Suppose someone dropped a black hole into our lovely Sun a few million years ago. It was big enough (far bigger than that) from the start to eat matter faster than radiating it away, and kept growing and growing. At some time in the future, it would consume most of the star and the change would be obvious to most. But there should be some less noticeable changes before that, something that we could detect with all the various instruments, earthbound and in space, directed at the Sun.
So, that is my question: what would be the first thing we would notice? Would it be increase in x-rays from accretion? Would it be some change in size or temperature due to slightly disrupted fusion? Or maybe something else? To be honest, I have no idea how to even start tackling this question, so any pointers are welcome.
- Assume current-day measurement tech. It is acceptable to include currently planned missions/projects (or those on their way, like Solar Orbiter). Nothing beyond year 2050 though.
- All that matters is that we notice something is not normal with our Sun, not figuring out that it's the black hole inside it. Anything that makes us go "Huh, stars don't do that" is preferable to things that have reasonable explanations, even if rare.
- Bonus if you'll also calculate how much time we would have left till the Sun is gone, but I can calculate that on my own (thanks to HDE 226868).
- Notice that since the black hole was added long ago, any measurements of Sun's mass included it, and since accretion doesn't destroy mass, gravity (probably) won't change in any noticeable way.
- I do not care how we arrived to the current situation. All the question is about is: we detect something today because of a black hole growing inside the Sun. What would that something be?