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very short Pages = blue
short = green
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pretty long = yellow
long = red
very long = purple

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See all the wonderful things Sylvanus Blimpo has made

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Go to comments to participate in local chat

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JOURNEY TO THE EDGE OF THE Universe | Space Documentary 2020 Full HD 1080p

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The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth.

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Explore National Geographic. A world leader in geography, cartography and exploration.

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from sun: 43 milinon miles

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Mercury is the smallest and innermost planet in the Solar System. Its orbit around the Sun takes only 87.97 days, the shortest of all the planets in the Solar System. It is named after the Roman deity Mercury, the messenger of the gods.

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From sun: 67 million miles

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Venus is the second planet from the Sun. It is named after the Roman goddess of love and beauty. As the second-brightest natural object in the night sky after the Moon, Venus can cast shadows and, rarely, is visible to the naked eye in broad daylight.

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Neil deGrasse Tyson on significance of finding possible signs of life on Venus

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From sun: 92 million miles

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Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago.

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10 Wonderful Facts About Earth You've Never Heard Before

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From sun: 141 million miles

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Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. In English, Mars carries a name of the Roman god of war and is often referred to as the 'Red Planet. people also look at mars as a possible tartget for colonization, humans could terraform mars by 2,100.

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from sun: varies

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The Kuiper belt, occasionally called the Edgeworth–Kuiper belt, is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger – 20 times as wide and 20–200 times as massive

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From sun: 484 million miles

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Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass one-thousandth that of the Sun, but two-and-a-half times that of all the other planets in the Solar System combined.

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Something slammed into Jupiter, it was visible form Earth

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From sun: 891 million miles

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Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius about nine times that of Earth. It has only one-eighth the average density of Earth; however, with its larger volume, Saturn is over 95 times more massive.

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From sun: 1.7 billion miles

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Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Uranus is similar in composition to Neptune, and both have bulk chemical compositions which differ from that of the larger gas giants Jupiter and Saturn.

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From sun: 2.7 billion miles

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Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. Neptune is 17 times the mass of Earth, slightly more massive than its near-twin Uranus.

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from sun: 39.5 AU

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Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It was the first and the largest Kuiper belt object to be discovered. Pluto was discovered by Clyde Tombaugh in 1930 and declared to be the ninth planet from the Sun, although of course now it is declared a "dwarf planet.

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That's Why Pluto Is Not a Planet Anymore

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Haumea is a likely dwarf planet located beyond Neptune's orbit. It was discovered in 2004 by a team headed by Mike Brown of Caltech at the Palomar Observatory in the United States.

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Haumea - The Egg Shaped World (Beyond Pluto Episode 1) 4K UHD

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from sun: 45.8 AU

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Makemake is a likely dwarf planet and perhaps the second largest Kuiper belt object in the classical population, with a diameter approximately two-thirds that of Pluto. Makemake has one known satellite.

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Makemake - The Icy Red World (Beyond Pluto Episode 2) 4K UHD

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Eris is the most massive and second-largest known dwarf planet in the Solar System. Eris was discovered in January 2005 by a Palomar Observatory-based team led by Mike Brown, and its discovery was verified later that year. In September 2006 it was named after the Greco-Roman goddess of strife and discord. lets say bye to the solar system cause this is our last stop!
(and sorry i could not get a appropiate video)

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Eris ( minor-planet designation: 136199 Eris) is the most massive and second-largest known dwarf planet in the Solar System. It is a trans-Neptunian object (TNO) in the scattered disk and has a high- eccentricity orbit. Eris was discovered in January 2005 by a Palomar Observatory-based team led by Mike Brown and verified later that year. It was named in September 2006 after the Greco-Roman goddess of strife and discord. Eris is the ninth-most massive known object orbiting the Sun and the sixteenth-most massive overall in the Solar System (counting moons). It is also the largest known object in the solar system that has not been visited by a spacecraft. Eris has been measured at 2,326 ± 12 kilometers (1,445 ± 7 mi) in diameter; its mass is 0.28% that of the Earth and 27% greater than that of Pluto, although Pluto is slightly larger by volume. Both Eris and Pluto have a surface area that is comparable to the area of Russia or South America.

Eris has one large known moon, Dysnomia. In February 2016, Eris's distance from the Sun was 96.3 AU (14.41 billion km; 8.95 billion mi), more than three times that of Neptune or Pluto. With the exception of long-period comets, Eris and Dysnomia were the most distant known natural objects in the Solar System until the discovery of and in 2018.

Because Eris appeared to be larger than Pluto, NASA initially described it as the Solar System's tenth planet. This, along with the prospect of other objects of similar size being discovered in the future, motivated the International Astronomical Union (IAU) to define the term planet for the first time. Under the IAU definition approved on August 24, 2006, Eris, Pluto and Ceres are " dwarf planets", reducing the number of known planets in the Solar System to eight, the same as before Pluto's discovery in 1930. Observations of a stellar occultation by Eris in 2010 showed that it was slightly smaller than Pluto, which was measured by New Horizons as having a mean diameter of 2,377 ± 4 kilometers (1,477 ± 2 mi) in July 2015.

Eris was discovered by the team of Mike Brown, Chad Trujillo, and David Rabinowitz on January 5, 2005, from images taken on October 21, 2003. The discovery was announced on July 29, 2005, the same day as Makemake and two days after Haumea, due in part to events that would later lead to controversy about Haumea. The search team had been systematically scanning for large outer Solar System bodies for several years, and had been involved in the discovery of several other large TNOs, including the dwarf planets Quaoar, Orcus, and Sedna.

Routine observations were taken by the team on October 21, 2003, using the 1.2 m Samuel Oschin Schmidt telescope at Palomar Observatory, California, but the image of Eris was not discovered at that point due to its very slow motion across the sky: The team's automatic image-searching software excluded all objects moving at less than 1.5 arcseconds per hour to reduce the number of false positives returned. When Sedna was discovered in 2003, it was moving at 1.75 arcsec/h, and in light of that the team reanalyzed their old data with a lower limit on the angular motion, sorting through the previously excluded images by eye. In January 2005, the re-analysis revealed Eris's slow orbital motion against the background stars.

Follow-up observations were then carried out to make a preliminary determination of Eris's orbit, which allowed the object's distance to be estimated. The team had planned to delay announcing their discoveries of the bright objects Eris and Makemake until further observations and calculations were complete, but announced them both on July 29 when the discovery of another large TNO they had been tracking-Haumea-was controversially announced on July 27 by a different team in Spain.

Precovery images of Eris have been identified back to September 3, 1954.

More observations released in October 2005 revealed that Eris has a moon, later named Dysnomia. Observations of Dysnomia's orbit permitted scientists to determine the mass of Eris, which in June 2007 was calculated to be , greater than Pluto's.

