What is the strongest magnetic field possible? Is there a limit?

Question: What is the strongest magnetic field possible? Is there a limit?
- Keywords:
  limit,
  magnetic field
Asked by Lone Wolf to Dominic, James, Jenny, Kevin, Norah on 8 Mar 2017.
- Dominic Doyle answered on 8 Mar 2017:
  
  Another great and profound question!
  I do not think that there is a physical upper limit.
  But certainly the interaction of a magnetic field with matter could have an impact.
  The strongest fields in the observable universe are associated with a class of stars called Magnetars
  http://www.universetoday.com/51970/magnetar/

Question: What is the strongest magnetic field possible? Is there a limit?