Astronomy test 3
Middleweights
-(or moderately-massive stars) are stars containing between 4 and 12 solar masses -Stages of a middleweight (or moderately-massive) star: 1)Protostar 2)Main sequence star with a mass of 4 to 12 solar masses and a core mass up to 3. 3)Red giant 4)Supernova 5)Supenova remnant nebula and a Pulsar
Heavyweights
-(or very massive stars) have over 12 solar masses. -A star that is 15 times as massive as the Sun burns up its hydrogen in only 10 million years because its core temperature is much higher than the Sun's and the reactions run faster. -These massive stars then expand to become supergiants, with luminosities a million times that of the Sun and absolute magnitudes of -10 -Betelgeuse in Orion is an example of a red supergiant. -Because of greater core temperatures and pressures, supergiants produce heavier elements, such as neon, silicon, and iron. -they differ primarily from middleweights in what happens to them when their core is compressed to a density greater than electron degeneracy can support. In a middleweight, the resulting supernova leaves a neutron star. In a heavyweight, the core has a mass greater than 3 solar masses and it swallows itself as a black hole.
Observation—The Crab Pulsar
-A pulsar was discovered in the Crab Nebula that has a period of 0.033 second (it blinks 30 times a second). -The Crab pulsar emits radiation in all parts of the spectrum, from radio waves to X-rays. Its energy output is more than 25,000 times that of the Sun. -The Crab pulsar is slowing down because of the "drag" of the electrons propelled out into the nebula surrounding the pulsar. -The Crab pulsar spins so rapidly because it it formed so recently. Over time it will lose rotational energy, slow down, and emit less energy. -More than 440 pulsars have been discovered, most with periods between 0.1 and 4 seconds.
spacetime
-Albert Einstein used the result of Michelson-Morley Experiment as the basis for his Theory of Special Relativity, which he published in 1905. -In this Theory Einstein introduced the notion of four-dimensional _________ in which we treat x,y,z, and time equally.
Eclipsing Binaries
-Algol, discovered by John Goodricke in 1783, is an eclipsing binary, in which one star moves in front of the other as viewed from Earth. -Algol's light curve—a graph of the numerical measure of the light received from a star versus time—shows peaks and dips that indicate an unseen companion.
More on Type II supernovae
-Because the iron fusion reaction absorbs more energy than it releases, the core shrinks, heats up, but produces no new more massive elements. Once its mass reaches the Chandrasekar limit, the core collapses violently. After reaching its minimum size, the core rebounds, colliding violently with infalling material -This collision between the infalling material and the rebounding core produces two effects: 1. Enough energy is produced to fuse iron into heavier elements. 2. Shock waves are sent outward that throw off the outer layers of the supergiant. These shock waves may be further heated by neutrinos escaping the collapsed core. -Elements heavier than iron cannot be formed without some source of energy. Heavy elements found here on Earth are thus the product of supernovae explosions in the distant past that ultimately became part of the interstellar material from which the Earth was formed.
