See also
- Levels of spaceflight: Suborbital, orbital, interplanetary, interstellar and intergalactic
- Space travel in science fiction
- Uploaded astronaut
Intergalactic travel is the hypothetical travel between galaxies. Because the Milky Way and its closest neighbors are separated by millions of light-years, any such venture would also require millions of years based on current physics. Thus, intergalactic travel is impossible within the human lifetime. The technology required to travel between galaxies is far beyond humanity's present capabilities, and currently only the subject of speculation, hypothesis, and science fiction.
Theorized in 1988, [1] and observed in 2005, [2] hypervelocity stars move faster than the escape velocity of the Milky Way, and are traveling out into intergalactic space. [3] There are several theories for their existence. One of the mechanisms would be that the supermassive black hole at the center of the Milky Way ejects some stars from the galaxy at a rate of about one every hundred thousand years. Another theorized mechanism might be a supernova explosion in a binary system. [4] Intergalactic travel using these stars would involve entering into an orbit around them and waiting for them to reach another galaxy. [5] [6]
While it takes light approximately 2.54 million years to traverse the gulf of space between Earth and, for instance, the Andromeda Galaxy, it would take a much shorter amount of time from the point of view of a traveler at close to the speed of light due to the effects of time dilation; the time experienced by the traveler depending both on velocity (anything less than the speed of light) and distance traveled (length contraction). Intergalactic travel for humans is therefore possible, in theory, from the point of view of the traveler. [7] For example, a rocket that accelerated at standard acceleration due to gravity toward the Andromeda Galaxy and started to decelerate halfway through the trip would arrive in about 28 years, from the frame of reference of the observer. [8]
The Alcubierre drive is a hypothetical concept that is able to propel a spacecraft to speeds faster than light (the spaceship itself would not move faster than light, but the space around it would). This could in theory allow practical intergalactic travel. There is no known way to create the space-distorting wave this concept needs to work, but the metrics of the equations comply with relativity and the limit of light speed. [9]
A wormhole is a hypothetical tunnel through space-time that would allow instantaneous intergalactic travel to the most distant galaxies even billions of light years away. Wormholes are allowed by general relativity. [10]
Faster-than-light travel and communication are the conjectural propagation of matter or information faster than the speed of light. The special theory of relativity implies that only particles with zero rest mass may travel at the speed of light, and that nothing may travel faster.
Interstellar travel is the hypothetical travel of spacecraft between star systems. Due to the vast distances between the Solar System and nearby stars, interstellar travel is not practicable with current propulsion technologies.
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation. The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a blueshift, or negative redshift. The terms derive from the colours red and blue which form the extremes of the visible light spectrum. The main causes of electromagnetic redshift in astronomy and cosmology are the relative motions of radiation sources, which give rise to the relativistic Doppler effect, and gravitational potentials, which gravitationally redshift escaping radiation. All sufficiently distant light sources show cosmological redshift corresponding to recession speeds proportional to their distances from Earth, a fact known as Hubble's law that implies the universe is expanding.
Time travel is the hypothetical activity of traveling into the past or future. Time travel is a concept in philosophy and fiction, particularly science fiction. In fiction, time travel is typically achieved through the use of a device known as a time machine. The idea of a time machine was popularized by H. G. Wells's 1895 novel The Time Machine.
The Alcubierre drive is a speculative warp drive idea according to which a spacecraft could achieve apparent faster-than-light travel by contracting space in front of it and expanding space behind it, under the assumption that a configurable energy-density field lower than that of vacuum could be created. Proposed by theoretical physicist Miguel Alcubierre in 1994, the Alcubierre drive is based on a solution of Einstein's field equations. Since those solutions are metric tensors, the Alcubierre drive is also referred to as Alcubierre metric.
Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more distant stars.
A warp drive or a drive enabling space warp is a fictional superluminal spacecraft propulsion system in many science fiction works, most notably Star Trek, and a subject of ongoing physics research. The general concept of "warp drive" was introduced by John W. Campbell in his 1957 novel Islands of Space and was popularized by the Star Trek series. Its closest real-life equivalent is the Alcubierre drive, a theoretical solution of the field equations of general relativity.
