← AST 309N Test 2 Test
5 Written Questions
5 Matching Questions
- U Sco
- Massive star binaries
- What must happen for a star to burn a thermonuclear fuel?
- Forming a neutron star by core collapse produces what?
- Jet-induced explosions
- a An example of a recurrent nova in the constellation of Scorpius. The white dwarf has been measured to
have a mass greater than 1.3 M and is thought to be headed to a thermonuclear supernova explosion.
- b Supercomputer computations show that sufficiently powerful jets can blow up a star.
The jets plow up and down along one axis creating a "breadstick" shape and driving bow shocks. The bow
shocks propagate away from the jets toward the equator where they collide. The result of this collision is to blow
much of the star out along the equator in a torus or "bagel" shape. The final configuration is far from spherical,
but has jets in one direction and a torus expanding at right angles to the jet.
- c about 100 times more energy than needed to create an
explosion, but most of that energy is carried off by neutrinos.
- d Explosions of massive stars in close binary systems are expected to occur in a bare thermal
pressure-supported core from which the outer layers of hydrogen have been transferred to the companion
star. The core, supported by the thermal pressure, will continue to evolve to iron, even in the absence of
the hydrogen envelope. This is probably the origin of Types Ib and Ic.
- e the star must get hotter to overcome the charge repulsion. This happens automatically in massive stars supported by the thermal pressure that regulates their burning. These stars
produce shells of ever-heavier elements and finally a core of iron.
5 Multiple Choice Questions
- Delayed mechanism: Neutrinos stirred out by the boiling neutron star deposit heat behind the standing
shock and reinvigorate it. Not clear this is sufficient
- a strong pressure wave that forms due to neutron-star bounce, but which stalls a certain
distance from the neutron star as outer material rains down on it.
- intermediate elements (O, Mg, Si, S, Ca) on outside and iron-like material on inside.
Consistent with models of Chandrasekhar mass carbon-oxygen white dwarfs that begin with a subsonic
deflagration and then ignite a supersonic detonation
- in addition to producing the jet/torus shape, the jet model predicts that iron is blown along the jet and other elements in the outer layers, He, is ejected in the equatorial torus. This may provide an observational test of the model
- matter streaming through inner Lagrangian point does not directly strike the tiny, orbiting,
white dwarf, but circles around and forms a flat spiraling disk. The disk has its own life in the system.
5 True/False Questions
1st way a core collapse of the outer layers of a star may occur → Prompt mechanism: The neutron star rebounds, driving a shock wave into the outer parts of the star.
The bounce shock occurs, but is insufficient to cause an explosion
All core-collapse supernovae measured to date, Type Ib, Ic, and II are not what? → spherical. They may be "breadstick"
shaped or "bagel" shaped or some combination of elongation and flattening.
Type Ib Supernovae → no hydrogen, but observe helium early on, O, Mg, Ca later. Occur in spiral arms, never in
elliptical galaxies. Massive star core collapse.
3rd way a core collapse of the outer layers of a star may occur → Jet mechanism: the collapsing rotating neutron star squeezes the magnetic field and sends a jet up the
rotation axis. Naturally makes asymmetric explosion, but not yet clear sufficiently strong jets are
Disk radiation → the outer parts of disks typically have temperatures comparable to the Sun and shine with
optical light. Middle parts are hotter and glow in ultraviolet light. This is appropriate for white dwarfs. The
innermost parts can be hot enough to emit X-rays. This is appropriate to neutron stars and black holes.