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115-467: A MACHO may be detected when it passes in front of or nearly in front of a star and the MACHO's gravity bends the light, causing the star to appear brighter in an example of gravitational lensing known as gravitational microlensing . Several groups have searched for MACHOs by searching for the microlensing amplification of light. These groups have ruled out dark matter being explained by MACHOs with mass in

230-441: A Belgian physicist and Roman Catholic priest , proposed that the recession of the nebulae was due to the expansion of the universe. He inferred the relation that Hubble would later observe, given the cosmological principle. In 1931, Lemaître went further and suggested that the evident expansion of the universe, if projected back in time, meant that the further in the past the smaller the universe was, until at some finite time in

345-638: A Russian cosmologist and mathematician , derived the Friedmann equations from the Einstein field equations, showing that the universe might be expanding in contrast to the static universe model advocated by Albert Einstein at that time. In 1924, American astronomer Edwin Hubble 's measurement of the great distance to the nearest spiral nebulae showed that these systems were indeed other galaxies. Starting that same year, Hubble painstakingly developed

460-428: A Solar Gravitational Lens Mission. The lens could reconstruct the exoplanet image with ~25 km-scale surface resolution, enough to see surface features and signs of habitability. Kaiser, Squires and Broadhurst (1995), Luppino & Kaiser (1997) and Hoekstra et al. (1998) prescribed a method to invert the effects of the point spread function (PSF) smearing and shearing, recovering a shear estimator uncontaminated by

575-504: A cluster of galaxies or a point particle , that bends light from a distant source as it travels toward an observer. The amount of gravitational lensing is described by Albert Einstein 's general theory of relativity . If light is treated as corpuscles travelling at the speed of light , Newtonian physics also predicts the bending of light, but only half of that predicted by general relativity. Orest Khvolson (1924) and Frantisek Link (1936) are generally credited with being

690-484: A future horizon , which limits the events in the future that we will be able to influence. The presence of either type of horizon depends on the details of the Friedmann–Lemaître–Robertson–Walker (FLRW) metric that describes the expansion of the universe. Our understanding of the universe back to very early times suggests that there is a past horizon, though in practice our view is also limited by

805-427: A constant speed of light along the parallel direction, d r ∥ ≈ c d t {\displaystyle dr_{\parallel }\approx c\,dt} , and that the light is only being deflected a small amount. After plugging these assumptions into the above equation and further simplifying, one can solve for the velocity boost in the perpendicular direction. The angle of deflection between

920-448: A corpuscle of mass m {\displaystyle m} feels a force where r {\displaystyle r} is the lens-corpuscle separation. If we equate this force with Newton's second law , we can solve for the acceleration that the light undergoes: The light interacts with the lens from initial time t = 0 {\displaystyle t=0} to t {\displaystyle t} , and

1035-525: A lens, for it has no focal length". If the (light) source, the massive lensing object, and the observer lie in a straight line, the original light source will appear as a ring around the massive lensing object (provided the lens has circular symmetry). If there is any misalignment, the observer will see an arc segment instead. This phenomenon was first mentioned in 1924 by the St. Petersburg physicist Orest Khvolson , and quantified by Albert Einstein in 1936. It

1150-410: A majority of dark matter because the black holes are at isolated points of the galaxy. The largest contributor to the missing mass must be spread throughout the galaxy to balance the gravity. A minority of physicists, including Chapline and Laughlin , believe that the widely accepted model of the black hole is wrong and needs to be replaced by a new model, the dark-energy star ; in the general case for

1265-406: A massive object as had already been supposed by Isaac Newton in 1704 in his Queries No.1 in his book Opticks . The same value as Soldner's was calculated by Einstein in 1911 based on the equivalence principle alone. However, Einstein noted in 1915, in the process of completing general relativity, that his (and thus Soldner's) 1911-result is only half of the correct value. Einstein became

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1380-419: A maximum deflection of light that passes closest to its center, and a minimum deflection of light that travels furthest from its center. Consequently, a gravitational lens has no single focal point , but a focal line. The term "lens" in the context of gravitational light deflection was first used by O. J. Lodge, who remarked that it is "not permissible to say that the solar gravitational field acts like

1495-550: A more generic early hot, dense phase of the universe. In either case, "the Big Bang" as an event is also colloquially referred to as the "birth" of our universe since it represents the point in history where the universe can be verified to have entered into a regime where the laws of physics as we understand them (specifically general relativity and the Standard Model of particle physics ) work. Based on measurements of

1610-504: A process in the very early universe has reached thermal equilibrium is the ratio between the rate of the process (usually rate of collisions between particles) and the Hubble parameter . The larger the ratio, the more time particles had to thermalize before they were too far away from each other. According to the Big Bang models, the universe at the beginning was very hot and very compact, and since then it has been expanding and cooling. In

1725-611: A search is done using well-calibrated and well-parameterized instruments and data, a result similar to the northern survey can be expected. The use of the Australia Telescope 20 GHz (AT20G) Survey data collected using the Australia Telescope Compact Array (ATCA) stands to be such a collection of data. As the data were collected using the same instrument maintaining a very stringent quality of data we should expect to obtain good results from

