data will enable a range of multiwavelength studies of the aforementioned source populations. This work serves as the first step toward joint projects between SPT and Euclid and provides a rich dataset containing information on galaxies, clusters, and their environments.

  PublisherDOI

• SPT-3G D1: CMB temperature and polarization power spectra and cosmology from 2019 and 2020 observations of the SPT-3G main field

  Physical review. D/Physical review. D. · 2026-01-05 · 10 citations

  preprintOpen access

  Plenary talk presented at the XXI International Workshop on Neutrino Telescopes - Padova 29 September - 3 October 2025 (https://agenda.infn.it/event/44606/)

  PublisherOA PDFDOI

• Towards constraining cosmological parameters with SPT-3G observations of 25% of the sky

  ArXiv.org · 2025-10-28

  articleOpen access

  International audience

  PublisherOA PDF

• The persistent shadow of the supermassive black hole of M87

  Astronomy and Astrophysics · 2025-01-01 · 20 citations

  articleOpen access

  The Event Horizon Telescope (EHT) observation of M87 ∗ in 2018 has revealed a ring with a diameter that is consistent with the 2017 observation. The brightest part of the ring is shifted to the southwest from the southeast. In this paper, we provide theoretical interpretations for the multi-epoch EHT observations for M87 ∗ by comparing a new general relativistic magnetohydrodynamics model image library with the EHT observations for M87 ∗ in both 2017 and 2018. The model images include aligned and tilted accretion with parameterized thermal and nonthermal synchrotron emission properties. The 2018 observation again shows that the spin vector of the M87 ∗ supermassive black hole is pointed away from Earth. A shift of the brightest part of the ring during the multi-epoch observations can naturally be explained by the turbulent nature of black hole accretion, which is supported by the fact that the more turbulent retrograde models can explain the multi-epoch observations better than the prograde models. The EHT data are inconsistent with the tilted models in our model image library. Assuming that the black hole spin axis and its large-scale jet direction are roughly aligned, we expect the brightest part of the ring to be most commonly observed 90 deg clockwise from the forward jet. This prediction can be statistically tested through future observations.

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• Constraints on Inflationary Gravitational Waves with Two Years of SPT-3G Data

  ArXiv.org · 2025-05-05

  preprintOpen access

  We present a measurement of the $B$-mode polarization power spectrum of the cosmic microwave background anisotropies at 32 $\le$ $\ell$ $<$ 502 for three bands centered at 95, 150, and 220 GHz using data from the SPT-3G receiver on the South Pole Telescope. This work uses SPT-3G observations from the 2019 and 2020 winter observing seasons of a $\sim$1500 deg$^2$ patch of sky that directly overlaps with fields observed with the BICEP/Keck family of telescopes, and covers part of the proposed Simons Observatory and CMB-S4 deep fields. Employing new techniques for mitigating polarized atmospheric noise, the SPT-3G data demonstrates a white noise level of 9.3 (6.7) $μ$K-arcmin at $\ell \sim 500$ for the 95 GHz (150 GHz) data, with a $1/\ell$ noise knee at $\ell$=128 (182). We fit the observed six auto- and cross-frequency $B$-mode power spectra to a model including lensed $Λ$CDM $B$-modes and a combination of Galactic and extragalactic foregrounds. This work characterizes foregrounds in the vicinity of the BICEP/Keck survey area, finding foreground power consistent with that reported by the BICEP/Keck collaboration within the same region, and a factor of $\sim$ 3 higher power over the full SPT-3G survey area. Using SPT-3G data over the BICEP/Keck survey area, we place a 95% upper limit on the tensor-to-scalar ratio of $r < 0.25$ and find the statistical uncertainty on $r$ to be $σ(r) = 0.067$.

  PublisherOA PDFDOI

• Cosmology from CMB lensing and delensed <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>E</mml:mi><mml:mi>E</mml:mi></mml:math> power spectra using 2019–2020 SPT-3G polarization data

