Sun and Stars

Astronomy Test

The Sun is very hot plasma. Why doesn't the plasma just expand into space and the Sun fly apart?

the Sun has a lot of mass, so the gravity holds it together

The Sun has a lot of mass. Why doesn't it all collapse to a single point at the center?

the plasma of the Sun is hot and wants to expand, and this pressure balances gravity 

The energy to heat the Sun comes from the core, where

small atoms are fused into larger ones in nuclear fusion

Fusion converts hydrogen in the core to helium. What happens to the helium generated in the core?

it stays in the core

What is the surface of the Sun like?

it’s not solid, it’s just where the plasma is thin enough that light can escape into space

The process where small nuclei are merged to form a heavier element, which can release energy

fusion

The part of the star where the plasma keeps thinning above the photosphere

atomosphere

The surface of a star, where the plasma is thin enough that light can escape freely into space

photosphere

The interior part of a star where fusion doesn’t occur and where the composition stays the same since the star was formed

envelope

The part of the star where energy is generated

core

The overall electric charge of the Sun

neutral

Two students are discussing the Sun. Which student is correct?

• Student 6: Nuclear fusion powers the Sun, so activity like sunspots and flares must be caused by a change in the fusion rate or the type of fusion.

• Student 7: Fusion is constant, keeping the Sun a nice temperature; changes on the surface are caused by the Sun's magnetic field.

student 7

Describe the balance of forces in the Sun that keeps it from either flying apart or collapsing in on itself. 

pressure build up generated by the core's fusion pushes outward, while the gravitational pull from the Sun's mass pushes inward.

How do we study the interior of the Sun? How do we build models of what the inside of the Sun looks like? 

With helioseismology, which allows you to study the interior of the Sun using the vibrations of the Sun. We build models using basic laws of physics and go off of what it should look like.

The Sun sends a powerful CME toward the Earth. Which of these could be side-effects of the resulting geomagnetic storm?

• more people would see aurora (northern and southern lights) at night 

• satellite orbits might degrade

• some areas would lose power and some satellites might short circuit

Consider the following graph of sunspot activity from the Space Weather Prediction Center. The year 1990 was probably a solar ___________, which is in the ___________ of a sunspot cycle.

maximum, middle 

Let's say a solar flare generates a CME. What order would we detect them on Earth and why? 

Light from the flare first, then particles from the CME afterward because light travels faster than sound.

When in the sunspot cycle do we have the best chance of seeing the aurora as far south as Toledo?

middle

On Earth we are used to solid land, liquid water, and gaseous atmosphere. We saw jovian planets had gas atmospheres and liquid interiors. The hydrogen and helium in the Sun exist in what state?

plasma, since they are so hot that their electrons are ripped off 

neutron star

high mass star

white dwarf

low mass star

a pulsar is a

neutron star that is spinning very quickly and emitting radiation

Neutron stars and black holes can have a few times the mass of the Sun and are about the size of

a city like Toledo

Think about what kinds of stars create which stellar corpses and how common those stars are. If you look at a really old collection of stars, where there has been enough time for a star of any mass to die, what kind of corpse would you expect to see more of?

white dwarfs

high mass star

supergiant

low mass star

red giant

what are stars mostly made of

hydrogen and helium

These objects are too low mass to initiate stable hydrogen fusion and cool as they age

brown dwarf

This represent the longest phase of a star's life, when it is stable and burning hydrogen

main sequence

These extremely luminous stars are among the largest ever observed and represent the very short-lived old age phase of high mass stars.

supergiants

These luminous stars represent the short-lived old age phase of low mass stars. When our Sun hits this phase, it could become large enough to engulf the Earth.

red giants

A high mass star has a lot more hydrogen as fuel than a low mass star; why does a high mass star have a much shorter lifespan?

a high mass star's core is hotter, so it goes through its fuel much faster than a low mass star 

Which generates more energy in old age, low or high mass stars?

high mass stars, fusion is running faster and there are more types of fusion 

In old age why can a more massive star fuse heavier elements (like carbon, oxygen, and silicon), while a low mass star might only be able to fuse hydrogen and helium?In old age why can a more massive star fuse heavier elements (like carbon, oxygen, and silicon), while a low mass star might only be able to fuse hydrogen and helium?

it has more mass, which crushes the core to higher pressure and temperature 

Why do stars get larger in old age?

different types of fusion generate more energy which makes the star expand 

Three stars are born at the same time

• Star #1 has 10% M_sun (10% the mass of the Sun)

• Star #2 has 1 M_sun (the same mass as the Sun)

• Star #3 has 10 M_sun (10 times the mass of the Sun)

Which one has the longest life span?