Harlow Shapely
-Cepheids could be valuable distance indicators if the distance to one could be determined. None are close enough to be measured by parallax, but beginning in 1917, the U. S. astronomer ______________ worked out a complex statistical method to determine distances to Cepheids in our own galaxy. -Their work led to a period-luminosity diagram for RR Lyrae variables
Chandrasekhar Limit
-Degenerate electrons can withstand pressures created by up to 1.4 solar masses. Beyond that point—known as the _____________________________—white dwarf stars cannot exist as white dwarfs. -Main sequence stars with masses up to 4 solar masses can end up as white dwarfs only if they lose mass during the red giant and planetary nebula phases, for otherwise they would exceed the above mass limit
Interstellar Gas
-Dust in space accounts for 10% of the total mass of the interstellar material. -The remaining 90% of the mass is in the form of interstellar gas. -Fluorescence is the process of absorbing radiation of one frequency and re-emitting it at a lower frequency
Henrietta Swan Leavitt
-Each Cepheid has a very constant period of variation, ranging from about 1 day to about 3 months for different Cepheids. -In 1908 __________________ discovered that for Cepheids, the brighter variables have the longer periods. -Cepheids are important because the period, which is easy to determine, allows the absolute magnitude to be determined
Length Compression
-Einstein also said that the two observers would disagree on the lengths each would measure, but only along the line of sight connecting them. -He said that each would perceive the other's lengths as being shorter than the other would measure
rest mass
-Einstein said that the smallest mass an object would appear to have would be its mass when it was not moving with respect to the observer who was making the measurement. -This minimum mass of an object Einstein called the ________________. Any moving object will appear to have a mass greater than its rest mass
Time Dilatation
-Einstein used algebra to state that each observer in relative motion at constant velocity with respect to another observer will appear to see that other observer's clock run more slowly than that observer will think his clock is running. -The amount of the stretching of time is governed by the relative velocity of the two
Type Ia supernova
-If accretion brings the mass of a white dwarf above the Chandrasekhar limit, electron degeneracy can no longer support the star, and it collapses. The collapse raises the core temperature and runaway carbon fusion begins, which ultimately leads to an explosion of the star. -Such an exploding white dwarf is called a ___________
Sir William Herschel
-In 1802 obtained the first evidence that some double stars orbit one another. -In 1781 counted the numbers of stars in different parts of the sky and came up with the Grindstone Model of the Milky Way.
Felix Savary
-In 1827 HE showed that the stars in a binary orbit each other in elliptical orbits. -There are triple star systems, double-double systems, and sextuple systems -Once a star system has about 10 or more members, it is called an open, or galactic, star cluster
Purcell and Ewen
-In 1951, _____________ used a specially built radio telescope to detect radiation emitted by interstellar neutral hydrogen. -Interstellar hydrogen emits radiation at a wavelength of 21 centimeters, which is in the radio portion of the e/m spectrum. -Other radio emission lines can be detected from other interstellar gases—water (H2O), carbon monoxide (CO), ammonia (NH3), formaldehyde (H2CO), and ethyl alcohol.
E=MC2
-In a separate paper in 1905 Einstein went on to claim that all matter and energy are equivalent. -He said this in his most famous equation: E=MC2 in which the M is the rest mass of the particle, C is the speed of light, and E is the equivalent energy. -As we discussed several weeks ago when we talked about the energy source of the Sun, it is this equation which is responsible for the energy source of all main sequence stars.
lepton families
-In addition to the electron and the muon the third family is the tau particle. -Also, each of these three families of __________ has its own anti-particle. -Also, each of the three families of __________ has an associated neutrino (Italian meaning "little neutral one").
Luminosity Classes
-In the 1880s the astronomer Antonia Maury discovered that absorption lines are also subject to a smearing effect, which has become valuable in classifying stars. This smearing effect is due to the density of the star's atmosphere. -Luminosity classes are different groupings into which stars can be placed based upon the differing widths of their spectral lines
reflection nebula
-Interstellar clouds can contain less than 1,000 molecules per cubic centimeter. -A _____________________________ is interstellar dust that is visible due to reflected light from a nearby star. Such reflection nebulae are bluish in color due to the reflected light. -Dust clouds can contain up to 1 million molecules per cm3, though this is still 20 million-million times less dense than Earth's atmosphere at sea level.
Gluons and Glueballs
-It is now believed that the different quarks that comprise the hadrons are held together by even smaller particles which are known as "gluons." -It has even been speculated that some matter may exist which is entirely comprised of gluons. Such objects are referred to as "glueballs."