Eris is named after the Greek goddess (Greek ), a personification of strife and discord. The name was proposed by the Caltech team on September 6, 2006, and it was assigned on September 13, 2006, following an unusually long period in which the object was known by the provisional designation , which was granted automatically by the IAU under their naming protocols for minor planets.

The name Eris has two competing pronunciations, with a "long" or with a "short" e, analogous to the two competing pronunciations of the word . Perhaps the more common form in English, used i.a. by Brown and his students, is with disyllabic laxing and a short e. However, the classical English pronunciation of the goddess is , with a long e.

The Greek and Latin oblique stem of the name is Erid-, as can be seen in Italian Eride and Russian Эрида Erida, so the adjective in English is Eridian .

Due to uncertainty over whether the object would be classified as a planet or a minor planet, because varying nomenclature procedures apply to these classes of objects, the decision on what to name the object had to wait until after the August 24, 2006, IAU ruling. For a period of time, the object became known to the wider public as Xena. "Xena" was an informal name used internally by the discovery team, inspired by the title character of the television series Xena: Warrior Princess. The discovery team had reportedly saved the nickname "Xena" for the first body they discovered that was larger than Pluto. According to Brown,

We chose it since it started with an X ( planet "X"), it sounds mythological ... and we've been working to get more female deities out there ( e.g. Sedna). Also, at the time, the TV show was still on TV, which shows you how long we've been searching!

Brown said in an interview that the naming process was stalled:

One reporter [Ken Chang] called me up from The New York Times who happened to have been a friend of mine from college, [and] ... asked me, "What's the name you guys proposed?" and I said, "Well, I'm not going to tell." And he said, "Well, what do you guys call it when you're just talking amongst yourselves?" ... As far as I remember this was the only time I told anybody this in the press, and then it got everywhere, which I only sorta felt bad about; I kinda like the name.

Choosing an official name

According to science writer Govert Schilling, Brown initially wanted to call the object " Lila", after a concept in Hindu mythology that described the cosmos as the outcome of a game played by Brahman. The name could be pronounced like "Lilah", the name of Brown's newborn daughter. Brown was mindful of not making his name public before it had been officially accepted. He had done so with Sedna a year previously, and had been heavily criticized. However, no objection was raised to the Sedna name other than the breach of protocol, and no competing names were suggested for Sedna.

He listed the address of his personal web page announcing the discovery as /~mbrown/planetlila and in the chaos following the controversy over the discovery of Haumea, forgot to change it. Rather than needlessly anger more of his fellow astronomers, he simply said that the webpage had been named for his daughter and dropped "Lila" from consideration.

Brown had also speculated that Persephone, the wife of the god Pluto, would be a good name for the object. The name had been used several times for planets in science fiction and was popular with the public, having handily won a poll conducted by New Scientist magazine. ("Xena", despite only being a nickname, came fourth.) This choice was not possible because there was already a minor planet with that name, 399 Persephone.

The discovery team proposed on September 6, 2006. On September 13, 2006, this was accepted as the official name by the IAU. Brown decided that, because the object had been considered a planet for so long, it deserved a name from Greek or Roman mythology like the other planets. The asteroids had taken the vast majority of Graeco-Roman names. Eris, whom Brown described as his favorite goddess, had fortunately escaped inclusion. "Eris caused strife and discord by causing quarrels among people," said Brown in 2006, "and that's what this one has done too."

The usage of ⟨⟨ planetary symbols are discouraged in astronomy, but NASA has used the Hand of Eris, ⟩ (U+2BF0), for Eris.[49] This is a symbol from Discordianism, a religion that worships the goddess Eris.[50] Most astrologers use this symbol, while some use a symbol resembling that of Mars but with the arrow pointing downward, ⟩ (U+2BF1).[50] Both symbols have been included in Unicode.[51]

Eris is a trans-Neptunian dwarf planet. Its orbital characteristics more specifically categorize it as a scattered-disk object (SDO), or a TNO that has been "scattered" from the Kuiper belt into more-distant and unusual orbits following gravitational interactions with Neptune as the Solar System was forming. Although its high orbital inclination is unusual among the known SDOs, theoretical models suggest that objects that were originally near the inner edge of the Kuiper belt were scattered into orbits with higher inclinations than objects from the outer belt.

Because Eris was initially thought to be larger than Pluto, it was described as the " tenth planet" by NASA and in media reports of its discovery. In response to the uncertainty over its status, and because of ongoing debate over whether Pluto should be classified as a planet, the IAU delegated a group of astronomers to develop a sufficiently precise definition of the term planet to decide the issue. This was announced as the IAU's Definition of a Planet in the Solar System, adopted on August 24, 2006. At this time, both Eris and Pluto were classified as dwarf planets, a category distinct from the new definition of planet. Brown has since stated his approval of this classification. The IAU subsequently added Eris to its Minor Planet Catalogue, designating it (136199) Eris.

The orbit of Eris (blue) compared to those of Saturn, Uranus, Neptune, and Pluto (white/gray). The arcs below the ecliptic are plotted in darker colors, and the red dot is the Sun. The diagram on the left is a polar view whereas the diagrams on the right are different views from the ecliptic.

Seen from Earth, Eris makes small loops in the sky through the constellation of Cetus.

Eris has an orbital period of 559 years. Its maximum possible distance from the Sun ( aphelion) is 97.5 AU, and its closest ( perihelion) is 38 AU. As the time of perihelion is defined at the epoch chosen using an unperturbed two-body solution, the further the epoch is from the date of perihelion, the less accurate the result. Numerical integration is required to predict the time of perihelion accurately. Numerical integration by JPL Horizons shows that Eris came to perihelion around 1699, to aphelion around 1977, and will return to perihelion around December 2257. Unlike those of the eight planets, whose orbits all lie roughly in the same plane as the Earth's, Eris's orbit is highly inclined: it is tilted at an angle of about 44 degrees to the ecliptic. When discovered, Eris and its moon were the most distant known objects in the Solar System, apart from long-period comets and space probes. It retained this distinction until the discovery of in 2018.

As of 2008, there were approximately forty known TNOs, most notably , and Sedna, that are currently closer to the Sun than Eris, even though their semimajor axis is larger than that of Eris (67.8 AU).

The Eridian orbit is highly eccentric, and brings Eris to within 37.9 AU of the Sun, a typical perihelion for scattered objects. This is within the orbit of Pluto, but still safe from direct interaction with Neptune (~37 AU). Pluto, on the other hand, like other plutinos, follows a less inclined and less eccentric orbit and, protected by orbital resonance, can cross Neptune's orbit. In about 800 years, Eris will be closer to the Sun than Pluto for some time (see the graph at the left).

