Misplaced Pages

#920079

32-531: The radius of the "cold spot" subtends about 5°; it is centered at the galactic coordinate l II = 207.8° , b II = −56.3° ( equatorial : α = 03 15 05 , δ = −19° 35′ 02″). It is, therefore, in the Southern Celestial Hemisphere , in the direction of the constellation Eridanus . Typically, the largest fluctuations of the primordial CMB temperature occur on angular scales of about 1°. Thus

64-409: A curve when its two rays pass through the endpoints of that arc, line segment, or curve section. Conversely, the arc, line segment or curve section confined within the rays of an angle is regarded as the corresponding subtension of that angle. It is also sometimes said that an arc is intercepted or enclosed by that angle. The precise meaning varies with context. For example, one may speak of

96-598: A German popular astronomical article by Otto Ule . Ule explained the oddity of a distance unit name ending in "year" by comparing it to a walking hour ( Wegstunde ). A contemporary German popular astronomical book also noticed that light-year is an odd name. In 1868 an English journal labelled the light-year as a unit used by the Germans. Eddington called the light-year an inconvenient and irrelevant unit, which had sometimes crept from popular use into technical investigations. Although modern astronomers often prefer to use

128-468: A cold region as large as the "cold spot" appears very unlikely, given generally accepted theoretical models. Various alternative explanations exist, including a so-called Eridanus Supervoid or Great Void that may exist between us and the primordial CMB (foreground voids can cause cold spots against the CMB). Such a void would affect the observed CMB via the integrated Sachs–Wolfe effect , and would be one of

160-462: A giant cosmic hole" and made the hypothesis that the WMAP cold spot is "... the unmistakable imprint of another universe beyond the edge of our own." If true, this provides the first empirical evidence for a parallel universe (though theoretical models of parallel universes existed previously). It would also support string theory . The team claims that there are testable consequences for its theory. If

192-513: A large void is present, as such a void would cause an increased cancellation between the "late-time" integrated Sachs–Wolfe effect and the "ordinary" Sachs–Wolfe effect. This effect would be much smaller if dark energy were not stretching the void as photons went through it. Rudnick et al . found a dip in NVSS galaxy number counts in the direction of the Cold Spot, suggesting the presence of

224-538: A large void. Since then, some additional works have cast doubt on the "supervoid" explanation. The correlation between the NVSS dip and the Cold Spot was found to be marginal using a more conservative statistical analysis. Also, a direct survey for galaxies in several one-degree-square fields within the Cold Spot found no evidence for a supervoid. However, the supervoid explanation has not been ruled out entirely; it remains intriguing, since supervoids do seem capable of affecting

256-444: A north and a south cold spot in the satellite data: "...among the high randomness regions is the southern non-Gaussian anomaly, the Cold Spot, with a stratification expected for the voids. Existence of its counterpart, a Northern Cold Spot with almost identical randomness properties among other low-temperature regions is revealed." These predictions and others were made prior to the measurements (see Laura Mersini ). However, apart from

288-628: Is approximately 5.88 trillion mi. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Despite its inclusion of the word "year", the term should not be misinterpreted as a unit of time . The light-year is most often used when expressing distances to stars and other distances on a galactic scale, especially in non-specialist contexts and popular science publications. The unit most commonly used in professional astronomy

320-454: Is exactly 299 792 458 metres or ⁠ 1 / 31 557 600 ⁠ of a light-year. Units such as the light-minute, light-hour and light-day are sometimes used in popular science publications. The light-month, roughly one-twelfth of a light-year, is also used occasionally for approximate measures. The Hayden Planetarium specifies the light month more precisely as 30 days of light travel time. Light travels approximately one foot in

352-561: Is the parsec (symbol: pc, about 3.26 light-years). As defined by the International Astronomical Union (IAU), the light-year is the product of the Julian year (365.25 days, as opposed to the 365.2425-day Gregorian year or the 365.24219-day Tropical year that both approximate) and the speed of light ( 299 792 458  m/s ). Both of these values are included in the IAU (1976) System of Astronomical Constants , used since 1984. From this,

