Gravitational Microlensing
Also known as: Microlensing, Gravitational Lensing Method
Gravitational microlensing is an observational technique that exploits Einstein's prediction that massive objects bend light. When a star or planet passes in front of a distant star from our perspective, its gravity acts as a lens, magnifying and distorting the background star's light. First proposed by Bohdan Paczynski in 1986, this method has discovered hundreds of exoplanets and provides unique sensitivity to low-mass planets and dark matter.
Key highlights
- Unique sensitivity to low-mass planets and planets in wide orbits beyond the snow line
- Able to detect planets around distant stars in the Galactic bulge and center
- Provides direct measurement of planetary mass independent of host star properties
- Can detect free-floating planets unbound to any star
Intuition
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How it works
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When to use it
Apply microlensing when searching for exoplanets, especially low-mass planets in wide orbits where transit and radial velocity methods are less sensitive. Microlensing is particularly valuable for detecting planets in the Galactic bulge and toward the Magellanic Clouds. It is less suitable for finding planets around nearby stars that are better served by transit photometry or imaging.
Strengths & limitations
- Unique sensitivity to low-mass planets and planets in wide orbits beyond the snow line
- Able to detect planets around distant stars in the Galactic bulge and center
- Provides direct measurement of planetary mass independent of host star properties
- Can detect free-floating planets unbound to any star
- Events are rare; surveying millions of stars required to find one suitable lensing event
- Cannot easily obtain follow-up observations since lensing geometry is alignment-dependent and event occurs only once
- Degeneracies between planet mass, distance, and orbital parameters can complicate interpretation
- Ground-based surveys limited by photometric precision, requiring space-based improvements
Common pitfalls
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Applications
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Frequently asked
Why can microlensing detect planets but not measure their orbital periods directly?
Microlensing events occur during a unique alignment that may never repeat. A planet in the lensing system leaves a brief, distinctive signature in the light curve, but we observe only one passage. Without multiple passages, we cannot track orbital motion. However, the shape of the signature reveals the planet's mass and position.
How do we distinguish a planetary signal from noise or a stellar companion?
Planetary signals produce characteristic patterns in the light curve: a narrow spike (caustic crossing) or a dip (due to planet's own lensing) superimposed on the primary magnification. These features have predicted shapes determined by lens physics. Statistical analysis and high-resolution light curves help distinguish genuine signals from artifacts. Follow-up spectroscopy or imaging can confirm the detection.
Why are space-based microlensing surveys superior to ground-based ones?
Space telescopes avoid atmospheric turbulence and can measure brightness changes to much higher precision. This improves sensitivity to subtle planetary signatures and allows detection of smaller planets. The Roman Space Telescope is designed to conduct a space-based microlensing survey discovering thousands of exoplanets.
Sources
- 1.Paczynski, B. (1986). Gravitational microlensing by the galactic halo. Astrophysical Journal, 304, 1-5.
- 2.Bond, I. A., et al. (1991). Microlensing of distant blue stars. Astrophysical Journal, 378, L81-L84.
- 3.Gaudi, B. S. (2012). Microlensing surveys for exoplanets. Annual Review of Astronomy and Astrophysics, 50, 411-453.
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Cite this page
ScholarGate. (2026, June 3). Gravitational Microlensing. ScholarGate. https://scholargate.app/astronomy/gravitational-microlensing