  Physical review. D/Physical review. D. · 2025-04-16 · 57 citations

  articleOpen access

  From CMB polarization data alone, we reconstruct the CMB lensing power spectrum, comparable in overall constraining power to previous temperature-based reconstructions, and an unlensed $E$-mode power spectrum, with clear detections of the third through the tenth acoustic peaks. The observations, taken in 2019 and 2020 with the South Pole Telescope (SPT) and the SPT-3G camera, cover $1500\text{ }\text{ }{\mathrm{deg}}^{2}$ at 95, 150, and 220 GHz with arcminute resolution and roughly $4.9\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{K}\text{\ensuremath{-}}\mathrm{arcmin}$ coadded noise in polarization. The power spectrum estimates, together with systematic parameter estimates and a joint covariance matrix, follow from a Bayesian analysis using the marginal unbiased score expansion (MUSE) method. The $E$-mode spectrum at $\ensuremath{\ell}&gt;2000$ and lensing spectrum at $L&gt;350$ are the most precise to date. Assuming the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model, and using only these SPT data and priors on $\ensuremath{\tau}$ and absolute calibration from Planck, we find ${H}_{0}=66.81\ifmmode\pm\else\textpm\fi{}0.81\text{ }\text{ }\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, comparable in precision to the Planck determination and in $5.4\ensuremath{\sigma}$ tension with the most precise ${H}_{0}$ inference derived via the distance ladder. We also find ${S}_{8}\ensuremath{\equiv}{\ensuremath{\sigma}}_{8}({\mathrm{\ensuremath{\Omega}}}_{\mathrm{m}}/0.3{)}^{0.5}=0.850\ifmmode\pm\else\textpm\fi{}0.017$, providing further independent evidence of a slight tension with low-redshift structure probes. The $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model provides a good simultaneous fit to the combined Planck, ACT, and SPT data, and thus passes a powerful test. Combining these CMB datasets with BAO observations, we explore extensions to the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. We find that the effective number of neutrino species, spatial curvature, and primordial helium fraction are consistent with standard model values, and that the 95% confidence upper limit on the neutrino mass sum is 0.075 eV, close to the minimum sum expected from observations of solar and atmospheric neutrino oscillations. The SPT data are consistent with the somewhat weak ($&lt;3\ensuremath{\sigma}$) preference for excess lensing power seen in Planck and ACT data relative to predictions of the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model given the combined Planck, ACT, and BAO datasets. We also detect at greater than $3\ensuremath{\sigma}$ the influence of nonlinear evolution in the CMB lensing power spectrum and discuss it in the context of the ${S}_{8}$ tension. Forthcoming SPT-3G analyses will feature deeper and wider observations in temperature and polarization, providing even tighter constraints and more powerful tests of the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model.

  PublisherOA PDFDOI

• Measurements of the Temperature and E-mode Polarization of the Cosmic Microwave Background from the Full 500-square-degree SPTpol Dataset

  arXiv (Cornell University) · 2025-01-12

  articleOpen access

  Using the full four-year SPTpol 500 deg$^2$ dataset in both the 95 GHz and 150 GHz frequency bands, we present measurements of the temperature and $E$-mode polarization of the cosmic microwave background (CMB), as well as the $E$-mode polarization auto-power spectrum ($EE$) and temperature-$E$-mode cross-power spectrum ($TE$) in the angular multipole range $50<\ell<8000$. We find the SPTpol dataset to be self-consistent, passing several internal consistency tests based on maps, frequency bands, bandpowers, and cosmological parameters. The full SPTpol dataset is well-fit by the $ΛCDM$ model, for which we find $H_0=70.48\pm2.16$ km s$^{-1}$ Mpc$^{-1}$ and $Ω_m=0.271\pm0.026$, when using only the SPTpol data and a Planck-based prior on the optical depth to reionization. The $ΛCDM$ parameter constraints are consistent across the 95 GHz-only, 150 GHz-only, $TE$-only, and $EE$-only data splits. Between the $\ell<1000$ and $\ell>1000$ data splits, the $ΛCDM$ parameter constraints are borderline consistent at the $\sim2σ$ level. This consistency improves when including a parameter $A_L$, the degree of lensing of the CMB inferred from the smearing of acoustic peaks. When marginalized over $A_L$, the $ΛCDM$ parameter constraints from SPTpol are consistent with those from Planck. The power spectra presented here are the most sensitive measurements of the lensed CMB damping tail to date for roughly $\ell > 1700$ in $TE$ and $\ell > 2000$ in $EE$.

  PublisherOA PDFDOI

• SPT-3G D1: Constraints on inflationary gravitational waves with two years of SPT-3G data

