Astronomy Exam 3

Front 1

gravitational equilibrium

Back 1

a state of balance in which the force of gravity pulling inward is precisely counteracted by the pressure pushing outward

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energy balance

Back 2

the balance between the rate at which fusion releases energy in the star's core and the rate at which the star's surface radiates this energy into space

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sunspots

Back 3

blotches on the surface of the Sun that appear darker than surrounding regions

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luminosity

Back 4

the total power output of an object, usually measured in watts or in units of solar luminosities

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solar wind

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a stream of charged particles ejected from the sun

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chromosphere

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the layer of the Sun's atmosphere below the corona; most of the Sun's ultra-violet light is emitted from this region, in which the temp. is about 10,000 K

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photosphere

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the visible surface of the Sun, where the temperature averages just under 6,000 K

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convection zone

Back 8

a region in which energy is transported outward by convection

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radiation zone

Back 9

a region of the interior in which energy is transported primarily by radiative diffusion

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core

Back 10

the central region of a star, in which nuclear fusion can occur

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nuclear fission

Back 11

the process in which a larger nucleus splits into two or more smaller particles

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nuclear fusion

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the process in which two or more smaller nuclei slam together and make one larger nucleus

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strong force

Back 13

one of the four fundamental forces; it is the force that holds atomic nuclei together

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proton-proton chain

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the chain of reactions by which low-mass stars fuse hydrogen into helium

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corona

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the tenuous uppermost layer of the Sun's atmosphere; most of the Sun's X rays are emitted from this region, in which the temperature is about 1 million K

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radiative diffusion

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the process by which photons gradually migrate from a hot region (such as the solar core) to a cooler region (such as the solar surface)

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solar activity

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short-lived phenomena on the Sun, including the emergence and disappearance of individual sunspots, prominences, and flares

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magnetic field lines

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lines that represent how the needles on a series of compasses would point if they were laid out in a magnetic field

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solar prominences

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vaulted loops of hot gas that rise above the Sun's surface and follow magnetic field lines

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solar flares

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huge and sudden releases of energy on the solar surface, probably caused when energy stored in magnetic fields is suddenly released

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coronal holes

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regions of the corona that barely show up in x ray images because they are nearly devoid of hot coronal gas

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coronal mass ejections

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bursts of charged particles from the Sun's corona that travel outward into space

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sunspot cycle

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the period of about 11 years over which the number of sunspots on the Sun rises and falls

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apparent brightness

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the amount of light reaching us per unit area from a luminous object

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luminosity

Back 25

the total power output of an object, usually measured in watts or in units of solar luminosities

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inverse square law for light

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the law stating that an object's apparent brightness depends on its actual luminosity and the inverse square of its distance from the observer

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total luminosity

Back 27

- see luminosity - makes clear we are talking about light across all wavelengths, not just visible light

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total apparent brightness

Back 28

- see apparent brightness - makes clear we are talking about light across all wavelengths, not just visible light

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parsec

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the distance to an object with a parallax angle of 1 arcsecond; approx. 3.26 light years

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magnitude system

Back 30

a system for describing stellar brightness by using numbers, called magnitudes, based on an ancient Greek way of describing the brightness of stars in the sky

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apparent magnitude

Back 31

a measure of the apparent brightness of an object in the sky, based on the ancient system developed by Hipparchus

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absolute magnitude

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a measure of an object's luminosity; defined to be the apparent magnitude the object would have if it were located exactly 10 parsecs away

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spectral type

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a way of classifying a star by the lines that appear in its spectrum; related to surface temperature, designated by letter and then number

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binary star systems

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a star system that contains two stars

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visual binary

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a binary star system in which both stars can be resolved through a telescope

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spectroscopic binary

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a binary star system whose binary nature is revealed because we detect the spectral lines of one or both stars alternately becoming blue shifted and redshifted as the stars orbit each other

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eclipsing binary

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a binary star system in which the two stars happen to be orbiting in the plane of our line of sight, so that each star will periodically eclipse the other

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Hertzsprung-Russell Diagram

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a graph plotting individual stars as points, with stellar luminosity on the vertical axis and spectral type on the horizontal axis

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main sequence

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the prominent line of points running from the upper left to lower right on an HR diagram

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super giant

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the very large and very bright stars that appear at the top of an HR diagram

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white dwarfs

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the hot, compact corpses of low-mass stars, typically with a mass similar to that of the Sun compressed to a volume the size of Earth

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luminosity class

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a category describing the region of the HR diagram in which a star falls

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main-sequence lifetime

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the length of time for which a star of a particular mass can shine by fusing hydrogen into helium in its core

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pulsating variable star

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stars that grow alternately brighter and dimmer as their outer layers expand and contrract in size

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open cluster

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a cluster of up to several thousand stars; found only in disks of galaxies and often contain younger stars

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globular cluster

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a spherically shaped cluster of up to a million or more stars; globular clusters are found in halos of galaxies and have old strs

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main-sequence turnoff point

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the point on a cluster's HR diagram where its stars turnoff from the main sequence; age of cluster is equal to main sequence lifetime