1840-467: A series of distance indicators, the forerunner of the cosmic distance ladder , using the 100-inch (2.5 m) Hooker telescope at Mount Wilson Observatory . This allowed him to estimate distances to galaxies whose redshifts had already been measured, mostly by Slipher. In 1929, Hubble discovered a correlation between distance and recessional velocity —now known as Hubble's law. Independently deriving Friedmann's equations in 1927, Georges Lemaître ,

1955-598: A short article discussing the "halo effect" of gravitation when the source, lens, and observer are in near-perfect alignment, now referred to as the Einstein ring . In 1936, after some urging by Rudi W. Mandl, Einstein reluctantly published the short article "Lens-Like Action of a Star By the Deviation of Light In the Gravitational Field" in the journal Science . In 1937, Fritz Zwicky first considered

2070-518: A singularity in which space and time lose meaning (typically named "the Big Bang singularity"). Physics lacks a widely accepted theory of quantum gravity that can model the earliest conditions of the Big Bang. In 1964 the CMB was discovered, which convinced many cosmologists that the competing steady-state model of cosmic evolution was falsified , since the Big Bang models predict a uniform background radiation caused by high temperatures and densities in

2185-452: A surrounding space, the Big Bang only describes the intrinsic expansion of the contents of the universe. Another issue pointed out by Santhosh Mathew is that bang implies sound, which is not an important feature of the model. An attempt to find a more suitable alternative was not successful. The Big Bang models developed from observations of the structure of the universe and from theoretical considerations. In 1912, Vesto Slipher measured

2300-430: A temperature of approximately 10 degrees Celsius. Even the very concept of a particle breaks down in these conditions. A proper understanding of this period awaits the development of a theory of quantum gravity . The Planck epoch was succeeded by the grand unification epoch beginning at 10 seconds, where gravitation separated from the other forces as the universe's temperature fell. At approximately 10 seconds into

2415-495: Is accelerating , an observation attributed to an unexplained phenomenon known as dark energy . The Big Bang models offer a comprehensive explanation for a broad range of observed phenomena, including the abundances of the light elements , the CMB , large-scale structure , and Hubble's law . The models depend on two major assumptions: the universality of physical laws and the cosmological principle . The universality of physical laws

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2530-422: Is assumed to be cold. (Warm dark matter is ruled out by early reionization .) This CDM is estimated to make up about 23% of the matter/energy of the universe, while baryonic matter makes up about 4.6%. In an "extended model" which includes hot dark matter in the form of neutrinos, then the "physical baryon density" Ω b h 2 {\displaystyle \Omega _{\text{b}}h^{2}}

2645-493: Is based on a key assumption that the PSF is circular with an anisotropic distortion. This is a reasonable assumption for cosmic shear surveys, but the next generation of surveys (e.g. LSST ) may need much better accuracy than KSB can provide. Big Bang The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature . The notion of an expanding universe

2760-451: Is defined as v e = 2 G m / r = β e c {\textstyle v_{\text{e}}={\sqrt {2Gm/r}}=\beta _{\text{e}}c} , this can also be expressed in simple form as Most of the gravitational lenses in the past have been discovered accidentally. A search for gravitational lenses in the northern hemisphere (Cosmic Lens All Sky Survey, CLASS), done in radio frequencies using

2875-403: Is estimated at 0.023. (This is different from the 'baryon density' Ω b {\displaystyle \Omega _{\text{b}}} expressed as a fraction of the total matter/energy density, which is about 0.046.) The corresponding cold dark matter density Ω c h 2 {\displaystyle \Omega _{\text{c}}h^{2}} is about 0.11, and

2990-399: Is far beyond the progress and equipment capabilities of space probes such as Voyager 1 , and beyond the known planets and dwarf planets, though over thousands of years 90377 Sedna will move farther away on its highly elliptical orbit. The high gain for potentially detecting signals through this lens, such as microwaves at the 21-cm hydrogen line , led to the suggestion by Frank Drake in

3105-425: Is interpreted as a Doppler shift, the recessional velocity of the object can be calculated. For some galaxies, it is possible to estimate distances via the cosmic distance ladder . When the recessional velocities are plotted against these distances, a linear relationship known as Hubble's law is observed: v = H 0 D {\displaystyle v=H_{0}D} where Hubble's law implies that

3220-493: Is modeled by a cosmological constant term in Einstein field equations of general relativity, but its composition and mechanism are unknown. More generally, the details of its equation of state and relationship with the Standard Model of particle physics continue to be investigated both through observation and theory. All of this cosmic evolution after the inflationary epoch can be rigorously described and modeled by

3335-427: Is no preferred (or special) observer or vantage point. To this end, the cosmological principle has been confirmed to a level of 10 via observations of the temperature of the CMB. At the scale of the CMB horizon, the universe has been measured to be homogeneous with an upper bound on the order of 10% inhomogeneity, as of 1995. An important feature of the Big Bang spacetime is the presence of particle horizons . Since

