An
ancient star cluster has three different groups of stars whose ages appear
out-of-sync, as seen by NASA’s Hubble Space Telescope.
Astronomers
used Hubble to find the dimmest stars in the NGC 6791 cluster. The cluster's location appears in the
Digital Sky Survey image (left image), with a closeup courtesy of Hubble on the stars in question (upper right image). Two of the star
populations appear as burned-out white dwarfs (lower right image), with one group (red circles)
appearing to be six billion years old and another group (blue circles)
appearing just four billion years old. The rest of the cluster’s normal stars
are eight billion years old.
The
finding puzzles the research team because they assume that stars in the same
cluster should have formed roughly at the same time. However, they soon
realized that the younger-looking white dwarfs might be paired off in binary
star systems, so that the paired stars appear as a brighter, younger single
star. That would explain why the different white dwarf groups appear to have
different ages, which just leaves the mystery of why the white dwarfs aged
slower than the cluster’s normal stars.
— NASA/ESA and SPACE.com Staff
Credit: NASA/ESA/L.
Bedin (STScI)
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