Cosmic string: Difference between revisions

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Revision as of 00:23, 26 February 2023

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The violent oscillations of cosmic strings generically lead to the formation of [[Cusp (singularity)|cusps]] and [[Sine-Gordon equation#Soliton solutions|kinks]]. These in turn cause parts of the string to pinch off into isolated loops. These loops have a finite lifespan and decay (primarily) via [[gravitational radiation]]. This radiation which leads to the strongest signal from cosmic strings may in turn be detectable in [[Gravitational-wave observatory|gravitational wave observatories]]. An important open question is to what extent do the pinched off loops backreact or change the initial state of the emitting cosmic string—such backreaction effects are almost always neglected in computations and are known to be important, even for order of magnitude estimates.

[[Gravitational lensing]] of a galaxy by a straight section of a cosmic string would produce two identical, undistorted images of the galaxy. In 2003 a group led by Mikhail Sazhin reported the accidental discovery of two seemingly identical galaxies very close together in the sky, leading to speculation that a cosmic string had been found.<ref>{{cite journal |arxiv=astro-ph/0302547 |bibcode=2003MNRAS.343..353S | doi=10.1046/j.1365-8711.2003.06568.x |title=CSL-1: Chance projection effect or serendipitous discovery of a gravitational lens induced by a cosmic string? |year=2003 |last1=Sazhin |first1=M. |last2=Longo |first2=G. |last3=Capaccioli |first3=M. |last4=Alcala |first4=J. M. |last5=Silvotti |first5=R. |last6=Covone |first6=G. |last7=Khovanskaya |first7=O. |last8=Pavlov |first8=M. |last9=Pannella |first9=M. |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=343 |issue=2 |pages=353|display-authors=9 |last10=Radovich |first10=M. |last11=Testa |first11=V. |s2cid=18650564 }}</ref> However, observations by the [[Hubble Space Telescope]] in January 2005 showed them to be a pair of similar galaxies, not two images of the same galaxy.<ref>{{cite journal |arxiv=astro-ph/0603838 |bibcode=2006PhRvD..73h7302A |doi=10.1103/PhysRevD.73.087302 |title=Hubble imaging excludes cosmic string lens |year=2006 |last1=Agol |first1=Eric |last2=Hogan |first2=Craig |last3=Plotkin |first3=Richard |journal=Physical Review D |volume=73 |issue=8|pages=87302 |s2cid=119450257 }}</ref><ref>{{cite arXiv |eprint=astro-ph/0601494 |last1=Sazhin |first1=M. V. |last2=Capaccioli |first2=M. |last3=Longo |first3=G. |last4=Paolillo |first4=M. |last5=Khovanskaya |first5=O. S. |last6=Grogin |first6=N. A. |last7=Schreier |first7=E. J. |last8=Covone |first8=G. |title=The true nature of CSL-1 |year=2006}}</ref> A cosmic string would produce a similar duplicate image of fluctuations in the [[cosmic microwave background]], which it was thought might have been detectable by the [[Planck Surveyor]] mission.<ref>{{cite journal |arxiv=0708.1162 |bibcode=2008PhRvD..78d3535F |doi=10.1103/PhysRevD.78.043535 |title=Small-angle CMB temperature anisotropies induced by cosmic strings |year=2008 |last1=Fraisse |first1=Aurélien |last2=Ringeval |first2=Christophe |last3=Spergel |first3=David |last4=Bouchet |first4=François |journal=Physical Review D |volume=78 |issue=4 |pages=43535 |s2cid=119145024 }}</ref> However, a 2013 analysis of data from the Planck mission failed to find any evidence of cosmic strings.<ref name="planck_strings">{{Cite journal|arxiv=1303.5085 |author1=Planck Collaboration |last2=Ade |first2=P. A. R. |last3=Aghanim |first3=N. |author3-link=Nabila Aghanim|last4=Armitage-Caplan |first4=C. |last5=Arnaud |first5=M. |last6=Ashdown |first6=M. |last7=Atrio-Barandela |first7=F. |last8=Aumont |first8=J. |last9=Baccigalupi |first9=C. |title=Planck 2013 results. XXV. Searches for cosmic strings and other topological defects |journal=Astronomy & Astrophysics |volume=571 |pages=A25 |year=2013|last10= Banday |first10=A. J. |last11= Barreiro |first11=R. B. |last12= Bartlett |first12=J. G. |last13= Bartolo |first13=N. |last14= Battaner |first14=E. |last15= Battye |first15=R. |last16= Benabed |first16=K. |last17= Benoît |first17=A. |last18= Benoit-Lévy |first18=A. |last19= Bernard |first19=J. -P. |last20= Bersanelli |first20=M. |last21= Bielewicz |first21=P. |last22= Bobin |first22=J. |last23= Bock |first23=J. J. |last24= Bonaldi |first24=A. |last25= Bonavera |first25=L. |last26= Bond |first26=J. R. |last27= Borrill |first27=J. |last28= Bouchet |first28=F. R. |last29= Bridges |first29=M. |last30= Bucher |first30=M. |display-authors=29 |doi=10.1051/0004-6361/201321621 |bibcode=2014A&A...571A..25P|s2cid=15347782 }}</ref>

A piece of evidence supporting cosmic string theory is a phenomenon noticed in observations of the "double [[quasar]]" called [[Twin Quasar|Q0957+561A,B]]. Originally discovered by [[Dennis Walsh]], Bob Carswell, and [[Ray Weymann]] in 1979, the double image of this quasar is caused by a galaxy positioned between it and the Earth. The [[gravitational lens]] effect of this intermediate galaxy bends the quasar's light so that it follows two paths of different lengths to Earth. The result is that we see two images of the same quasar, one arriving a short time after the other (about 417.1 days later). However, a team of astronomers at the [[Harvard-Smithsonian Center for Astrophysics]] led by [[Rudolph Schild]] studied the quasar and found that during the period between September 1994 and July 1995 the two images appeared to have no time delay; changes in the brightness of the two images occurred simultaneously on four separate occasions. Schild and his team believe that the only explanation for this observation is that a cosmic string passed between the Earth and the quasar during that time period traveling at very high speed and oscillating with a period of about 100 days.<ref>{{cite journal |arxiv=astro-ph/0406434 |bibcode=2004A&A...422..477S|doi=10.1051/0004-6361:20040274 |title=Anomalous fluctuations in observations of Q0957+561 A,B: Smoking gun of a cosmic string? |year=2004 |last1=Schild |first1=R. |last2=Masnyak |first2=I. S. |last3=Hnatyk |first3=B. I. |last4=Zhdanov |first4=V. I. |journal=Astronomy and Astrophysics |volume=422 |issue=2 |pages=477–482|s2cid=16939392}}</ref>