Astronomy Test 4
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)
