Astronomy Test 4

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The largest possible mass for a white dwarf is __________ because

1.4 solar masses; if a star had a greater mass then its gravity would be strong enough to crush the electron degeneracy pressure

The least massive stars are about

1/12 the mass of our sun

The Schwarzschild radius of Sgr A* (the ultra massive black hole at the center of our Milky Way galaxy) is about

1/5 the radius of the orbit of Mercury

A star of one solar mass (like our sun) will have a main sequence lifetime of about

10 billion years

The most massive stars are about

100-200 times the mass of the Sun

About how many new stars form in our galaxy every year?

3

As she'll burning expands a star and its outer layers cool

It grows to enormous size and becomes redder

If an astronauts were to fall into an extremely massive black hole

It would take an infinite amount of time to fall through the event horizon as seen from far away but to the astronaut it time passes normally

Research supports the possibility that

Planets can migrate and travel inward after formation

General relativity was

Put forward by Einstein in 1916

Pulsars we're determined to be

Rapidly spinning neutron stars whose jets happened to sweep over and point toward Earth

As helium accumulates in the core of a main sequence star

Temperature and density in the inert region slowly increase

The shift in the wavelength and frequency of the light emitted by an object as it moves toward or away is called

The Doppler effect

When the distorting mass is small

The prediction of general relativity must agree with those resulting from Newton's law of universal gravitation

General relativity states that

The presence of matter curves or warps spacetime

Which discovery method allows astronomers to learn something about the composition of the exoplanet's atmosphere?

Transit

The method of detecting exoplanets that relies on small periodic dimming in the light observed from a star is called the

Transit method

The easiest extrasolar planets to find by observing the motion of the parent star would be

Very massive and orbiting close in

The carbon and oxygen in your body

Was created by nuclear fusion in the cores of long dead stars

Most stars form

With planets

Electrons in a white dwarf resist further collapse because of

degenerate pressure

_________ transits (The Transit Method) must be observed in order to "discover" an exoplanet using this method

3

In our solar neighborhood, the typical spacing between stars is anout

3 LY

About how many exoplanets (planets orbiting stars other than our sun) have been discovered?

3,500

If our sun were crushed so that its diameter was a little less than about _________ no light could escape its surface.

6 km or 3.7 mi

The rate of fusion in a star goes approximately as the temperature to the fourth power, so if the temperature of a star tripled the rate of fusion would increase by a factor of

81

A hot Jupiter is

A giant exoplanet that orbits very close to its star

An exoplanet is

A planet outside our solar system

A transit occurs when

A planet passes in front of its star, blocking a small fraction of light from being seen from Earth

When hydrogen runs out in the core of a main sequence star and gravity begins to crush it

A shell of hydrogen just outside the core that wasn't hot enough to fuse before now is, and can dust into helium

When gravity overcomes the electron degeneracy pressure in a very massive star, the core is crushed from something about the size of earth to something about ten miles across in less than one second. this initiates

A supernova explosion

The calculated lower limit to the possible mass of stars is

About 0.075 solar masses

If the collapsing core of a star is greater than _________ then nothing we are ware of can stop it from collapsing to an infinitely small volume.

About 3 Msun

When our sun dies and becomes a white dwarf, it will be

About the size of earth

High-mass stars

Achieve much higher core temperatures and can fuse carbon into heavier elements

After the helium supply is exhausted and a star's core is entirely carbon and perhaps a little oxygen

All fusion will cease in low-mass stars and their cores cannot get hot enough to fuse carbon into heavier elements

Observing star clusters is useful because

All stars in the cluster likely formed from the same molecular cloud at about the same time, so would only differ in mass

A black hole is

An object whose escape velocity is faster than the speed of light

Globular clusters

Are among the oldest structures in our Milky Way galaxy

Gravitational waves

Are disturbances in spacetime resulting from the rearrangement of matter

Stars near the top right of an H-R diagram

Are extremely bright

Open clusters

Are found in the flat disk of the Milky Way galaxy

Stars with a final mass less than about 1.4 solar masses just before death

Become white dwarfs

Matter falling toward the event horizon of a black hole

Becomes so hot it emits x-rays

The upper limit of the possible mass of stars is

Between 100 and 200 solar masses

For a growing planetesimal to be able to capture and hold hydrogen it must have a mass

Bigger than about 10 time the mass of earth

The helium accumulated during a star's main sequence period

Can only be fused into carbon if the core shrinks and reaches a temperature of at least 100 million K

Higher temperatures are required to fuse carbon than were required to fuse helium becuase

Carbon nuclei contain more protons and therefore peel each other more vigorously

In order to test Newton's model of gravity and Einstein's general relativity to see which one is more accurate, it is possible to

Carefully measure the orbit of mercury and the light from distant stars passing near the surface of our Sun

As a star ages and dies its position on an H-R diagram

Changes, moving off the main sequence

Newton considered gravity to be a force of attraction between objects, while Einstein

Considered gravity to be the consequence of curved spactime

Ultimately, a white dwarf will

Cool over billions of years and solidify into a cold, dark stellar corpse

Sampling bias refers to

Details regarding how data is collected that make some members of the population observed less likely to be included than others.