  Physical review. D/Physical review. D. · 2025-12-08 · 6 citations

  article

  We present a measurement of the $B$-mode polarization power spectrum of the cosmic microwave background anisotropies at $32\ensuremath{\le}\ensuremath{\ell}&lt;502$ for three bands centered at 95, 150, and 220 GHz using data from the SPT-3G receiver on the South Pole Telescope. This work uses SPT-3G observations from the 2019 and 2020 winter observing seasons of a $\ensuremath{\sim}1500\text{ }\text{ }{\mathrm{deg}}^{2}$ patch of sky that directly overlaps with fields observed with the BICEP/Keck family of telescopes and covers part of the proposed Simons Observatory and CMB-S4 deep fields. Employing new techniques for mitigating polarized atmospheric noise, the SPT-3G data demonstrates a white noise level of 9.3 $(6.7)\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{K}\text{\ensuremath{-}}\mathrm{arcmin}$ at $\ensuremath{\ell}\ensuremath{\sim}500$ for the 95 GHz (150 GHz) data, with a $1/\ensuremath{\ell}$ noise knee at $\ensuremath{\ell}=128$ (182). We fit the observed six auto- and cross-frequency $B$-mode power spectra to a model including lensed $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ $B$-modes and a combination of Galactic and extragalactic foregrounds. This work characterizes foregrounds in the vicinity of the BICEP/Keck survey area, finding foreground power consistent with that reported by the BICEP/Keck collaboration within the same region and a factor of $\ensuremath{\sim}3$ higher power over the full SPT-3G survey area. Using SPT-3G data over the BICEP/Keck survey area, we place a 95% upper limit on the tensor-to-scalar ratio of $r&lt;0.25$ and find the statistical uncertainty on $r$ to be $\ensuremath{\sigma}(r)=0.067$.

  PublisherDOI

• CMB-S4 Science Case and Instrument Overview

  2025-01-07

  article1st authorCorresponding

  The next generation cosmic microwave background experiment CMB-S4 was conceived by the community as the path forward to realizing the enormous potential of CMB measurements for understanding the origin and evolution of the Universe, from the highest energies at the dawn of time through the growth of structure to the present day. Based on its spectacular and transformative science promise and its technical maturity, CMB-S4 was highly ranked (tied for 2nd priority) by U.S. 2020 Decadal Survey of Astronomy and Astrophysics and was ranked as the highest priority, new large project by the 2023 report of the U.S. Particle Physics Project Prioritization Panel.

  PublisherDOI

• Detection of Millimeter-Wavelength Flares from Two Accreting White Dwarf Systems in the SPT-3G Galactic Plane Survey

  ArXiv.org · 2025-09-10

  preprintOpen access

  Blind discoveries of millimeter-wave (mm-wave) transient events in non-targeted surveys, as opposed to follow-up or pointed observations, have only become possible in the past decade using cosmic microwave background surveys. Here we present the first results from the SPT-3G Galactic Plane Survey -- the first dedicated high-sensitivity, wide-field, time-domain, mm-wave survey of the Galactic Plane, conducted with the South Pole Telescope (SPT) using the SPT-3G camera. The survey field covers approximately 100 $\text{deg}^2$ near the Galactic center. In 2023 and 2024, this survey consists of roughly 1,500 individual 20-minute observations in three bands centered at 95, 150, and 220 GHz, with plans for more observations in the coming years. We report the detection of two transient events exceeding a 5$σ$ threshold in both the 95 and 150 GHz bands in the first two years of SPT-3G Galactic Plane Survey data. Both events are unpolarized and exhibit durations of approximately one day, with peak flux densities at 150 GHz of at least 50 mJy. The peak isotropic luminosities at 150 GHz are on the order of $10^{31}~\text{erg}~\text{s}^{-1}$. Both events are associated with previously identified accreting white dwarfs. Magnetic reconnection in the accretion disk is a likely explanation for the observed millimeter flares. In the future, we plan to expand the transient search in the Galactic Plane by lowering the detection threshold, enabling single-band detections, analyzing lightcurves on a range of timescales, and including additional data from future observations.

  PublisherOA PDFDOI

Recent grants

• South Pole Observations to Test Cosmological Models

  NSF · $17.6M · 2002–2010

• Development of an Advanced Heterogeneous Array for Probing the High-Redshift Universe

  NSF · $2.8M · 2001–2007

• Collaborative Research: Astronomy with CARMA

  NSF · $1.1M · 2009–2013

• Collaborative Research: Development of an Enhanced CARMA for High-Fidelity Astronomical Imaging from cm to mm Wavelengths

  NSF · $449k · 2010–2014

• Collaborative Research: Building an Event Horizon Telescope: (Sub)millimeter VLBI from the South Pole Telescope

  NSF · $120k · 2012–2016

Frequent coauthors

• B. A. Benson

  Netherlands Institute for Radio Astronomy

  854 shared

• C. L. Chang

  Argonne National Laboratory

  734 shared

• K. K. Schaffer

  University of Chicago

  649 shared

• J. J. Mohr

  619 shared

• S. S. Meyer

  575 shared

• L. E. Bleem

  University of Chicago

  541 shared

• G. Desvignes

  470 shared

• M. Dobbs

  Canadian Institute for Advanced Research

  427 shared

Labs

• Department of Physics, The University of ChicagoPI

Education

• Ph.D., Physics

  University of California Berkeley

  1988

Awards & honors

• 2020 Breakthrough Prize in Fundamental Physics