American Museum of Natural History

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Michael Shara

Curator

Ph.D., Tel-Aviv University, 1978 "Hydrodynamic Simulations of Stellar Collisions Involving a White Dwarf Star"

RESEARCH

Dr. Shara and his research group are conducting an exhaustive survey to inventory and "weigh" all 100,000 stars nearest to Earth. More than one billion stars are being examined in the search. The survey has already determined that many low luminosity stars remain undiscovered just a few light years away, and that a significant portion of the local "dark" matter is concentrated in stars 100 to 100,000 times fainter than the Sun.

Most of the gravitating matter in the Universe is "dark"-possessing mass but radiating very little light. What is this dark matter made of? Astronomers don't know if this mass exists in the form of stars, planets, or something more exotic, because a majority of the Sun's nearest stellar neighbors have not yet been discovered; most are intrinsically much dimmer than the Sun. The oscillatory motion of the Sun in our Milky Way Galaxy demonstrates the presence of local dark matter.

The Milky Way and most other galaxies are orbited by the oldest objects in the Universe-globular star clusters. Inhabited by as many as one million stars, these spherical clusters have such high densities that physical collisions between stars are rather commonplace. Numerical simulations predict that stellar collisions often be amalgamative, producing massive, luminous stars in environments where only cool, low mass stars should exist.

Dr. Shara uses the Hubble Space Telescope to survey the densest cores of globular clusters to retrieve and characterize the predicted collision products. These include some of the most exotic stars known to astrophysicists: "blue stragglers." By accurately weighing these stars, Shara and his collaborators have demonstrated that many are at least twice as massive as all other stars in a globular cluster. This strongly supports the hitherto theoretical collisional origin for blue stragglers.

RECENT SIGNIFICANT PUBLICATIONS

Rich, R. M., M. M. Shara, S. M. Fall, and D. Zurek. "Two Groups of Old Star Clusters in the Small Magellanic Cloud." Astronomical Journal 119 (2000): 197-206.

Shara, M. M., A. F. J. Moffat, L. F. Smith, V. S. Niemela, M. Potter, and R. LaMontagne. "A Deep Survey For Galactic Wolf-Rayet Stars: II. Implications for Galactic Structure and Massive Star Formation." Astronomical Journal 118 (1999): 390.

Shara, M. M., S. M. Fall, R. M. Rich, and D. Zurek. "Hubble Space Telescope Turnoff Photometry and First Detection of Extragalactic Globular Blue Stragglers in the Old SMC Cluster NGC 121." Astrophysical Journal 508 (1998): 570.

Shara, M. M., D. Zurek, R.E. Williams, D. Prialnik, and A. F. J. Moffat. "HST Imagery of the Non-Expanding, Clumped 'Shell' of the Recurrent Nova T Pysxidis." Astronomical Journal 114 (1997): 258.

Shara, M. M., R. A. Saffer, and M. Livio. "The First Direct Measurement of the Mass of a Blue Straggler in the Core of a Globular Cluster: B22-19 in 47 Tuc." Astrophysical Journal Letters 489 (1997): L59.

Shara, M. M., E. Bergeron, R. Gilliland, A. Saha, and L. Petro. "Cataclysmic and Close Binaries in Star Clusters. 1v. The Remarkably Small Number of Catacysmics in the Core of 47 Tuc." Astrophysical Journal 471 (1996): 804.

Shara, M. M. and L. Drissen. "Cataclysmic and Close Binaries in Star Clusters. III. Recovery of the Quiescent Nova 1860 A.D. (T. Scorpii) in the Core of the Globular Cluster M80." Astrophysical Journal 448 (1995): 203.