Gravitational lens
In 1784, Henry Cavendish wrote an unpublished manuscript suggesting that Newtonian gravity could bend starlight around a massive object. Johann Georg von Soldner published similar calculations in 1801, deriving the same value as Cavendish had found earlier. Isaac Newton himself speculated about this bending of light in his book Opticks, originally released in 1704 within Queries No.1. Albert Einstein calculated the deflection angle for light passing near a mass in 1911 using only the equivalence principle alone. His result matched Soldner's figure exactly, yet it remained incomplete. In 1915, while completing general relativity, Einstein realized his previous calculation was only half the correct value. He became the first person to calculate the accurate amount of light bending required by the full theory. The difference arises because classical physics treats light speed as observer-dependent, whereas special relativity establishes a universal constant for that speed.
Orest Khvolson discussed the halo effect of gravitation in print during 1924 when source, lens, and observer align nearly perfectly. Frantisek Link followed with a discussion in 1936, though the phenomenon remains most commonly associated with Einstein. Einstein reluctantly published an article titled Lens-Like Action of a Star By the Deviation of Light In the Gravitational Field in 1936 after Rudi W. Mandl urged him to do so. Fritz Zwicky posited in 1937 that galaxy clusters could act as gravitational lenses since their mass and size made observation more likely than single stars. Quasars were recognized as ideal light sources for this effect independently by Yu. G. Klimov, S. Liebes, and Sjur Refsdal in 1963. The first actual discovery occurred in 1979 when Dennis Walsh, Bob Carswell, and Ray Weymann used the Kitt Peak National Observatory 2.1 meter telescope. They identified the Twin QSO SBS 0957+561, which initially appeared as two identical quasistellar objects before astronomers realized it was one object split by gravity.
Strong lensing produces easily visible distortions such as Einstein rings, arcs, and multiple images despite being relatively small in magnitude. A galaxy with a mass exceeding 100 billion times that of the Sun creates multiple images separated by only a few arcseconds. Galaxy clusters can produce separations reaching several arcminutes while both cases involve sources hundreds of megaparsecs away from the Milky Way. Weak lensing involves much smaller distortions detectable only through statistical analysis of large numbers of background sources. These surveys find coherent distortions of just a few percent stretching perpendicular to the direction toward the lens center. Microlensing shows no shape distortion but changes the amount of light received from a background object over time. The star MACS J1149 Lensed Star 1, also known as Icarus, provided the first example where microlensing boosted flux significantly. Gravitational lenses act equally on all electromagnetic radiation including radio waves and x-rays as well as gravitational waves themselves.
Weak lensing surveys reconstruct mass distribution by measuring shapes and orientations of many distant galaxies to determine shear in any region. This process allows astronomers to map the background distribution of dark matter across vast cosmic distances. Surveys must carefully account for intrinsic galaxy shapes, camera point spread function distortions, and atmospheric seeing effects to avoid systematic errors. Results help estimate cosmological parameters and improve upon the Lambda-CDM model used to describe our universe. They provide consistency checks against other cosmological observations and may constrain future understanding of dark energy. Research published the 30th of September 2013 in Physical Review Letters discovered B-modes formed due to gravitational lensing using the South Pole Telescope. This discovery opened possibilities for testing theories about how the universe originated. Statistical analysis of microlensing events between 2002 and 2007 found most stars in the Milky Way host at least one orbiting planet within 0.5 to 10 AU.
Albert Einstein predicted in 1936 that light rays skirting the Sun's edges would converge to a focal point approximately 542 astronomical units from the star. A probe positioned at this distance or beyond could use the Sun as a gravitational lens to magnify distant objects on the opposite side. Frank Drake suggested sending such a probe during early SETI days because high gain signals like microwaves at the 21-cm hydrogen line could be detected. The ESA received proposals for multipurpose probes named SETISAIL and later FOCAL in 1993, though these remain difficult tasks requiring advanced technology. Current space probes like Voyager 1 have not yet reached this distance which lies far beyond known planets and dwarf planets. NASA physicist Slava Turyshev presented an idea in 2020 for Direct Multipixel Imaging and Spectroscopy of an Exoplanet with a Solar Gravitational Lens Mission. This lens could reconstruct exoplanet images with roughly 25-kilometer-scale surface resolution sufficient to see surface features and signs of habitability.
Continue Browsing
Common questions
When did Henry Cavendish write about light bending by gravity?
Henry Cavendish wrote an unpublished manuscript suggesting that Newtonian gravity could bend starlight around a massive object in 1784. This work predated Johann Georg von Soldner's published calculations from 1801 which derived the same value.
Who first calculated the accurate amount of light bending required by general relativity?
Albert Einstein became the first person to calculate the accurate amount of light bending required by the full theory in 1915 while completing general relativity. His previous calculation from 1911 using only the equivalence principle was exactly half the correct value found later.
What year did astronomers discover the Twin QSO SBS 0957+561 gravitational lens?
The first actual discovery occurred in 1979 when Dennis Walsh, Bob Carswell, and Ray Weymann used the Kitt Peak National Observatory 2.1 meter telescope. They identified the Twin QSO SBS 0957+561 as one object split by gravity after it initially appeared as two identical quasistellar objects.
How far is the focal point for a solar gravitational lens probe from the Sun?
Albert Einstein predicted in 1936 that light rays skirting the Sun's edges would converge to a focal point approximately 542 astronomical units from the star. A probe positioned at this distance or beyond could use the Sun as a gravitational lens to magnify distant objects on the opposite side.
When was B-mode formation due to gravitational lensing discovered using the South Pole Telescope?
Research published the 30th of September 2013 in Physical Review Letters discovered B-modes formed due to gravitational lensing using the South Pole Telescope. This discovery opened possibilities for testing theories about how the universe originated.