Supermassive Black Holes Preserving a Galactic Treasure
Galaxy Structure and Classification (Easy)
Galaxy Structure and Classification (Harder)
Parts of a Spiral Galaxy (Supermassive Black Hole) Creative Commons
Supermassive Black Holes (SBH) Sgr A* (pronounced: Sagittarius A-star) – Strong radio source in the center of the Milky Way galaxy (our galaxy) – Mass = 4 x 10 6 M M87 (supergiant elliptical galaxy) – Contains a SBH at its center – Mass = 6.6 x 10 9 M Creative Commons
Proof of Existence for Sgr A* The mass of the central (and not visible) object can be found from the velocities of nearby stars orbiting it. These images/animations were created by Prof. Andrea Ghez and her research team at UCLA and are from data sets obtained with the W. M. Keck Telescopes.
How to Weigh a Black Hole Assume the mass of the star is insignificant compared to the mass of the central object – Assumption based on the fact that the central object does not appear to move. – This eliminates the “M 2 ” term. Use a form of Kepler’s Third Law. See equation practice sheet for quantities and units.
Schwarzschild Radius How big is a black hole? Based on the mass, we can calculate the distance from the singularity from which no light can escape. – This is called the Schwarzschild radius. Equation is derived using the escape velocity. See equation practice sheet for quantities and units.
Diameter of a Black Hole If we have both the linear diameter (R Sch ) and the distance to the black hole, we can calculate the angular diameter. Relate these using the small angle formula See equation practice sheet for quantities and units.
Trying to Observe the Galactic Center Radio – Observable but very low resolution Microwave – Observable but requires VLBI for good resolution Infrared – Observable but highly blurred by Earth’s atmosphere Visible – Cannot pass through all the dust in the galactic disk UV/X-ray/Gamma – Not observable on Earth
What We Expect to see in Radio When We Observe Sgr A* Used with Permission
Supermassive Black Hole Activity