3450-410: Is one of the underlying principles of the theory of relativity . The cosmological principle states that on large scales the universe is homogeneous and isotropic —appearing the same in all directions regardless of location. These ideas were initially taken as postulates, but later efforts were made to test each of them. For example, the first assumption has been tested by observations showing that

3565-432: Is the proper distance, v {\displaystyle v} is the recessional velocity, and v {\displaystyle v} , H {\displaystyle H} , and D {\displaystyle D} vary as the universe expands (hence we write H 0 {\displaystyle H_{0}} to denote the present-day Hubble "constant"). For distances much smaller than

Massive compact halo object - Misplaced Pages Continue

3680-410: Is usually referred to in the literature as an Einstein ring , since Khvolson did not concern himself with the flux or radius of the ring image. More commonly, where the lensing mass is complex (such as a galaxy group or cluster ) and does not cause a spherical distortion of spacetime, the source will resemble partial arcs scattered around the lens. The observer may then see multiple distorted images of

3795-533: The Hubble Space Telescope and WMAP. Cosmologists now have fairly precise and accurate measurements of many of the parameters of the Big Bang model, and have made the unexpected discovery that the expansion of the universe appears to be accelerating. "[The] big bang picture is too firmly grounded in data from every area to be proved invalid in its general features." — Lawrence Krauss The earliest and most direct observational evidence of

3910-602: The Hubble Space Telescope and with proper motion surveys. These searches have ruled out the possibility that these objects make up a significant fraction of dark matter in our galaxy. Another group, the EROS2 collaboration, does not confirm the signal claims by the MACHO group. They did not find enough microlensing effect with a sensitivity higher by a factor 2. Observations using the Hubble Space Telescope's NICMOS instrument showed that less than one percent of

4025-483: The Milky Way galaxy hosted at least one orbiting planet within 0.5 to 10 AU. In 2009, weak gravitational lensing was used to extend the mass-X-ray-luminosity relation to older and smaller structures than was previously possible to improve measurements of distant galaxies. As of 2013 the most distant gravitational lens galaxy, J1000+0221 , had been found using NASA 's Hubble Space Telescope . While it remains

4140-491: The Milne model , the oscillatory universe (originally suggested by Friedmann, but advocated by Albert Einstein and Richard C. Tolman ) and Fritz Zwicky 's tired light hypothesis. After World War II , two distinct possibilities emerged. One was Fred Hoyle's steady-state model, whereby new matter would be created as the universe seemed to expand. In this model the universe is roughly the same at any point in time. The other

4255-417: The cosmic microwave background (CMB) radiation , and large-scale structure . The uniformity of the universe, known as the flatness problem , is explained through cosmic inflation : a sudden and very rapid expansion of space during the earliest moments. Extrapolating this cosmic expansion backward in time using the known laws of physics , the models describe an increasingly concentrated cosmos preceded by

4370-512: The cosmic microwave background as well as galaxy surveys . Strong lenses have been observed in radio and x-ray regimes as well. If a strong lens produces multiple images, there will be a relative time delay between two paths: that is, in one image the lensed object will be observed before the other image. Henry Cavendish in 1784 (in an unpublished manuscript) and Johann Georg von Soldner in 1801 (published in 1804) had pointed out that Newtonian gravity predicts that starlight will bend around

4485-488: The dwarf galaxy problem of cold dark matter. Dark energy is also an area of intense interest for scientists, but it is not clear whether direct detection of dark energy will be possible. Inflation and baryogenesis remain more speculative features of current Big Bang models. Viable, quantitative explanations for such phenomena are still being sought. These are unsolved problems in physics. Observations of distant galaxies and quasars show that these objects are redshifted:

4600-416: The universe is not thought to be old enough for any stars to have reached this stage. Brown dwarfs have also been proposed as MACHO candidates. Brown dwarfs are sometimes called "failed stars" as they do not have enough mass for nuclear fusion to begin once their gravity causes them to collapse. Brown dwarfs are about thirteen to seventy-five times the mass of Jupiter. The contraction of material forming

4715-410: The "four pillars" of the Big Bang models. Precise modern models of the Big Bang appeal to various exotic physical phenomena that have not been observed in terrestrial laboratory experiments or incorporated into the Standard Model of particle physics. Of these features, dark matter is currently the subject of most active laboratory investigations. Remaining issues include the cuspy halo problem and

Massive compact halo object - Misplaced Pages Continue

4830-451: The Big Bang models. After its initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles , and later atoms . The unequal abundances of matter and antimatter that allowed this to occur is an unexplained effect known as baryon asymmetry . These primordial elements—mostly hydrogen , with some helium and lithium —later coalesced through gravity , forming early stars and galaxies. Astronomers observe

4945-533: The Big Bang. Then, from the 1970s to the 1990s, cosmologists worked on characterizing the features of the Big Bang universe and resolving outstanding problems. In 1981, Alan Guth made a breakthrough in theoretical work on resolving certain outstanding theoretical problems in the Big Bang models with the introduction of an epoch of rapid expansion in the early universe he called "inflation". Meanwhile, during these decades, two questions in observational cosmology that generated much discussion and disagreement were over