SECTION 10

#1732801353921

384-477: Is the product of a mean Gregorian year (365.2425 days or 31 556 952  s ) and the defined speed of light ( 299 792 458  m/s ). Another value, 9.460 528 405 × 10  m , is the product of the J1900.0 mean tropical year and the defined speed of light. Abbreviations used for light-years and multiples of light-years are: The light-year unit appeared a few years after the first successful measurement of

416-492: The Sloan Great Wall run up into the billions of light-years. Distances between objects within a star system tend to be small fractions of a light-year, and are usually expressed in astronomical units . However, smaller units of length can similarly be formed usefully by multiplying units of time by the speed of light. For example, the light-second , useful in astronomy, telecommunications and relativistic physics,

448-402: The largest structures in the observable universe . This would be an extremely large region of the universe, roughly 150 to 300 Mpc or 500 million to one billion light-years across and 6 to 10 billion light years away, at redshift z ≃ 1 {\displaystyle z\simeq 1} , containing a density of matter much smaller than the average density at that redshift. In

480-511: The parsec , light-years are also popularly used to gauge the expanses of interstellar and intergalactic space. Distances expressed in light-years include those between stars in the same general area, such as those belonging to the same spiral arm or globular cluster . Galaxies themselves span from a few thousand to a few hundred thousand light-years in diameter, and are separated from neighbouring galaxies and galaxy clusters by millions of light-years. Distances to objects such as quasars and

512-547: The CMB measurably. A 2015 study shows the presence of a supervoid that has a diameter of 1.8 billion light years and is centered at 3 billion light-years from our galaxy in the direction of the Cold Spot, likely being associated with it. This would make it the largest void detected, and one of the largest structures known. Later measurements of the Sachs–Wolfe effect show too its likely existence. Although large voids are known in

544-502: The Julian year) and a measured (not defined) speed of light were included in the IAU (1964) System of Astronomical Constants, used from 1968 to 1983. The product of Simon Newcomb 's J1900.0 mean tropical year of 31 556 925 .9747 ephemeris seconds and a speed of light of 299 792 .5 km/s produced a light-year of 9.460 530 × 10  m (rounded to the seven significant digits in

576-565: The Southern Cold Spot, the varied statistical methods in general fail to confirm each other regarding a Northern Cold Spot. The 'K-map' used to detect the Northern Cold Spot was noted to have twice the measure of randomness measured in the standard model. The difference is speculated to be caused by the randomness introduced by voids (unaccounted-for voids were speculated to be the reason for the increased randomness above

608-426: The accuracy of his parallax data due to multiplying with the uncertain parameter of the speed of light. The speed of light was not yet precisely known in 1838; the estimate of its value changed in 1849 ( Fizeau ) and 1862 ( Foucault ). It was not yet considered to be a fundamental constant of nature, and the propagation of light through the aether or space was still enigmatic. The light-year unit appeared in 1851 in

640-426: The angle subtended by an arc of a circle when the angle's vertex is the centre of the circle. This elementary geometry -related article is a stub . You can help Misplaced Pages by expanding it . Light year A light-year , alternatively spelled light year ( ly or lyr ), is a unit of length used to express astronomical distances and is equal to exactly 9 460 730 472 580 .8 km , which

672-472: The cold spot was generated by the standard mechanism of quantum fluctuations during cosmological inflation , which in most inflationary models gives rise to Gaussian statistics. The cold spot may also, as suggested in the references above, be a signal of non-Gaussian primordial fluctuations. Some authors called into question the statistical significance of this cold spot. In 2013, the CMB Cold Spot

SECTION 20

#1732801353921

704-568: The correlation between the Eridanus supervoid and the CMB cold spot. In late 2007, ( Cruz et al. ) argued that the Cold Spot could be due to a cosmic texture , a remnant of a phase transition in the early Universe. A controversial claim by Laura Mersini-Houghton is that it could be the imprint of another universe beyond our own, caused by quantum entanglement between universes before they were separated by cosmic inflation . Laura Mersini-Houghton said, "Standard cosmology cannot explain such

