Medterm 2 - Midterm PDF

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Compared to an open cluster, a globular cluster will have more hot, blue stars. False

Interstellar gas is composed mainly of 90% hydrogen, 9% helium by weight.

During the T-Tauri phase of a protostar, it may develop very strong winds.

How long does it take an M-type star to reach the main sequence, compared to a solar-type star? about twenty times longer

The dust particles have exactly the same chemical composition as the gases of the interstellar medium. False

High luminosity K and M type supergiant stars are usually responsible for exciting the gases within emission nebulae. False

What is the primary visible color of an emission nebula? red due to the Hα line of hydrogen

Which is characteristic of globular star clusters? old age and hundreds of thousands of stars, only about 30 ly wide

Interstellar matter is distributed very evenly throughout the galaxy.

False

Which of these events is not possible? white dwarfs and companion stars producing recurrent Type I supernova events

The single most important determinant of the temperature, density, radius, luminosity, and pace of evolution of a protostar is its mass.

The most common molecule in a molecular cloud is molecular hydrogen, H2.

Neutral hydrogen atoms are best studied from their energy given off as 21-cm waves in the radio region.

Emission nebulae like M8 and M20 occur only near stars that emit large amounts of ultraviolet radiation.

When an electron in a hydrogen atom changes its spin from the same to the opposite direction as the proton, it emits a radio wave photon.

Which statement about the stages of starbirth is false? nuclear reactions begin in the core by stage 4.

Why are dark dust clouds largely misnamed?

They contain much more gas than dust.

A cloud fragment too small to collapse into a main sequence star becomes a brown dwarf.

Which statement about dark dust clouds is true? They can be penetrated only with longer wavelengths such as radio and infrared.

A newly formed protostar will radiate primarily at which wavelength? infrared

Most stars in our part of the Galaxy are formed in open clusters of a few dozen.

What happens to light passing through even thin clouds of dust? It dims and reddens the light of all more distant stars.

What are the characteristics of an open cluster of stars? a few hundred, mostly main-sequence stars

We usually find dark molecular clouds beside bright emission nebulae. True

On an H-R diagram, a protostar would be above and to the right of the main sequence.

The spectra of interstellar gas clouds show that they have the same basic composition as stars.

An iron core cannot support a star because iron cannot fuse with other nuclei to produce energy.

The main reason that stars evolved off the main sequence is because they are becoming less massive as energy is lost into space from the proton-proton cycle. False

What was most surprising about SN1987A? The parent star was a blue supergiant, much like Deneb or Rigel.

In a supernova explosion, the amount of time it takes from the start of the giant star's collapse until the star starts to rip itself apart is... 1 seconds

The observed brightening of a typical nova to its peak during the explosion event takes about 3 days. True

Blue supergiant stars cannot explode as supernovae until they evolve into a different star type. False

A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object? nova

The Chandrasekhar limit is the upper-mass limit for a white dwarf.

If it gains sufficient mass from a binary companion, a white dwarf can become a Type I supernova.

____________________________ show little variation in their properties from one to another, no matter when or where they occur. Their consistent bright and equal luminosities make them excellent "standard candle" tools for mapping out distances to objects all around the universe. type I supernovae

What temperature is needed to fuse helium into carbon? 100 million K

While the core of the red giant is contracting and heating up, its radiation pressure actually causes its photosphere to swell up and cool off. True

The brightest stars in a young open cluster will be massive blue main-sequence stars.

Which of the following best describes the evolutionary track of the most massive stars? horizontal right, then back to the left, then back to the right

As a star's evolution approaches the Type II supernova, we find All of the above are correct.

Noting the main sequence turnoff mass in a star cluster allows you to determine its age.

Which stars in globular clusters are believed to be examples of mergers? blue stragglers

Can a star become a red giant more than once? yes, before and after the helium flash

Black dwarfs are not found yet; the oldest, coldest white dwarf in the Galaxy has not cooled enough yet.

What is the typical age for a globular cluster associated with our Milky Way? 10-12 billion years

A star is on the horizontal branch of the H-R diagram. It is burning both hydrogen and helium.

