Superbubble

Superbubble is the astronomical term used to describe a cavity hundreds of light years across filled with 10⁶ K gas blown into the interstellar medium by multiple supernovae and stellar winds. The solar system lies near the center of an old superbubble, known as the Local Bubble, whose boundaries can be traced by a sudden rise in dust extinction of stars at distances greater than a few hundred light years.

Formation

The most massive stars, with masses ranging from eight to roughly one hundred solar masses and spectral types of O and early B are usually found in groups called OB associations. Massive O stars have strong stellar winds, and all of these stars explode as supernovae at the ends of their lives.

The strongest stellar winds release kinetic energy of 10⁵¹ ergs (10⁴⁴ J), equivalent to a supernova explosion. These winds can blow stellar wind bubbles dozens of light years across. [cite journal| url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1975ApJ...200L.107C| last= Castor| first=J.| coauthors=McCray, R., & Weaver, R.| title=Interstellar Bubbles| year=1975| journal=Astrophys. J. (Letters)| volume=200| pages=L107–L110| doi=10.1086/181908] Supernova explosions, similarly, drive blast waves thatcan reach even larger sizes, with expansion velocities of as much asseveral hundred km s^-1.

Stars in OB associations are not gravitationally bound, but only driftapart at speeds of around 20 km s^-1. As a result,most of their supernova explosions occur within the cavity carved bythe strongest stellar wind bubbles. [cite journal| url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1981Ap%26SS..78..273T| last= Tomisaka| first= K.| coauthors=Habe, A., & Ikeuchi, S.| title=Sequential explosions of supernovae in an OB association and formation of a superbubble| year=1981| journal=Astrophys. Space Sci.| volume=78| pages=273–285| doi=10.1007/BF00648941] [cite journal| url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1987ApJ...317..190M| last=McCray| first=R.| coauthors=Kafatos, M.| title=Supershells and Propagating Star Formation| year=1987| journal=Astrophys. J.| volume=317| pages=190–196| doi=10.1086/165267] They never form a visible supernova remnant, butinstead efficiently deposit their energy into the hot interior as sound waves. Large enough superbubbles can blow entirely through the galactic disk, releasing their energy into the surrounding galactic halo or even into the intergalactic medium. [cite journal| url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1986PASJ...38..697T| last= Tomisaka| first=K.| coauthors=Ikeuchi, S.| title=Evolution of superbubble driven by sequential supernova explosions in a plane-stratified gas distribution| year=1986| journal=Publ. Astron. Soc. Japan| volume=38| pages=697–715] [cite journal| url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1988ApJ...324..776M | last=Mac Low| first=M.-M.| coauthors=McCray, R.| title=Superbubbles in Disk Galaxies| year=1988| journal=Astrophys. J.| volume=324| pages=776–785| doi=10.1086/165936]

The interstellar gas swept up by superbubbles generally cools, forming a dense shell around the cavity. These shells were first observed in line emission at twenty-one centimeters from hydrogen, [cite journal| year=1979| url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1979ApJ...229..533H| last= Heiles| first=C.| title=H I shells and supershells| journal=Astrophys. J.| volume=229| pages=533–544| doi=10.1086/156986] leading to the formulation of the theory of superbubble formation. They are also observed in X-ray emission from their hot interiors, in optical line emission from their ionized shells, and in infrared continuum emission from dust swept up in their shells. X-ray and human optical emission are typically observed from younger superbubbles, while older, larger objects seen in twenty-one centimeters may even result from multiple superbubbles combining, and so are sometimes distinguished by calling them supershells.

uperbubble examples

* Anticenter shell, a supershell once called "Snickers"
* Henize 70 [ [http://antwrp.gsfc.nasa.gov/apod/ap991130.html Henize 70: A SuperBubble In The LMC] , Astronomy Picture of the Day, 1999-11-30]
* Local Bubble, which contains the Solar system
* Monogem Ring [ [http://www.daviddarling.info/encyclopedia/M/Monogem_Ring.html Monogem Ring] , The Internet Encyclopedia of Science]
* N44 Superbubble [ [http://antwrp.gsfc.nasa.gov/apod/ap060206.html N44 Superbubble] , Astronomy Picture of the Day]
* Ophiuchus Superbubble [Yurii Pidopryhora, Felix J. Lockman, and Joseph C. Shields. [http://arxiv.org/abs/astro-ph/0610894v1 The Ophiuchus Superbubble: A Gigantic Eruption from the Inner Disk of the Milky Way] , The Astrophysical Journal 656:2, 928-942 (2007)] cite news | title=Huge 'Superbubble' of Gas Blowing Out of Milky Way | date=2006-01-13 | publisher= | url =http://www.physorg.com/news9882.html | work =PhysOrg.com | accessdate = 2008-07-04 |]
* The Scutum Supershell [ [http://www.journals.uchicago.edu/doi/abs/10.1086/318411 STIS and GHRS Observations of Warm and Hot Gas Overlying the Scutum Supershell (GS 018−04+44] , The Astrophysical Journal] [ [http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2000ApJ...532..943C Observational Evidence of Supershell Blowout in GS 018-04+44: The Scutum Supershell] , The Astrophysical Journal, Volume 532, Issue 2, pp. 943-969. ]

External links

* Tenorio-Tagle, G., & Bodenheimer, P. " [http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1988ARA%26A..26..145T Large-scale expanding superstructures in galaxies] ". 1988, "Annual Review of Astronomy and Astrophysics" 26, 145-197. General overview.

References