Going to try this.

Surtur's dimensional portal, busted by Thor and BRB's hammer throws:

Spoiler:

You can see it's clearly bigger than the stars around it.

The star to the upper right looks main sequence, so I suppose we can scale it as being the size of the sun.

Spoiler:

Now the portal is irregularly shaped, but we can probably treat it as a sphere. As for the material, it looks like some kind of metal from the outside so iron sounds like a good low-end. Not sure how to treat the center, it's obviously not filled with the same material as the rest of it, but then again it was the center where the hammers collided and created an expanding explosion powerful enough to blow the thing up. I guess I can do two calcs, one for treating the whole thing as solid and one subtracting the volume of the center.

Anyway, diameter of the sun = 1392684 km, so diameter of the portal = 8342450.235 km. Volume = 3.040041388e20 km^3.
Using the scaling again, diameter of the interior part = 3358826.118 km, meaning it has a volume of 1.984089172e19 km^3, making the volume of the portal minus the inner area 2.841632471e20 km^3. For this calc we'll treat it as a smaller sphere, so we need a new radius, which is 4,078,430 km.

Density of iron = 7.874 g/cm^3.

Now to the gravity calculator:

Surface gravity for this thing is crazy, 917.41 g.

Going to the SD.net calculator, we get a GBE of 4.937e46j.

Now let's try it without cutting out the center area. Surface gravity for this version is 938.28 g. This raises the overall GBE to 5.525e46.

Again, both of these are very low-end, as the portal was behind the star I scaled it from, and it exploded pretty damn quickly, so way more than the minimum GBE was unleashed there. At the very least, we can say Thor and BRB are each packing a minimum of 2.7625e46 joules in their hammer throws.