Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
40 Cards in this Set
- Front
- Back
|
Core-Hydrogen-Burning |
The energy burning stage for main-sequence stars, in which the helium is produced by hydrogen fusion in the central region of the star. A typical star spends up to 90 percent of its lifetime in hydrostatic equilibrium brought about by the balance between gravity and the energy generated by the core hydrogen burning. |
|
|
Red-Giant Branch |
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 a star. As the star gets larger in radius and its surface temperature cools, it becomes a red-giant. |
|
|
Horizontal Branch |
Region of the Hertzsprung-Russel diagram where post-main-sequence stars, once again, reach hydrostatic equilibrium. At this point, the star is burning helium in its core and fusing hydrogen in a shell surrounding the core. |
|
|
Black Dwarf |
The end point of the evolution of an isolated, low mass star. After the white-dwarf stage, the star cools to the point where it is called a dark "clinker" in interstellar space. |
|
|
Nova |
A star that suddenly increases in brightness, often by a factor of as much as 10,000, then slowly fades back to its original luminosity. Is the result of an explosion on the surface of a white-dwarf star, caused by matter falling onto its surface from the atmosphere of a binary companion. |
|
|
Supernovae |
Explosive death of a star, caused by the sudden onset of nuclear burning (Type I) or an enormously energetic shock wave (Type II). One of the most energetic events of the universe, it might temporarily outshine the rest of the galaxy in which it resides. |
|
|
Carbon-Detonation Supernova |
Often referred to as A Type I Supernova, which is one possible death of a star in which a white dwarf in a binary system can accrete enough mass that it cannot support its own weight. The star collapses and temperatures become high enough for carbon fusion to occur. Fusion begins throughout the white dwarf almost simultaneously and an explosion results. |
|
|
Helium Capture |
The formation of heavy elements by the capture of a helium nucleus. For example, carbon can form heavier elements by fusion with other carbon nuclei, but it is much more likely to occur by this because it requires less energy. |
|
|
Remnant |
The object left behind after a supernova explosion. Can refer to either (1) the expanding and cooling shell of glowing gas resulting from the event, or (2) the neutron star or black hole that remains at the center of the explosion. |
|
|
Pulsar |
Object that emits radiation in the form of rapid pulses with a characteristic pulse period and duration. Charged particles, accelerated by the magnetic field of a rapidly rotating neutron star, flow among the magnetic field lines, producing radiation that beams outward as the star spins on its axis. |
|
|
Gamma-Ray Burtsts |
Objects that radiate tremendous amounts of energy in the form of gamma rays, possible due to the collision and merger of two neutron stars initially in orbit around one another. |
|
|
Black Hole |
A region of space where the pull of gravity is so great that nothing-not even light- can escape. A possible outcome of the evolution of a very massive star. |
|
|
Gravitational Redshift |
A prediction of Einstein's theory of relativity. Photons lose energy as they escape the gravitational field of a massive object. Because a photon's energy is proportional to its frequency, a photon that loses energy suffers a decrease in frequency, which corresponds to an increase, or redshift, in wavelength. |
|
|
Hydrogen-Shell-Burning |
Fusion of hydrogen in a shell that is driven by contraction and heating of the helium core. Once hydrogen is depleted in the core of a star, hydrogen burning stops and the core contracts due to gravity, causing the temperature to rise , heating the surrounding layers of hydrogen in the star, and increasing the burning rate there. |
|
|
Electron Degeneracy Pressure |
The pressure produced by the resistance of electrons to further compression once they are squeezed to the point of contact. |
|
|
Asymptotic-Giant Branch |
Path on the Hertzsprung-Russell diagram corresponding to the changes that a star undergoes after helium burning ceases in the core. At this stage, the carbon core shrinks and drives the expansion of the envelope, and the star becomes a swollen red giant for a second time. |
|
|
Main-Sequence Turnoff |
Special point on the Hertzsprung-Russell diagram for a cluster, indicative of the cluster's age. If all the stars are plotted, the lower mass stars will trace out the main-sequence toward the red giant branch, the point where stars are just beginning to evolve off is called the... |
|
|
Accretion Disk |
Flat disk of matter spiraling down onto the surface of a neutron star or black hole. Often, the matter originated on the surface of a companion star in a binary-star system. |
|
|