Cepheid variables or cepheids
-John Goodricke discovered the first of these stars in 1784. This star is the star Delta Cephei -Soon after, other stars were seen that exhibit Delta Cephei's characteristic light curve—a rapid brightening followed by a slower dimming. -Doppler effect data showed that these stars are pulsating in rhythm with their changes in luminosity
The Quark Theory
-Physicists now believe that all of the baryons and the other hadrons are composed of tinier particles known as quarks. -There are six "flavors" of quarks and there are three different "colors" of each flavor, so there is actually a total of 18 quarks
Daniel M. Popper
-The American astronomer made many of the mass measurements of stars -Eclipsing binaries that are also spectroscopic binaries provide us with a way of measuring not only the masses of the two stars but also their sizes. We can derive this information by measuring their changing Doppler shifts during each orbit
The Interstellar Medium
-The cirrus emits infrared radiation because it is warmed slightly by light that it absorbs. -Interstellar clouds span huge volumes of space, from parsecs to tens of parsecs across. -Interstellar extinction is the effect by which starlight is absorbed completely by interstellar material. -The light from distant stars is reddened by the dust through which it passes because dust grains scatter blue light more than red. -Interstellar dust grains are smaller than the wavelength of light. -Spectral analysis indicates that interstellar dust contains carbon in the form of graphite
Walter Baade and Fritz Zwicky
-The theory of neutron stars was discussed by THESE TWO MEN of Caltech in the 1930s. A typical neutron star: •Mass = 1.5 solar masses •Diameter = 20 km (width of small city) •Density = 1015 g/cm3 •Temperature = 10,000,000 K
detecting supernovae
-Three naked eye supernovae that have been seen in our Galaxy in recent times occurred in 1054, 1572, and 1604. -The supernova of 1572 was seen by Tycho Brahe, and the one of 1604 was observed by Kepler. Unfortunately, both of these supernovae occurred just before the invention of the telescope
stellar masses from binary star data
-To determine how the system's total mass is distributed between the two stars, we need to measure the ratio of the two stars' distances to the center of mass. -Because the inclination of spectroscopic binary orbits are usually not known, exact mass calculations cannot be done. However, by assuming an average inclination, we can get information about the average masses of such binary stars
hadrons and leptons
-Today we no longer believe that the proton and neutron in the nuclei of atoms are the most fundamental of particles. -Rather, we now believe that there are two major classes of particles: ______________________ -Electrons and neutrinos are leptons and neither of them are thought to be comprised of smaller particles.
Type II supernovae
-Type II supernovae are thought to occur in very massive single, supergiant stars whose out hydrogen and helium layers have not been lost. -Because Type II supernovae are thought to occur in such massive stars, they are also only found in regions where recent star formation has occurred -Type II supernovae, which result from massive stars, reveal prominent hydrogen lines. -The process by which Type II supernovae occur is not well known but is thought to begin with the conversion of silicon to iron. The fusing of silicon to iron in a supergiant star will take only a few days, which is a remarkably short period of time
Star Death
-Until their lives end on the main sequence, the main difference between the evolution of stars of various masses is the amount of time they spend as protostars and main sequence stars. -Stars can be grouped by mass as flyweights, lightweights, super lightweights, middleweights, and heavyweights.
fusion reactions
-We now believe that the energy sources of the stars are the thermonuclear fusion reactions which are constantly converting hydrogen into helium inside the cores of most stars. These ________________ occur when the sub-atomic particles which comprise different nuclei interact with each other and energy is liberated when these particles interact to create heavier nuclei
2 types of supernova
-While a nova may reach an absolute magnitude of -8 (about 100,000 Suns), a supernova attains a magnitude of -19 (10 billion Suns). -There are two major types of supernova: Type I: no prominent lines of hydrogen seen in their spectra. Type II: contains prominent hydrogen lines; results from explosion of single star
pulsar
-a celestial object of small angular size that emits pulses of radio waves with a regular period between about 0.03 and 5 seconds -Objects that emit pulsing signals with a duration of 0.001 second cannot have a diameter any greater than 0.001 light-seconds, which is a few hundred kilometers. -Such a small size ruled out white dwarfs (Earth-sized objects), leaving the hypothesized neutron star as the explanation for pulsars.
dark nebula
-a cloud of interstellar dust that blocks light from stars on the other side of it. -Within a radius of a thousand parsecs from Earth, astronomers estimate that interstellar matter contributes about 15%-30% of the total mass of dust, gas, and stars
Lightweight stars
-a group that includes the Sun—include stars with masses between 0.4 and 2 solar masses. -In contrast to the flyweight stars, the lightweight stars are stars which are not fully convective in their interiors. -Because the lightweight stars are not fully convective, they do not use up all of their hydrogen fuel supply; only the hydrogen in their cores is used up on the main sequence -About 90% of the stars in the sky are in the main sequence phase of their lives today. -For most of these stars the next step after leaving the main sequence is to become a red giant. A typical star begins to contract once its core is depleted of hydrogen. This gravitational contraction causes the star to heat up. -A red giant can have a lower surface temperature (less radiation per square meter) but a higher luminosity because its diameter will have expanded 200 times or more. -In red giant stars it is thought that core instabilities and pulsations are responsible for the large mass loss. A typical red giant loses 10-7 solar masses a year.
