Astronomy chapter 13: Test 3 – Flashcards

the corpse of a low-mass star, supported against the crush of gravity by electron degeneracy pressure.

Degeneracy pressure

degeneracy pressure arises in white dwarfs from closely packed electrons.

Because a white dwarf is the core left over after a star has ceased nuclear fusion, its composition reflects the products of the stars final fusion stage. Which is mostly carbon.

The density of a white dwarf is extremely high.

The more dense a white dwarf is the smaller it is.

Since nothing can travel faster than the speed of light, no white dwarf can have a mass greater than 1.4M_sun.

A white dwarf can gradually gain mass if its companion is a main-sequence or giant star. The clump of mass spills over from the companion and has some small orbital velocity. As the clump falls toward the WD, it must move faster and faster.

The falling clump of mass which forms a whirl-pool like disk around the white dwarf.

The WD blazes back to life while fusion in its hydrogen layer supplies energy. The thermonuclear flash causes the binary system to shine for a few glorious weeks, which is a nova.

A nova is caused by hydrogen fusion on the surface of a white dwarf in a binary star system.

If a white dwarf gains enough matter to exceed the 1.4 solar mass white dwarf limit, it will explode completely in a white dwarf supernova.

The iron catastrophe that leads to a supernova ending the life of a high mass star.

the ball of neutrons created by the collapse of the iron core in a massive star supernova.

neutron stars are giant atomic nuclei made almost entirely of neutrons and held together by gravity. Neutron stars resist the crush of gravity with degeneracy pressure that arises when particles are packed closely together.

It is neutrons rather than protons that are closely packed together, so its neutron degeneracy pressure that supports neutron stars.

A graduate student discovered a strange source of radio waves in which they pulsed on and off at precise 1.337301-second intervals.

Rapidly pulsing radio sources

As angular momentum gets carried away it causes the neutron stars rotation to slow gradually.

Like a white dwarf, a neutron star in a close binary system can brilliantly burst back to life.

A black hole is a place where gravity is so strong that nothing, not even light, can escape from within it.

Space and time are not distinct as we usually think of them, but instead are bound up together.

The boundary between the inside of a black hole and the universe outside. Essentially marks the point of no return for objects.

The event horizon is a sphere with a well defined radius known as this. It depends only on the black holes mass.

The point where all the matter in a black hole must be crushed to an infinitely tiny and dense point.

The prediction from einsteins general theory of relativity which predicts that light coming out of a strong gravitational field should show a redshift.

The black holes gravity would pull more strongly on an individuals feet than on his head, stretching him length wise and squeezing him from side to side.

Evidence today suggest that they must really exist.