Which discovery method allows astronomers to estimate the mass of an exoplanet?

Doppler

The method of detecting exoplanets that relies on small periodic red shifts and blue shifts in the spectrum of a star's light is the

Doppler method

Elements heavier than iron (such as copper and zinc in your body) are created

During a supernova explosion

Which of the following are accurate statements?

Each second our sun fuses about 600 million tons of hydrogen into 596 million tons of helium, converting 4 million tons of mass into energy; our sun is a type G2 star; the mass of our Sun is defined to be one solar mass.

As the core of a massive star (at least 10 solar masses) collapses, gravity is so intense that

Electrons are forced into nuclei where they combine with protons to form neutrons and neutrinos

TRUE OR FALSE: Although indirect methods have discovered many exoplanets orbiting other stars, direct direction (imaging exoplanets through telescopes) has never been accomplished with current technology.

False

Main sequence stars

Fuse hydrogen into helium

Main sequence stars

Fuse hydrogen into helium in their cores

When hydrogen runs out in the core of a main sequence star

Fusion stops, gravity crushes the star, and it heats up

Stars form from

Giant molecular clouds

As compared to low-mass stars, massive stars

Go through all stages of evolution faster

For Earth to become a black hole it would have to be crushed to smaller than a

Grape

The force responsible for the collapse of molecular clouds and ultimately the formation of stars is

Gravity

Stars near the left of an H-R diagram

Have extremely high surface temperatures

Compared to our sun, red giant stars

Have much hotter cores but cooler surfaces

Why does helium fusion require higher temperatures than hydrogen fusion?

Helium nuclei each have two protons (instead of just one as in hydrogen nuclei) and so the electric repulsion between them is greater

Globular clusters are

Huge groups of hundreds of thousands (or even millions) of old stars

There is an upper limit to the range of masses a star might have because

If the mass of a protostar is too high then its radiated energy will be so intense that additional material cannot fall onto its surface.

There is a lower limit to the range of masses a star might have because

If the mass of a protostar is too low then its core temperature will never be hot enough to fuse into helium.

According to the best models of the very early universe

In the beginning there was only hydrogen, helium, and a tiny bit of lithium

Red giant stars are very bright but have a relatively cool surface temperature. On an H-R diagram they would be located

In the top right corner

The very first generation of stars

Initially contained only hydrogen and helium

When very massive stars run out of hydrogen the begin to fuse helium. When that runs out they begin to fuse carbon. The most massive stars can fuse heavier and heavier elements. The heaviest element that can be produced in the core of a star is

Iron because fusing iron does not release energy but requires the input of energy

The helium fusion stage of a star's life

Is much shorter than the main sequence stage

The heavy-element abundance of globular cluster stars

Is only a small fraction of the heavy-element abundance in our Sun

The triple alpha process

Is the process in which helium is fused into carbon in the cores of red giants

The analysis of transit data collected by space telescopes such as Kepler

Is usually done by computer but also by non-astronomer citizen scientists

As a main sequence star ages

Its composition changes, hydrogen is gradually depleted and helium accumulates, its luminosity and temperature change, and its position of the H-R diagram moves away from the zero-age main sequence.

When our Sun runs out of hydrogen

Its core temperature will get hot enough to fuse helium into carbon

When a star of about 10 solar masses dies and collapses

Its gravity is so strong electrons are forced into the nuclei where they combine with protons to form neutrons

When very massive stars run out of hydrogen the begin to fuse helium. When that runs out they begin to fuse carbon. The most massive stars can fuse heavier and heavier elements. Each successive round of fusion

Lasts less than the one before because as heavier nuclei fuse less energy is released and higher temperatures result in greater rate of fusion

Extremely low mass stars

Live extremely long lifetimes since their weaker gravity allows them to frugally fuse hydrogen very slowly

Extremely massive stars

Live relatively short lifetimes since they must fuse hydrogen very quickly to balance their crushing gravity

Which of the following are accurate statements?

