Hubble's Hot Stars

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Hunt for ionizing hot stars in nearby galaxies

Young stars are typically surrounded by dust and gas. In such an environment, if the stars are hot enough (more than five times as hot as the Sun), they ionize the hydrogen gas around them. Such hot ionizing stars (called O stars by astronomers) are extremely rare, but can shine with a million times the energy output of the sun. Debate still exists about whether all O stars are formed in stellar clusters or if, under just the right circumstances, they can form in relative isolation. We will rely on your image classification skills to narrow down the answer to this important issue in a set of nearby galaxies observed as part of the Legacy ExtraGalactic Ultraviolet Survey (LEGUS) on the Hubble Space Telescope.

We have selected hot star candidates based upon their estimated temperatures, determined from comparison of Hubble Space Telescope data with stellar models, and we've marked these candidates with cross hairs in our HST images. Our photometry can tell whether a star is hot or not, but can't conclusively indicate if it belongs in the exclusive O type class. We would like you to help us confirm which of the isolated hot star candidates are actually hot enough to ionize their surrounding gas by telling us whether you see a reddish-pink cloud of ionized hydrogen around each star of interest (centered, marked with an orange cross hair).

To get trained before starting, we suggest that you read the information under the About heading above, and then watch the Video Tutorial (top right). You can also check out the Field Guide (tab at right) to get a preview of the types of ionized clouds you’ll be helping to find.