5060-462: The Big Bang. Since the early universe did not immediately collapse into a multitude of black holes, matter at that time must have been very evenly distributed with a negligible density gradient . The earliest phases of the Big Bang are subject to much speculation, given the lack of available data. In the most common models the universe was filled homogeneously and isotropically with a very high energy density and huge temperatures and pressures , and

5175-480: The Sun's corona. A critique of the concept was given by Landis, who discussed issues including interference of the solar corona, the high magnification of the target, which will make the design of the mission focal plane difficult, and an analysis of the inherent spherical aberration of the lens. In 2020, NASA physicist Slava Turyshev presented his idea of Direct Multipixel Imaging and Spectroscopy of an Exoplanet with

5290-594: The Very Large Array (VLA) in New Mexico, led to the discovery of 22 new lensing systems, a major milestone. This has opened a whole new avenue for research ranging from finding very distant objects to finding values for cosmological parameters so we can understand the universe better. A similar search in the southern hemisphere would be a very good step towards complementing the northern hemisphere search as well as obtaining other objectives for study. If such

5405-464: The absence of a perfect cosmological principle , extrapolation of the expansion of the universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past. This irregular behavior, known as the gravitational singularity , indicates that general relativity is not an adequate description of the laws of physics in this regime. Models based on general relativity alone cannot fully extrapolate toward

5520-508: The age measured today). This issue was later resolved when new computer simulations, which included the effects of mass loss due to stellar winds , indicated a much younger age for globular clusters. Significant progress in Big Bang cosmology has been made since the late 1990s as a result of advances in telescope technology as well as the analysis of data from satellites such as the Cosmic Background Explorer (COBE),

5635-411: The big-bang predictions by Alpher, Herman and Gamow around 1950. Through the 1970s, the radiation was found to be approximately consistent with a blackbody spectrum in all directions; this spectrum has been redshifted by the expansion of the universe, and today corresponds to approximately 2.725 K. This tipped the balance of evidence in favor of the Big Bang model, and Penzias and Wilson were awarded

5750-491: The brightness of millions of stars to be measured each night. In a dense field, such as the galactic center or the Magellanic clouds, many microlensing events per year could potentially be found. This led to efforts such as Optical Gravitational Lensing Experiment , or OGLE, that have characterized hundreds of such events, including those of OGLE-2016-BLG-1190Lb and OGLE-2016-BLG-1195Lb . Newton wondered whether light, in

5865-529: The brown dwarf heats them up so they only glow feebly at infrared wavelengths, making them difficult to detect. A survey of gravitational lensing effects in the direction of the Small Magellanic Cloud and Large Magellanic Cloud did not detect the number and type of lensing events expected if brown dwarfs made up a significant fraction of dark matter. Theoretical work simultaneously also showed that ancient MACHOs are not likely to account for

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5980-406: The case where the newly discovered galaxies (which were called 'nebulae' at the time) could act as both source and lens, and that, because of the mass and sizes involved, the effect was much more likely to be observed. In 1963 Yu. G. Klimov, S. Liebes, and Sjur Refsdal recognized independently that quasars are an ideal light source for the gravitational lens effect. It was not until 1979 that

6095-470: The corpuscle’s initial and final trajectories is therefore (see, e.g., M. Meneghetti 2021) Although this result appears to be half the prediction from general relativity, classical physics predicts that the speed of light c {\displaystyle c} is observer-dependent (see, e.g., L. Susskind and A. Friedman 2018) which was superseded by a universal speed of light in special relativity . In general relativity, light follows

6210-432: The corresponding neutrino density Ω v h 2 {\displaystyle \Omega _{\text{v}}h^{2}} is estimated to be less than 0.0062. Independent lines of evidence from Type Ia supernovae and the CMB imply that the universe today is dominated by a mysterious form of energy known as dark energy , which appears to homogeneously permeate all of space. Observations suggest that 73% of

6325-440: The curvature of spacetime, hence when light passes around a massive object, it is bent. This means that the light from an object on the other side will be bent towards an observer's eye, just like an ordinary lens. In general relativity the path of light depends on the shape of space (i.e. the metric). The gravitational attraction can be viewed as the motion of undisturbed objects in a background curved geometry or alternatively as

6440-413: The dear Lord. The theory is correct anyway." In 1912, Einstein had speculated that an observer could see multiple images of a single light source, if the light were deflected around a mass. This effect would make the mass act as a kind of gravitational lens. However, as he only considered the effect of deflection around a single star, he seemed to conclude that the phenomenon was unlikely to be observed for

6555-452: The determination of the Hubble constant is known as Hubble tension . Techniques based on observation of the CMB suggest a lower value of this constant compared to the quantity derived from measurements based on the cosmic distance ladder. In 1964, Arno Penzias and Robert Wilson serendipitously discovered the cosmic background radiation, an omnidirectional signal in the microwave band. Their discovery provided substantial confirmation of

6670-426: The distant past. A wide range of empirical evidence strongly favors the Big Bang event, which is now essentially universally accepted. Detailed measurements of the expansion rate of the universe place the Big Bang singularity at an estimated 13.787 ± 0.020   billion years ago, which is considered the age of the universe . There remain aspects of the observed universe that are not yet adequately explained by

