With 60M articles in more than 300 language versions, Wikipedia is the largest platform for open and freely accessible knowledge. While the available content has been growing continuously at a rate of around 200K new articles each month, very little attention has been paid to the accessibility of the content. One crucial aspect of accessibility is the integration of hyperlinks into the network so the articles are visible to readers navigating Wikipedia. In order to understand this phenomenon, we conduct the first systematic study of orphan articles, which are articles without any incoming links from other Wikipedia articles, across 319 different language versions of Wikipedia. We find that a surprisingly large extent of content, roughly 15\% (8.8M) of all articles, is de facto invisible to readers navigating Wikipedia, and thus, rightfully term orphan articles as the dark matter of Wikipedia. We also provide causal evidence through a quasi-experiment that adding new incoming links to orphans (de-orphanization) leads to a statistically significant increase of their visibility in terms of the number of pageviews. We further highlight the challenges faced by editors for de-orphanizing articles, demonstrate the need to support them in addressing this issue, and provide potential solutions for developing automated tools based on cross-lingual approaches. Overall, our work not only unravels a key limitation in the link structure of Wikipedia and quantitatively assesses its impact, but also provides a new perspective on the challenges of maintenance associated with content creation at scale in Wikipedia.

翻译：拥有超过300种语言版本的6000万篇文章，维基百科是开放且免费获取知识的最大平台。虽然可用内容以每月约20万篇新文章的速度持续增长，但内容的可访问性却很少受到关注。可访问性的一个关键方面是将超链接集成到网络中，使读者在浏览维基百科时能够看到这些文章。为了理解这一现象，我们首次对319种不同语言版本的维基百科中的孤儿文章（即没有任何来自其他维基百科文章入链的文章）进行了系统性研究。我们发现，令人惊讶的是，大约15%（880万篇）的文章实际上对于浏览维基百科的读者是不可见的，因此，我们有理由将孤儿文章称为维基百科的暗物质。我们还通过准实验提供了因果证据，表明为孤儿文章添加新的入链（去孤儿化）会使其页面浏览量在统计上显著增加。我们进一步强调了编辑者在去孤儿化过程中面临的挑战，展示了支持他们解决这一问题的必要性，并提出了基于跨语言方法开发自动化工具的潜在解决方案。总体而言，我们的工作不仅揭示了维基百科链接结构的一个关键局限性并定量评估了其影响，还为维基百科中与大规模内容创作相关的维护挑战提供了新视角。