Topic: Astronomy/Astronomical objects

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Dyson sphere

Spaceflight Astronomy Engineering Astronomy/Astronomical objects

A Dyson sphere is a hypothetical megastructure that completely encompasses a star and captures a large percentage of its power output. The concept is a thought experiment that attempts to explain how a spacefaring civilization would meet its energy requirements once those requirements exceed what can be generated from the home planet's resources alone. Only a tiny fraction of a star's energy emissions reach the surface of any orbiting planet. Building structures encircling a star would enable a civilization to harvest far more energy.

The first contemporary description of the structure was by Olaf Stapledon in his science fiction novel Star Maker (1937), in which he described "every solar system... surrounded by a gauze of light traps, which focused the escaping solar energy for intelligent use." The concept was later popularized by Freeman Dyson in his 1960 paper "Search for Artificial Stellar Sources of Infrared Radiation." Dyson speculated that such structures would be the logical consequence of the escalating energy needs of a technological civilization and would be a necessity for its long-term survival. He proposed that searching for such structures could lead to the detection of advanced, intelligent extraterrestrial life. Different types of Dyson spheres and their energy-harvesting ability would correspond to levels of technological advancement on the Kardashev scale.

Since then, other variant designs involving building an artificial structure or series of structures to encompass a star have been proposed in exploratory engineering or described in science fiction under the name "Dyson sphere". These later proposals have not been limited to solar-power stations, with many involving habitation or industrial elements. Most fictional depictions describe a solid shell of matter enclosing a star, which was considered by Dyson himself the least plausible variant of the idea. In May 2013, at the Starship Century Symposium in San Diego, Dyson repeated his comments that he wished the concept had not been named after him.

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Hoag's Object

Astronomy Astronomy/Astronomical objects

Hoag's Object is a non-typical galaxy of the type known as a ring galaxy. The galaxy is named after Arthur Hoag who discovered it in 1950 and identified it as either a planetary nebula or a peculiar galaxy with eight billion stars, spanning roughly 100,000 light years.

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The fastest pulsar spins at 716Hz; its equator spins at 24% the speed of light

Astronomy Astronomy/Astronomical objects

PSR J1748−2446ad is the fastest-spinning pulsar known, at 716 Hz, or 716 times per second. This pulsar was discovered by Jason W. T. Hessels of McGill University on November 10, 2004 and confirmed on January 8, 2005.

If the neutron star is assumed to contain less than two times the mass of the Sun, within the typical range of neutron stars, its radius is constrained to be less than 16 km. At its equator it is spinning at approximately 24% of the speed of light, or over 70,000 km per second.

The pulsar is located in a globular cluster of stars called Terzan 5, located approximately 18,000 light-years from Earth in the constellation Sagittarius. It is part of a binary system and undergoes regular eclipses with an eclipse magnitude of about 40%. Its orbit is highly circular with a 26-hour period. The other object is at least 0.14 solar masses, with a radius of 5–6 solar radii. Hessels et al. state that the companion may be a "bloated main-sequence star, possibly still filling its Roche Lobe". Hessels et al. go on to speculate that gravitational radiation from the pulsar might be detectable by LIGO.

SN 1006

Physics China Astronomy History of Science Astronomy/Astronomical objects Arab world

SN 1006 was a supernova that is likely the brightest observed stellar event in recorded history, reaching an estimated −7.5 visual magnitude, and exceeding roughly sixteen times the brightness of Venus. Appearing between April 30 and May 1, 1006 AD in the constellation of Lupus, this "guest star" was described by observers across the modern day countries of China, Japan, Iraq, Egypt, and the continent of Europe, and possibly recorded in North American petroglyphs. Some reports state it was clearly visible in the daytime. Modern astronomers now consider its distance from Earth to be about 7,200 light-years.

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Wolf 359

Astronomy Astronomy/Astronomical objects

Wolf 359 is a red dwarf star located in the constellation Leo, near the ecliptic. At a distance of approximately 7.9 light years from Earth, it has an apparent magnitude of 13.54 and can only be seen with a large telescope. Wolf 359 is one of the nearest stars to the Sun; only the Alpha Centauri system (including Proxima Centauri), Barnard's Star and the brown dwarfs Luhman 16 and WISE 0855−0714 are known to be closer. Its proximity to Earth has led to its mention in several works of fiction.

