A new study suggests a there's a gender bias in the approval process for research teams looking to use the Hubble Telescope. Researchers at the Space Telescope Science Institute (STScI), the organization that runs the Hubble Space Telescope program, found that male-led proposals are more likely to be approved and granted time with the telescopes than female-led research projects.

Only a third of applying research teams are granted time on the telescopes, so the odds are stacked against scientists to begin with. But the new study, carried out by STScI researcher Neill Reid found the odds of approval are even less if a woman is the team's principle investigator. Reid said the discrepancy in any given year is small, but worryingly consistent.

"The offsets are small enough that they might be ascribed to chance for any single cycle," Reid wrote, "but the consistent pattern suggests the presence of a systematic effect."

The study is currently publicly available in the early-release online journal arXiv, and it is set to be published in the upcoming issue of the journal Publications of the Astronomical Society of the Pacific.

"There is growing recognition in the community that unconscious biases can play an important role in all decision making processes, even those related to the 'hard' sciences," Reid wrote in 2013, explaining the motivation for his ongoing research.

The researchers acknowledged it's possible the female-led proposals are simply less compelling than other proposals, but said such a scenario is unlikely, given that almost research proposals are written by a team of males and females. The only relevant variable seems to be the gender of the principle investigator.