1) We can only estimate gravitational fields remotely when objects are interacting, by measuring the time it takes them to orbit each other - the article specifically says that the object is "floating alone in space".

2) The paper (https://assets.researchsquare.com/files/rs-2029380/v1_covere...) discusses the possibility of a magnetic field being responsible for the two-sided effect, but doesn't mention that they specifically measured it. Apparently measurement is possible for large magnetic fields by looking for circular polarisation but I don't think they have found that in this case.

3) There is no fusion happening in a white dwarf - they glow with residual heat from the original star.

Wikipedia has a lot of detail in their article: https://en.wikipedia.org/wiki/White_dwarf