The visibility of stellar transients in the Galactic Centre

Sammanfattning: A semi-analytical simulation was developed to evaluate the K-band magnitudes of Red Giants [0.96 - 1.02 M⊙] orbiting the supermassive black hole in the galactic centre. The model assumed star formation between 10-12 Gyrs ago and by following the IMF and applying a random age condition, a stellar population was created. It was established that stars with mK ≤ 16 can be observed and then they become too faint and difficult to observe. The magnitude means that Red Giants on and beyond the Red Clump phase are observable, which means only 12% of a total population of Red Giants can be observed. Secondly mass transfers between the remnants of a Red Giant and a Red Giant star can happen as the dense core passes through the envelope of the star. The result will be a ”fuzzball” with observable properties. It showed that larger radius is more important than higher temperature at the region where the envelope is just bound. However after the thermal time scale has passed, the fuzzballs apparent K-band magnitude increases as its luminosity decreases, hence decreasing their observability. This in combination with their cooler temperature and decrease in luminosity would be one way to differentiate them from Red Giants. It was concluded that if the G2, a stellar gas cloud, orbiting the supermassive black hole is a fuzzball, then it should have a black hole core and be older than 100 000 years since its observed magnitude is higher than expected for the fuzzball model.