A starship, starcraft, or interstellar spacecraft is a theoretical spacecraft designed for traveling between planetary systems. The term is mostly found in science fiction. Reference to a "star-ship" appears as early as 1882 in Oahspe: A New Bible.
The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a D25 isophotal diameter of about 46.56 kiloparsecs (152,000 light-years) and is approximately 765 kpc (2.5 million light-years) from Earth. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after the princess who was the wife of Perseus in Greek mythology.
A sleeper ship is a hypothetical type of crewed spacecraft, or starship in which most or all of the crew spend the journey in some form of hibernation or suspended animation. The only known technology that allows long-term suspended animation of humans is the freezing of early-stage human embryos through embryo cryopreservation, which is behind the concept of embryo space colonization.
Omega Centauri is a globular cluster in the constellation of Centaurus that was first identified as a non-stellar object by Edmond Halley in 1677. Located at a distance of 17,090 light-years, it is the largest known globular cluster in the Milky Way at a diameter of roughly 150 light-years. It is estimated to contain approximately 10 million stars, with a total mass of 4 million solar masses, making it the most massive known globular cluster in the Milky Way.
A Krasnikov tube is a speculative mechanism for space travel involving the warping of spacetime into permanent superluminal tunnels. The resulting structure is analogous to a wormhole or an immobile Alcubierre drive with the endpoints displaced in time as well as space. The idea was proposed by Sergey Krasnikov in 1995.
The Milky Way is the galaxy that includes the 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.
HE 0437-5439 is a massive, unbound hypervelocity star (HVS), also called HVS3. It is a main sequence B-type star located in the Dorado constellation. It was discovered in 2005 with the Kueyen 8.2-metre (320 in) telescope, which is part of the European Southern Observatory's Very Large Telescope array. HE 0437-5439 is a young star, with an age of around 30 million years. The mass of the star is almost nine times greater than the mass of the Sun and the star is located 200,000 light years away in the direction of the Dorado constellation, 16 degrees northwest of the Large Magellanic Cloud (LMC) and farther away than the LMC. The star appears to be receding at an extremely high velocity of 723 kilometres per second (449 mi/s), or 2,600,000 kilometres per hour (1,600,000 mph). At this speed, the star is no longer gravitationally bound and will leave the Milky Way galaxy system and escape into intergalactic space. It was thought to have originated in the LMC and been ejected from it soon after birth. This could happen if it originally was one of a pair of stars and if there is a supermassive black hole in the LMC.
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, though some stars will be ejected.
Black holes, objects whose gravity is so strong that nothing—including light—can escape them, have been depicted in fiction since at least the pulp era of science fiction, before the term black hole was coined. A common portrayal at the time was of black holes as hazards to spacefarers, a motif that has also recurred in later works. The concept of black holes became popular in science and fiction alike in the 1960s. Authors quickly seized upon the relativistic effect of gravitational time dilation, whereby time passes more slowly closer to a black hole due to its immense gravitational field. Black holes also became a popular means of space travel in science fiction, especially when the notion of wormholes emerged as a relatively plausible way to achieve faster-than-light travel. In this concept, a black hole is connected to its theoretical opposite, a so-called white hole, and as such acts as a gateway to another point in space which might be very distant from the point of entry. More exotically, the point of emergence is occasionally portrayed as another point in time—thus enabling time travel—or even an entirely different universe.
The following outline is provided as an overview of and topical guide to black holes:
In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space.
An intergalactic star, also known as an intracluster star or a rogue star, is a star not gravitationally bound to any galaxy. Although a source of much discussion in the scientific community during the late 1990s, intergalactic stars are now generally thought to have originated in galaxies, like other stars, before being expelled as the result of either galaxies colliding or of a multiple-star system traveling too close to a supermassive black hole, which are found at the center of many galaxies.
US 708 is a hyper-velocity class O subdwarf in Ursa Major, in the halo of the Milky Way Galaxy. One of the fastest-moving stars in the galaxy, the star was first surveyed in 1982.
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