Astrophysics and Stellar Evolution: Key Concepts and Laws

How do the laws of physics change for moving observers?

None of the laws change.

What did Einstein show about Newton's physics?

Accurate only at low velocities.

What ultimately determines an isolated star's fate?

Mass.

As a star moves along the red giant branch, how does it move on the HR diagram?

Upward and to the right.

During which evolutionary phases will the Sun undergo fusion in its core?

Main sequence and horizontal branch.

How were essentially all elements heavier than iron formed in our Milky Way?

By supernovae.

Why is the Schwarzschild radius significant?

It is the distance within which nothing can escape a black hole.

What do astronomers believe exists in the center of nearly every galaxy?

A black hole.

What happens to the central temperature and luminosity of a low-mass protostar as it approaches the main sequence?

Temperature increases; luminosity decreases.

Why do massive stars use the CNO cycle instead of the proton-proton chain?

Massive stars have hotter cores; increased temperature sensitivity of the CNO cycle allows for greater energy production.

What kind of stars are most likely to form black holes?

Stars with masses greater than 30 solar masses.

What stops the collapse of the most massive stars at the end of their lives?

Nothing.

Which type of light is most strongly affected by interstellar dust?

Visible light.

Why does stellar fusion end with an iron core?

Iron does not produce energy when it undergoes fusion.

What will the Sun end its life as?

White dwarf.

Which object is closest in radius to a neutron star?

A small city.

What does the general theory of relativity explain?

Gravity and space-time.

Why does a satellite orbit Earth according to general relativity?

Earth has deformed space-time so the satellite falls freely through it.

How has stellar evolution been best understood?

By analyzing the properties of a large number of stars at a single instant.

What quantities must be measured to calculate the luminosity of a star?

Brightness and distance.

Which energy transport mechanism does NOT occur significantly in the Sun?

Conduction.

What forces maintain hydrostatic equilibrium in an object?

Pressure and gravity.

What determines the location of a star on the main sequence?

Mass.

How do massive stars burn their fuel compared to low-mass stars?

They burn their fuel rapidly, so they have shorter lifetimes.

What can an astronomer determine from an HR diagram of a star cluster?

The age of the cluster.

What powers a star?

Fusion.

What has provided the best data about the interior of the Sun?

Helioseismology.

What is created by solar magnetic activity?

All of the above (sunspots, prominences, coronal mass ejections, solar flares).

When does a fusion reaction between nuclei A and B release energy?

If the resulting nucleus is less massive than the total mass of A and B.

What is a key constituent of the interstellar medium?

Gas and dust.

What principle is responsible for accretion disks forming around protostars?

Conservation of angular momentum.

When does a protostar become a star?

When nuclear fusion begins.

What is a brown dwarf?

A failed star.

What is the order of spectral types of stars from hottest to coolest?

OBAFGKM.

Why can Type Ia supernovae be used to determine a galaxy's distance?

Most Type Ia supernovae have approximately the same luminosity.

How do neutrinos help us understand the core of the Sun?

Neutrinos from the interior of the Sun easily escape.

What does the Initial Mass Function tell astronomers about stellar masses?

There are more low mass stars than high mass stars.

What is required for nuclear fusion to occur?

Extremely high temperatures for protons and neutrons to collide at high velocities.

What describes changes to a star when it first moves off the main sequence?

Increased radius and decreased surface temperature, increased luminosity.

What are the seven spectral categories of stars in order from coolest to hottest?

MKGFABO.

When do the predictions of Special Relativity match those of Newtonian physics?

When objects are moving slowly.

What is the definition of a standard candle?

An object whose luminosity is known.

How is heat transported from the bottom of a pot to the water's surface?

Convection.

What energy source begins nuclear fusion in a protostar?

The gravitational potential energy of the protostar.

What primarily makes it difficult to observe star formation?

They occur in dusty regions.

What is the result of mass distorting the fabric of spacetime?

Gravity.

What primarily causes solar activity?

The magnetic field of the Sun.

What does the Chandrasekhar limit refer to?

The maximum mass of a white dwarf.

What will observers in different inertial frames of reference always agree on?

The laws of physics.

What forms a planetary nebula?

The ejection of mass from a low-mass star.

How can black holes that are stellar remnants be found?

By searching for variable X-ray sources.

What does the HR diagram of a cluster not tell astronomers?

The rotation of the cluster.

What is true about white dwarfs?

They first appear at the center of a planetary nebula.

Why are about 90% of the stars we observe on the main sequence?

Stars spend most of their life on the main sequence.

Why can an iron core not support a massive main-sequence star?

Because iron cannot fuse to make heavier nuclei and produce energy.

What is the order of the layers of the Sun from inside to outside?

Core → Radiative Zone → Convective Zone → Photosphere → Chromosphere → Corona.

Why do sunspots appear dark?

They are cooler than their surroundings.

What type of star is located on the upper right of the HR diagram?

A giant.

What does the main sequence show?

The distribution of core hydrogen-fusing stars by mass.

Which type of star has the highest density?

Neutron star.

How often does the number of sunspots and their location change?

Over an 11-year cycle.

How are elements heavier than iron formed?

In supernova explosions.

Which figure represents the oldest star cluster?

Figure D.

The Sun will undergo fusion in its core during which evolutionaery phases?

Main sequence and horizontal branch

Nuclear fusion requires extremely high temperatures so that collisions of protons and neutrons occur at velocities high enough to overcome the strong nuclear force

True

Why do massive stars use the CNO cycle to generate energy, rather than the proton-proton chain?

Because massive stars have hotter cores; the increased temperature sensitivity of the CNO cycle allows for greater energy production.