01:750:109 Chapter Notes - Chapter 10.3: Starflight, Supermassive Black Hole, Accretion Disk
Searching for Black Holes
Do black holes really exist?
●A black hole's gravity can influence its surroundings in ways that reveal its presence
●Search for telltale signs of an unseen gravitational influence with a large enough mass to suggest
that it is a black hole
○Objects showing these signs have been found in 2 diff environments:
■Black holes in binary systems (born in supernova explosions)
■Supermassive black holes (too massive to come from a single supernova)
Black Holes in Binary Systems
●Strong observational evidence for black holes formed by supernovae comes from studies of
X-ray binaries
○Recall: accretion disk around neutron stars in close binary systems can emit strong X-ray
radiation, making an X-ray binary
■Accretion disk forms bc neutron star's strong gravity pulls in mass from the
companion star
■Bc a black hole has even stronger gravity than a neutron star, a black hole in a
close binary system should also be surrounded by a hot, X-ray-emitting
accretion disk
○AKA an X-ray binary can contain either a black hole or a neutron star
■Can tell diff by measuring the object's mass
Supermassive Black Holes
●Supermassive black holes are those w masses millions or billions of times that of our Sun
●Center of Milky Way contains a source of radio emission called Sagittarius A*
(Sagittarius A-Star)
The Bottom Line
●Confirming that black holes are real with 100% certainty diff bc our detection methods remain
indirect
○But our current theories explain neutron stars, and the general theory of relativity that
leads to the idea of black holes is also well established
●Can understand entire life cycle of a star in terms of the changing balance between pressure and
gravity. Balance changes over time and those changes depend on a star's birth mass
○Stars beginning with less than 0.08MSun never become stars bc degeneracy pressure
halts their contraction before fusion can bring them into balance
○Stars beginning with less than 8 Msun end up as white dwarfs bc degeneracy pressure
stops their cores from contracting before fusion starts to make iron
Document Summary
A black hole"s gravity can influence its surroundings in ways that reveal its presence. Search for telltale signs of an unseen gravitational influence with a large enough mass to suggest that it is a black hole. Objects showing these signs have been found in 2 diff environments: Black holes in binary systems (born in supernova explosions) Supermassive black holes (too massive to come from a single supernova) Strong observational evidence for black holes formed by supernovae comes from studies of. Recall: accretion disk around neutron stars in close binary systems can emit strong x-ray radiation, making an x-ray binary. Accretion disk forms bc neutron star"s strong gravity pulls in mass from the companion star. Bc a black hole has even stronger gravity than a neutron star, a black hole in a close binary system should also be surrounded by a hot, x-ray-emitting accretion disk. Aka an x-ray binary can contain either a black hole or a neutron star.
