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52 Cards in this Set

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Equilibrium of a star is maintained by:

The outward push of pressure and inward pull of gravity

Core hydrogen burning:

Fusion of hydrogen to helium

Helium core process:

Helium content increases fastest in the center as hydrogen is depleted. As hydrogen burns the location of burning moves upward, weakening the pressure. The temperature is driven up because of helium's greater positive charge, and hydrogen burns even faster. The star glows as a result of the hydrogen shell burning.

Red giant branch process:

As the core of helium shrinks and heats up, the overlying layers expand and cool, going from subgiant branch to red giant.

Helium fusion process:

When the temperature of the star reaches 10^8 K, helium fuses into carbon through the triple-alpha process.

Helium flash:

An explosion- like release of energy where temperature rises and helium burns furiously. The helium flash stabilizes the core and reduces overall energy output. It moves the star into the horizontal branch.

Carbon core process:

Eventually the nonburning carbon core shrinks which causes helium and hydrogen burning layers to burn faster. The star is now a red supergiant.

Planetary Nebulae:

As the radius of a star fluctuates, the outer envelope is eventually ejected. Cool and thin matter roughly the size of our solar system is a planetary nebula.It eventually diffuses into the atmosphere.

White dwarfs:

The carbon core at the center of the planetary nebula continues to evolve. The core is small and has a white hot surface. White dwarfs will eventually die and become an ember called a black dwarf.

Evolution of high mass stars:

High mass stars evolve faster because of their higher temperature and energy output. They do not have helium flashes and can burn past carbon and heavy elements. They die explosively.

Stellar evolution in star clusters:

As time moves forward, a cluster's stars can be seen evolving from higher to lower masses first. By comparing a cluster's turnoff mass with predictions, astronomers can measure the age of a cluster.

Evolution in a Binary Star System:

The zone in which matter belongs to a star in a binary system is called a Roche lobe. The larger a star, the larger the area of the lobe. As a star in a binary evolves, it may overflow its own lobe forming a mass transfer binary. If both stars overflow they form a contact binary.

Nova:

A white dwarf undergoing an explosion (rapid increase in luminosity). It occurs when a white dwarf builds up with stolen gas. It becomes hotter and denser until the hydrogen ignites. Materials leaving the nova form an accretion disk.

Death of a high mass star:

A highly evolved high mass star will use the mass of each burning stage as fuel for the next. Each cycle sustains the star for less time.

Type 1 Supernova (Core Collapse):

Iron cannot be fused or split for energy. The iron core of a star eventually grows in mass and collapses, sending a violent shockwave through the star.

Type 2 Supernova (Carbon detonation):

When an accreting white dwarf exceeds 1.4 solar masses, the pressure of the degenerate electrons cannot withstand gravity and the star begins to collapse. Carbon fusion occurs everywhere making it explode.

Supernova remnants:

An example could be the crab nebula, which carries the appearance of exploded interstellar debris.

Stellar nucleosynthesis:

Elements beside hydrogen and helium (primordial) are formed from nuclear fusion in the hearts of stars

Helium capture:

The process by which elements beyond carbon tend to form

Neutron capture:

The process by which elements beyond iron tend to form

Neutron star:

The remaining core of a supernova. Formed when electrons in the core violently strike with protons, forming neutrons. Neutrons leave the scene at the speed of light. Neutrons tars are small, solid, and dense.

Pulsars:

Objects that appear to emit regular bursts of electromagnetic energy

X ray bursters:

Emit much of their energy in violent eruptions in a few seconds (more luminous than the Sun) An x-ray burst is more violent than a nova because of a neutron star's stronger gravity.

Gamma ray bursts:

Bright irregular flashes of gamma rays lasting a few seconds. They are very distant and energetic, 100x brighter than a supernova. May be caused by collapse of neutron star binaries.

Black hole:

A stage in stellar evolution in which a massive core remnant collapses in on itself and vanishes.

Variable star:

Stars that have their luminosity change with time. Luminosity of Cepheids can be determined with period-luminosity relation

Galactic disk:

White, flat spinning, contains young & old stars, gas&dust, star birth, and spiral arms

Galactic halo:

Red, spherical, random motion, old stars, no gas&dust

Galactic bulge:

White yellow, elongated football shape, similar to disk but more random motion and dust

Formation of Milky way:

Stars and clusters originally had moved freely in space, slow rotation eventually flattened them out in a disk. The halo's stars have burned out leaving red stars that give the halo its red/pink glow. The chaotic orbit of stars can be explained by the slow rotation, as they could have chosen more pathways in the past.

Spiral arms:

Pinwheel like structures originating close to the bulge and extending through the disk. They are coiled waves of compressed gas that move through clouds of interstellar gas and triggering star formation.

Dark mass/dark halo:

Luminous regions of the galaxy are surrounded by a dark halo, implying that most matter exists as invisible dark matter (90%). Brown dwarfs and red dwarfs could make up dark matter.

Galactic center:

Billions of densely packed stars with a 400 pc accretion disk. Orbital speed of 100 km/s.

Cosmic rays:

Energetic particles that collide with the Earth. They are composed of hydrogen, helium, and an abundance of other elements.

Spiral galaxy:

Flattened disks, central bulge, spiral arms. Halos contain old stars, disks contain lots of gas.

Barred Spiral:

Contains an extended bar of material projecting beyond central bulge.

Elliptical:

No disk and no gas/dust. Consists mostly of old stars. Ranges in size from dwarf to giant.

S0 and SB0:

Contains halos, disks, and bulges, but has no gas/dust.

Irregular:

Does not fit any category of galaxy.

Standard candles:

Objects used to measure distance because of their recognizable light curves, spectra, etc. A type 1 supernova is an example

Tully-Fisher relation

A spectral line that gets smeared out by the galaxy's rotation. By measuring the amount of broadening, the rotation speed can be determined and thus the luminosity.

Local Group:

Few spiral galaxies (MW, M31-Andromeda, M33), D of about 1 Mpc

Cluster of Cluster:

Local group plus other nearby clusters, D about 30 Mpc

Super Cluster:

2200 galaxies, D about 150 Mpc

Formation of galaxies:

Galaxies grow by repeated merging of smaller objects. Spiral galaxies are rare compared to elliptical, so it can be theorized that spirals collided with each other to form elliptical today.

Hubble's Law/Constant:

The rate at which a galaxy recedes is directly proportional to its distance from us (cosmological redshift). Recessional Velocity = Hubble's constant * Distance

Active galaxies:

Luminous, active, and energetic galaxies

Seyfert galaxies:

An active galaxy characterized by its radiation stemming from a galactic nucleus, emitting energy in visible and invisible spectra, and spectral lines bearing little to no resemblance to ordinary stars

Radio galaxies:

Emit most of their energy in the radio portion of the electromagnetic spectrum

Energy production:

The combination of huge centra magnetic fields and accretion disks of ionized material resulting in synchrotron radiation.

Quasars:

Star like radio sources with broad spectral lines. They are extremely distant and the most luminous objects ever known. They are like active galaxies, possibly representing a violent phase.

Evolutionary sequence:

If enough gases were present, quasars could form from black holes, then it would dim to an active galaxy, and dim even further to a normal galaxy.