As of 2007, Eris has an apparent magnitude of 18.7, making it bright enough to be detectable to some amateur telescopes. A 200-millimeter (7.9 in) telescope with a CCD can detect Eris under favorable conditions. The reason it had not been noticed until now is its steep orbital inclination; searches for large outer Solar System objects tend to concentrate on the ecliptic plane, where most bodies are found.

Because of the high inclination of its orbit, Eris passes through only a few constellations of the traditional Zodiac; it is now in the constellation Cetus. It was in Sculptor from 1876 until 1929 and Phoenix from roughly 1840 until 1875. In 2036 it will enter Pisces and stay there until 2065, when it will enter Aries. It will then move into the northern sky, entering Perseus in 2128 and Camelopardalis (where it will reach its northernmost declination) in 2173.

Size, mass and density

In November 2010, Eris was the subject of one of the most distant stellar occultations yet from Earth. Preliminary data from this event cast doubt on previous size estimates. The teams announced their final results from the occultation in October 2011, with an estimated diameter of 2326±12 km.

This makes Eris a little smaller than Pluto by area and diameter, which is across, although Eris is more massive. It also indicates a geometric albedo of 0.96. It is speculated that the high albedo is due to the surface ices being replenished because of temperature fluctuations as Eris's eccentric orbit takes it closer and farther from the Sun.

The mass of Eris can be calculated with much greater precision. Based on the accepted value for Dysnomia's period at the time-15.774 days-Eris is 27% more massive than Pluto. Using the 2011 occultation results, Eris has a density of , substantially denser than Pluto, and thus must be composed largely of rocky materials.

Models of internal heating via radioactive decay suggest that Eris could have an subsurface ocean of liquid water at the mantle-core boundary. Tidal heating of Eris by its moon Dysnomia may additionally contribute to the preservation of its possible subsurface ocean. More research concluded that Eris, Pluto and Makemake could harbor active subsurface oceans and show active geothermal activity.

In July 2015, after nearly a decade of Eris being thought to be the ninth-largest known object to directly orbit the Sun, close-up imagery from the New Horizons mission determined the volume of Pluto to be slightly larger than that of Eris. Eris is now understood to be the tenth-largest known object to directly orbit the Sun by volume, but remains the ninth-largest by mass.

The discovery team followed up their initial identification of Eris with spectroscopic observations made at the 8 m Gemini North Telescope in Hawaii on January 25, 2005. Infrared light from the object revealed the presence of methane ice, indicating that the surface may be similar to that of Pluto, which at the time was the only TNO known to have surface methane, and of Neptune's moon Triton, which also has methane on its surface. In 2022, near-infrared spectroscopy of Eris by the James Webb Space Telescope (JWST) revealed the presence of deuterated methane ice on its surface, at abundances lower than those in Jupiter-family comets like 67P/Churyumov-Gerasimenko. Eris's comparatively low deuterium abundance suggests that its methane is not primordial and instead may have been produced from subsurface geochemical processes. Substantial quantities of nitrogen ice on Eris was also detected by the JWST, and it is presumed to have originated from subsurface processes similar to Eris's likely non-primordial methane. The abundance of nitrogen ice on Eris is estimated to be one-third of that of methane by volume.

Unlike the somewhat reddish and variegated surfaces of Pluto and Triton, the surface of Eris appears almost white and uniform. Pluto's reddish color is thought to be due to deposits of tholins on its surface, and where these deposits darken the surface, the lower albedo leads to higher temperatures and the evaporation of methane deposits. In contrast, Eris is far enough from the Sun that methane can condense onto its surface even where the albedo is low. The condensation of methane uniformly over the surface reduces any albedo contrasts and would cover up any deposits of red tholins. This methane sublimation and condensation cycle could produce bladed terrain on Eris, similar to those on Pluto. Alternatively, Eris's surface could be refreshed through radiogenic convection of a global methane and nitrogen ice glacier, similar to Pluto's Sputnik Planitia. Spectroscopic observations by the JWST support the idea that Eris's surface is continually refreshing, as no signs of ethane, a byproduct of radiolyzed methane, were detected on Eris's surface.

Due to the distant and eccentric orbit of Eris, its surface temperature is estimated to vary from about 30 to 56 K (−243.2 to −217.2 °C; −405.7 to −358.9 °F). Even though Eris can be up to three times farther from the Sun than Pluto, it approaches close enough that some of the ices on the surface might warm enough to sublime to form an atmosphere. Because methane and nitrogen are both highly volatile, their presence shows either that Eris has always resided in the distant reaches of the Solar System, where it is cold enough for methane and nitrogen ice to persist, or that the celestial body has an internal source to replenish gas that escapes from its atmosphere. This contrasts with observations of another discovered TNO, Haumea, which reveal the presence of water ice but not methane.

Eris displays very little variation in brightness as it rotates due to its uniform surface, making measurement of its rotation period difficult. Precise long-term monitoring of Eris's brightness indicates that it is tidally locked to its moon Dysnomia, with a rotation period synchronous with the moon's orbital period of 15.78 Earth days. Dysnomia is also tidally locked to Eris, which makes the Eris-Dysnomia system the second known case of double-synchronous rotation, after Pluto and Charon. Previous measurements of Eris's rotation period obtained highly uncertain values ranging tens of hours to several days due to insufficient long-term coverage of Eris's rotation. The axial tilt of Eris has not been measured, but it can be reasonably assumed that it is the same as Dysnomia's orbital inclination, which would be about 78 degrees with respect to the ecliptic. If this were the case, most of Eris's northern hemisphere would be illuminated by sunlight, with 30% of the hemisphere experiencing constant illumination in 2018.

In 2005, the adaptive optics team at the Keck telescopes in Hawaii carried out observations of the four brightest TNOs (Pluto, Makemake, Haumea, and Eris), using the newly commissioned laser guide star adaptive optics system. Images taken on September 10 revealed a moon in orbit around Eris. In keeping with the "Xena" nickname already in use for Eris, Brown's team nicknamed the moon " Gabrielle", after the television warrior princess's sidekick. When Eris received its official name from the IAU, the moon received the name after the Greek goddess of lawlessness who was Eris's daughter. Brown says he picked it for similarity to his wife's name, Diane. The name also retains an oblique reference to Eris's old informal name Xena, portrayed on television by Lucy Lawless, though the connection was unintentional.

Eris was observed from afar by the outbound New Horizons spacecraft in May 2020, as part of its extended mission following its successful Pluto flyby in 2015. Although Eris was farther from New Horizons (112 AU) than it was from Earth (96 AU), the spacecraft's unique vantage point inside the Kuiper belt permitted observations of Eris at high phase angles that are otherwise unobtainable from Earth, enabling the determination of the light scattering properties and phase curve behavior of the Eridian surface.

