ASTR Test 2 HW 6: Evolution & Death

What type of object is found at the center of this type of nebula (seen here in the optical)?

A white dwarf

T or F) Planetary nebulae are sites of planet formation.

False

T or F) Supergiants are about as common as the sun

False

When a star finishes `core hydrogen burning', and transitions to `burning' hydrogen in a shell around its core, what would we observe if we could look at the star from the outside?

It would get larger and cooler, moving off the main sequence toward the red giant branch of the H-R diagram.

The astrophysicist who first calculated the highest mass that a dying star can have and still be a white dwarf was

S. Chandrasekhar

Which of the following statements about the mass of the Sun during its lifetime is correct?

The Sun will lose a significant amount of mass during and after its red giant phase

The fact that this nebula (from the previous question) is emitting light tells us what about the object at its center?

The object is hot enough to emit significant amounts of ultraviolet radiation.

Why don't we see any of the cold black dwarfs that white dwarfs eventually cool to become?

The universe isn't old enough for this long cooling processes to have finished yet.

T or F) Because more massive stars have more gravitational energy, they can fuse heavier nuclear fuels.

True

T or F) No known white dwarf has a mass greater than the Chandrasekhar limit.

True

In a supernova like SN1987A, once the crisis of iron fusion has begun, roughly how long does it take the star's core to collapse?

a few tenths of a second

Elements heavier than iron can be created during:

a supernova explosion

Which of the following statements about the life of a star with a mass like the Sun is correct?

as the star is dying, a considerable part of its mass will be lost into space

Because white dwarfs are small, as their name implies, they are hard to see. What is a way astronomers have to find white dwarfs that distinguishes them from main sequence stars?

because white dwarfs get really hot, we can search for their ultraviolet radiation

After the core of a massive star becomes a neutron star, the rest of the star's material

explodes outward as a supernova

If stars with masses like our Sun's cannot make elements heavier than oxygen, where are heavier elements like silicon produced in the universe?

heavier elements are made in the cores of significantly more massive stars than the Sun, which can get hotter in the middle

When stars become giants, which of the following does NOT usually happen?

heir mass grows significantly as they incorporate planets and interstellar matter near the star

If you trace back the history of a carbon atom in your little finger through all of cosmic history, where did this atom most likely originate?

it was fused from 3 helium nuclei in the core of a red giant star long before the Sun existed

In a collapsing star of high mass, when electrons and protons are squeezed together with enormous force, they turn into a neutron and a:

neutrino

After it experiences a "helium flash" a star like the Sun will have a brief period of stability, fusing helium into carbon (and sometimes oxygen). During this brief stable stage, the star

none of these

If most stars are low-mass stars, and low-mass stars typically eject a planetary nebula, why then do astronomers see relatively few planetary nebulae in the sky?

planetary nebulae expand rapidly and soon become too faint to be visible

Astronomers observe a young cluster of stars, where stars with three times the mass of the Sun are still on the main sequence of the H-R diagram. Yet the cluster contains two white dwarfs, each with a mass less than 1.4 times the mass of the Sun. If we can show that the white dwarfs are definitely part of the cluster, how can their presence so soon in the life of the cluster be explained?

some stars can lose a lot of mass on their way to becoming white dwarfs; thus the white dwarfs could have started out as quite massive stars

Which of the following stages will the Sun definitely go through as it gets older?

source of a planetary nebula white dwarf black dwarf red giant Correct! all of these choices

Astronomers believe that the many supernova explosions that happened in the Milky Way Galaxy could have played a role in the evolution of life over billions of years. How would they have influenced the development of life on Earth?

the cosmic rays produced by supernova explosions would have contributed to the rate of mutations over many generations

If observations of supernovae in other galaxies show that such an explosion happens in a spiral galaxy like the Milky Way on average every 25 to 100 years, why have astronomers on Earth not seen a supernova explosion in our Galaxy since 1604?

the disk of our Galaxy contains a great deal of dust, which tends to block the light of supernova explosions from more distant parts of our Galaxy

Which of the following is a characteristic of degenerate matter in a white dwarf star?

the electrons get as close to each other as possible and resist further compression

If we look back to the first generation of stars made when the Galaxy was first forming, how do they differ from stars being formed today?

the first generation stars contain little or no elements heavier than helium

Many names used by astronomers are misleading or outdated. A good example is the term planetary nebula, which astronomers use to refer to:

the shell let go by a dying low-mass star

Your sweetheart gives you a piece of gold jewelry as a present to celebrate your passing your astronomy class. Where did the gold atoms in that gift originally come from (where were they most likely made)?

they were built up from smaller nuclei during a supernova explosion

Which of the following stages can only occur in the life of a low-mass star (whose final mass is less than 1.4 times the mass of the Sun)?

white dwarf