Andromeda-Milky Way collision
Encyclopedia
The collision seen from a hypothetical extragalactic planet. The galaxies will be at this relative angleThe Andromeda–Milky Way collision is a predicted galaxy collision that could possibly take place in approximately 3 to 5 billion years' time between the two largest galaxies in the Local Group
—the Andromeda Galaxy
and the Milky Way
, which contains Earth
.
is Proxima Centauri
, about thirty million solar diameters away. If the sun were a ping-pong ball in Paris, the equivalent Proxima would be a pea-sized ball in Berlin (and our galaxy would be 12 million miles wide—about a third of the distance to Mars).
Stars are much denser near the galactic centers—the average separation is only 100 billion miles. But that is still a density which is about equal to one ping-pong ball every two miles. Thus, it is very, very unlikely that any two stars will collide.
of the Andromeda galaxy with respect to the Milky Way can be measured by examining the Doppler shift
of spectral lines from stars in the galaxy, but the transverse velocity cannot be directly measured. Thus, while it is known that the Andromeda galaxy is getting closer to the Milky Way by about 120 km/s, there is no way to tell whether it is going to collide or miss. The best indirect estimates of the transverse velocity indicate that it is less than 100 km/s. This suggests that the dark matter halo
s, although possibly not the actual disks, of the galaxies will collide.
Frank Summers of the Space Telescope Science Institute
has created a CGI
visualization of the predicted event, based on research by Professors Chris Mihos of Case Western Reserve University
and Lars Hernquist
of Harvard University
.
Such collisions are relatively common, however. Andromeda, for example, is believed to have collided with at least one other galaxy in the past, and several dwarf galaxies
such as SagDEG are currently colliding with the Milky Way and being merged into it.
will be ejected from the new galaxy some time during the collision. Such an event would have no adverse effect on the system and chances of any sort of disturbance to the Sun or planets themselves may be remote.
Without intervention
, by the time that the two galaxies collide, the surface of the Earth will have already become far too hot for liquid water to exist, ending all terrestrial life, which is currently estimated to occur in about 1.4 billion years due to gradually increasing luminosity of the Sun.
Local Group
The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...
—the Andromeda Galaxy
Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...
and the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
, which contains Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
.
Stellar Collisions
Each galaxy contains over a hundred billion stars, which is 100 million trillion possible collisions. Nevertheless, the chance of even two stars colliding is negligible because of the huge distances between them. For example, the nearest star to the SunSun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
is Proxima Centauri
Proxima Centauri
Proxima Centauri is a red dwarf star about 4.2 light-years distant in the constellation of Centaurus. It was discovered in 1915 by Robert Innes, the Director of the Union Observatory in South Africa, and is the nearest known star to the Sun, although it is too faint to be seen with the naked eye...
, about thirty million solar diameters away. If the sun were a ping-pong ball in Paris, the equivalent Proxima would be a pea-sized ball in Berlin (and our galaxy would be 12 million miles wide—about a third of the distance to Mars).
Stars are much denser near the galactic centers—the average separation is only 100 billion miles. But that is still a density which is about equal to one ping-pong ball every two miles. Thus, it is very, very unlikely that any two stars will collide.
Uncertainty
There is, as yet, no way to know whether the possible collision is definitely going to happen or not. The radial velocityRadial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...
of the Andromeda galaxy with respect to the Milky Way can be measured by examining the Doppler shift
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
of spectral lines from stars in the galaxy, but the transverse velocity cannot be directly measured. Thus, while it is known that the Andromeda galaxy is getting closer to the Milky Way by about 120 km/s, there is no way to tell whether it is going to collide or miss. The best indirect estimates of the transverse velocity indicate that it is less than 100 km/s. This suggests that the dark matter halo
Dark matter halo
A dark matter halo is a hypothetical component of a galaxy, which extends beyond the edge of the visible galaxy and dominates the total mass. Since they consist of dark matter, halos cannot be observed directly, but their existence is inferred through their effects on the motions of stars and gas...
s, although possibly not the actual disks, of the galaxies will collide.
Frank Summers of the Space Telescope Science Institute
Space Telescope Science Institute
The Space Telescope Science Institute is the science operations center for the Hubble Space Telescope and for the James Webb Space Telescope...
has created a CGI
Computer-generated imagery
Computer-generated imagery is the application of the field of computer graphics or, more specifically, 3D computer graphics to special effects in art, video games, films, television programs, commercials, simulators and simulation generally, and printed media...
visualization of the predicted event, based on research by Professors Chris Mihos of Case Western Reserve University
Case Western Reserve University
Case Western Reserve University is a private research university located in Cleveland, Ohio, USA...
and Lars Hernquist
Lars Hernquist
Lars Hernquist is a theoretical astrophysicist and Mallinckrodt Professor of Astrophysics at the Harvard-Smithsonian Center for Astrophysics. He is best known for his research on dynamical processes in cosmology and galaxy formation/galaxy evolution.-Research:...
of Harvard University
Harvard University
Harvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...
.
Such collisions are relatively common, however. Andromeda, for example, is believed to have collided with at least one other galaxy in the past, and several dwarf galaxies
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...
such as SagDEG are currently colliding with the Milky Way and being merged into it.
The fate of the Solar System
Two scientists with the Harvard–Smithsonian Center for Astrophysics stated that when, and even whether, the two galaxies collide will depend on Andromeda's transverse velocity. Based on current calculations they predict a 50% chance that in a merged galaxy the solar system will be swept out three times farther from the galactic core than it is currently located. They also predict a 12% chance that the Solar SystemSolar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
will be ejected from the new galaxy some time during the collision. Such an event would have no adverse effect on the system and chances of any sort of disturbance to the Sun or planets themselves may be remote.
Without intervention
Planetary engineering
Planetary engineering is the application of technology for the purpose of influencing the global properties of a planet. The goal of this theoretical task is usually to make other worlds habitable for life....
, by the time that the two galaxies collide, the surface of the Earth will have already become far too hot for liquid water to exist, ending all terrestrial life, which is currently estimated to occur in about 1.4 billion years due to gradually increasing luminosity of the Sun.
See also
- Antennae GalaxiesAntennae GalaxiesThe Antennae Galaxies are a pair of interacting galaxies in the constellation Corvus. They are currently going through a phase of starburst. They were discovered by William Herschel in 1785...
– A later stage in collision - NGC 2207 and IC 2163NGC 2207 and IC 2163NGC 2207 and IC 2163 are a pair of colliding spiral galaxies about 80 million light-years away in the constellation Canis Major. Both galaxies were discovered by John Herschel in 1835. So far three supernovae have been observed in NGC 2207...
– An example of two colliding galaxies