Galaxies are pretty big. The Milky Way's stellar disk, for example, spans some 100,000 light-years. But new observations show that galaxies' extent is actually much greater than that — more like millions of light-years across.

Sanksriti Das (Ohio State University) presented X-ray observations of the Milky Way-size spiral galaxy NGC 3221 at this week’s virtual meeting of the American Astronomical Society. She and her colleagues took spectra of X-rays emitted by hot gas all around this galaxy, using the XMM-Newton and Suzaku space telescopes to provide direct evidence of the existence of a halo that extends well beyond the galaxy's stars. 

Read the rest of the article in Sky and Telescope.