I would like to know what is the recent progress about the group homomorphism
$$ \mathrm{Gal}(\overline{\mathbf{Q}}/\mathbf{Q})\rightarrow \mathrm{Out}(\hat{F\_{2}})$$


* $\mathrm{Gal}(\overline{\mathbf{Q}}/\mathbf{Q})$ is the absolute Galois group of $\mathbf{Q}$.
* $\mathrm{Out}(\hat{F\_{2}})$ is the group of outer automorphisms of the procompletion of the free group generated by two elements.


It is know to be injective homomorphism, what can we say about the image ?



Dessins d'enfants and absolute Galois group
For the sake of getting this off the unanswered stack...


Please refer to the following reference:



> 
> Guillot, P. *An elementary approach to dessins d'enfants and the Grothendieck-Teichmüller group*, Enseign. Math. vol 60, 2014. [[arXiv version](http://arxiv.org/abs/1309.1968) | [journal version](http://www.ems-ph.org/journals/show_abstract.php?issn=0013-8584&vol=60&iss=3&rank=5)]
> 
> 
> 


The article just cited develops the theory of dessins d'enfants from scratch. The final section discusses the image of the homomorphism mentioned in the OP's question. 


In particular,


1. Guillot includes a proof that the image must lie in the group
$\widehat{GT\_0}$, a proper subgroup of ${\rm Out}(\hat{F\_2})$, first
defined (I believe) by Drinfeld;
2. Guillot discusses (but does not prove) a stronger result due to
Ihara that the image must lie in the Grothendieck-Teichmuller group,
$\widehat{GT}$, a proper subgroup of $\widehat{GT\_0}$.


Please consult the bibliography of the given reference to find the relevant works of Drinfeld and Ihara.


