IMAGE: This ancient stellar jewelry box, a globular cluster called NGC 6397, glitters with the light from hundreds of thousands of stars. This image is composed of a series of observations taken from July 2004 to June 2005 with Hubble’s Advanced Camera for Surveys. CREDIT: NASA, ESA, T. Brown, S. Casertano, and J. Anderson (STScI)
Our first story looks deep into the heart of the nearby globular cluster NGC 6397. Observable from the southern hemisphere, this knot of thousands of stars is the second closest globular cluster to our solar system and is close enough for the Gaia and Hubble space telescopes and larger ground scopes to readily resolve individual stars in all but the densest part of the system’s core.
With Gaia and Hubble, high-resolution images taken over time make it possible to actually measure how stars’ positions on the sky change as the stars orbit. The Very Large Telescope’s MUSE spectrograph also allowed motions along the line of sight, that direction in and out of the sky, to also be measured. Put together, these three-dimensional orbital motions make it possible to map out the distribution of unseen mass in the cluster.
In a new paper in ...