neutron star
-a middleweight star that has collapsed to the point at which it is supported by neutron degeneracy. -The diameter of a typical neutron star is only 0.2% of the diameter of a white dwarf and the neutron star is a billion times more dense. -have masses of less than 3 solar masses.
Hertzsprung-Russell diagram
-a plot of the absolute magnitude (or luminosity) versus the surface temperature (or spectral class) for most stars. -About 90% of all stars fall into a band running diagonally across the diagram that is called the main sequence*. Stars on the H-R diagram fall into categories such as main sequence stars, white dwarf stars, red giant stars, and supergiant stars
accretion disk
-a rotating disk of gas orbiting a star, formed by material falling toward the star. -The hydrogen build-up on the surface of the white dwarf can ignite into an explosive fusion reaction that blows off a shell of gas. Though this shell contains a tiny amount of mass (0.0001 MSun) it can cause the white dwarf to brighten by 10 magnitudes (10,000 times) in a few days.
planetary nebula
-a spherical shell of gas that is expelled by a red giant near the end of its life. -The material in the shell glows because UV radiation from the central hot star causes it to fluoresce. -Pulsations and/or stellar winds are thought to cause planetary nebulae.
nova
-a star that suddenly and temporarily brightens, thought to be due to new material being deposited on the surface of a white dwarf. -Because so little mass is blown off during a nova, the explosion does not disrupt the binary system. Ignition of the infalling hydrogen can recur again with periods ranging from months to thousands of years.
binary star system
-a system of two stars that are gravitationally bound together. -The two stars in the pair orbit each other
black hole
-an object whose escape velocity exceeds the speed of light and therefore whose radius is equal to or less than the Schwarzschild radius -The density of a black hole is inversely proportional to its mass -As long as the radius of a collapsing star is greater than the Schwarzschild radius, the star is not considered to be a black hole. -Once its radius is equal to the Schwarzschild radius, the star is said to have become a black hole and it will remain a black hole even when its radius shrinks to become smaller than the size of the event horizon -A black hole can be described by three numbers: mass, electric charge, angular momentum. -thought to spin very rapidly
Prominences
-channels of solar material above the disk of the Sun -When seen in front of the photosphere ____________ are called filaments -may reach heights from a few thousand to even a million kilometers above the photosphere. Stable ones can last for several days, while explosive ones can reach speeds of 1,500 km/s
stephen hawking
-claimed that black holes might disappear or "evaporate" when the particles inside them would meet anti-particles from the outside universe. -also said that angular momentum can be removed from a spinning black hole even though no mass can escape from it. -also claimed that our entire Universe might be viewed as one gigantic black hole
Ian Shelton
-discovered SN1987A in the Large Magellanic Cloud in 1987 at the Las Campanas Observatory in Chile. -It appears that the ejected shell of material was shed by a red supergiant with a mass of about 20 times that of the Sun. The star ejected the material about 170,000 years ago, leaving a star with a hotter, bluer surface. -An increase in neutrinos was observed some three hours before the supernova was seen, confirming an important part of the theory of supernovae
binary pulsar
-discovered in 1974 by Joseph Taylor and Russell Hulse. -Because the system has a short period of revolution (< 8 hours), it could be determined that the pulsar's orbit precesses at the rate of 4° per century. -The pulsar has a mass of 1.441 solar masses and its companion's mass is 1.3874 solar masses. -important because it confirms predictions made by general relativity, was the first instance of the use of general relativity to calculate a stellar property, and the first precise determination of the mass of a neutron star. -As the two pulsars orbit each other, gravitational waves are given off. These waves take energy from the orbital motion of the stars and their orbital period shortens
super lightweight stars
-have masses between 2 and 4 times the mass of the Sun. -The super lightweight stars have massive enough cores that these cores never become degenerate and therefore they do not experience a helium flash. -Otherwise, they evolve like the other lightweight stars we have just described.