Type I Supernovae |
One possible explosive death of a star. A white dwarf in a binary-star system can accrete enough mass that it cannot support its own weight. The star collapses and the temperatures become high enough for carbon fusion to occur. Fusion begins throughout the white dwarf almost simultaneously and an explosion results. |
|
|
Supernova Remnant |
The scattered glowing remains of a supernova that happened in the past. The Crab Nebula is a great example and one of the most studied. |
|
|
Neutron Capture |
The primary mechanism by which very massive nuclei are formed in the violent aftermath of a supernova. Instead of fusion of like nuclei, heavier elements are created by the addition of more and more neutrons to existing nuclei. |
|
|
Neutron Star |
A dense ball of neutrons that remains at the core of a star after a supernova explosion has destroyed the rest of the star. They are typically 20 km across yet contain more mass than the Sun. |
|
|
X-Ray Burster |
X-ray source that radiates thousands of times more energy than our Sun in short bursts lasting only a few seconds. A neutron star in a binary-star system accretes matter onto its surface until temperatures reach the level needed for hydrogen fusion to occur. The result is a sudden -period of rapid nuclear burning and release of energy. |
|
|
General Theory of Relativity |
The theory proposed by Albert Einstein to incorporate gravity into the framework of special relativity |
|
|
Schwarzschild Radius |
The distance from the center of an object such that, if all the mass were compressed within that region, the escape speed would equal the speed of light. Once a stellar remnant collapses within this radius, light cannot escape and the object is no longer visible. |
|
|
Time Dilation |
A prediction of the theory of relativity, closely related to the gravitational redshift. To an outside observer, a clock lowered into a strong gravitational field will appear to run slow. |
|
|
Subgiant Branch |
The section of the evolutionary track of a star corresponding to changes that occur just after hydrogen is depleted in the core, and core hydrogen burning ceases. Shell hydrogen burning heats the outer layers of the star, which causes a general expansion of the stellar envelope. |
|
|
Helium Flash |
An explosive event in the post-main-sequence evolution of a low-mass star. When helium fusion begins in a dense stellar core, the burning is explosive in nature. It continues until the energy released is enough to expand the core, at which point the star is able to achieve stable equilibrium again. |
|
|
Planetary Nebula |
The ejected envelope of a red-giant star, spread over a volume roughly the size of our solar system. |
|
|
Roche Lobe |
An imaginary surface around a star. Each star in a binary system can be pictured as being surrounded by a teardrop-shaped zone of gravitational influence. Any material within this part of a star can be considered as being a part of that star. During evolution, one member of the binary system can expand so that this overflows in its own region and begins to transfer matter to the other. |
|
|
Core-Collapse Supernova |
Often referred as A Type II Supernova which is one possible death of a star, in which the highly evolved stellar core rapidly implodes then explodes, destroying the surrounding star. |
|
|
Type II Supernova |
One possible explosive death of a star, in which the highly evolved stellar core rapidly implodes then explodes, destroying the surrounding star. |
|
|
Stellar Nucleosynthesis |
The formation of heavy elements by the fusion of lighter nuclei in the hearts of stars. Except for hydrogen and helium, all other elements in our universe resulted from this system. |
|
|
Supermassive Black Holes |
Black hole having a mass a million to a billion times that of our Sun; usually found in the center nucleus of a galaxy. |
|
|
Lighthouse Model |
The leading explanation for pulsars. A small region of the neutron star, near one of the magnetic poles, emits a steady stream of radiation that sweeps past Earth every time the star rotates. The period of the pulses is the star's rotation speed. |
|
|
Millisecond Pulsar |
A pulsar whose period indicates that the neutron star is rotating nearly 1000 times each second. The most likely explanation for these rapid rotators is that the neutron star has been spun up by drawing in a companion star. |
|
|
Spacetime |
Single entity combining space and time in special and general relativity. |
|
|
Event Horizon |
Imaginary spherical surface surrounding a collapsing star, with a radius equal to the Schwarzschild radius, within which no event can be seen, heard or known about by an outside observer. |
|
|
Singularity |
A point in the universe where the density of matter and the gravitational field are infinite, such as at the center of black hole. |
|
|
Chandrasekhar Limit |
The maximum mass of a stable white dwarf |
