Second PhD in Astro after a PhD in CMT (Physics) Okay here is the current situation. I am entering my second year in my PhD program and most of my options of joining the Theoretical astrophysics groups are closed ( no professors working in that field and two of them who were working are leaving the university). Right now the only open option for me is to work in computational condensed matter theory which I am not sure I am interested in (But I do know that given a option between this and theoretical astro I would choose the latter) ie.. interest in Astro theory >> Interest in CMT. okay given this background the questions are,

1) what are the cons of doing another PhD in astro after completing my PhD in CMT (let us say it would take me 5 years here to complete my PhD and if I am applying to an university in UK for my second PhD I would complete it in 3 years so in total i would have spent around 8 years with 2 PhD's in my hand) cons ?

2) I know most of you would ask me to just reapply to other schools, But I am not sure how certain I am in getting an admission again and I dont want this entire two years here to go waste ( just 3 of more years I would have my PhD). So my second question is it even possible to get a PhD position in Europe after having PhD in US ?

So basically my reason for second PhD is not for a better career path, but instead to shift to my area of interest but as well as to not let these 2 years of my life go waste. Is it a good choice to make ?

Edit 1- I did read all the answers for double PhD questions but all the questions were in the line of "I want a better job/career, should I do double PhD?" mine is, "Let us say I complete my current PhD, is there any disadvantage of doing another one just because I would love to work in that field?"

PS: Yes I am working in US university right now, and yup as I am in my second year I have completed few course work and started the project. Rather than saying I "have to complete this PhD", I would put it this way - "I don't hate the work I am doing here, it is just that I would like working in the other field much more than this"

Edit 2- Thanks for the helpful answers. Let me explain my personal bias towards astrophysics. I am a math person by nature, and previously had my undergraduate in engineering.I wanted to move to physics mainly because of the rigorous mathematical structure of it compared to engineering, I self studied several physics stuff and hence wanted to do theoretical physics. But later (now) my views about theoretical physics is changing. On the whole this is what I think is the timeline chart in theoretical physics area apart from Astro) -

Experimentalists collect data of physical world 
Theorists build model to explain the data  
The new theory might lead experimentalists to further prob the physical world to test the theory  
If it does, verify that theory, if not inform the theorist  
Theorist then builds a new (or modify the old model) to explain the existing results.  

So at the end of the day theorists keep on modifying their model until it agrees with all the experiments. At the end of the day, this is just model building/modifying till my theory fits the data(this creates a bound purpose to building the theory unlike mathematics). But in Astro, since there are very few experiments to verify, the set of all possible theories is large and theorists in this field actually have the freedom to keep on building theories(or models) to explain. And it is this abstract nature of this field (which is analogous to mathematics) where one needs no reason to build theory other than building it just for the fun of it interests me. These are my personal thoughts about general theoretical physics and the reason I want to move to Astro.
Don't plan on doing two PhD for all the reasons in the comments.

Whether to stay and throw yourself fully into the best and most active and dynamic CMT group (try to be a CMT star for goodness sakes)  or leave for another university depends on being honest with yourself about your reasons for choosing one over the other. (Is it 'liking' to call yourself an astrophysicist? ) Intellectually - they are both fascinating fields. You will find the smartest of the smart in either. 

You talk about losing work, but did not mention being involved in any research projects with either of the astrophysics faculty who are leaving. If you had, they likely would be already talking to you about whether a plan could be put in place to help you finish your project somehow.

It wasn't clear if you were in UK or US. In the US- those 2 years are typically core courses and preparation for the qualifiers. If so, those core courses will transfer pretty easily to any similar department, and if you did stellar in them, will probably make it easier to get into a department that matches your interests. You will not have to take the core again and in particular, the pressure will be that you should hit the ground running and  get involved in a significant way in a project (even if you have less time because you are supported initially on TA instead of RA). If you can pass the qualifier will be the main issue. 

As an additional note - most faculty understand if a student wants to switch schools because the subfield of interest is not represented. They will write recommendation letters without qualms and wish you the best.