Many things in the universe are hard to see without massive telescopes. When we look at star clusters, we try to understand them by looking at the most massive and easily seen stars.
It turns out bright stars aren’t the only tools we have to understand what’s going on. In a new study of the elliptical galaxy M105, researchers carefully mapped the population of objects – stars and planetary nebulae – and found that the planetary nebulae traced a diffuse population of metal-poor stars in the outer halo of the galaxy. While the majority of the star’s material lies within three kiloparsecs (kpc) of the galaxy center, this halo spans from 15-50 kpc. This large halo only produces about 4% of M105’s light, but its large size means the motions of these stars and planetary nebulae can be used to trace the effects of dark matter.
M105 is located in the Leo I galaxy group, which is just ten megaparsecs away and is the closest group to have all the major kinds of galaxies. This research hints at how planetary nebulae can be used as tracers of metal-poor populations in other galaxies.
“The Halo of M105 and Its Group Environment as Traced by Planetary Nebula Populations: I. Wide-field Photometric Survey of Planetary Nebulae in the Leo I Group,” J. Hartke et al., 2020, Astronomy & Astrophysics (preprint on arxiv.org)