Telling a Neighbor's Age

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Science  16 Jun 2000:
Vol. 288, Issue 5473, pp. 1933
DOI: 10.1126/science.288.5473.1933e

The Large Magellanic Cloud (LMC), one of the largest and closest galaxies to our Milky Way, is an irregular barred galaxy with one spiral arm that has only about one tenth the mass of the Milky Way. The bar is thought to have formed only 1 to 5 billion years ago, which would help to explain the differences between the LMC and the Milky Way, which is 9 billion years old.

Alcock et al. have completed a photometric survey of about 9 million stars in the LMC as part of the massive astrophysical compact halo object (MACHO) project that takes advantage of microlensing events to boost the brightness of background stars. Billions of photometric measurements were collected and used to create a color versus magnitude diagram that distinguishes the age, distribution, and population of different types of stars. This massive survey indicates that there is a discrete population of stars about 9 billion years old in the LMC bar, thus requiring revisions to models of the LMC's evolution.—LR

Astron. J.119, 2194 (2000).

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