6785-448: The early days of SETI that a probe could be sent to this distance. A multipurpose probe SETISAIL and later FOCAL was proposed to the ESA in 1993, but is expected to be a difficult task. If a probe does pass 542 AU, magnification capabilities of the lens will continue to act at farther distances, as the rays that come to a focus at larger distances pass further away from the distortions of

6900-510: The ellipticity of a galaxy image. The shear is proportional to the ellipticity. The objects in lensed images are parameterized according to their weighted quadrupole moments. For a perfect ellipse, the weighted quadrupole moments are related to the weighted ellipticity. KSB calculate how a weighted ellipticity measure is related to the shear and use the same formalism to remove the effects of the PSF. KSB's primary advantages are its mathematical ease and relatively simple implementation. However, KSB

7015-591: The expansion using Type Ia supernovae and measurements of temperature fluctuations in the cosmic microwave background, the time that has passed since that event—known as the " age of the universe "—is 13.8 billion years. Despite being extremely dense at this time—far denser than is usually required to form a black hole —the universe did not re-collapse into a singularity. Commonly used calculations and limits for explaining gravitational collapse are usually based upon objects of relatively constant size, such as stars, and do not apply to rapidly expanding space such as

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7130-400: The expansion, a phase transition caused a cosmic inflation , during which the universe grew exponentially , unconstrained by the light speed invariance , and temperatures dropped by a factor of 100,000. This concept is motivated by the flatness problem , where the density of matter and energy is very close to the critical density needed to produce a flat universe . That is, the shape of

7245-415: The first Doppler shift of a " spiral nebula " (spiral nebula is the obsolete term for spiral galaxies), and soon discovered that almost all such nebulae were receding from Earth. He did not grasp the cosmological implications of this fact, and indeed at the time it was highly controversial whether or not these nebulae were "island universes" outside our Milky Way . Ten years later, Alexander Friedmann ,

7360-582: The first gravitational lens would be discovered. It became known as the " Twin QSO " since it initially looked like two identical quasistellar objects. (It is officially named SBS 0957+561 .) This gravitational lens was discovered by Dennis Walsh , Bob Carswell, and Ray Weymann using the Kitt Peak National Observatory 2.1 meter telescope . In the 1980s, astronomers realized that the combination of CCD imagers and computers would allow

7475-399: The first to calculate the correct value for light bending. The first observation of light deflection was performed by noting the change in position of stars as they passed near the Sun on the celestial sphere . The observations were performed in 1919 by Arthur Eddington , Frank Watson Dyson , and their collaborators during the total solar eclipse on May 29 . The solar eclipse allowed

7590-482: The first to discuss the effect in print, but it is more commonly associated with Einstein, who made unpublished calculations on it in 1912 and published an article on the subject in 1936. In 1937, Fritz Zwicky posited that galaxy clusters could act as gravitational lenses, a claim confirmed in 1979 by observation of the Twin QSO SBS 0957+561. Unlike an optical lens , a point-like gravitational lens produces

7705-408: The foreseeable future since the necessary alignments between stars and observer would be highly improbable. Several other physicists speculated about gravitational lensing as well, but all reached the same conclusion that it would be nearly impossible to observe. Although Einstein made unpublished calculations on the subject, the first discussion of the gravitational lens in print was by Khvolson, in

7820-459: The form of corpuscles, would be bent due to gravity. The Newtonian prediction for light deflection refers to the amount of deflection a corpuscle would feel under the effect of gravity, and therefore one should read "Newtonian" in this context as the referring to the following calculations and not a belief that Newton held in the validity of these calculations. For a gravitational point-mass lens of mass M {\displaystyle M} ,

7935-404: The gravitational effects of an unknown dark matter surrounding galaxies. Most of the gravitational potential in the universe seems to be in this form, and the Big Bang models and various observations indicate that this excess gravitational potential is not created by baryonic matter , such as normal atoms. Measurements of the redshifts of supernovae indicate that the expansion of the universe

8050-437: The halo mass is composed of red dwarfs. This corresponds to a negligible fraction of the dark matter halo mass. Therefore, the missing mass problem is not solved by MACHOs. MACHOs may sometimes be considered to include black holes . Isolated black holes without any matter around them are truly black in that they emit no light and any light shone upon them is absorbed and not reflected. A black hole can sometimes be detected by

8165-430: The halo of bright gas and dust that forms around it as an accretion disk being pulled in by the black hole's gravity. Such a disk can generate jets of gas that are shot out away from the black hole because it cannot be absorbed quickly enough. An isolated black hole, however, would not have an accretion disk and would only be detectable by gravitational lensing. Cosmologists doubt non- direct collapse black holes make up

8280-411: The lambda-CDM model of cosmology, which uses the independent frameworks of quantum mechanics and general relativity. There are no easily testable models that would describe the situation prior to approximately 10 seconds. Understanding this earliest of eras in the history of the universe is one of the greatest unsolved problems in physics . English astronomer Fred Hoyle is credited with coining