White dwarfs
-hot but dim stars because they are small. They may be 0.01 the Sun's size. -Sirius B has about the same mass as Sirius A, but B is small and hard to see because it is a white dwarf. -Astronomers estimate that 10% of all stars are white dwarfs. -White dwarfs are the cores of red giants that remain after the outer parts of the original stars have blown away. -Lighter white dwarfs are composed of helium and carbon. White dwarfs formed from more massive stars may contain nuclei of oxygen, neon, sodium, and even iron. White dwarfs have observed surface temperatures between 4,000 K and 85,000 K. Their masses range from perhaps 0.02 solar masses up to 1.4 solar masses -A typical white dwarf will have 0.8 solar masses, a diameter of 10,000 km (3/4 of Earth's), and a density of 106 g/cm3. A teaspoon of white dwarf material would weigh two tons. -To get to the white dwarf stage, a star will have gone through these stages: protostar, main sequence star, red giant, planetary nebula.
Michelson-Morley Experiment
-in 1887 showed convincingly that the speed of light cannot depend upon the motion of the observer (which was the Earth in that case). -This experiment was conducted by the American physicists Albert A. Michelson** (of speed of light fame) and Edward W. Morley** in Cleveland, Ohio at what is now Case Western Reserve University
emission nebula
-interstellar gas that fluoresces due to ultraviolet light from a star near or within the nebula. -A cloud is called a nebula if it is dense enough or bright enough to show up in a photograph. -Interstellar gas causes absorption lines in the stellar spectra
schwarzschild radius
-is the radius of a sphere around a black hole from within which no light can escape. RS = 3M (RS in km; M in solar masses) -The size of the Schwarzschild radius depends only upon the mass of the star. -Neutron degeneracy cannot support a neutron star whose mass is greater than about 3 solar masses
Mass-luminosity diagram
-plots the mass versus the luminosity of a number of stars. -More massive stars are more luminous. -The mass-luminosity relationship holds only for main sequence stars. -The mass-luminosity relationship is valuable in investigating less accessible stars and in constructing and evaluating hypotheses on the life cycle of stars
special theory of relativity
-predicts that the observed behavior of matter is due to its speed relative to the person who makes the observation. This theory applies to two observers who are traveling at constant velocities i.e., who are not accelerating. (by einstein) -also says that all observers will measure the same speed of light regardless of their own motions, as Michelson and Morley had observed.
Kelvin-Helmholtz theory
-proposed by von Helmholtz and Kelvin that a slow gravitational contraction was the source of the Sun's energy. Such a mechanism would power the Sun for only a few tens of millions of years at the current solar luminosity, which not a problem for them because they did not how old the sun is -By the early 20th century, however, geologists showed that the Earth was billions of years old—a period 100 times longer than the gravitational contraction theory could produce energy -this theory then had to be abandoned
Einstein
-proposed in 1905 that mass and energy are interchangeable. During the 1930s physicists worked out the theory of nuclear reactions. -went on to claim that all matter and energy are equivalent. -E=MC2 in which the M is the rest mass of the particle, C is the speed of light, and E is the equivalent energy. It is this equation which is responsible for the energy source of all stars.
Principle of Relativity
-states that all observers moving at constant velocity relative to each other are equivalent. -All such observers will find the same physical laws of motion and none of them can perform any experiment which will allow him to detect his own state of relative motion. -There is no absolute frame of reference.
Anthony Hewish and Martin Ryle
-the first suggested explanation for the regular pulses was the "little green men" hypothesis. -This idea was suggested and then rejected by Bell's thesis advisor, ___________________, of Cambridge. Later he and his colleague ________________ shared in the Nobel Prize in Physics for saying that pulsars are rapidly rotating neutron stars.