______________________ have the strongest stellar winds of any type of star type by far. Hot highly luminous supergiants

When a low mass star first starts running short of hydrogen in its core, it becomes brighter because the core contracts, raising the temperature and enlarging the hydrogen burning shell outward which then heats and expands the outer layers.

Which of these is true of planetary nebulae? They are ejected envelopes surrounding a highly evolved low-mass star.

Two important properties of young neutron stars are extremely rapid rotation and a strong magnetic field.

The largest known black holes lie in the cores of the most massive galaxies.

Most pulsars are observed only as ________ sources. radio

Which of the following is the most most luminous type of object yet observed from Earth? gamma-ray burster

In a hypernova, a very energetic supernova creates a black hole.

X-ray bursters occur in binary star systems. The two types of stars that must be present to make up such an object are a main-sequence or giant star and a neutron star in a mass transfer binary.

Which of the following statements about black holes is not true? Due to the extremely strong gravity near a black hole, objects accelerating in towards it will experience time at a faster rate than objects that are far away.

Two-thirds of all known millisecond pulsars are found in what type of object? globular clusters

A proposed explanation for gamma-ray bursters is Both A and B are possible.

hypernova-making black holes and bipolar jets. coalescence of a neutron star binary.

An X-ray burster is similar to a nova. True

What is Cygnus X-1? the leading candidate for an observable black hole

Newly-formed neutron stars start with weak magnetic fields, but they spin up and strengthen over time into pulsars. False

Einstein's Theory of General Relativity states that All matter tends to curve/warp space in its vicinity.

You would expect millisecond pulsars to be part of a binary system.

The densely packed neutrons of a neutron star will collapse under the inward pull of gravity...

if the total mass is greater than Schwartzschild's limit of 3 solar masses.

The first three planets found outside our solar system (also terrestrial-sized planets) were discovered in 1992 in close orbits near a millisecond pulsar.

Neutron stars have very strong bipolar magnetic fields.

The mass range for neutron stars is 1.4 to 3 solar masses.

Which statement about gamma ray bursters is not correct? They are scaled up X-ray bursters, with more massive objects involved.

A spaceship traveling at 30% the speed of light ( 0.3 c ) fires a laser beam directly ahead of itself. An astronaut watching this from a nearby stationary asteroid see the laser beam traveling at 1.3 x the speed of light (1.3 c ) False

Why do some pulsars, as seen from earth, go through repeating cycles of disappearing from view for a while then reappearing in their regular flashing mode? The pulsar's rotational axis wobbles as it spins (it precesses)

Which statement about black holes is true? Their escape velocity is greater than the speed of light.

Pulsars spin very rapidly when they're young.

The "pulse" from a pulsar is due to the rapid fusion of small amounts of hydrogen gas being systematically dumped on it from an accretion disk. False

A method for identifying a black hole is to look for its effects on a nearby companion. QUESTION 3 Plotting the luminosities and spectral types of many stars in a star cluster on an HR diagram, you note that there is a particular mass at which the stars "turn off" the main sequence. By finding the particular mass of the stars at which this turn off of the main sequence occurs, you can estimate the cluster's... radial velocity. distance. age. total mass. number of stars.

1.

QUESTI ON 12 A white dwarf gravitationally captures matter from the atmosphere of its binary companion which then accumulates on its surface. Eventually, this build up causes a sudden massive surface explosion, where nuclear fusion detonates this layer on the white dwarf all at once. What do we call this phenomenon? hypernova gamma ray burster Type I supernova nova shell star

1.

QUESTI ON 15 Which of the following is not a factor that causes supernova remnants to continue to glow well after the star has ripped itself apart?

x-rays and gamma-rays radiating from materials being crushed as they accrete onto the neutron star or black hole left behind radioactive decay of newly created elements gravitational waves oscillating back and forth through the expanding debris cloud ringing particles within like a bell and exciting them material in the supernova shockwave plowing into the interstellar medium, compressing and exciting atoms there

1.

QUESTI ON 23 In the final stages of the evolutionary process of a very massive star, we find the temperature in the core much reach 300 million K for helium fusion to start. As each new heavier element is created in the core, a longer period of time is required in the fusion process to create it. the photo-disintegration of iron nuclei creates the final supernova shockwave. the heavier the element being created in the core, the higher the temperature needed to fuse it. all of the above are correct....