Editing X-ray astronomy (section)

==Theoretical X-ray astronomy==
Theoretical X-ray astronomy is a branch of [[theoretical astronomy]] that deals with the theoretical [[astrophysics]] and theoretical [[astrochemistry]] of [[X-ray generation]], emission, and detection as applied to [[astronomical object]]s.

Like [[theoretical astrophysics]], theoretical X-ray astronomy uses a wide variety of tools which include [[Mathematical model|analytical model]]s to approximate the behavior of a possible X-ray source and [[computation]]al [[Numerical analysis|numerical simulation]]s to approximate the observational data. Once potential observational consequences are available they can be compared with experimental observations. Observers can look for data that refutes a model or helps in choosing between several alternate or conflicting models.

Theorists also try to generate or modify models to take into account new data. In the case of an inconsistency, the general tendency is to try to make minimal modifications to the model to fit the data. In some cases, a large amount of inconsistent data over time may lead to total abandonment of a model.

Most of the topics in [[astrophysics]], [[astrochemistry]], [[astrometry]], and other fields that are branches of [[astronomy]] studied by theoreticians involve X-rays and X-ray sources. Many of the beginnings for a theory can be found in an Earth-based laboratory where an X-ray source is built and studied.

===Dynamos===
{{main|Dynamo theory}}
{{See also|Solar dynamo}}
Dynamo theory describes the process through which a rotating, convecting, and electrically conducting fluid acts to maintain a [[magnetic field]]. This theory is used to explain the presence of anomalously long-lived magnetic fields in astrophysical bodies. If some of the stellar magnetic fields are really induced by dynamos, then field strength might be associated with rotation rate.<ref name=Trimble>{{Cite journal|author=Trimble V |title=White dwarfs in the 1990s |journal=Bull Astron Soc India|date=1999 |volume=27 |page=549 |bibcode=1999BASI...27..549T}}</ref>

===Astronomical models===
[[File:NASA-2015IYL-MultiPix-ChandraXRayObservatory-20150122.jpg|thumb|right|Images released to celebrate the [[International Year of Light|International Year of Light 2015]]<br>([[Chandra X-Ray Observatory]]).]]
From the observed X-ray spectrum, combined with spectral emission results for other wavelength ranges, an astronomical model addressing the likely source of X-ray emission can be constructed. For example, with Scorpius X-1 the X-ray spectrum steeply drops off as X-ray energy increases up to 20 keV, which is likely for a thermal-plasma mechanism.<ref name=Morrison/> In addition, there is no radio emission, and the visible continuum is roughly what would be expected from a hot plasma fitting the observed X-ray flux.<ref name=Morrison/> The plasma could be a [[coronal cloud]] of a central object or a transient plasma, where the energy source is unknown, but could be related to the idea of a close binary.<ref name=Morrison/>

In the Crab Nebula X-ray spectrum there are three features that differ greatly from Scorpius X-1: its spectrum is much harder, its source diameter is in [[light-year]]s (ly)s, not [[astronomical unit]]s (AU), and its radio and optical synchrotron emission are strong.<ref name=Morrison/> Its overall X-ray luminosity rivals the optical emission and could be that of a nonthermal plasma. However, the Crab Nebula appears as an X-ray source that is a central freely expanding ball of dilute plasma, where the energy content is 100 times the total energy content of the large visible and radio portion, obtained from the unknown source.<ref name=Morrison/>

The [[Astrophysical X-ray source#X-ray dark stars|"Dividing Line"]] as [[giant star]]s evolve to become [[red giant]]s also coincides with the Wind and Coronal Dividing Lines.<ref name=Kashyap>{{Cite journal|author=Kashyap V|author2= Rosner R|author3=Harnden FR Jr.|author4=Maggio A|author5=Micela G|author6=Sciortino S |title=X-ray emission on hybrid stars: ROSAT observations of alpha Trianguli Australis and IOTA Aurigae |journal=Astrophys J|date=1994|volume=431 |page=402|doi=10.1086/174494 |bibcode=1994ApJ...431..402K}}</ref> To explain the drop in X-ray emission across these dividing lines, a number of models have been proposed:
# low transition region densities, leading to low emission in coronae,
# high-density wind extinction of coronal emission,
# only cool coronal loops become stable,
# changes in a magnetic field structure to that an open topology, leading to a decrease of magnetically confined plasma, or
# changes in the magnetic dynamo character, leading to the disappearance of stellar fields leaving only small-scale, turbulence-generated fields among red giants.<ref name=Kashyap/>