You don't need to know everything about a niche to write articles in it. You just need to know enough to get started. So if you want to research a niche topic, what you would do is go down to a library and grab some books on the topic, read some articles on the Internet, and visit a few forums to see what people are talking about and also to get content ideas. You may also want to subscribe to different mailing lists in your market.
What I do is that once I have an idea for an article, I would do a search on the topic on Google to get more information, then write my own article based on the information I have learnt. This is how you should go about your article writing. It's how I go about mine. It might be right for you, it might not be.
It's not hard at all to generate content to write about. For any popular topic, there are literally tons of books out there. It's not hard to write hundreds of articles on any topic as long as you put your mind to it.
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