This document analyzes the Twitter usage of 37 astrophysicists. It finds that on average, 23% of their tweets contained hashtags. The top 10 hashtags were identified, with #fb being the most common. Regular Twitter users tended to include hashtags more than infrequent users. However, the astrophysicist community did not strongly share hashtags, as many were only used once, suggesting hashtags were not used to build communities. This analysis provides insight into how scholars are using Twitter affordances like hashtags, but their value for altmetrics and scholarly communication requires more understanding.