In the 2010s, there were multiple studies for follow-on missions to explore the Kuiper belt, among which Eris was evaluated as a candidate. It was calculated that a flyby mission to Eris would take 24.66 years using a Jupiter gravity-assist, based on launch dates of April 3, 2032, or April 7, 2044. Eris would be 92.03 or 90.19 AU from the Sun when the spacecraft arrives.

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Eris ( minor-planet designation: 136199 Eris) is the most massive and second-largest known dwarf planet in the Solar System. It is a trans-Neptunian object (TNO) in the scattered disk and has a high- eccentricity orbit. Eris was discovered in January 2005 by a Palomar Observatory-based team led by Mike Brown and verified later that year.

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from sun: 0.98 ly - 1.02 ly

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distance from sun: 4.423 ly

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Alpha Centauri is a triple star system located just over four light years, or about 25 trillion miles, from Earth. While this is a large distance in terrestrial terms, it is three times closer than the next nearest Sun-like star.

The stars in the Alpha Centauri system include a pair called “A” and “B,” (AB for short) which orbit relatively close to each other. Alpha Cen A is a near twin of our Sun in almost every way, including age, while Alpha Cen B is somewhat smaller and dimmer but still quite similar to the Sun. The third member, Alpha Cen C (also known as Proxima), is a much smaller red dwarf star that travels around the AB pair in a much larger orbit that takes it more than 10 thousand times farther from the AB pair than the Earth-Sun distance. Proxima currently holds the title of the nearest star to Earth, although AB is a very close second.

The Chandra data reveal that the prospects for life in terms of current X-ray bombardment are actually better around Alpha Cen A than for the Sun, and Alpha Cen B fares only slightly worse. Proxima, on the other hand, is a type of active red dwarf star known to frequently send out dangerous flares of X-ray radiation, and is likely hostile to life. Planets in the habitable zone around Proxima receive an average dose of X-rays about 500 times larger than the Earth, and 50,000 times larger during a big flare.

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some other stars include barnard's star, sirius. here is a link to other stars. https://www.cosmos.esa.int/web/hipparcos/closest-stars

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From Sun: 642.5 ly

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Betelgeuse is usually the tenth-brightest star in the night sky and, after Rigel, the second-brightest in the constellation of Orion. It is a distinctly reddish semiregular variable star whose apparent magnitude, varying between +0.0 and +1.6, has the widest range displayed by any first-magnitude star. betelgeuse is a ticking time-bomb. it is expected to supernova in the next 1,000 years. it could supernova at any time! it could even supernova tommorow! if it did, it would be beautiful at night, and as bright as the moon!

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Will Betelgeuse Explode? This Is What Scientists Know So Far

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from sun: about 25,000 ly

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The Milky Way is the galaxy that contains our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. Radius: 52,850 light years

Age: 13.51 billion years

Escape velocity: 550 km/s

Number of stars: 250–500 billion

Shape: Spiral

Constellations: Orion, Sagittarius, Scorpius, Carina, Ara

Sagittarius A* is a bright and very compact supermassive black hole and astronomical radio source at the Galactic Center of the Milky Way, near the border of the constellations Sagittarius and Scorpius, about 5.6° south of the ecliptic.

Distance to Earth: 25,640 light years

Radius: 13.67 million mi

Discovered: February 13, 1974

Coordinates: RA 17h 45m 40s | Dec -29° 0′ 28″

Distance: 8178±13 pc

The Andromeda–Milky Way collision is a galactic collision predicted to occur in about 4.5 billion years between the two largest galaxies in the Local Group—the Milky Way and the Andromeda Galaxy. The stars involved are sufficiently far apart that it is improbable that any of them will individually collide. The galaxies will pass through each other, get snapped back together by gravity, and eventually merge cores.

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The Local Group is the galaxy group that includes the Milky Way. It has a total diameter of roughly 3 megaparsecs, and a total mass of the order of 2×10¹² solar masses. There are over 30 galaxies that are considered to be in the local group, and they are spread over a diameter of nearly 10 million light years, with the center of them being somewhere between the Milky Way and M31. M31 and the Milky Way are the most massive members of the Local Group, with M33 being the 3rd largest. did you know most galaxies are between 10 billion and 13.6 billion years old. Our universe is about 13.8 billion years old, so most galaxies formed when the universe was quite young! Astronomers believe that our own Milky Way galaxy is approximately 13.6 billion years old.

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The Andromeda Galaxy, also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula, is a barred spiral galaxy approximately 2.5 million light-years from Earth and the nearest major galaxy to the Milky Way. Wikipedia

Distance to Earth: 2.537 million light years

Radius: 110,000 light years

Age: 10.01 billion years

Constellation: Andromeda

Apparent size (V): 3.167° × 1°

Coordinates: RA 0h 42m 44s | Dec +41° 16′ 9″

Four billion years from now, our galaxy, the Milky Way, will collide with our large spiraled neighbor, Andromeda. The galaxies as we know them will not survive. In fact, our solar system is going to outlive our galaxy. ... Currently, Andromeda and the Milky Way are about 2.5 million light-years apart.

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What will happen if Andromeda galaxy and Milky way galaxy collides?

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The Triangulum Galaxy is a spiral galaxy 2.73 million light-years from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC 598. The Triangulum Galaxy is the third-largest member of the Local Group of galaxies, behind the Milky Way and the Andromeda Galaxy. Wikipedia

Distance to Earth: 2.723 million light years

Radius: 30,000 light years

Magnitude: 5.72

Coordinates: RA 1h 33m 50s | Dec +30° 39′ 37″

Apparent size (V): 70.8 × 41.7 moa

Constellation: Triangulum

Say hello to the much-photographed Triangulum galaxy – aka Messier 33 – a face-on pinwheel of swarming suns and the second-nearest spiral galaxy to our Milky Way. This galaxy is only about 2.7 million light-years away. It’s huge, with a diameter about half that of our Milky Way. But it’s turned face on to us and thus has a low surface brightness in our sky. Although theoretically visible to the unaided eye under dark sky conditions, it’s still not easy to spot in binoculars or even a telescope. Keep reading to learn more about this nearby, face-on, very beautiful spiral galaxy.

The Andromeda galaxy shines eight to nine times more brightly than the Triangulum galaxy, which is the most distant object that you can easily see with the unaided eye. Fortunately, the Triangulum and Andromeda galaxies are a relatively close 15 degrees apart (for reference, a fist-width at an arm length approximates 10 degrees).

Star-hop to the Andromeda galaxy to orient yourself to the Triangulum galaxy. As seen on the sky chart, the star Mirach stands about midway between the two galaxies. Once you find Mirach and the Andromeda galaxy, you can draw a line between them to point in the general direction of the Triangulum galaxy.

