Nearby lethal supernovae may be responsible for the mysteriously small dark energy
戸谷 友則 (天文学教室)
The observed value Lambda_obs of the cosmological constant Lambda is extremely smaller than theoretical expectations, and the anthropic argument has been proposed as a solution to this problem because galaxies do not form when Lambda >> Lambda_obs. However, the contemporary galaxy formation theory predicts that stars form even with a high value of Lambda / Lambda_obs ~ 50, which makes the anthropic argument less persuasive. Here we calculate the probability distribution of Lambda using a model of cosmological galaxy formation, considering extinction of observers caused by radiation from nearby supernovae. The life survival probability decreases in a large Lambda universe because of higher stellar density. Using a reasonable rate of lethal supernovae, we find that the mean expectation value of Lambda can be close to Lambda_obs, and hence this effect may be essential to understand the small but nonzero value of Lambda. It is predicted that we are located on the edge of habitable regions about stellar density in the Galaxy, which may be tested by future exoplanet studies.
hongo-astrotalks (at-sign) astron.s.u-tokyo.ac.jp