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Gravitational Microlensing
Gravitational microlensing is an astronomical phenomenon caused by the gravitational lens effect. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit much light (stars) or large objects that block background light (clouds of gas and dust). These objects make up only a minor portion of the mass of a galaxy. Microlensing allows the study of objects that emit little or no light. When a distant star or quasar gets sufficiently aligned with a massive compact foreground object, the bending of light due to its gravitational field, as discussed by Albert Einstein in 1915, leads to two distorted images (generally unresolved), resulting in an observable magnification. The time-scale of the transient brightening depends on the mass of the foreground object as well as on the relative proper motion between the background 'source' and the foreground 'l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomy
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include planets, natural satellite, moons, stars, nebulae, galaxy, galaxies, meteoroids, asteroids, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond atmosphere of Earth, Earth's atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole. Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Egyptian astronomy, Egyptians, Babylonian astronomy, Babylonians, Greek astronomy, Greeks, Indian astronomy, Indians, Chinese astronomy, Chinese, Maya civilization, M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Limb Darkening
Limb darkening is an optical effect seen in stars (including the Sun) and planets, where the central part of the disk appears brighter than the edge, or '' limb''. Its understanding offered early solar astronomers an opportunity to construct models with such gradients. This encouraged the development of the theory of radiative transfer. Basic theory Optical depth, a measure of the opacity of an object or part of an object, combines with effective temperature gradients inside the star to produce limb darkening. The light seen is approximately the integral of all emission along the line of sight modulated by the optical depth to the viewer (i.e. 1/e times the emission at 1 optical depth, 1/e2 times the emission at 2 optical depths, etc.). Near the center of the star, optical depth is effectively infinite, causing approximately constant brightness. However, the effective optical depth decreases with increasing radius due to lower gas density and a shorter line of sight distance ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Caustic (optics)
In optics, a caustic or caustic network is the Envelope (mathematics), envelope of Ray (optics), light rays which have been Reflection (physics), reflected or refraction, refracted by a curved surface or object, or the Projection (mathematics), projection of that envelope of rays on another surface. The caustic is a curve or Surface (mathematics), surface to which each of the light rays is tangent, defining a boundary of an envelope of rays as a curve of concentrated light. In some cases caustics can be seen as patches of light or their bright edges, shapes which often have cusp (singularity), cusp singularities. Explanation Concentration of light, especially sunlight, can burn. The word ''caustic'', in fact, comes from the Greek καυστός, burnt, via the Latin ''causticus'', burning. A common situation where caustics are visible is when light shines on a drinking glass. The glass casts a shadow, but also produces a curved region of bright light. In ideal circumstances ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravitational
In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force between objects and the Earth. This force is dominated by the combined gravitational interactions of particles but also includes effect of the Earth's rotation. Gravity gives weight to physical objects and is essential to understanding the mechanisms responsible for surface water waves and lunar tides. Gravity also has many important biological functions, helping to guide the growth of plants through the process of gravitropism and influencing the circulation of fluids in multicellular organisms. The gravitational attraction between primordial hydrogen and clumps of dark matter in the early universe caused the hydrogen gas to coalesce, eventually condensing and fusing to form stars. At larger scales this results in galaxies and clusters, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Light Curve
In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis and with time on the ''x''-axis. The light is usually in a particular frequency interval or frequency band, band. Light curves can be periodic, as in the case of eclipsing binary, eclipsing binaries, Cepheid variables, other periodic variables, and Methods of detecting extrasolar planets#Transit photometry, transiting extrasolar planets; or aperiodic, like the light curve of a nova, cataclysmic variable star, supernova, gravitational microlensing, microlensing event, or binary as observed during occultation events. The study of a light curve and other observations can yield considerable information about the physical process that produces such a light curve, or constrain the physical theories about it. Variable stars Graphs of the ap ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photometry (astronomy)
In astronomy, photometry, from Greek '' photo-'' ("light") and '' -metry'' ("measure"), is a technique used in astronomy that is concerned with measuring the flux or intensity of light radiated by astronomical objects. This light is measured through a telescope using a photometer, often made using electronic devices such as a CCD photometer or a photoelectric photometer that converts light into an electric current by the photoelectric effect. When calibrated against standard stars (or other light sources) of known intensity and colour, photometers can measure the brightness or apparent magnitude of celestial objects. The methods used to perform photometry depend on the wavelength region under study. At its most basic, photometry is conducted by gathering light and passing it through specialized photometric optical bandpass filters, and then capturing and recording the light energy with a photosensitive instrument. Standard sets of passbands (called a photometric system) are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Time-domain Astronomy