The Helium Flash
-the runaway helium fusion reaction that occurs during the evolution of a red giant. -In some stars the helium flash can consume the star's helium in a matter of seconds -As a red giant evolves and hydrogen burning takes place in outer layers of the star, the helium "ashes" are dumped back onto the degenerate core, raising the temperature of the core -When the core temperature reaches 100 million Kelvin degrees, helium nuclei begin to combine, forming carbon -Following the helium flash, the star forms four layers—1)an inner degenerate carbon core, 2)a layer of helium that fuses to carbon in a conventional manner, 3) an outer hydrogen-fusing shell, and 4) an outer layer below 10 million Kelvin in temperature where no fusion can take place The red giant star then expands further
Electron Degeneracy
-the state of a gas in which its electrons are packed as densely as nature permits. The temperature of such a high-density gas is not dependent on the pressure as it is in a "normal" gas -The core of red giant will not continue to contract indefinitely because of electron degeneracy
lighthouse model
-the theory that explains pulsar behavior as being due to a spinning neutron star whose beam of radiation is only seen as it sweeps by the Earth. -A pulsar's extremely strong magnetic field causes a beam of radiation to be emitted near each magnetic pole of the pulsar. -The pulsar's rapid rotation causes the beam to sweep through space in a very short period.
Types Ib and Ic supernovae
-thought to originate from more massive single supergiant stars which have shed their hydrogen layers -Types Ib and Ic occur only in regions where recent star formation has occurred because these two types of supernovae only come from very young, massive stars.
nuclear fusion
-two nuclei combine to form a larger nucleus, releasing energy in the process. -In a series of nuclear reactions which occur within the core of the Sun, 4 hydrogen nuclei are fused to form 1 helium nucleus. In the process energy in the form of gamma rays is given off. These reactions inside the Sun convert only 0.7% of the original mass of the four hydrogen nuclei into energy
Experimental Tests of General Relativity
1. Deflection of starlight by the Sun. 2. Perihelion advance of planet Mercury . 3. The gravitational redshift of photons leaving a star. 4. The time delays of the Viking radio signals
Jocelyn Bell
1967 British graduate student who discovered an unknown source of rapidly pulsating radio waves. Subsequent discoveries of similar sources gave rise to the name pulsar
Novae
A close binary star system consisting of a white dwarf and a newly formed red giant will result in the formation of an accretion disk around the white dwarf
more interstellar medium facts
Absorption lines due to interstellar gas tend to be narrower than those produced by a star's atmosphere. Lines caused by stellar atmospheres will have a different Doppler shift than those caused by the stellar atmosphere gas. Interstellar gas will generally be much cooler than the gas of the stellar atmosphere.
Daniel Popper
American astronomer who first measured the gravitational redshift of photons in 1954 for a white dwarf star. It was only measured later for the Sun because the Sun does not curve spacetime as much as does a white dwarf and hence the redshift is much smaller (and harder to measure) for the Sun
Detecting Stellar Mass Black Holes
If a black hole and red giant or supergiant form a binary system, material will be pulled from the giant and will swirl around the black hole, causing X-rays to be released from the heated material in the disk. This is one way to detect a black hole.
Ejnar Hertzsprung
In 1911 the Danish astronomer compared the apparent magnitudes and spectral classes of the stars in different star clusters
Henry Norris Russell
In 1913 the American astronomer studied the absolute magnitudes and spectral classes of the stars whose distances were known then
supermassive black holes
In addition to black hole which contain the mass of a single large star, another class of black hole which contains the mass of several hundred thousand or a few million stars. Such black holes are known as __________________________. They are thought to exist in the nuclear regions of many galaxies, including our own.