736-588: The distance to a star other than the Sun, by Friedrich Bessel in 1838. The star was 61 Cygni , and he used a 160-millimetre (6.2 in) heliometre designed by Joseph von Fraunhofer . The largest unit for expressing distances across space at that time was the astronomical unit , equal to the radius of the Earth's orbit at 150 million kilometres (93 million miles). In those terms, trigonometric calculations based on 61 Cygni's parallax of 0.314 arcseconds, showed

768-409: The distance to the star to be 660 000 astronomical units (9.9 × 10  km; 6.1 × 10  mi). Bessel added that light takes 10.3 years to traverse this distance. He recognized that his readers would enjoy the mental picture of the approximate transit time for light, but he refrained from using the light-year as a unit. He may have resisted expressing distances in light-years because it would reduce

800-619: The first year of data recorded by the Wilkinson Microwave Anisotropy Probe (WMAP), a region of sky in the constellation Eridanus was found to be colder than the surrounding area. Subsequently, using the data gathered by WMAP over 3 years, the statistical significance of such a large, cold region was estimated. The probability of finding a deviation at least as high in Gaussian simulations was found to be 1.85%. Thus it appears unlikely, but not impossible, that

832-521: The following conversions can be derived: The abbreviation used by the IAU for light-year is "ly", International standards like ISO 80000:2006 (now superseded) have used "l.y." and localized abbreviations are frequent, such as "al" in French, Spanish, and Italian (from année-lumière , año luz and anno luce , respectively), "Lj" in German (from Lichtjahr ), etc. Before 1984, the tropical year (not

864-521: The line of sight could have caused the CMB Cold Spot and concluded that it may instead have a primordial origin. One important thing to confirm or rule out the late time integrated Sachs–Wolfe effect is the mass profile of galaxies in the area as ISW effect is affected by the galaxy bias which depends on the mass profiles and types of galaxies. In December 2021, the Dark Energy Survey (DES), analyzing their data, put forward more evidence for

896-728: The parallel-universe theory is true, there will be a similar void in the Celestial sphere 's opposite hemisphere (which New Scientist reported to be in the Southern celestial hemisphere; the results of the New Mexico array study reported it as being in the Northern). Other researchers have modeled the cold spot as potentially the result of cosmological bubble collisions, again before inflation. A sophisticated computational analysis (using Kolmogorov complexity ) has derived evidence for

928-423: The speed of light) found in several modern sources was probably derived from an old source such as C. W. Allen 's 1973 Astrophysical Quantities reference work, which was updated in 2000, including the IAU (1976) value cited above (truncated to 10 significant digits). Other high-precision values are not derived from a coherent IAU system. A value of 9.460 536 207 × 10  m found in some modern sources

960-464: The standard model). The cold spot is mainly anomalous because it stands out compared to the relatively hot ring around it; it is not unusual if one only considers the size and coldness of the spot itself. More technically, its detection and significance depends on using a compensated filter like a Mexican hat wavelet to find it. Subtended angle In geometry , an angle is subtended by an arc , line segment , or any other section of

992-458: The universe, a void would have to be exceptionally vast to explain the cold spot, perhaps 1,000 times larger in volume than expected typical voids. It would be 6 billion–10 billion light-years away and nearly one billion light-years across, and would be perhaps even more improbable to occur in the large-scale structure than the WMAP cold spot would be in the primordial CMB. A 2017 study reported surveys showing no evidence that associated voids in

CMB cold spot - Misplaced Pages Continue

1024-518: Was also observed by the Planck satellite at similar significance, discarding the possibility of being caused by a systematic error of the WMAP satellite. The large 'cold spot' forms part of what has been called an ' axis of evil ' (so-called because it was unexpected to see a structure like this). One possible explanation of the cold spot is a huge void between us and the primordial CMB . A region cooler than surrounding sightlines can be observed if

#920079