What Les said...
that looks like a bark inclusion to me, but hard to tell scale. They add interest to the finished piece, but can be unstable and hard to work with.
As you know I use a bean to cup coffee machine, and that makes a great filler for this colouration, if it is smaller than it looks then something finer e.g. metal powder or sawdust, next time you are around or remind me before the club night and I will give you a bag out of the bottom of the bandsaw, it is the perfect grain size!
as a general rule, but not always followed
- Very small hairline cracks I use CA glue with metal powder or fine sawdust
- medium cracks around 2 or 3mm I use epoxy with appropriate filler
- larger and I really want to turn it, I may use fiberglass resin instead of epoxy
- I have not done it but have seen great stuff done with coloured crystic resin
Epoxy needs at least 8 hours probably 24 before you attempt to turn it, I am told Crystic may need a month.
Some caution needs to be applied, if the split is looking like it will reach your chuck, expansion or contraction it will at some point leave the lathe and aim for your head! I am not saying never turn it, but make sure it is worth the risk, keep the speed reasonable, and be certain your face shield is on properly!