Now for a word of warning: even if you’re staring right at the Triangulum galaxy, it’s still possible to miss it. You won’t see the galaxy’s stars at all. Sometimes, this galaxy looks almost transparent, like a water spot on a window. The small blob in your binocular field might resemble an unwashed spot on an otherwise clean window. If you’ve never seen this deep-sky object before, it’s hard to know what to look for.

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Astrophotography - M33 The Triangulum Galaxy

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The Large Magellanic Cloud is a satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs, the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal and the possible dwarf irregular galaxy known as the Canis Major Overdensity.

Distance to Earth: 158,200 light years

Radius: 7,000 light years

Apparent mass: ~10 billion M☉

Coordinates: RA 5h 23m 34s | Dec -69° 45′ 22″

Apparent size (V): 10.75° × 9.17°

Constellations: Dorado, Mensa

he Large Magellanic Cloud (LMC), which is visible to the unaided human eye, is a familiar sight to observers in Earth’s Southern Hemisphere. Along with the Small Magellanic Cloud (SMC), not far from it on our sky’s dome, it looks like nothing so much as a small, faint bit of the Milky Way that has broken off. And yet it is not part of our Milky Way galaxy. It is a separate small galaxy, thought to be orbiting our larger Milky Way.

How to find the Large Magellanic Cloud. For observers south of about 20 degrees south latitude, the LMC is circumpolar, meaning that it can be seen (at least in part) all night every night of the year, weather permitting.

In the Northern Hemisphere, only observers south of about 20 degrees north latitude can ever see it at all. This excludes North America (except southern Mexico), Europe, northern Africa and northern Asia.

The LMC is located about 22 degrees from the South Celestial Pole, approximately on the border between the constellations Dorado and Mensa in a region of faint stars. It covers an area of the sky about 9 by 11 degrees, and shines with a total integrated magnitude of approximately zero. If all of its light were concentrated in a starlike pinpoint, it would be one of the brightest stars in the heavens. However, since the light is spread over nearly 100 square degrees, it appears only as a faint smudge.

From tropical latitudes in the Northern Hemisphere, where it still can be observed, the LMC is best seen in the evening from December to April. When the constellation Orion reaches its highest point in the sky, so does the Large Magellanic Cloud. But even at 15 degrees north latitude (the latitude of Central America), the LMC never gets far above the southern horizon.

However, it’s fairly easy to star-hop to this southern treasure by using the two brightest stars in the nighttime sky: Sirius and Canopus. Draw a line from Sirius and past the right side of Canopus to descend to the LMC. Our sky chart is designed for about 15 degrees north. Farther south, the LMC sits higher in the southern sky.

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Large Magellanic Cloud | Gallery Explorer | NASA Spitzer

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The Largest galaxy is IC 1101.  IC 1101 is a supergiant elliptical galaxy at the center of the Abell 2029 galaxy cluster and is one of the largest known galaxies. Its halo extends about 600 kiloparsecs from its core, and it has a mass of about 100 trillion stars. The galaxy is located 320 megaparsecs from Earth. Wikipedia

Radius: 1.9569 million light years

Distance to Earth: 1.045 billion light years

Age: 12.31 billion years

Apparent mass: ~2,500,000 billion M☉

Apparent size (V): 1'.2 × 0'.6

Number of stars: 100 trillion (10¹⁴)

-Wiki-
The galaxy is classified as a supergiant elliptical (E) to lenticular (S0)[3] and is the brightest galaxy in A2029 (hence its other designation A2029-BCG; BCG meaning brightest cluster galaxy).[5][6] The galaxy's morphological type is debated due to it possibly being shaped like a flat disc but only visible from Earth at its broadest dimensions. However, most lenticulars have sizes ranging from 15 to 37 kpc (50 to 120 thousand ly).[7][specify]

IC 1101 is among the largest known galaxies, but there is debate in the astronomical literature about how to define the size of such a galaxy. Photographic plates of blue light from the galaxy (sampling stars excluding the diffuse halo) yield an effective radius (the radius within which half the light is emitted) of 65 ± 12 kpc (212 ± 39 thousand ly).[4] The galaxy has a very large halo of much lower intensity "diffuse light" extending to a radius of 600 kpc (2 million ly).[8] The authors of the study identifying the halo conclude that IC 1101 is "possibly one of the largest and most luminous galaxies in the universe".[8]

Like most large galaxies, IC 1101 is populated by a number of metal-rich stars, some of which are seven billion years older than the Sun, making it appear golden yellow in color. It has a bright radio source at the center, which is likely associated with an ultramassive black hole in the mass range of 40–100 billion

☉, one of the largest known black holes in the universe.[9][10]

The galaxy was discovered on 19 June 1790, by the British astronomer Frederick William Herschel I.[11] It was catalogued in 1895 by John Louis Emil Dreyer as the 1,101st object of the Index Catalogue of Nebulae and Star Clusters (IC). At its discovery, it was identified as a nebulous feature. Following Edwin Hubble's 1932 discovery that some of the "nebulous features" were actually independent galaxies, subsequent analysis of objects in the sky were conducted and IC 1101 was therefore found to be one of the independent galaxies.

The object can not be seen by the naked eye from Earth, you need a telescope to see it. IC 1101 has a radius of 1,956,900 light years or to put it another way, it has a diameter of 3,913,800 light years. It would take a space ship 3,913,800 years travelling at the speed of light to get from one side to the other.
We sure do look tiny. Now multiply our one star by 200-400 billion – that's the number of stars in the Milky Way – and consider that many of them likely harbor planets. Impressive place this Milky Way … until you park it alongside IC 1101 with its 100 trillion stars.

1.045 billion light years

IC 1101/Distance to Earth

-futuristic.com-
The largest galaxy in the known universe is simply staggering in size. But in order to understand its breadth, you need to understand a little something about our own corner of the universe. For starters, the Milky Way galaxy (our little home) is about 100,000 light-years across. Astronomers estimate that we have somewhere around 200 billion stars. Our closest neighbor, the Andromeda galaxy, is 2.5 million light-years away. It is about twice our size, coming in at 200,000 light-years.

The largest known galaxy is IC 1101. And it is nearly 6 million light-years across in total. Take a moment to try and fathom that. This galaxy could easily swallow the Milky Way, Andromeda, and all of the space in between. It’s not just larger than our galaxy; it’s larger than our corner of the universe.

The Milky Way is a mere 100 thousand light-years. This beast is 6 million.

To help you understand just how immense this is, let’s talk about how long it might take to travel from one side of the galaxy to the other.

