01:750:109 Chapter Notes - Chapter 11.3: Seyfert Galaxy, Gravitational Energy, Solar Mass
Seeking Supermassive Black Holes
●Supermassive black holes have extreme amounts of radiation emanating from a tiny central
region, accompanied by powerful jets of material shooting outward at nearly the speed of light
What is the evidence for supermassive black holes at the centers of galaxies?
●Active galaxies
○Galaxies w unusually bright centers
○The bright central regions themselves are known as active galactic nuclei
■Most luminous examples are known as quasars
and can produce luminosities
1000 that of the Milky Way
●Activity in center of a galaxy linked to galaxy evolution bc quasars more common early in time
than they are now
○Engines responsible for supplying luminosities of quasars have become dormant as
galaxies have aged
Sizes of Active Galactic Nuclei
●Astronomers noticed 1% of galaxies (sometimes called Seyfert galaxies
) have really bright
centers
●Variations in luminosities gives us clues about an object's size
The Black Hole Hypothesis
●Use model in which central object is a supermassive black hole surrounded by a swirling
accretion disk of very hot gas (similar to the x-ray binary star systems)
○Gravitational potential energy of matter falling toward a black hole is converted into
kinetic energy and collisions btwn infalling particles convert kinetic energy into thermal
energy
○Resulting heat causes this matter to emit the intense radiation we observe
○As in x-ray binaries, we expect that the infalling matter swirls through an accretion disk
before it disappears within the vent horizon of the black hole
●Matter falling into black hole can generate awesome amounts of energy
○As much as 10-40% of its mass energy can be converted into thermal energy and
ultimately into radiation
●Accretion by black holes can therefore produce light far more efficiently than nuclear fusion
○So efficient that it can account for the enormous luminosity of a quasar if we assume
that the black hole swallows the equivalent of about one star per year
●Also accounts for the small sizes implied by quasar variability
○A black hole accreting a solar mass of matter per year could eventually attain a mass of a
billion solar masses if accretion continued at that rate for a billion yrs
Mounting Evidence
Document Summary
Supermassive black holes have extreme amounts of radiation emanating from a tiny central region, accompanied by powerful jets of material shooting outward at nearly the speed of light. The bright central regions themselves are known as active galactic nuclei. Most luminous examples are known as quasars and can produce luminosities. Activity in center of a galaxy linked to galaxy evolution bc quasars more common early in time. 1000 that of the milky way than they are now. Engines responsible for supplying luminosities of quasars have become dormant as galaxies have aged. Astronomers noticed 1% of galaxies (sometimes called seyfert galaxies ) have really bright. Variations in luminosities gives us clues about an object"s size centers. Use model in which central object is a supermassive black hole surrounded by a swirling accretion disk of very hot gas (similar to the x-ray binary star systems)
