CSU AA 100 Exam 3

Brown Dwarf

"Failed" star; Star not massive enough to sustain nuclear fusion. a celestial object intermediate in size between a giant planet and a small star, believed to emit mainly infrared radiation.

Double Shell Fusion

-After core helium fusion stops, He fuses into carbon in a shell around the carbon core, and H fuses to He in a shell around the helium layer -This double shell-- fusion stage never reaches equilibrium--the fusion rate periodically spikes upward in a series of thermal pulses -With each spike, convection dredges carbon up from the core and transports it to the surface A star that is fusing helium into carbon in a shell around an inert carbon core and is fusing hydrogen into helium in a shell at the top of the helium layer.

What two pieces of information must an astronomer know in order to measure a star's radius if it just looks like a dot of light on the sky?

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luminosity class

A category describing the region of the H-R diagram in which a star falls. Luminosity class I represents supergiants, III represents giants, and V represents main-sequence stars; luminosity classes II and IV are intermediate to the others.

Protostar

A contracting cloud of gas and dust; the earliest stage of a star's life

Sunspots

A dark area of gas on the sun's surface that is cooler than surrounding gases.

CNO cycle

A fusion process in which a carbon atom transmutes to oxygen and back, creating a helium atom in the process the cycle of reactions by which intermediate and high mass stars fuse hydrogen into helium

Chromosphere

A gaseous layer of the sun's atmosphere (extending from the photosphere to the corona) that is visible during a total eclipse of the sun

Molecular Cloud

A large, cold cloud made up mostly of molecular hydrogen and helium, but with some other gases, such as carbon monoxide. It is in these clouds that new stars are born.

Fission

A nuclear reaction in which a massive nucleus splits into smaller nuclei with the simultaneous release of energy

singularity

A point in which matter is infinitely dense, as in the center of a black hole or the universe at the very beginning.

radiation zone

A region of very tightly packed gas in the sun's interior where energy is transferred mainly in the form of light.

Triple Alpha Process

A sequence of two thermonuclear reactions in which three helium nuclei combine to form one carbon nucleus.

red giant

A star that expands and cools once it runs out of hydrogen fuel a very large star of high luminosity and low surface temperature. Red giants are thought to be in a late stage of evolution when no hydrogen remains in the core to fuel nuclear fusion.

Radius

A straight line from the center to the circumference of a circle or sphere.

Which stars have the strongest hydrogen lines?

A type temp?

spectral type

A way of classifying a star by the lines that appear in its spectrum; it is related to surface temperature. The basic spectral types are designated by a letter (OBAFGKM), with O for the hottest stars and M for the coolest, and are subdivided with numbers from 0 through 9.

Black Dwarf

A white dwarf that has burnt out completely.

black hole

An object in space whose gravity is so strong not even light can escape. a region of space having a gravitational field so intense that no matter or radiation can escape.

What two pieces of information must an astronomer know in order to measure a star's luminosity?

Apparent brightness and distance.

yellow giant

Burns helium in core, middle of HR diagram

How do astronomers determine a star's luminosity class, and why isn't the spectral type (OBAFGKM) a sufficient classification?

By studying details of the spectrum for each star, astronomers can determine which luminosity class they fall in (whether they are main-sequence stars, giant stars, or supergiant stars). With both its spectral and luminosity classes known, a star's position on the H-R diagram is uniquely determined.

How does the CNO cycle produce helium and why does it require higher temperatures than the proton-proton chain?

CNO cycle requires a much higher temperature than the proton-proton chain, to overcome the stronger Coulomb barrier. Main Sequence fuse hydrogen into helium

strong force

Causes protons and neutrons to be attracted to each other attractive force that acts between protons and neutrons in an atomic nucleus

core

Center of the earth

Why can't photons produced during fusion immediately escape the Sun?

Collisions. In the core of the sun the protons and helium nuclei are so thick that an emitted gamma ray can't get very far before it is absorbed

Hipparchus of Nicaea

Constructed an ingenious and complicated geocentric model of the universe that did a good job of accounting for the movements of the sun, the moon, and the planets - trig

Fusion

Creation of energy by joining the nuclei of two hydrogen atoms to form helium.

