Mystery of the fast moving object G2 at the Galactic center: will there be fireworks?

Tuan Do

July 15, 2013

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Abstract: The object G2 was recently discovered at the Galactic center moving rapidly toward the black hole. Its properties are unlike most of the fast moving stars in this region: it is very red with no detectable K-band continuum, and has strong hydrogen line emission features. These properties have led to the hypothesis that G2 is a gas cloud on approach toward Sgr A*. If G2 is a gravitationally unbound gas cloud, then it will be tidally stripped by Sgr A* as it goes through closest approach, providing us with an unprecedented view of accretion onto a supermassive black hole. However, a gravitationally unbound gas cloud should not be able to survive in this region for very long. Alternatively, G2 may be of stellar nature — such as a proto-planetary disk, embedded protostar, etc. Such a source will result in significantly less accretion onto black hole. I will present imaging and spectroscopic observations of G2 from the Keck Telescopes. These data show that the orbit of G2 is more eccentric and has a later time of closest approach to the black hole compared to previously reported results. This orbit also places G2 away from a structure which was previously proposed as the gas tail of the object. I will also discuss the temporal evolution of the spectra of the object, and how the current imaging and spectroscopic data compares to the hypotheses that G2 is a gas cloud or star.