Andromeda–Milky Way collision

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A NASA conception of the collision using computer-generated imagery.

The Andromeda–Milky Way collision is a galactic collision predicted to occur in about 4 billion years between the two largest galaxies in the Local Group—the Milky Way (which contains our Solar System and Earth) and the Andromeda Galaxy[1][2][3] although the stars involved are sufficiently far apart that it is improbable that any of them will individually collide.[4]

Stellar collisions[edit]

While the Andromeda Galaxy contains about 1 trillion (1012) stars and the Milky Way contains about 300 billion (3×1011), the chance of even two stars colliding is negligible because of the huge distances between the stars. For example, the nearest star to the Sun is Proxima Centauri, about 4.2 light-years (4.0×1013 km; 2.5×1013 mi) or 30 million (3×107) solar diameters away. If the Sun were a ping-pong ball, Proxima Centauri would be a pea about 1,100 km (680 mi) away, and the Milky Way would be about 30 million km (19 million mi) wide. Although stars are more common near the centres of each galaxy, the average distance between stars is still 160 billion (1.6×1011) km (100 billion mi). That is analogous to one ping-pong ball every 3.2 km (2.0 mi). Thus, it is extremely unlikely that any two stars from the merging galaxies would collide.[4]

Black hole collisions[edit]

The Milky Way and Andromeda galaxies each contain a central supermassive black hole, these being Sagittarius A* (ca. 3.6 x 106 solar masses) and an object within the P2 concentration of Andromeda's nucleus (1-2 x 108 solar masses). These black holes will converge near the center of the newly formed galaxy, transferring orbital energy to stars that will be moved to higher orbits by gravitationally interacting with them, in a process that may take millions of years. When they come within one light year of one another, they will emit gravitational waves that will radiate further orbital energy until they merge completely. Gas taken up by the combined black hole could create a luminous quasar or an active galactic nucleus. As of 2006, simulations indicated that the future Earth might be brought near the center of the combined galaxy, potentially coming near one of the black holes before being ejected entirely out of the galaxy.[5]

Certainty[edit]

Based on data from the Hubble Space Telescope, Milky Way galaxy and Andromeda galaxy are predicted to distort each other with tidal pull in 3.75 billion years, as shown in this illustration.

The Andromeda Galaxy is approaching the Milky Way at about 110 kilometres per second (68 mi/s).[1] Up until 2012, there was no way to know whether the possible collision was definitely going to happen or not.[6] In 2012, researchers came to the conclusion that the collision is definite after using the Hubble Space Telescope between 2002 and 2010 to track the motion of Andromeda.[1] Andromeda's tangential or side-ways velocity with respect to the Milky Way was found to be relatively much smaller than the approaching velocity and therefore we expect it to directly collide with the Milky Way in about 4 billion years.

Such collisions are relatively common. Andromeda, for example, is believed to have collided with at least one other galaxy in the past,[7] and several dwarf galaxies such as SagDEG are currently colliding with the Milky Way and being merged into it.

These studies also suggest that M33, the Triangulum Galaxy – the third largest and brightest galaxy of the Local Group – will participate in this event. Its most likely fate is to end up orbiting the merger remnant of the Milky Way and Andromeda galaxies, to merge with it in an even farther future, but a collision with the Milky Way before our galaxy collides with M31 (the Andromeda Galaxy), or being ejected from the Local Group cannot be ruled out.[8]

The fate of the Solar System[edit]

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.[2] 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 its current distance.[2] They also predict a 12% chance that the Solar System will be ejected from the new galaxy sometime during the collision.[9] Such an event would have no adverse effect on the system and the chances of any sort of disturbance to the Sun or planets themselves may be remote.[9][10]

Without intervention, by the time 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; that is currently estimated to occur in about 3.75 billion years due to gradually increasing luminosity of the Sun (it will have risen by 35–40% above the current luminosity).[11][12]

Possible triggered stellar events[edit]

When two spiral galaxies collide, the hydrogen present on their disks is compressed producing strong star formation as can be seen on interacting systems like the Antennae Galaxies. In the case of the Andromeda–Milky Way collision, it is believed that there will be little gas remaining in the disks of both galaxies, so the mentioned starburst will be relatively weak, though it still may be enough to form a quasar.[10]

Merger remnant[edit]

The galaxy product of the collision has been nicknamed Milkomeda or Milkdromeda. According to simulations, this object will look like a giant elliptical galaxy, but with a center showing less stellar density than current elliptical galaxies.[10]

In the far future the remaining galaxies of the Local Group will coalesce into this object, that being the next evolutionary stage of our group of galaxies.[13]

See also[edit]

References[edit]

  1. ^ a b c Cowen, R. (31 May 2012). "Andromeda on collision course with the Milky Way". Nature. doi:10.1038/nature.2012.10765.  edit
  2. ^ a b c Muir, Hazel. (4 May 2007) "Galactic merger to 'evict' Sun and Earth". New Scientist.
  3. ^ Loeb, Abraham; Cox, TJ. (June 2008). Astronomy. p. 28.
  4. ^ a b NASA (2012-05-31). "NASA's Hubble Shows Milky Way is Destined for Head-On Collision". NASA. Retrieved 2012-10-13. 
  5. ^ John Dubinski (October 2006). "The Great Milky Way-Andromeda Collision". Sky & Telescope. 
  6. ^ van der Marel, G. et al. (2012). "The M31 Velocity Vector. III. Future Milky Way M31-M33 Orbital Evolution, Merging, and Fate of the Sun". The Astrophysical Journal 753: 9. arXiv:1205.6865. Bibcode:2012ApJ...753....9V. doi:10.1088/0004-637X/753/1/9. 
  7. ^ "Andromeda involved in galactic collision" MSNBC 10:38 a.m. PT 29 January 2007.
  8. ^ The M31 Velocity Vector. III. Future Milky Way-M31-M33 Orbital Evolution, Merging, and Fate of the Sun
  9. ^ a b Cain, Fraser (2007). "When Our Galaxy Smashes Into Andromeda, What Happens to the Sun?". Universe Today. Archived from the original on 17 May 2007. Retrieved 2007-05-16. 
  10. ^ a b c Cox, T. J.; Loeb, Abraham (2007). "The Collision Between The Milky Way And Andromeda". Monthly Notices of the Royal Astronomical Society 386: 461. arXiv:0705.1170. Bibcode:2008MNRAS.tmp..333C. doi:10.1111/j.1365-2966.2008.13048.x. 
  11. ^ Schröder, K.-P.; Smith, R. C. (2008). "Distant future of the Sun and Earth revisited". Monthly Notices of the Royal Astronomical Society 386 (1): 155. arXiv:0801.4031. Bibcode:2008MNRAS.386..155S. doi:10.1111/j.1365-2966.2008.13022.x. 
  12. ^ Carrington, D. (2000-02-21). "Date set for desert Earth". BBC News. Retrieved 2007-03-31. 
  13. ^ A dying universe: the long-term fate and evolution of astrophysical objects, Fred C. Adams and Gregory Laughlin, Reviews of Modern Physics 69, #2 (April 1997), pp. 337–372. Bibcode1997RvMP...69..337A. doi:10.1103/RevModPhys.69.337 arXiv:astro-ph/9701131.

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