Time-domain astronomy is the study of how astronomical objects change with time. Said to have begun with Galileo's '' Letters on Sunspots'', the field has now naturally expanded to encompass variable objects beyond the Solar System. Temporal variation may originate from movement of the source, or changes in the object itself. Common targets include novae, supernovae, pulsating stars, flare stars, blazars and active galactic nuclei. Optical time domain surveys include OGLE, HAT-South, PanSTARRS, SkyMapper, ASAS, WASP, CRTS, GOTO, and the forthcoming LSST at the Vera C. Rubin Observatory. Time-domain astronomy studies transient astronomical events ("''transients''"), which include various types of variable stars, including periodic, quasi-periodic, high proper motion stars, and lifecycle events (supernovae, kilonovae) or other changes in behavior or type. Non-stellar transients include asteroids, planetary transits and comets. Transients characterize astronomical obje ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hubble Space Telescope
The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most versatile, renowned as a vital research tool and as a public relations boon for astronomy. The Hubble Space Telescope is named after astronomer Edwin Hubble and is one of NASA's Great Observatories program, Great Observatories. The Space Telescope Science Institute (STScI) selects Hubble's targets and processes the resulting data, while the Goddard Space Flight Center (GSFC) controls the spacecraft. Hubble features a mirror, and its five main instruments observe in the ultraviolet, visible spectrum, visible, and near-infrared regions of the electromagnetic spectrum. Hubble's orbit outside the distortion of atmosphere of Earth, Earth's atmosphere allows it to capture extremely high-resolution images with substantially lower background lig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weak Gravitational Lensing
While the presence of any mass bends the path of light passing near it, this effect rarely produces the giant arcs and multiple images associated with strong gravitational lensing. Most lines of sight in the universe are thoroughly in the weak lensing regime, in which the deflection is impossible to detect in a single background source. However, even in these cases, the presence of the foreground mass can be detected, by way of a systematic alignment of background sources around the lensing mass. Weak gravitational lensing is thus an intrinsically statistical measurement, but it provides a way to measure the masses of astronomical objects without requiring assumptions about their composition or dynamical state. Methodology Gravitational lensing acts as a coordinate transformation that distorts the images of background objects (usually galaxies) near a foreground mass. The transformation can be split into two terms, the convergence and shear. The convergence term magnif ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strong Gravitational Lensing
Strong gravitational lensing is a gravitational lensing effect that is strong enough to produce multiple images, arcs, or Einstein rings. Generally, for strong lensing to occur, the projected lens mass density must be greater than the '' critical density'', that is \Sigma_. For point-like background sources, there will be multiple images; for extended background emissions, there can be arcs or rings. Topologically, multiple image production is governed by the odd number theorem. Strong lensing was predicted by Albert Einstein's general theory of relativity and observationally discovered by Dennis Walsh, Bob Carswell, and Ray Weymann in 1979. They determined that the Twin Quasar Q0957+561A comprises two images of the same object. Observations Most strong gravitational lenses are detected by large-scale galaxy surveys. Galaxy lensing The foreground lens is a galaxy. When the background source is a quasar or unresolved jet, the strong lensed images are usually point-like ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MACS J1149 Lensed Star 1
MACS J1149 Lensed Star 1, also known as Icarus,Other names include ''LS1'', ''MACS J1149 LS1'', ''MACS J1149 Lensed Star 1 (LS1)'' and ''MACS J1149+2223 Lensed Star 1'' is a blue supergiant star observed through a gravitational lens. It is the seventh most distant individual star to have been detected so far (after Earendel, Godzilla, Mothra, Quyllur, star-1 and star-2), at approximately 14 billion light-years from Earth (redshift z=1.49; comoving distance of 14.4 billion light-years; lookback time of 9.34 billion years). Light from the star was emitted 4.4 billion years after the Big Bang. According to co-discoverer Patrick Kelly, the star is at least a hundred times more distant than the next-farthest non-supernova star observed, SDSS J1229+1122, and is the first magnified individual star seen. History In April and May 2018, the star was found in the course of studying the supernova SN Refsdal with the Hubble Space Telescope. Astronomer Patrick Kelly of the University o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monthly Notices Of The Royal Astronomical Society
''Monthly Notices of the Royal Astronomical Society'' (MNRAS) is a peer-reviewed scientific journal in astronomy, astrophysics and related fields. It publishes original research in two formats: papers (of any length) and letters (limited to five pages). MNRAS publishes more articles per year than any other astronomy journal. The learned society journal has been in continuous existence since 1827 and became online only in 2020. It operates as a partnership between the Royal Astronomical Society (RAS), who select and peer-review the contents, and Oxford University Press (OUP), who publish and market the journal. Despite its name, MNRAS is no longer monthly, nor does it carry the notices of the RAS. In 2024 MNRAS became a purely gold open access journal. History The first issue of MNRAS was published on 9 February 1827 as ''Monthly Notices of the Astronomical Society of London'' and it has been in continuous publication ever since. It took its current name from the second vo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