8395-431: The large amounts of dark matter now thought to be present in the universe. The Big Bang as it is currently understood could not have produced enough baryons and still be consistent with the observed elemental abundances, including the abundance of deuterium . Furthermore, separate observations of baryon acoustic oscillations , both in the cosmic microwave background and large-scale structure of galaxies, set limits on

8510-493: The largest possible deviation of the fine-structure constant over much of the age of the universe is of order 10 . Also, general relativity has passed stringent tests on the scale of the Solar System and binary stars . The large-scale universe appears isotropic as viewed from Earth. If it is indeed isotropic, the cosmological principle can be derived from the simpler Copernican principle , which states that there

8625-405: The light emitted from them has been shifted to longer wavelengths. This can be seen by taking a frequency spectrum of an object and matching the spectroscopic pattern of emission or absorption lines corresponding to atoms of the chemical elements interacting with the light. These redshifts are uniformly isotropic, distributed evenly among the observed objects in all directions. If the redshift

8740-550: The most distant quad-image lensing galaxy known, an even more distant two-image lensing galaxy was subsequently discovered by an international team of astronomers using a combination of Hubble Space Telescope and Keck telescope imaging and spectroscopy. The discovery and analysis of the IRC 0218 lens was published in the Astrophysical Journal Letters on June 23, 2014. Research published Sep 30, 2013 in

8855-453: The notions of space and time would altogether fail to have any meaning at the beginning; they would only begin to have a sensible meaning when the original quantum had been divided into a sufficient number of quanta. If this suggestion is correct, the beginning of the world happened a little before the beginning of space and time. During the 1930s, other ideas were proposed as non-standard cosmologies to explain Hubble's observations, including

8970-460: The observational evidence, most notably from radio source counts , began to favor Big Bang over steady state. The discovery and confirmation of the CMB in 1964 secured the Big Bang as the best theory of the origin and evolution of the universe. In 1968 and 1970, Roger Penrose , Stephen Hawking , and George F. R. Ellis published papers where they showed that mathematical singularities were an inevitable initial condition of relativistic models of

9085-632: The online edition of Physical Review Letters , led by McGill University in Montreal , Québec , Canada, has discovered the B-modes , that are formed due to gravitational lensing effect, using National Science Foundation 's South Pole Telescope and with help from the Herschel space observatory. This discovery would open the possibilities of testing the theories of how our universe originated. Albert Einstein predicted in 1936 that rays of light from

9200-482: The opacity of the universe at early times. So our view cannot extend further backward in time, though the horizon recedes in space. If the expansion of the universe continues to accelerate, there is a future horizon as well. Some processes in the early universe occurred too slowly, compared to the expansion rate of the universe, to reach approximate thermodynamic equilibrium . Others were fast enough to reach thermalization . The parameter usually used to find out whether

9315-404: The original matter particles and none of their antiparticles . A similar process happened at about 1 second for electrons and positrons. After these annihilations, the remaining protons, neutrons and electrons were no longer moving relativistically and the energy density of the universe was dominated by photons (with a minor contribution from neutrinos ). A few minutes into the expansion, when

9430-529: The other astronomical structures observable today. The details of this process depend on the amount and type of matter in the universe. The four possible types of matter are known as cold dark matter (CDM), warm dark matter , hot dark matter , and baryonic matter . The best measurements available, from the Wilkinson Microwave Anisotropy Probe (WMAP), show that the data is well-fit by a Lambda-CDM model in which dark matter

9545-469: The other forces, with only the electromagnetic force and weak nuclear force remaining unified. Inflation stopped locally at around 10 to 10 seconds, with the observable universe's volume having increased by a factor of at least 10 . Reheating followed as the inflaton field decayed, until the universe obtained the temperatures required for the production of a quark–gluon plasma as well as all other elementary particles . Temperatures were so high that

9660-427: The past all the mass of the universe was concentrated into a single point, a "primeval atom" where and when the fabric of time and space came into existence. In the 1920s and 1930s, almost every major cosmologist preferred an eternal steady-state universe, and several complained that the beginning of time implied by the Big Bang imported religious concepts into physics; this objection was later repeated by supporters of

9775-512: The photon radiation . The recombination epoch began after about 379,000 years, when the electrons and nuclei combined into atoms (mostly hydrogen ), which were able to emit radiation. This relic radiation, which continued through space largely unimpeded, is known as the cosmic microwave background. After the recombination epoch, the slightly denser regions of the uniformly distributed matter gravitationally attracted nearby matter and thus grew even denser, forming gas clouds, stars, galaxies, and

9890-506: The picture becomes less speculative, since particle energies drop to values that can be attained in particle accelerators . At about 10 seconds, quarks and gluons combined to form baryons such as protons and neutrons . The small excess of quarks over antiquarks led to a small excess of baryons over antibaryons. The temperature was no longer high enough to create either new proton–antiproton or neutron–antineutron pairs. A mass annihilation immediately followed, leaving just one in 10 of

10005-488: The precise values of the Hubble Constant and the matter-density of the universe (before the discovery of dark energy, thought to be the key predictor for the eventual fate of the universe ). In the mid-1990s, observations of certain globular clusters appeared to indicate that they were about 15 billion years old, which conflicted with most then-current estimates of the age of the universe (and indeed with