The fastest spacecrafts that we’ve ever built are the Helios probes. They were able to reach 157,000 mph (253,000 km/hr). This is pretty fast, especially when you consider that the average commercial airplane only travels some 600 mph (960 km/hr). In fact, these probes traveled 9 times faster than the International Space Station (ISS). Yet, even at this speed, it would still take more than 4,300 years to travel just 1 light-year. That means that it would take you 430 million years to travel across the Milky Way (a long time, to be sure). But it would take you 25.8 billion years to travel across IC 1101. You would literally need to start before the dawn of time in order to complete the journey.

“But,” some may say, “technology has advanced a lot since the Helios probes.” Very true. So let’s give ourselves the benefit of the doubt. Let’s say that we could theoretically travel 670 million miles an hour (1 billion km/hr), which is roughly the speed of light. Would that shorten our journey much? Sure. But not as much as you might hope. It would still take 6 million years to cross this galaxy, even at light-speed.

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IC 1101 - The Largest Galaxy Ever Discovered [OOTW]

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The Virgo Cluster is a cluster of galaxies whose center is 53.8 ± 0.3 million ly away in the constellation Virgo. Comprising approximately 1300 member galaxies, the cluster forms the heart of the larger Virgo Supercluster, of which the Local Group is a member. The Virgo cluster is a massive cluster of galaxies which dominates the Virgo supercluster. There are roughly 2000 galaxies in this cluster (although ninety percent of them are dwarf galaxies). This cluster has a diameter of approximately 15 million light years which is not much larger than our Local Group but it contains fifty times the number of galaxies. This map shows 600 of the brightest galaxies within 7.5 degrees of the centre of the cluster - this is an arbitary border, there are many other galaxies beyond this limit especially to the south of the cluster where there are several additional galaxy groups.

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The Local Supercluster, Local SCl, or Laniakea Supercluster, is the galaxy supercluster that is home to the Milky Way and approximately 100,000 other nearby galaxies.  Radius: 250 million light years

Distance to Earth: 251.1 million light years

Number of galaxies: 100000–150000

Binding mass: 1×10¹⁷ M☉

Coordinates: RA 10h 32m 0s | Dec -46° 0′ 0″

Brightest member: Milky Way (mag –5.0)

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The Unsolved Mystery of Universe - The Great Attractor | Laniakea Supercluster

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The number of superclusters in the observable universe is estimated to be 10 million.

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The biggest supercluster known in the universe is the Hercules-Corona Borealis Great Wall. It was first reported in 2013 and has been studied several times. It's so big that light takes about 10 billion years to move across the structure.

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Short Documentary: Hercules Corona Borealis Great Wall

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distance from earth: 13.8 billion ly

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of course, it would be impossible to do this, and nobody knows what is at the edge of the universe. maybe there is no edge. but our mission is finished.

For now...

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Does Anything Exist Outside Of the Universe? | Unveiled

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NASA scientists detect evidence of parallel universe where time runs backward | New York Post

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Why Parallel Universes Are Probably Real

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Outside The Universe (Questions Answered)

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Outside The Universe (Questions Answered)

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Thank you Wikipedia.

What is outside of the universe?
Roughly 13.75 billion years ago, our universe came into existence. Very shortly thereafter, primordial light started shooting across the cosmos and spreading throughout the early universe. At this juncture, the universe itself was also expanding. The inflation of the universe slowed after the first initial burst, but since then, the rate of expansion has been steadily increasing due to the influence of dark energy.

Essentially, since its inception, the cosmos has been growing at an ever increasing rate. Cosmologists estimate that the oldest photons that we can observe have traveled a distance of 45-47 billion light-years since the Big Bang. That means that our observable universe is some 93 billion light-years wide (give or take a few light-years). These 93 some-odd billion light-years contain all of the quarks, quasars, stars, planets, nebulae, black holes…and everything else that we could possibly observe; however, the observable universe only contains the light that has had time to reach us. How can the universe be 93 billion light-years across if it is only 13.8 billion years old? Light hasn’t had enough time to travel that far…? (⊙_⊙;) Ultimately, understanding this facet of physics is the key to understanding what lies beyond the edge of the observable universe and whether we could ever get there.

To break this down, according to special relativity, objects that are close together cannot move faster than the speed of light with respect to one another; however, there is no such law for objects that are extremely distant from one another when the space between them is, itself, expanding. In short, it’s not that objects are traveling faster than the speed of light, but that the space between objects is expanding, causing them to fly away from each other at amazing speeds.

Ultimately, this means that we could only reach the edge of the observable universe if we develop a method of transport that allows us to either 1) Travel faster than the speed of light (something which most physicists think is impossible) 2) Transcend spacetime (by using wormholes or warp drive, which most physicists also think is impossible).

According to the theory of cosmic inflation, the entire universe’s size is at least 10^23 times larger than the size of the observable universe. That’s a lot of universe that we are missing. So, what *exactly* are we missing? What is outside the observable universe? Unfortunately, since we can’t see it or measure it, we don’t know what lies beyond the bounds of the observable universe. However, we have several theories regarding what exists in the great unknown.

Despite its strangeness, this first idea is one of the easiest to digest. Astronomers think space outside of the observable universe might be an infinite expanse of what we see in the cosmos around us, distributed pretty much the same as it is in the observable universe. This seems logical. After all, it doesn’t make sense that one section of the universe would be different than what we see around us. And honestly, who can envision a universe that has an end—a huge brick wall lurking at its edge? So, in some ways, infinity makes sense. But “infinity” means that, beyond the observable universe, you won’t just find more planets and stars and other forms of material…you will eventually find every possible thing. Every. Possible. Thing. That means that, if this holds true and we follow it to its logical conclusion, somewhere out there, there is another person who is identical to you in every possible way, and there is also a you who is only slightly different from you in every possible way (one is an inch shorter; one got hit by a bus 5 years ago and died; one has a missing finger etc.). In fact, this “other you” may be reading this article right now; the only difference is that they just picked their nose while you didn’t (or did you?). This notion seems inconceivable. But then, infinity is rather inconceivable. Another theory deals with something called “dark flow.” In 2008, astronomers discovered something very strange and unexpected—galactic clusters were all streaming in the same direction at immense speed, over two million miles per hour. One possible cause: Massive structures outside the observable universe exerting gravitational influence. As for the structures themselves, they could be literally anything: Amazingly huge accumulations of matter and energy (on scales we can hardly imagine) or even bizarre warps in space-time that are funneling gravitational forces from other universes. We simply don’t know what these massive objects could be. Notably, recent analyses have claimed to debunk the dark flow model, but this debunking is still being disputed.

Another option involves a universe of universes. Some believe that the whole of our universe could exist in a small “bubble” in the midst of a vast array of other bubbles. Theorists call this a “multiverse.”

Interestingly, the idea asserts that these universes can come into contact with one another—gravity can flow between these parallel universes, and when they connect, a Big Bang like the one that created our universe may occur.