Wolf 359 is one of the faintest and lowest-mass stars known. At the light-emitting layer called the photosphere, it has a temperature of about 2,800 K, which is low enough for chemical compounds to form and survive. The absorption lines of compounds such as water and titanium(II) oxide have been observed in the spectrum. The surface has a magnetic field that is stronger than the average magnetic field on the Sun. As a result of magnetic activity caused by convection, Wolf 359 is a flare star that can undergo sudden increases in luminosity for several minutes. These flares emit strong bursts of X-ray and gamma ray radiation that have been observed by space telescopes. Wolf 359 is a relatively young star with an age of less than a billion years. Two planetary companions are suspected but as yet no debris disks have been unmasked.

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Tabby's Star

Astronomy Astronomy/Astronomical objects

Tabby's Star (also known as Boyajian's Star and WTF Star, and designated KIC 8462852 in the Kepler Input Catalog) is an F-type main-sequence star in the constellation Cygnus approximately 1,470 light-years (450 pc) from Earth. Unusual light fluctuations of the star, including up to a 22% dimming in brightness, were discovered by citizen scientists as part of the Planet Hunters project. In September 2015, astronomers and citizen scientists associated with the project posted a preprint of an article describing the data and possible interpretations. The discovery was made from data collected by the Kepler space telescope, which observed changes in the brightness of distant stars to detect exoplanets.

Several hypotheses have been proposed to explain the star's large irregular changes in brightness as measured by its light curve, but none to date fully explain all aspects of the curve. One explanation is that an "uneven ring of dust" orbits Tabby's Star. In another explanation, the star's luminosity is modulated by changes in the efficiency of heat transport to its photosphere, so no external obscuration is required. A third hypothesis, based on a lack of observed infrared light, posits a swarm of cold, dusty comet fragments in a highly eccentric orbit; however, the notion that disturbed comets from such a cloud could exist in high enough numbers to obscure 22% of the star's observed luminosity has been doubted. Another hypothesis is that a large number of small masses in "tight formation" are orbiting the star. Furthermore, spectroscopic study of the system has found no evidence for coalescing material or hot close-in dust or circumstellar matter from an evaporating or exploding planet within a few astronomical units of the mature central star. It has also been hypothesized that the changes in brightness could be signs of activity associated with intelligent extraterrestrial life constructing a Dyson swarm; however, further analysis based on data through the end of 2017 showed wavelength-dependent dimming consistent with dust but not an opaque object such as an alien megastructure, which would block all wavelengths of light equally.

Tabby's Star is not the only star that has large irregular dimmings, but other such stars include young stellar objects called YSO dippers, which have different dimming patterns. An example of such an object is EPIC 204278916.

New fluctuations ran from mid-May 2017 until July 2018, assuming their continuance in late-December 2017 to mid-February 2018 when obscured by the Sun.

In September 2019, astronomers reported that the observed dimmings of Tabby's Star may have been produced by fragments resulting from the disruption of an orphaned exomoon. An overall study of other similar stars has been presented. In January 2021, a distant stellar-mass companion was reported, making Tabby's Star a binary stellar system.

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White Hole

Physics Astronomy Physics/relativity Astronomy/Astronomical objects

In general relativity, a white hole is a hypothetical region of spacetime and singularity that cannot be entered from the outside, although energy-matter, light and information can escape from it. In this sense, it is the reverse of a black hole, which can be entered only from the outside and from which energy-matter, light and information cannot escape. White holes appear in the theory of eternal black holes. In addition to a black hole region in the future, such a solution of the Einstein field equations has a white hole region in its past. This region does not exist for black holes that have formed through gravitational collapse, however, nor are there any observed physical processes through which a white hole could be formed.

Supermassive black holes (SBHs) are theoretically predicted to be at the center of every galaxy and that possibly, a galaxy cannot form without one. Stephen Hawking and others have proposed that these SBHs spawn a supermassive white hole/Big Bang.

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