10120-461: The predominance of matter over antimatter in the present universe. The universe continued to decrease in density and fall in temperature, hence the typical energy of each particle was decreasing. Symmetry-breaking phase transitions put the fundamental forces of physics and the parameters of elementary particles into their present form, with the electromagnetic force and weak nuclear force separating at about 10 seconds. After about 10 seconds,

10235-427: The random motions of particles were at relativistic speeds , and particle–antiparticle pairs of all kinds were being continuously created and destroyed in collisions. At some point, an unknown reaction called baryogenesis violated the conservation of baryon number , leading to a very small excess of quarks and leptons over antiquarks and antileptons—of the order of one part in 30 million. This resulted in

10350-508: The range 1 × 10 solar masses (0.3 lunar masses) to 100 solar masses. One group, the MACHO collaboration, claimed in 2000 to have found enough microlensing to predict the existence of many MACHOs with mean mass of about 0.5 solar masses , enough to make up perhaps 20% of the dark matter in the galaxy. This suggests that MACHOs could be white dwarfs or red dwarfs which have similar masses. However, red and white dwarfs are not completely dark; they do emit some light, and so can be searched for with

10465-406: The ratio of baryons to the total amount of matter. These observations show that a large fraction of non-baryonic matter is necessary regardless of the presence or absence of MACHOs; however, MACHO candidates such as primordial black holes could be formed of non-baryonic matter (from pre-baryonic epochs of the early Big Bang). Gravitational lensing A gravitational lens is matter, such as

10580-640: The response of objects to a force in a flat geometry. The angle of deflection is toward the mass M at a distance r from the affected radiation, where G is the universal constant of gravitation , and c is the speed of light in vacuum. Since the Schwarzschild radius r s {\displaystyle r_{\text{s}}} is defined as r s = 2 G m / c 2 {\displaystyle r_{\text{s}}=2Gm/c^{2}} , and escape velocity v e {\displaystyle v_{\text{e}}}

10695-458: The same direction that skirt the edges of the Sun would converge to a focal point approximately 542 AU from the Sun. Thus, a probe positioned at this distance (or greater) from the Sun could use the Sun as a gravitational lens for magnifying distant objects on the opposite side of the Sun. A probe's location could shift around as needed to select different targets relative to the Sun. This distance

10810-453: The same source; the number and shape of these depending upon the relative positions of the source, lens, and observer, and the shape of the gravitational well of the lensing object. There are three classes of gravitational lensing: Gravitational lenses act equally on all kinds of electromagnetic radiation , not just visible light, and also in non-electromagnetic radiation, like gravitational waves. Weak lensing effects are being studied for

10925-455: The search. The AT20G survey is a blind survey at 20 GHz frequency in the radio domain of the electromagnetic spectrum. Due to the high frequency used, the chances of finding gravitational lenses increases as the relative number of compact core objects (e.g. quasars) are higher (Sadler et al. 2006). This is important as the lensing is easier to detect and identify in simple objects compared to objects with complexity in them. This search involves

11040-410: The singularity. In some proposals, such as the emergent Universe models, the singularity is replaced by another cosmological epoch. A different approach identifies the initial singularity as a singularity predicted by some models of the Big Bang theory to have existed before the Big Bang event. This primordial singularity is itself sometimes called "the Big Bang", but the term can also refer to

11155-495: The size of the observable universe , the Hubble redshift can be thought of as the Doppler shift corresponding to the recession velocity v {\displaystyle v} . For distances comparable to the size of the observable universe, the attribution of the cosmological redshift becomes more ambiguous, although its interpretation as a kinematic Doppler shift remains the most natural one. An unexplained discrepancy with

11270-731: The stars near the Sun to be observed. Observations were made simultaneously in the cities of Sobral, Ceará , Brazil and in São Tomé and Príncipe on the west coast of Africa. The observations demonstrated that the light from stars passing close to the Sun was slightly bent, so that stars appeared slightly out of position. The result was considered spectacular news and made the front page of most major newspapers. It made Einstein and his theory of general relativity world-famous. When asked by his assistant what his reaction would have been if general relativity had not been confirmed by Eddington and Dyson in 1919, Einstein said "Then I would feel sorry for

11385-406: The steady-state theory. This perception was enhanced by the fact that the originator of the Big Bang concept, Lemaître, was a Roman Catholic priest. Arthur Eddington agreed with Aristotle that the universe did not have a beginning in time, viz ., that matter is eternal . A beginning in time was "repugnant" to him. Lemaître, however, disagreed: If the world has begun with a single quantum ,

11500-587: The suggested new model, the cosmological distribution of dark energy would be slightly lumpy and dark-energy stars of primordial type might be a possible candidate for MACHOs. Neutron stars , unlike black holes, are not heavy enough to collapse completely, and instead form a material rather like that of an atomic nucleus called neutron matter . After sufficient time these stars could radiate away enough energy to become cold enough that they would be too faint to see. Likewise, old white dwarfs may also become cold and dead, eventually becoming black dwarfs , although