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interstellar medium

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the gas and dust that fills the space between stars in a galaxy

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molecular clouds

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cool, dense interstellar clouds in which the low temps. allow hydrogen atoms to pair up into hydrogen molecules

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interstellar dust

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tiny solid flecks of carbon and silicon minerals found in cool interstellar clouds

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interstellar reddening

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the change in color of starlight as it passes through dusty gas

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thermal pressure

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

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protostellar disk

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a disk of material surrounding a protostar; essentially the same as a proto-planetary disk, but may not lead to planet formation

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protostellar wind

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the relatively strong wind from a protostar

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jets

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high-speed streams of gas ejected from an object into space

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close binary

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a binary star system in which the two stars are very close together

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life track

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a track drawn on an HR diagram to represent the changes in a star's surface temp. and luminosity during its life; also called an evolutionary track

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degeneracy pressure

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a type of pressure unrelated to an objects temp., which arises when electrons or neutrons are packed so tightly that eh exclusion and uncertainty principles come into play

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brown dwarf

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an object too small to become an ordinary star because electron degeneracy pressure halts its gravitational collapse before fusion becomes self sustaining

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radiation pressure

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pressure exerted by photons of light

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low-mass stars

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stars born with masses less than about 2Msun, end lives in white dwarf

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intermediate mass stars

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stars born with masses in between 2M and 8M sun, end with a white dwarf

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high-mass stars

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stars born with masses above 8M sun and end lives in supernovae

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flare stars

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a small, spectral type M star that displays particularly strong flares on its surface

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red giant

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a giant star that is red in color

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hydrogen shell fusion

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hydrogen fusion that occurs in a shell surrounding a stellar core

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helium fusion

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the fusion of three helium nuclei into one carbon nucleus (triple alpa reaction)

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helium flash

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the event that marks the sudden onset of helium fusion in the previously inert helium core of a low-mass star

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horizontal branch

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the horizontal line of stars that represents helium-fusing stars on an HR diagram for a cluster

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thermal pulses

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the predicted upward spikes in the rate of helium fusion, occurring every few thousand years, that occur near the end of a low-mass stars life

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carbon stars

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stars whose atmospheres are especially carbon-rich, thought to be near the ends of their lives: primary sources of carbon in universe

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planetary nebula

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the glowing cloud of gas ejected form a low-mass star at the end of its life

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CNO cycle

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the cycle of reactions by which intermediate and high-mass stars fuse hydrogen into helium

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helium-capture reactions

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fusion reactions that fuse a helium nucleus into some other nucleus (makes heavier nuclei)

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supernova

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the explosion of a star

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neutron star

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the compact corpse of a high-mass star left over after a supernova; typically contain mass comparable to that of the sun

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supernova remnant

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a glowing, expanding cloud of debris from a supernova explosion

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Supernova 1987A

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a supernova witnessed on Earth in 1987; nearest supernova seen in nearly 400 years

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mass exchange

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the process in which tidal forces cause matter to spill from one star to a companion star in a close binary system

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white dwarf limit

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Chandrasekhar limit - the maximum possible mass for a white dwarf, which is approximately 1.4M sun

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accretion disk

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a rapidly rotating disk of material that gradually falls inward as it orbits a starlike object

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electron degeneracy pressure

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degeneracy pressure exerted by electrons, as in brown dwarfs and white dwarfs

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nova

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the dramatic brightening of a star that lasts for a few weeks and then subsides; it occurs when a burst of hydrogen fusion ignites in a shell on the surface of an accreting white dwarf in a binary star system

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white dwarf supernova

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a supernova that occurs when an accreting white dwarf reaches the white-dwarf limit, ignites runaway carbon fusion, and explodes like a bomb, often called a Type 1a supernova

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massive star supernova

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a supernova that occurs when a massive star dies, initiated by the catastrophic collapse of its iron core; often called a Type II Supernova

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neutron star

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the compact corpse of a high-mass star left over after a supernova; it typically contains a mass comparable to the mass of the Sun in a volume just a few kilometers radius

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neutron degeneracy pressure

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degeneracy pressure exerted by neutrons, as in neutron stars

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pulsar

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a neutron star from which we see rapid pulses of radiation as it rotates

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x-ray binaries

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a binary star system that emits substantial amounts of X-rays, thought to be form an accretion disk around a neutron star or black hole

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x-ray bursts

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bursts of x-rays (duh) coming form sudden ignition of fusion on the surface of an accreting neutron star in an x-ray binary system

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x-ray bursters

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an object that emits a burst of x rays every few hours to every few days; each burst lasts a few seconds and is thought to be caused by helium fusion on the surface of an accreting neutron star in a binary system

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event horizon

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the boundary that marks the "point of no return" between a black hole and the outside universe; events that occur within the event horizon can have no influence on our observable universe

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spacetime

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the inseparable, four-dimensional combination of space and time

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Schwarzschild Radius

Back 94

a measure of the size of the event horizon of a black hole

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singularity

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the place at the center of a black hole where, in principle, gravity crushes all matter to an infinitely tiny and dense point