Star 1

Three stars are born at the same time

• Star #1 has 10% M_sun (10% the mass of the Sun)

• Star #2 has 1 M_sun (the same mass as the Sun)

• Star #3 has 10 M_sun (10 times the mass of the Sun)

Which one has the shortest life span?

Star 3

Three stars are born at the same time

• Star #1 has 10% M_sun (10% the mass of the Sun)

• Star #2 has 1 M_sun (the same mass as the Sun)

• Star #3 has 10 M_sun (10 times the mass of the Sun)

Which one has the middle life span?

Star 2

Why does generating too much iron in a star's core trigger a supernova?

It absorbs energy instead of releasing it, causing the core to lose its outward thermal pressure and collapse under gravity.

How will our Sun die?

It will run out of the ability to create fusion and the Sun will violently expand and form a planetary nebula.

What is a planetary nebula?

the gas cloud thrown off a low mass star when it dies

If I could change the mass of a star, which of these would also change?

Everything, the mass of a star affected everything

Why can't brown dwarfs fuse hydrogen and be called stars?

They have really low mass which means, they can't make the extreme core temperatures and pressure to fuse hydrogen.

Consider a star with the same mass as the Sun. Why will the star be much larger in the red giant phase than during the main sequence phase?

 in the red giant phase fusion reactions are generating more energy than on the main sequence, which inflates the envelope more

Why is the surface of a giant star redder than when it was a main sequence star?

the surface is farther from the core and is therefore cooler 

original gas clump from which solar system formed

nebula

disk-shaped cloud from which our sun and the planets would eventually form

protoplanetary disk

process by which planets move around in the disk

planetary migration

thing that would eventually ignite fusion and become our Sun

protostar

What happened to the molecules of the "ices" (water, methane, ammonia) present inside the frost line?

they existed as a gas

Jovian planets grew larger and faster than terrestrials because Jovians formed _____, where there were solid particles of ice, rock, and metal --- rather than just rock & metal

farther from the Sun than the frost line

What event cleared out the gas from the protoplanetary disk?

the Sun became a star and its solar wind blew away the gas

What is a star? 

A massive luminous celestial object held together by its own gravity

What is the composition of the Sun? What are the “metals? (just the most abundant ones)

Hydrogen, Helium, and Metals (oxygen, carbon, neon, iron)

What makes the core of the Sun so hot?

Gravity pushes pushes inward and the pressure heats the inner layers

What force balances the gravitational pressure and keeps the Sun from collapsing?

gravity

What is plasma?

A gas that is super heated so the electrons are stripped from the atoms and it becomes ionized

How does the core of the Sun generate energy? 

Nuclear fusion occurs when hydrogen nuclei combine to form helium, releasing immense energy.

How do we study the interior of the Sun?

Helioseismology

What is the core of a star? What is happening in the core?

The core of a star is its central region where nuclear fusion occurs, generating energy by fusing hydrogen into helium. This process sustains the star's energy output and counteracts gravitational collapse.

What is the envelope of a star? What is true about the composition of the envelope? 

The envelope of a star is the outer region surrounding the core, which includes layers where energy transport occurs. It is typically composed of hydrogen and helium.

What is the “surface” of a star called? Does a star have a hard surface like Earth?

The surface of a star is called the photosphere. Unlike Earth, stars do not have a hard surface; they transition from gas to plasma.

The plasma of a star keeps thinning above the photosphere. What do we call this? How is it heated?

The sun’s atmosphere,including the chromosphere and corona, is called the star's atmosphere. It is heated by processes such as magnetic reconnection and wave heating.

What is the Solar wind?

The solar wind is a stream of charged particles, primarily electrons and protons, ejected from the sun's outer layers, extending throughout the solar system.

The Sun is made of rapidly rotating plasma that generates what? How far out from the Sun does it extend?

A magnetic field that extends past the Kuiper Belt and our entire solar system.

What causes sunspots? How does their temperature compare to the surrounding parts of the Sun?