Flyweight Stars
In stars with a mass of less than about 0.4 solar masses, convection occurs throughout most or all of the volume of the star. Hydrogen from throughout the star is cycled through the core, and the entire star runs low on hydrogen at the same time. -A flyweight star will take 100 billion years to completely burn its hydrogen -Ultimately, flyweights will become white dwarfs through gravitational shrinkage. -Since the hypothetical lifetime of a flyweight is more than 6 times the assumed age of the universe, there has not been enough time for any flyweight star to become a white dwarf; hence,the low-mass white dwarfs that are currently observed must have originated in a different manner
total mass calculation
Knowledge of the size of one of the star's ellipses, along with knowledge of the period of its motion, permits calculation of the total mass of the two stars.
john wheeler
The U. S. physicist who was the first to employ the term "black hole."
synchrotron radiation
The extremely narrow beam of radio-frequency radiation is caused by a process called ______________________ in which electrons traveling near the speed of light spiral around the pulsar's intense magnetic field lines.
coronal mass ejection
The gas that is spewed out when a prominence erupts
Subrahmanyan Chandrasekhar
The leading theorist in the study of white dwarf stars was an Indian-American astrophysicist named Subrahmanyan Chandrasekhar. He shared the 1983 Nobel Prize in physics with William Fowler of Caltech
nucleogenesis
The process by which the nuclei of heavy atoms are created inside the cores of Type II supernovae
Type Ia Supernova
There are 4 sub-classes of Type I supernovae -Type Ia are thought to result from the rapid accretion of matter onto the surface of a white dwarf star from a neighboring companion star; -Type .Ia are thought to be carbon-oxygen rich white dwarfs that have had helium dumped onto them from an orbiting companion helium white dwarf. They are called Type .Ia because they only reach one-tenth the peak brightnesses of the Type Ia. -There are differences in the locations of the four sub-classes of Type I supernovae: -Type Ia and Type .Ia are found in regions of recent star formation and also in regions where no star formation has occurred recently -reaches maximum brightness in a few days, fades quickly for about a month, and dissipates after a year. -Models indicate that the energy of a Type Ia (following the explosion) comes from radioactive decay of nuclei produced in the explosion.
Karl Schwarzschild
U.S. astrophysicist who was the first to point out that there was a solution to one of Einstein's Field Equations in his Theory of General Relativity which has a singularity (i.e. a point of infinite density and zero volume) as one possible solution. In his honor the radius of a black hole's event horizon is now called the Schwarzschild Radius.
double-lined spectroscopic binary
a binary star system with stars having spectra that are different enough to distinguish them from one another. That is to say that both sets of spectral lines are visible
Deuterium
a hydrogen nucleus that contains one neutron and one proton
positron
a positively charged electron emitted from the nucleus in some nuclear reactions.
supergiant
a star of very great luminosity and size and may be several hundred times larger in diameter than the Sun.
giant star
a star one of great luminosity and large size
neutrino
an elementary particle that was previously thought to have no rest mass and no charge but which is now thought to possess mass and which carries energy from a nuclear reaction.
astrometric binary
an orbiting pair of stars in which wiggles in the proper motion of one of the stars reveals the presence of the other.
spectroscopic binary
an orbiting pair of stars that can be distinguished as two due to the changing Doppler shifts in their spectra. The first such binary was discovered by E.C. Pickering** in 1889.
visual binary
an orbiting pair of stars that can be resolved (normally with a telescope) as two stars
John Baptiste Riccioli
discovered the first binary star in 1650, although this star was not recognized as being a true binary then
general theory of relativity
expands special relativity to include accelerated systems and it presents an alternative way of explaining the phenomenon of gravitation. (by einstein)
principle of equivalence
holds that the effects of the force of gravity are indistinguishable from those of acceleration.
black dwarf
is the theorized final state of a star with a main sequence mass less than about 6 solar masses, in which all of its energy sources have been depleted so that it emits no radiation. Note that a black dwarf is not the same thing as a black hole.
barycenter
the center of mass of a binary pair of stars.
proton-proton chain
the series of nuclear reactions that begins with 4 protons and ends with a helium nucleus
event horizon
the surface of the sphere around a black hole from which nothing can escape. Its radius is the Schwarzschild radius
Optical doubles
two stars that have a small angular separation as seen from Earth but are not gravitationally linked. The stars in such a pair are at very different distances
An atom's nucleus is composed of:
•protons: the massive, positively charged particles in the nucleus of an atom •neutrons: the massive nuclear particles with no electric charge -Nuclear reactions involve forces between nuclear particles. These forces are known as the strong nuclear force and the weak nuclear force.
