Comprehensive Blackbody Radiation, Stellar Spectra, and Star Properties

What is an astronomical Planck blackbody?

An object that absorbs all light that falls on it and re-emits it in a characteristic spectrum.

What does the shape of the blackbody spectrum look like?

It is asymmetric about the peak intensity, with the blue side falling off steeply and the red side more slowly.

What is the peak wavelength (λpeak) in blackbody radiation?

The wavelength at which the highest intensity of light is emitted, corresponding to the surface temperature of the blackbody.

What types of objects emit continuous Planck blackbody radiation?

Dense objects such as solids, liquids, and cores of stars.

What is Wien's Law?

It describes the relationship between the surface temperature of an object and the peak wavelength at which it emits the highest intensity.

What is the formula for Wien's Law in meters?

λpeak = 2.90×10−3 [m K] / T

What does the Stefan-Boltzmann Law describe?

It describes the total energy emitted per unit area of a blackbody as a function of its temperature.

What is the formula for the Stefan-Boltzmann Law?

F = σT^4, where F is the flux, σ is the Stefan-Boltzmann constant, and T is the surface temperature.

How does distance affect the brightness of an object?

Brightness is proportional to the inverse square of the distance.

What causes a Doppler shift?

Motion toward or away from an observer causes a shift in the wavelength of light.

What is blueshift?

A phenomenon where light emitted from an object moving toward an observer has a shorter (bluer) wavelength.

What is redshift?

A phenomenon where light emitted from an object moving away from an observer has a longer (redder) wavelength.

What is the difference between luminosity and brightness?

Luminosity is the actual amount of light emitted by a star, while brightness is the amount of light observed from Earth.

What is the formula relating brightness, luminosity, and distance?

B ∝ L / d^2

What is apparent magnitude?

The brightness that an observer measures on Earth, which depends on distance.

What is absolute magnitude?

A star's actual amount of light emitted, measured at a standard distance of 10 parsecs.

What does the magnitude scale represent?

A logarithmic scale for comparing and ranking the brightness of stars.

How does the brightness of a star change with distance?

The brightness decreases as the square of the star's distance from the observer increases.

What is the significance of spectral fingerprints?

They help identify elements in stars by showing unique patterns of emission and absorption lines.

What is the role of electrons in atoms regarding light?

Electrons can absorb or emit photons, leading to unique emission or absorption spectra.

What is a continuum spectrum?

A spectrum that appears as a solid rainbow, emitted by solids or liquids.

What type of spectrum do stars primarily emit?

Absorption spectra, also known as dark line spectra.

What determines the color of an object according to Wien's Law?

The peak wavelength of emitted light, where hotter objects appear bluer and cooler objects appear redder.

What is the relationship between surface temperature and emitted energy?

Hotter objects emit more energy at every wavelength than cooler objects.

What is the formula for the luminosity of a star?

Lstar = 4πR^2 σT^4

What does the symbol '∝' mean in the context of brightness and luminosity?

It means 'proportional to'.

What is the effect of temperature on the color of emitted light?

An object that is hotter is bluer, while a cooler object is redder.

How can we determine the distance to a star?

By knowing the brightness and luminosity of the star.

What is the photosphere of a star?

The surface layer from which light is emitted.

What happens when a photon is absorbed by an electron in a star?

The photon is removed from the continuum of light, creating absorption lines.

What does Wien's Law state about the color of a star?

The color of a star is inversely proportional to its surface temperature.

What color are hotter stars?

Hotter stars are bluer.

What color are cooler stars?

Cooler stars are redder.

What spectral type has weak hydrogen absorption lines?

Spectral Type O.

Which spectral type has strong hydrogen absorption lines?

Spectral Type A.

What is the mnemonic to remember the order of spectral types?

Oh Be A Fine Gal/Guy, Kiss Me!

What defines a brown dwarf?

A brown dwarf has a mass less than 0.08 solar masses and cannot sustain hydrogen fusion.

What is the Doppler Effect in relation to stars?

It describes how the motion of a star affects the observed wavelength of light, causing blueshift or redshift.

What is proper motion in astronomy?

The motion of a star relative to distant background stars.

How can the mass of binary stars be determined?

By observing their orbital motion and applying Kepler's third law.

What do the regions of the H-R diagram represent?

They represent different stages of stellar evolution, including main sequence, white dwarfs, and red giants.

What is the relationship between star size and spectral absorption lines?

Wider lines indicate smaller radius stars with higher pressure; narrower lines indicate larger radius stars with lower pressure.

What is the significance of luminosity in stars?

Luminosity is the intrinsic amount of light emitted by a star, measured at a standard distance.

How is distance to a star measured?

Using parallax, which observes the apparent shift of a star against background stars over time.

What are the characteristics of red dwarf stars?

They are small, cool, and the most common type of star in the universe.

What is the lifespan of red dwarf stars compared to blue giants?

Red dwarfs have the longest lifespans, while blue giants have the shortest.

What is the effect of a star's motion towards an observer?

It causes a blueshift in the dark lines of the star's spectrum.

What happens to the light from a star in an eclipsing binary system?

The total light decreases when one star passes in front of the other.

What is space velocity?

The true velocity and direction of an object in space.

What is the significance of the H-R diagram?

It is key to understanding stellar evolution and the relationship between temperature and luminosity.