11615-421: The systematic distortion of the PSF. This method (KSB+) is the most widely used method in weak lensing shear measurements. Galaxies have random rotations and inclinations. As a result, the shear effects in weak lensing need to be determined by statistically preferred orientations. The primary source of error in lensing measurement is due to the convolution of the PSF with the lensed image. The KSB method measures

11730-447: The temperature was about a billion kelvin and the density of matter in the universe was comparable to the current density of Earth's atmosphere, neutrons combined with protons to form the universe's deuterium and helium nuclei in a process called Big Bang nucleosynthesis (BBN). Most protons remained uncombined as hydrogen nuclei. As the universe cooled, the rest energy density of matter came to gravitationally dominate that of

11845-465: The term "Big Bang" during a talk for a March 1949 BBC Radio broadcast, saying: "These theories were based on the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past." However, it did not catch on until the 1970s. It is popularly reported that Hoyle, who favored an alternative " steady-state " cosmological model, intended this to be pejorative, but Hoyle explicitly denied this and said it

11960-452: The total energy density of the present day universe is in this form. When the universe was very young it was likely infused with dark energy, but with everything closer together, gravity predominated, braking the expansion. Eventually, after billions of years of expansion, the declining density of matter relative to the density of dark energy allowed the expansion of the universe to begin to accelerate. Dark energy in its simplest formulation

12075-416: The universe has no overall geometric curvature due to gravitational influence. Microscopic quantum fluctuations that occurred because of Heisenberg's uncertainty principle were "frozen in" by inflation, becoming amplified into the seeds that would later form the large-scale structure of the universe. At a time around 10 seconds, the electroweak epoch begins when the strong nuclear force separates from

12190-411: The universe emerged from a "primeval atom " in 1931, introducing the modern notion of the Big Bang. Various cosmological models of the Big Bang explain the evolution of the observable universe from the earliest known periods through its subsequent large-scale form. These models offer a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements ,

12305-422: The universe has a finite age, and light travels at a finite speed, there may be events in the past whose light has not yet had time to reach earth. This places a limit or a past horizon on the most distant objects that can be observed. Conversely, because space is expanding, and more distant objects are receding ever more quickly, light emitted by us today may never "catch up" to very distant objects. This defines

12420-490: The universe is uniformly expanding everywhere. This cosmic expansion was predicted from general relativity by Friedmann in 1922 and Lemaître in 1927, well before Hubble made his 1929 analysis and observations, and it remains the cornerstone of the Big Bang model as developed by Friedmann, Lemaître, Robertson, and Walker. The theory requires the relation v = H D {\displaystyle v=HD} to hold at all times, where D {\displaystyle D}

12535-402: The use of interferometric methods to identify candidates and follow them up at higher resolution to identify them. Full detail of the project is currently under works for publication. Microlensing techniques have been used to search for planets outside our solar system. A statistical analysis of specific cases of observed microlensing over the time period of 2002 to 2007 found that most stars in

12650-449: The validity of the theory are the expansion of the universe according to Hubble's law (as indicated by the redshifts of galaxies), discovery and measurement of the cosmic microwave background and the relative abundances of light elements produced by Big Bang nucleosynthesis (BBN). More recent evidence includes observations of galaxy formation and evolution , and the distribution of large-scale cosmic structures . These are sometimes called

12765-541: The velocity boost the corpuscle receives is If one assumes that initially the light is far enough from the lens to neglect gravity, the perpendicular distance between the light's initial trajectory and the lens is b (the impact parameter ), and the parallel distance is r ∥ {\displaystyle r_{\parallel }} , such that r 2 = b 2 + r ∥ 2 {\displaystyle r^{2}=b^{2}+r_{\parallel }^{2}} . We additionally assume

12880-477: Was Lemaître's Big Bang theory, advocated and developed by George Gamow , who introduced BBN and whose associates, Ralph Alpher and Robert Herman , predicted the CMB. Ironically, it was Hoyle who coined the phrase that came to be applied to Lemaître's theory, referring to it as "this big bang idea" during a BBC Radio broadcast in March 1949. For a while, support was split between these two theories. Eventually,

12995-538: Was first scientifically originated by physicist Alexander Friedmann in 1922 with the mathematical derivation of the Friedmann equations . The earliest empirical observation of the notion of an expanding universe is known as Hubble's Law , published in work by physicist Edwin Hubble in 1929, which discerned that galaxies are moving away from Earth at a rate that accelerates proportionally with distance. Independent of Friedmann's work, and independent of Hubble's observations, physicist Georges Lemaître proposed that

13110-411: Was just a striking image meant to highlight the difference between the two models. Helge Kragh writes that the evidence for the claim that it was meant as a pejorative is "unconvincing", and mentions a number of indications that it was not a pejorative. The term itself has been argued to be a misnomer because it evokes an explosion. The argument is that whereas an explosion suggests expansion into

13225-478: Was very rapidly expanding and cooling. The period up to 10 seconds into the expansion, the Planck epoch , was a phase in which the four fundamental forces —the electromagnetic force , the strong nuclear force , the weak nuclear force , and the gravitational force , were unified as one. In this stage, the characteristic scale length of the universe was the Planck length , 1.6 × 10  m , and consequently had

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