How might the universe end?
by Wikipedia

The fate of the universe is determined by its density. The preponderance of evidence to date, based on measurements of the rate of expansion and the mass density, favors a universe that will continue to expand indefinitely, resulting in the "Big Freeze" scenario below.[1] However, observations are not conclusive, and alternative models are still possible.[2]

Big Freeze or heat death

Main articles: Future of an expanding universe and Heat death of the universe

The Big Freeze (or Big Chill) is a scenario under which continued expansion results in a universe that asymptotically approaches absolute zero temperature.[3] This scenario, in combination with the Big Rip scenario, is gaining ground as the most important hypothesis.[4] It could, in the absence of dark energy, occur only under a flat or hyperbolic geometry. With a positive cosmological constant, it could also occur in a closed universe. In this scenario, stars are expected to form normally for 10¹² to 10¹⁴ (1–100 trillion) years, but eventually the supply of gas needed for star formation will be exhausted. As existing stars run out of fuel and cease to shine, the universe will slowly and inexorably grow darker. Eventually black holes will dominate the universe, which themselves will disappear over time as they emit Hawking radiation.[5] Over infinite time, there would be a spontaneous entropy decrease by the Poincaré recurrence theorem, thermal fluctuations,[6][7] and the fluctuation theorem.[8][9]

A related scenario is heat death, which states that the universe goes to a state of maximum entropy in which everything is evenly distributed and there are no gradients—which are needed to sustain information processing, one form of which is life. The heat death scenario is compatible with any of the three spatial models, but requires that the universe reach an eventual temperature minimum.[10]

Big Rip

Main article: Big Rip

The current Hubble constant defines a rate of acceleration of the universe not large enough to destroy local structures like galaxies, which are held together by gravity, but large enough to increase the space between them. A steady increase in the Hubble constant to infinity would result in all material objects in the universe, starting with galaxies and eventually (in a finite time) all forms, no matter how small, disintegrating into unbound elementary particles, radiation and beyond. As the energy density, scale factor and expansion rate become infinite the universe ends as what is effectively a singularity.

In the special case of phantom dark energy, which has supposed negative kinetic energy that would result in a higher rate of acceleration than other cosmological constants predict, a more sudden big rip could occur.

Big Crunch

Main article: Big Crunch

The Big Crunch. The vertical axis can be considered as expansion or contraction with time.

The Big Crunch hypothesis is a symmetric view of the ultimate fate of the universe. Just as the Big Bang started as a cosmological expansion, this theory assumes that the average density of the universe will be enough to stop its expansion and the universe will begin contracting. The end result is unknown; a simple estimation would have all the matter and space-time in the universe collapse into a dimensionless singularity back into how the universe started with the Big Bang, but at these scales unknown quantum effects need to be considered (see Quantum gravity). Recent evidence suggests that this scenario is unlikely but has not been ruled out, as measurements have been available only over a short period of time, relatively speaking, and could reverse in the future.[4]

This scenario allows the Big Bang to occur immediately after the Big Crunch of a preceding universe. If this happens repeatedly, it creates a cyclic model, which is also known as an oscillatory universe. The universe could then consist of an infinite sequence of finite universes, with each finite universe ending with a Big Crunch that is also the Big Bang of the next universe. A problem with the cyclic universe is that it does not reconcile with the second law of thermodynamics, as entropy would build up from oscillation to oscillation and cause the eventual heat death of the universe. Current evidence also indicates the universe is not closed. This has caused cosmologists to abandon the oscillating universe model. A somewhat similar idea is embraced by the cyclic model, but this idea evades heat death because of an expansion of the branes that dilutes entropy accumulated in the previous cycle. [citation needed]

Big Bounce

Main article: Big Bounce

The Big Bounce is a theorized scientific model related to the beginning of the known universe. It derives from the oscillatory universe or cyclic repetition interpretation of the Big Bang where the first cosmological event was the result of the collapse of a previous universe.

According to one version of the Big Bang theory of cosmology, in the beginning the universe was infinitely dense. Such a description seems to be at odds with other more widely accepted theories, especially quantum mechanics and its uncertainty principle. [citation needed] It is not surprising, therefore, that quantum mechanics has given rise to an alternative version of the Big Bang theory. Also, if the universe is closed, this theory would predict that once this universe collapses it will spawn another universe in an event similar to the Big Bang after a universal singularity is reached or a repulsive quantum force causes re-expansion.

In simple terms, this theory states that the universe will continuously repeat the cycle of a Big Bang, followed up with a Big Crunch.

Big Slurp

Main article: False vacuum

This theory posits that the universe currently exists in a false vacuum and that it could become a true vacuum at any moment.

In order to best understand the false vacuum collapse theory, one must first understand the Higgs field which permeates the universe. Much like an electromagnetic field, it varies in strength based upon its potential. A true vacuum exists so long as the universe exists in its lowest energy state, in which case the false vacuum theory is irrelevant. However, if the vacuum is not in its lowest energy state (a false vacuum), it could tunnel into a lower energy state.[11] This is called vacuum decay. This has the potential to fundamentally alter our universe; in more audacious scenarios even the various physical constants could have different values, severely affecting the foundations of matter, energy, and spacetime. It is also possible that all structures will be destroyed instantaneously, without any forewarning.[12]

Cosmic uncertainty.

what is a singularity?

thanks again, wiki.
So a gravitational singularity, spacetime singularity or simply singularity is a location in spacetime where the gravitational field of a celestial body is predicted to become infinite by general relativity in a way that does not depend on the coordinate system. The quantities used to measure gravitational field strength are the scalar invariant curvatures of spacetime, which includes a measure of the density of matter. Since such quantities become infinite at the singularity, the laws of normal spacetime break down.[1][2]

Gravitational singularities are mainly considered in the context of general relativity, where density apparently becomes infinite at the center of a black hole, and within astrophysics and cosmology as the earliest state of the universe during the Big Bang. Physicists are undecided whether the prediction of singularities means that they actually exist (or existed at the start of the Big Bang), or that current knowledge is insufficient to describe what happens at such extreme densities.

General relativity predicts that any object collapsing beyond a certain point (for stars this is the Schwarzschild radius) would form a black hole, inside which a singularity (covered by an event horizon) would be formed.[3] The Penrose–Hawking singularity theorems define a singularity to have geodesics that cannot be extended in a smooth manner.[4] The termination of such a geodesic is considered to be the singularity.

