Galactic superwind
{{short description|Strong stellar winds of a galactic scale in size}}
File:M82 Galaxy from the Mount Lemmon SkyCenter Schulman Telescope courtesy Adam Block.jpg, a starburst galaxy often referred to as the "Cigar Galaxy", is thought to exhibit strong superwinds.{{Cite journal|last1=Lehnert|first1=Matthew D.|last2=Heckman|first2=Timothy M.|last3=Weaver|first3=Kimberly A.|date=1999-10-01|title=Very Extended X-Ray and Halpha Emission in M82: Implications for the Superwind Phenomenon|journal=The Astrophysical Journal|volume=523|issue=2|pages=575–584|doi=10.1086/307762|issn=0004-637X|arxiv=astro-ph/9904227|bibcode=1999ApJ...523..575L|s2cid=18155360}}]]
A galactic superwind, or just galactic wind, is a high velocity stellar wind emanating from either newly formed massive stars, spiral density waves, or as the result of the effects of supermassive black holes.{{Cite web|url=http://astronomy.swin.edu.au/cosmos/G/Galactic+Winds|title=Galactic Winds {{!}} COSMOS|website=astronomy.swin.edu.au|language=en|access-date=2018-03-01}} They are normally observed in starburst galaxies.{{Cite web|url=http://ned.ipac.caltech.edu/level5/March01/Heckman/frames.html|title=Galactic Superwinds - T.M. Heckman et al.|website=ned.ipac.caltech.edu|access-date=2017-12-14}}{{Cite web|url=http://www.eso.org/public/news/eso1036/|title=The Superwind Galaxy NGC 4666|last=|website=www.eso.org|language=en-GB|access-date=2017-12-14}}
Description
Galactic winds are strong stellar winds made up of charged particles, ejecta, and varying amounts of hot and cool gas, interacting with enough force that the ejecta's kinetic energy is converted to thermal energy.{{Cite web|url=https://ned.ipac.caltech.edu/level5/March12/Veilleux/frames.html|title=Galactic Winds - S. Veilleux et al.|website=ned.ipac.caltech.edu|access-date=2018-03-01}} The resulting effect is a massive gust of rapidly expanding super-heated gases that can span the length of a galaxy.{{Cite journal|last=Heckman|first=Timothy|date=2000-07-15|title=The role of starbursts in the formation of galaxies and active galactic nuclei|journal=Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences|language=en|volume=358|issue=1772|pages=2077–2091|doi=10.1098/rsta.2000.0631|issn=1364-503X|arxiv=astro-ph/9912029|bibcode=2000RSPTA.358.2077H|s2cid=12888083}}
In galaxies with active galactic nuclei, galactic winds can also be driven by the effects of super-massive black holes.
Galactic winds are considered an important function in the evolution of a galaxy.{{Cite web|url=http://www.astro.wisc.edu/our-science/research-areas/extragalactic-astronomy/distant-univserse/galactic-winds/|title=Galactic Winds {{!}} UW-Madison Astronomy|website=www.astro.wisc.edu|language=en|access-date=2018-03-01}}{{cite book|last1=Heckman|first1=Timothy M.|last2=Thompson|first2=Todd A.|title=Handbook of Supernovae|date=2017|publisher=Springer, Cham|isbn=9783319218458|pages=2431–2454|language=en|arxiv=1701.09062v1|chapter=Galactic Winds and the Role Played by Massive Stars|doi=10.1007/978-3-319-21846-5_23|s2cid=125856372}} The winds cause an outflow of gas and other material into the halo of a galaxy, while also facilitating the spread of metals around a galaxy. Galactic winds are also capable of blowing material out of a galaxy entirely and into the intergalactic medium.
= Formation =
Superwinds are theorized to form in compact starburst galaxies in which star growth is much higher than in other types of galaxies. This accelerated star growth results in more prevalent stellar winds being present in starburst galaxies. Superwinds form when ejecta released either by supernovae or stellar winds collide with such force that the shock from the impact converts the kinetic energy of the ejecta into thermal energy. The violent conversion from kinetic to thermal energy prevents a significant amount of energy from being radiated away. This in turn creates an incredibly hot bubble of gas that is under much greater pressure than it surroundings are. Eventually the gas bubble will expand to encompass other particles of ejected gases, further increasing the force and size of its expansion. This "snowplow" effect results in a gust of stellar wind and gas that can span the width of a galaxy. It has been theorized that superwinds can potentially be traveling at a velocity of several thousand kilometers per second by the time they enter the intergalactic medium.
See also
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- Cosmic wind
- Stellar wind
- Solar wind
- Planetary wind
- Stellar-wind bubble
- Colliding-wind binary
- Pulsar wind nebula
- Superwind
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