What spectral types are associated with the hottest and coolest stars?

Spectral Type O for hottest (blue) and Spectral Type M for coolest (red).

What are the new spectral types for very cool brown dwarfs?

Spectral types L, T, and Y.

How does the rotation of stars affect their absorption lines?

It causes the absorption lines to broaden due to Doppler shifts.

How does mass vary on the HR diagram?

Mass increases from the lower right corner (low luminosity, low temperature) to the upper left corner (high luminosity, high temperature).

What type of stars are found in the lower right corner of the HR diagram?

Red dwarfs.

What type of stars are found in the upper left corner of the HR diagram?

Blue giants.

Where is the largest radius found on the HR diagram?

In the upper right corner (high luminosity, low temperature) where red supergiants are located.

What is parallax in astronomy?

A geometric distance finding method that measures the apparent shift of nearby stars against background stars as Earth orbits the Sun.

What is the formula to find distance in parsecs using parallax?

d (parsec) = 1 / α, where α is the parallactic angle in arcseconds.

What is a parsec in terms of light-years?

1 parsec = 3.26 light-years.

What is the significance of variable stars like Cepheids?

They exhibit a period-luminosity relationship, allowing astronomers to determine distances to galaxies.

Who discovered the period-luminosity relationship for Cepheid stars?

Henrietta Swan Leavitt.

What did Hubble use Cepheid stars to determine?

That the Andromeda Nebula was a separate galaxy, expanding the understanding of the universe.

What is spectroscopic parallax?

A method using clusters of stars to find distances by comparing their brightness and temperatures on an HR diagram.

How do astronomers classify stars into luminosity classes?

By examining the width of spectral lines in the star's spectrum.

What characterizes dwarf stars in terms of spectral lines?

Dwarf stars have wider absorption lines due to higher surface pressures.

What is interstellar extinction?

The phenomenon where interstellar dust obscures light from stars behind it.

What effect does interstellar dust have on light?

It scatters blue light more efficiently than red light, making distant stars appear redder.

What is the typical size range of interstellar dust grains?

From 10−8 to 10−7 meters (1/100 to 1/10 of a micron).

What is the 21-centimeter line?

A radio emission line emitted by neutral hydrogen when an electron flips its spin.

What is the primary composition of interstellar dust?

A core of rocky material or graphite surrounded by a mantle of ices.

Where do stars typically form?

In star clusters from the same giant cloud of gas and dust.

How does the mass of a star affect its evolutionary track?

The mass determines the rate of evolution and future stages of the star.

What is the lifetime of a low-mass star compared to a high-mass star?

Low-mass stars have longer lifetimes, while high-mass stars burn fuel quickly and have shorter lifetimes.

What is the lifetime of our Sun as a main sequence star?

Approximately 10 billion years.

What type of stars are most common on the main sequence?

Red dwarfs.

What happens to high-mass stars at the end of their life cycle?

They evolve quickly and have very short lifetimes.

What leads to more efficient and faster nuclear fusion in high mass stars?

Higher temperature and pressure in the core.

What happens to hydrogen in the core of a star as fusion progresses?

Hydrogen is converted into helium.

What occurs when a main sequence star runs out of hydrogen in its core?

The star begins to die.

How does a main-sequence star's luminosity change over its lifetime?

It slowly increases as the core contracts and fusion becomes more efficient.

What is hydrostatic equilibrium in a star?

The balance between radiation pressure outward and gravitational pressure inward.

What happens when hydrogen fusion in the core stops?

The star becomes unstable.

What is the main-sequence turnoff on the H-R diagram?

The point where the highest mass star has started to evolve off the main sequence.

What does the location of the main-sequence turnoff indicate?

The age of the star cluster.

What is the fate of a low mass star like our Sun?

It will evolve through stages: main sequence, red giant, helium flash, AGB, planetary nebula, white dwarf, and eventually black dwarf.

What is the primary fusion process in low mass main-sequence stars?

Hydrogen is fused into helium via the proton-proton chain.

What occurs during the red giant phase of a star's evolution?

Hydrogen fusion occurs in a shell around a shrinking, electron-degenerate core.

What is a helium flash?

A sudden onset of helium fusion in a hot, dense core.

What happens during the asymptotic giant branch (AGB) phase?

Helium fusion occurs in an innermost shell while hydrogen fuses in an outer shell.

What is a planetary nebula?

Ejected outer layers of a star that create a glowing gas cloud.

What is the characteristic of a white dwarf?

It is hot but not luminous, emitting radiation as it cools down.

What is a black dwarf?

A theoretical stage of a white dwarf that has cooled and emits no detectable light.

What happens in low mass binary star systems during evolution?

The more massive star evolves first, becoming a red giant and then a white dwarf.

What can occur when the second star in a binary system becomes a red giant?

It can transfer material onto the white dwarf if they are close enough.

What happens to a red giant when it loses material?

It begins to lose material due to the gravitational pull of a white dwarf companion.

What is mass transfer in the context of binary stars?

Material flowing from a red giant to a white dwarf companion.

What is a nova?

A temporary brightening of a star that occurs when nuclear reactions on the surface of a white dwarf begin.

How much more luminous can a nova be compared to the Sun?

A nova can be half a million times more luminous than the Sun.

What is the Chandrasekhar limit?

The maximum mass for a white dwarf, which is 1.4 solar masses (M⊙).