Stefan-Boltzmann Law

Each square meter of a hotter object's surface emits more light at all wavelengths The relationship stating that an object emits energy at a rate proportional to the fourth power of its temperature, in Kelvins.

blue supergiant

Extremely hot and large stars; Rigel is the best known example. Found in the upper left corner of the H-R diagram. They have a short and violent existence. the very largest of the large, hot, bright stars at the uppermost-left end of the main sequence on the H-R diagram

neutron star/pulsar

Fifth and final stage for stars less than 4 times the mass of the Sun. Remnants of super squeezed materials from the supernova explosion. The particles in the core become neutrons. If the neutrons are spinning a pulse of radiation is emitted and it is called a pulsar. the end stage of a high mass star life cycle . It is a star that emits light and a beam of very high energy radio waves

Granules

Hot cells of gas that rise and fall in the photosphere.

What determines whether a core collapse supernova produces a neutron star or a black hole?

If it is less than about three solar masses it remains as a neutron star. If the neutron star is more than about three solar masses then the pressure exceeds the neutron degeneracy pressure. This causes the neutron star to collapse into a black hole.

Coronal Loops

Magnetic loops with very strong magnetic fields. They often contain the dense, hot gas that emits intense x-ray radiation.

Subrahmanyan Chandrasekhar

Major Discovery: Found that stars that were bigger than about 1.4 times the mass of our sun would ultimately collapse, smaller masses would not; critical mass is called Chandrasekhar limit. How it was discovered: Used Einstein's special theory of relativity to stars. Impacts: People now know when a star explodes an why it happens.

Solar Activity Cycle

Minimum to maximum sunspots, a reversal of polarity, and minimum to maximum sunspots over a period of 22.4 years.

VOCAB LIST ENDS HERE

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red supergiants

Supergiant stars of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive.

asymptotic giant branch

The asymptotic giant branch (AGB) is a region of the Hertzsprung-Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (0.6-10 solar masses) late in their lives.

radiation pressure

The force exerted by electromagnetic radiation from an object such as the Sun.

Photosphere

The inner layer of the sun's visible atmosphere

gravitational redshift

The lengthening of the wavelength of a photon due to its escape from a gravitational field. an increase in wavelength of an electromagnetic wave (light) when propagating from or near a massive object

Why aren't there any stars smaller than 0.08 solar masses?

The lower mass limit on stars seems to be about 0.08 solar masses. Below this mass limit, internal temperatures and pressures are too low to sustain thermonuclear conversion of hydrogen to helium.

What causes sunspots? Why are they always associated with solar flares or other prominences?

The magnetic field of the Sun stops hot bubbles of gas from rising, causing the region to cool off. Solar flares are a sudden explosion of energy caused by tangling, crossing or reorganizing of magnetic field lines near sunspots.

Corona

The outer layer of the sun's atmosphere.

main-sequence turnoff

The point on a cluster's H-R diagram where its stars turn off from the main sequence; the age of the cluster is equal to the main-sequence lifetime of stars at the main-sequence turnoff point.

Solar Luminosity

The total energy emitted by the Sun each second in all directions

What triggers the initial implosion of a core collapse supernova, and what triggers its explosion?

There the burnt out stellar iron core collapses due to electron captures and photo-disintegration of heavy nuclei to a neutron star or black hole thereby liberating the energy which causes the supernova explosion

main sequence

a diagonal area on an H-R diagram that includes more than 90 percent of all stars

subgiant

a giant star smaller and lower in luminosity than normal giant stars of the same spectral type; evolve to become giants A star that is between being a main-sequence star and being a giant; subgiants have inert helium cores and hydrogen-fusing shells.

Hertzsprung-Russell diagram

a graph relating the surface temperatures and absolute brightness of stars

giant star

a large star with great luminosity and a diameter 10 to 100 times greater than that of the sun

main sequence fitting

a method for measuring the distance to a cluster of stars by comparing the apparent brightness of the cluster's main sequence with that of the standard main sequence

Helium Flash

a nearly explosive ignition of helium in the triple-alpha process in the dense core of a red giant star the event that marks the sudden onset of helium fusion in the previously inert helium core of a low-mass star

planetary nebula

a ring-shaped nebula formed by an expanding shell of gas around an aging star. a nebula that was once thought to be a star with its planets but is now thought to be a very hot star surrounded by an expanding envelope of ionized gases that emit a fluorescent glow because of intense radiation from the star

open cluster

a star cluster that has a loose, disorganized appearance and contains no more than a few thousand stars

Nova

a star showing a sudden large increase in brightness and then slowly returning to its original state over a few months.

binary star

a star system with two stars

flux

a state of continual change or movement

white dwarf supernova

a supernova that occurs when an accreting white dwarf reaches the white dwarf limit, ignites runaway carbon fusion, and explodes like a bomb Carbon fusion suddenly begins as a white dwarf in close binary system reaches white dwarf limit, causing total explosion.

globular cluster

a tight group of stars that looks like a ball and contains up to 1 million stars a large compact spherical star cluster, typically of old stars in the outer regions of a galaxy.

