Professor Bernstein's research is focused on the use of gravitational lensing, the deflection of light by gravity as predicted by General Relativity. These deflections can cause dramatic distortions of background objects, or subtle weak lensing effects which can only be detected as statistical correlations among the shapes of millions of galaxies. These gravitational lensing effects have been used to measure the mass of dark matter halos around typical galaxies, the power spectrum of matter in the Universe, and the properties of the dark energy that is causing the expansion of the Universe to accelerate. Professor Bernstein is also working on methods to produce the best possible lensing results from future surveys, such as the Supernova Acceleration Probe in space, and the Large Synoptic Survey Telescope on the ground. The Penn astrophysics group is a partner in the largest funded US lensing survey, the Dark Energy Survey, which will obtain multicolor imaging of 5000 square degrees of the Southern sky.
Past (and possible future) projects have included surveys of the Kuiper Belt, the reservoir of many thousands of small icy bodies orbiting the Sun beyond Neptune, remnants of the early phases of the formation of our Solar System. Professor Bernstein also constructed one of the first mosaic CCD cameras to be placed on a large telescope, which was used to measure weak gravitational lensing, the Kuiper Belt, and many of the high-redshift supernovae that first gave evidence of the acceleration of the Universe.
Ph.D., Physics, University of California, Berkeley (1989)
A.B., Physics, summa cum laude, Princeton University, (1983)
Astrophysics, Gravitational Lensing, Cosmology
Weak Gravitational Lensing: The dark matter in the Universe reveals its presence by its gravitational deflection of passing light rays. This causes very subtle distortions in the appearance of background galaxies, which can be used to unveil the structure of this dark matter. We have used this weak gravitational lensing effect to measure the mass of dark matter halos around typical galaxies, and the power spectrum of matter in the Universe. We have also worked extensively on methods to produce the best possible lensing results from future surveys, which will allow us to track the evolution of dark matter in the Universe. Here's a summary talk (19 MB) about weak lensing presented (not very recently!) at SLAC. The Kuiper Belt: There are many thousands of small icy bodies orbiting the Sun beyond Neptune, remnants of the early phases of the formation of our Solar System. These Kuiper Belt Objects (KBOs) contain many clues to the early steps of planet formation. We have worked from the ground to discover many of these KBOs, confirming that very few exist beyond Pluto's orbit. Using the Hubble Space Telescope we have found the faintest Solar System objects ever discovered - but not enough of them! There are surprisingly few small Kuiper Belt Objects. SNAP: The SuperNova Acceleration Probe is a planned wide-field imaging space telescope for measuring distant supernovae and gravitational lensing. Both measurements will be focussed on measuring the evolution of the dark matter and dark energy components of the Universe, which remain totally unexplained despite being the dominant contents of the Universe. I am a member of the SNAP collaboration, working on calculation and optimization of its imaging and spectroscopic capabilities (e.g. the ETC++ exposure-time calculator). LSST: The Large Synoptic Survey Telescope is a proposed 8-meter ground-based telescope capable of imaging the entire accessible sky every 4 days. It would be extraordinarily capable for locating near-Earth asteroids, Kuiper Belt objects, nearby supernovae, large-scale gravitational lensing, and many other phenomena. I was a member of the Science Working Group for LSST.
Astronomy 503: Astronomical Methods and Instrumentation
Physics 016: Energy, Oil & Global Warming
- Shear recovery accuracy in weak lensing analysis with elliptical Gauss-Laguerre method
Nakajima, R., & Bernstein, G. 2007, AJ 133:1763-1779
- Dark energy constraints from lensing-detected galaxy clusters
Marian, L. & Bernstein, G. 2006, PRD 73 123525.
- Systematic Errors in Future Weak Lensing Surveys: Requirements and Prospects for Self-Calibration, Huterer, D., Takada, M., Bernstein, G., & Jain, B. 2005, MNRAS 366 101-114
- Metric Tests for Curvature from Weak Lensing and Baryon Acoustic Oscillations
Bernstein, G. 2006, ApJ 637 598-607
- Dark Energy Constraints from the CTIO Lensing Survey
Jarvis, M., Jain, B., & Bernstein, G. 2006, AJ 644:71-79
- Shapes, Shears, Stars, and Smears: Optimal Measurements for Weak Lensing
Bernstein, G. & Jarvis, M., 2002, AJ 123 583-618.
- The Size Distribution of Trans-Neptunian Bodies
Bernstein, G. M., Trilling, D. E., Allen, R. L., Brown, M. E., Holman, M., & Malhotra, R. 2004, AJ 128 1364-1390
- The Edge of the Solar System
Allen, R. L., Bernstein, G., & Malhotra, R. 2001, ApJ Letters 549 L241-244.
- Big Throughput Camera: The First Year
Wittman, D. et al. 1998, Proc SPIE 3355 626-634 (3.4 MB).