I am a PhD student in mathematics. Talking to some colleagues on my department I wrote a paper whose subject lies somewhat beyond the interests of my advisor. I gave a talk on it on a couple of seminars.

Unexpectedly I was invited to give a talk on a conference in another country. I have a feeing that my advisor might be unhappy if I go there, in particular he refused to give me any funds for travel. (It might be he does not have any funds, but I still have a feeling that he does not want me to be involved in activities in other fields.) Nevertheless I am interested to present my results to a broader audience and one of the colleagues on the department I talked to agrees to help me with the travel funds.

Would it be ok if I will go to the conference? Is it ethical with respect to my supervisor?