From the Southworth Planetarium
“Under foot and out of sight”
THE DAILY ASTRONOMER
July 13, 2010
Evening Nucleus
It is no illusion. The summer Milky Way is brighter than the winter Milky Way. By which we mean that the Milky Way’s light band visible in the summer evening is more luminous than the band visible in the winter evening. The reason for this difference is simple. In the summer, we look toward the galactic center, a region called the nucleus. The space surrounding the nucleus is the galaxy’s central city: a region that abounds in stars and energy: a galactic central city. In the winter, we peer into the galaxy’s outer suburbs. a section of the galaxy where stars aren’t as plentiful and therefore appears less bright than the center.
This evening, the galactic nucleus rises in the southeast around sunset. One can pinpoint this nucleus in the constellation Sagittarius, the Archer. Sagittarius resembles a teapot and the nucleus is just west of the spout. While one can pinpoint the nucleus’ position, one can’t actually observe it in visible light, as it is obscured by the vast fields of gas and dust occupying the 23,000 light years of space that separate us from it. Consequently, we cannot directly scrutinize the nucleus and discern its contents. Instead, astronomers must surmise its structure by both analysis of the radiation that can penetrate the galactic dust, such as radio waves and observations of other galactic nuclei. From these studies, astronomers believe that the nucleus contains a super-massive black hole.
Measuring between a few million up to a billion times more massive than the Sun, this hypothesized black hole could be responsible for the frenetic activity observed in the nucleus. Astronomers think that these mammoth black holes might still be devouring innumerable stars and dust swaths within the galactic halo, thereby increasing the black hole’s mass and gravitational power. Fortunately for us, this black hole (or, perhaps, black holes) are too distant to pose any threat to us. They are safely displaced from us, while providing the centralized attractive force required to maintain the galaxy’s shape.
Watch tonight for the nucleus area to rise in the southeastern sky. We can’t see it because of its distance, but such inconveniences are the often the price of safety.