Degeneracy Pressure

a type of pressure unrelated to an object's temperature, which arises when electrons or neutrons are packed so tightly that the exclusion and uncertainty principles come into play

Standard Candle

an object for which we have some means of knowing its true luminosity, so that we can use its apparent brightness to determine its distance with the luminosity-distance formula

How do astronomers measure stellar masses?

by analysis of the orbit of binary stars

Dust extinction

causes stars to appear redder and dimmer than they actually are.

Solar flares

clouds of charged particles that are ejected from the Sun. create strong magnetic field, can destroy electronic circuits in satellites if get close enough to Earth Produces surges of magnetism in large metal loops (electricity distribution networks e.g. national grid) which can cause pulses of current that can burn out transformers cutting of power supply.

Jocelyn Bell Burnell

discovered first radio pulsars

Cecilia Payne-Gaposchkin

discovered the relative amounts of each element in the sun + discovered helium in sun

Annie Jump Cannon

early twentieth century astronomer who catalouged the spectra of over 225,000 stars. Her most significant contribution to society was carefully categorized spectra of light emmitted from stars, allowing others who followed to build off her work

Geomagnetic Storms

electromagnetic storms influenced by solar wind that can affect our electrical systems

Why aren't there any stars larger than 300 solar masses?

hard to find enough material to sustain

Horizontal Giant Branch

helium fusion in the core and hydrogen fusion in a shell

How do astronomers determine the age of a star cluster?

looking at the main sequence turnoff point and comparing it with models of stellar evolution.

Coronal Mass Ejections

send bursts of energetic charged particles out through the solar system bursts of charged particles from the Sun's corona that travel outward into space

How do astronomers determine the distance to a star cluster?

stellar parallax, or trigonometric parallax. Simply put, they measure a star's apparent movement against the background of more distant stars as Earth revolves around the sun.

Why does the solar activity cycle peak every 11 years?

the Sun's magnetic field completely flips. This means that the Sun's north and south poles switch places. Then it takes about another 11 years for the Sun's north and south poles to flip back again

Mass

the amount of matter in an object

electric force

the attraction or repulsion between electric charges

white dwarf (on list twice)

the blue-white hot core of a star that is left behind after its outer layers have expanded and drifted out into space Stage in which a star has used up its helium and its outer layers escape into space, leaving behind a hot, dense core that contracts

Why is the magnitude scale backwards

the brighter a star is, the smaller its magnitude

apparent magnitude

the brightness of a star as seen from Earth

proton-proton chain

the chain of fusion reactions, leading from hydrogen to helium, that powers main-sequence stars

How does the proton-proton chain produce helium?

the chain of reactions by which low-mass stars (including the Sun) fuse hydrogen into helium

Why can't white dwarfs be larger than 1.4 solar masses?

the degeneracy pressure is not adequate to hold up the star, and the star collapses

Schwarzschild radius

the distance from the center to the event horizon in any black hole

Event Horizon

the location around a black hole where the escape velovity equals the speed of light; the boundary of a black hole

Chandrasekhar limit

the maximum mass of a white dwarf above which it collapses. Approximately 1.4 solar masses.

thermal pressure

the ordinary pressure in a gas arising from motions of particles that can be attributed to the object's temperature

Random Walk

the path of a variable whose changes are impossible to predict

center of mass

the point in an object that moves as if all the object's mass were concentrated at that point

Spaghettification

the process by which an object would be stretched and ripped apart by gravitational forces on falling into a black hole

Metallicity

the proportion of the material of a star or other celestial object that is in elements other than hydrogen or helium

Differential Rotation

the rotation of a body in which different parts of the body have different periods of rotation

Luminosity

the true brightness of an object

Why does fusion require such high temperatures?

to give hydrogen atoms enough energy to overcome repulsion between the protons

red giant branch

vertically above the sub-giant branch of the HR diagram. The section of the evolutionary track of a star corresponding to intense hydrogen shell burning, which drives a steady expansion and cooling of the outer envelope of the star. As the star gets larger in radius and its surface temperature cools, it becomes a red giant. a region on the H-R diagram defined by low-mass stars evolving from the main sequence toward the horizontal branch

core-collapse supernova

when the core becomes so dense that the neutrons are effectively brought into physical contact with one another, their resistance to further squeezing stops the collapse and the core rebounds, sending a violent shock wave out through the rest of the star. The star explodes in a

Convection Zone

where hot gas moves up toward the surface and cooler gas moves deeper into the interior