Low mass stars are much more common than high mass stars

The conditions for star formation are

Low temperature and high density

Nearly 90 percent of stars observed are

Main sequence stars

The particular evolutionary track a forming star will follow on an H-R diagram is most influenced by the star's

Mass

The discovery of so many hot Jupiters indicates

Nothing about which planets are most common because hot Jupiters are the easiest planets to find using current technology

General relativity is

Our current and best understanding of gravity

Stars in the top right corner of an H-R diagram are called

Red giant stars

Open clusters are

Relatively small groups of younger stars that remain together as a cluster typically for a few hundred million years

Stars

Remain on the main sequence for most of their lives

Planetary nubulae are

Shells of ejected material blown off red giants as they collapse and die

As the clumps within a molecular cloud collapse, they will

Spin faster and faster

The presence of a type O star (a very hot and luminous star) in a stellar association would indicate

Star formation has occurred very recently, in the last million years or so

Which of the following are accurate?

Stars lose more mass in the red giant stage and white dwarfs can form from stars even if their main sequence mass is as much as 8 solar masses

An H-R diagram is a graph that plots a star's

Surface temperature on the x-axis and luminosity (or brightness) on the y-axis

__________ has/have been responsible for the discovery of most exoplanets.

The Kepler space telescope

One example of a molecular cloud is

The Orion Nebula

Newton would say that since the Earth orbits the Sun in a nearly circular orbit instead of moving in a straight line there just be a force on earth. If there was not then the Earth would move in a straight line. Einstein would say

The Sun warps or stretches spacetime so the Earth does not move in a straight line because there are no straight lines

A protostar is

The contracting dense core in the process of becoming a star before fusion has begun

When hydrogen runs out in the core of a star

The core begins to contract and heat up but its surface temperature cools

A stars habitable zone is

The distance from the star at which conditions are right for water to exist as a liquid

The basis for general relativity is the equivalence principle that states

The effects of gravity are indistinguishable from the effects of acceleration (free fall is indistinguishable from zero gravity)

When she'll burning begins around the core of a star

The energy produced by renewed hydrogen fusion expands the star, but as the outer layers expand they cool

The singularity is

The heart of a black hole; a place where spacetime ceases to exist and the laws of physics break down; the infinitely squozen point- a place of zero volume and infinite density- to which the star core collapses.

For a star, its time of death is considered to be

The moment all fusion stops

The data collected by the Kepler space telescope suggests

The most common types of planets in our solar system are super-Earths and mini-Neptunes

As gravity collapses clumps within a molecular cloud

The particle falling inward go faster and faster, resulting in an increase in temperature.

As gravity collapses clumps within a molecular cloud

The particles falling inward go faster and faster, increasing internal pressure

The event horizon is

The point of no return begin which nothing, not even light can escape; the boundary of a black hole; the distance from a black hole (singularity) at which the escape velocity equals that of light.

To specify such an event, such as lunch with a friend at the Sun Dial restaurant, would require three space dimensions and one time dimension such ss

The street address of the Westin Peachtree Plaza Hotel, the floor on which the Sun Dial is located, and the date/time you plan to meet

Which of these statements are correct?

The vast majority of stars in the Milky Way galaxy are low-mass stars; almost all stars start as a contracting protostar, spend most of their lives as a main sequence star, and then move toward the red giant region of the H-R diagram; stars with an initial mass of up to twice that of our sun (2solar masses) are considered low-mass stars.

Once the first stars form in a molecular cloud

Their radiation and stellar wind (and possibly their explosive deaths) compress the surrounding gas triggering the formation of the next generation of stars.

Astronomers have observed that

There are far more low-mass stars than high-mass stars

It is extremely difficult to detect planets around other stars because

They are lost in the glare of their much brighter parent stars.

Science fiction sometimes describes trips into regions of strong gravity, or extreme spacetime curvature, such as near a black hole. In the movie Interstellar every hour spent on Miller's planet equals 7 years earth time.

This is scientifically accurate, time would pass more slowly near a black hole than on Earth and a human would age accordingly

A region of star formation like the Orion molecular cloud can contain

Thousands of stars in a region only about a dozen light years accross

According to general relativity

Time will pass more slowly in the basement of a building than on the top floor

Which discovery method allows astronomers to estimate the size of an exoplanet?

Transit

Stars in the bottom left corner of an H-R diagram are called

White Dwarfs

Which of the following are accurate statements?

Without an understanding of general relativity, consumer technology such as GPS would not be accurate.

Which would have the larger radius (which would be physically bigger), a 0.8 solar mass white dwarf or a 1.2 solar mass white dwarf?

a 0.8 solar mass white dwarf

Stars produce energy through

nuclear fusion (joining smaller nuclei units larger ones)


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