The initial state of the universe, at the beginning of the Big Bang, is also predicted by modern theories to have been a singularity.[5] In this case the universe did not collapse into a black hole, because currently-known calculations and density limits for gravitational collapse are usually based upon objects of relatively constant size, such as stars, and do not necessarily apply in the same way to rapidly expanding space such as the Big Bang. Neither general relativity nor quantum mechanics can currently describe the earliest moments of the Big Bang,[6] but in general, quantum mechanics does not permit particles to inhabit a space smaller than their wavelengths.[7]

Many theories in physics have mathematical singularities of one kind or another. Equations for these physical theories predict that the ball of mass of some quantity becomes infinite or increases without limit. This is generally a sign for a missing piece in the theory, as in the ultraviolet catastrophe, re-normalization, and instability of a hydrogen atom predicted by the Larmor formula.
A conical singularity occurs when there is a point where the limit of every diffeomorphism invariant quantity is finite, in which case spacetime is not smooth at the point of the limit itself. Thus, spacetime looks like a cone around this point, where the singularity is located at the tip of the cone. The metric can be finite everywhere coordinate system is used.

An example of such a conical singularity is a cosmic string and a Schwarzschild black hole.[9]

Solutions to the equations of general relativity or another theory of gravity (such as supergravity) often result in encountering points where the metric blows up to infinity. However, many of these points are completely regular, and the infinities are merely a result of using an inappropriate coordinate system at this point. In order to test whether there is a singularity at a certain point, one must check whether at this point diffeomorphism invariant quantities (i.e. scalars) become infinite. Such quantities are the same in every coordinate system, so these infinities will not "go away" by a change of coordinates.

An example is the Schwarzschild solution that describes a non-rotating, uncharged black hole. In coordinate systems convenient for working in regions far away from the black hole, a part of the metric becomes infinite at the event horizon. However, spacetime at the event horizon is regular. The regularity becomes evident when changing to another coordinate system (such as the Kruskal coordinates), where the metric is perfectly smooth. On the other hand, in the center of the black hole, where the metric becomes infinite as well, the solutions suggest a singularity exists. The existence of the singularity can be verified by noting that the Kretschmann scalar, being the square of the Riemann tensor i.e. {\displaystyle R_{\mu \nu \rho \sigma }R^{\mu \nu \rho \sigma }}, which is diffeomorphism invariant, is infinite.

While in a non-rotating black hole the singularity occurs at a single point in the model coordinates, called a "point singularity", in a rotating black hole, also known as a Kerr black hole, the singularity occurs on a ring (a circular line), known as a "ring singularity". Such a singularity may also theoretically become a wormhole.[10]

More generally, a spacetime is considered singular if it is geodesically incomplete, meaning that there are freely-falling particles whose motion cannot be determined beyond a finite time, being after the point of reaching the singularity. For example, any observer inside the event horizon of a non-rotating black hole would fall into its center within a finite period of time. The classical version of the Big Bang cosmological model of the universe contains a causal singularity at the start of time (t=0), where all time-like geodesics have no extensions into the past. Extrapolating backward to this hypothetical time 0 results in a universe with all spatial dimensions of size zero, infinite density, infinite temperature, and infinite spacetime curvature.

Some theories, such as the theory of loop quantum gravity, suggest that singularities may not exist.[8] This is also true for such classical unified field theories as the Einstein–Maxwell–Dirac equations. The idea can be stated in the form that due to quantum gravity effects, there is a minimum distance beyond which the force of gravity no longer continues to increase as the distance between the masses becomes shorter, or alternatively that interpenetrating particle waves mask gravitational effects that would be felt at a distance.

Until the early 1990s, it was widely believed that general relativity hides every singularity behind an event horizon, making naked singularities impossible. This is referred to as the cosmic censorship hypothesis. However, in 1991, physicists Stuart Shapiro and Saul Teukolsky performed computer simulations of a rotating plane of dust that indicated that general relativity might allow for "naked" singularities. What these objects would actually look like in such a model is unknown. Nor is it known whether singularities would still arise if the simplifying assumptions used to make the simulation were removed. However, it is hypothesized that light entering a singularity would similarly have its geodesics terminated, thus making the naked singularity look like a black hole.[11][12][13]

Disappearing event horizons exist in the Kerr metric, which is a spinning black hole in a vacuum, if the angular momentum ({\displaystyle J}) is high enough. Transforming the Kerr metric to Boyer–Lindquist coordinates, it can be shown[14] that the coordinate (which is not the radius) of the event horizon is, {\displaystyle r_{\pm }=\mu \pm (\mu ^{2}-a^{2})^{1/2}}, where {\displaystyle \mu =GM/c^{2}}, and {\displaystyle a=J/Mc}. In this case, "event horizons disappear" means when the solutions are complex for {\displaystyle r_{\pm }}, or {\displaystyle \mu ^{2}<a^{2}}. However, this corresponds to a case where {\displaystyle J} exceeds {\displaystyle GM^{2}/c} (or in Planck units, {\displaystyle J>M^{2}}), i.e. the spin exceeds what is normally viewed as the upper limit of its physically possible values.

Similarly, disappearing event horizons can also be seen with the Reissner–Nordström geometry of a charged black hole if the charge (sorry fot the displacement) ({\displaystyle Q}) is high enough. In this metric, it can be shown[15] that the singularities occur at {\displaystyle r_{\pm }=\mu \pm (\mu ^{2}-q^{2})^{1/2}}, where {\displaystyle \mu =GM/c^{2}}, and {\displaystyle q^{2}=GQ^{2}/(4\pi \epsilon _{0}c^{4})}. Of the three possible cases for the relative values of {\displaystyle \mu } and {\displaystyle q}, the case where {\displaystyle \mu ^{2}<q^{2}} causes both {\displaystyle r_{\pm }} to be complex. This means the metric is regular for all positive values of {\displaystyle r}, or in other words, the singularity has no event horizon. However, this corresponds to a case where {\displaystyle Q/{\sqrt {4\pi \epsilon _{0}}}} exceeds {\displaystyle M{\sqrt {G}}} (or in Planck units, {\displaystyle Q>M}), i.e. the charge exceeds what is normally viewed as the upper limit of its physically possible values. Also, actual astrophysical black holes are not expected to possess any appreciable charge.

A black hole possessing the lowest {\displaystyle M} value consistent with its {\displaystyle J} and {\displaystyle Q} values and the limits noted above, i.e., one just at the point of losing its event horizon, is termed extremal.

Before Stephen Hawking came up with the concept of Hawking radiation, the question of black holes having entropy had been avoided. However, this concept demonstrates that black holes radiate energy, which conserves entropy and solves the incompatibility problems with the second law of thermodynamics. Entropy, however, implies heat and therefore temperature. The loss of energy also implies that black holes do not last forever, but rather evaporate or decay slowly. Black hole temperature is inversely related to mass.[16] All known black hole candidates are so large that their temperature is far below that of the cosmic background radiation, which means they will gain energy on net by absorbing this radiation. They cannot begin to lose energy on net until the background temperature falls below their own temperature. This will occur at a cosmological redshift of more than one million, rather than the thousand or so since the background radiation formed.