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Intro Astronomy > Exam 4 > Flashcards

Exam 4 Flashcards

1
Q

What is a Black Hole?

A

A collapsed old star with such dense mass that even EM radiation cannot escape.

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2
Q

The first suggestion that there were collections of stars beyond our Milky Way in the universe was made by

A

Edwin Hubble in 1923.

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2
Q

What is a singularity?

A

Singularity: a mathematical point of infinite density with zero radius inside a black hole.

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3
Q

What separates a black hole from the rest of the universe?

A

Its event horizon.

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4
Q

The distance from a black hole singularity to the point where nothing can escape a black hole (its event horizon) is called what?

A

Its Schwarzschild radius RSCH.

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4
Q

A nonrotating black hole is called what?

A

A Schwarzschild black hole.

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4
Q

What important role do Cepheid variables stars have in astronomy?

A

Distance measurements to distant galaxies

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5
Q

Where is the event horizon of a black hole located?

A

RSCH = 2M/c2

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5
Q

What is a successful technique for finding candidates for black holes in our galaxy?

A

Detection of x-rays from a binary star undergoing mass exchange, where mass of component star can be determined.

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5
Q

A rotating black hole is called what?

A

A Kerr or Hawking black hole

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6
Q

Beside rotating and non-rotating black holes, how many other types are known to exist?

A

None

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6
Q

If nothing can escape from a black hole, how can we detect black hole candidates by the x-rays they emit?

A

The x-rays come from the highly compressed accretion disk just outside the event horizon.

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7
Q

The Andromeda Galaxy (M31) can be described as

A

an extension of the Milky Way.

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7
Q

An orbiting disk of matter spiraling in towards a black hole is called what?

A

An accretion disk

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7
Q

What can you never know about a black hole?

A

What type of material is inside it.

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8
Q

In terms of black holes, What is a wormhole?

A

A hypothetical direct connection from one black hole to another part of spacetime.

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8
Q

The Milky Way Galaxy

A

is one of many billions of galaxies in the Universe.

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8
Q

The Milky Way in which the Sun resides is an example of which type of galaxy?

A

A spiral galaxy (i.e., with a regular pattern of spiral arms)

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8
Q

What is a virtual particle?

A

A particle and its antiparticle are created simultaneously in pairs and then are annihilated so quickly that we cannot even know that they ever existed.

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9
Q

The dimensions of the disk of our Milky Way Galaxy are

A

diameter 100,000 ly; thickness 2000 ly.

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9
Q

What is it that makes the study of the structure of our own Galaxy more difficult than that of much more distant spiral galaxies?

A

Most of our galaxy is hidden behind dense gas and dust clouds in the galactic plane.

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10
Q

What is the significance of the object Sagittarius A* (“Sagittarius A-star”) in our Galaxy?

A

It appears to be a jet of material ejected from an accretion disk around a supermassive black hole in the galactic nucleus.

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10
Q

Where is the solar system located in our Galaxy?

A

In the galactic disk

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10
Q

The Andromeda Galaxy (M31) can also be described as

A

a spiral collection of stars, dust, and gas, 300,000 ly across.

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11
Q

Approximately how far is the Sun from the center of our Galaxy?

A

26,000 ly

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12
Q

Much of the mass of our Galaxy appears to be in the form of “dark” matter of unknown composition. At present, this matter can be detected only because

A

its gravitational pull affects orbital motions in the Galaxy.

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13
Q

Who developed the classification system that divides galaxies into spiral, elliptical, and irregular and classifies spirals by the size of their nuclear region and the tightness of winding of their arms?

A

Edwin Hubble

14
Q

How are galaxies spread throughout the universe?

A

Galaxies are densest near the Milky Way Galaxy and become less and less numerous the farther we look out into the universe.

15
Q

In discussing galaxies and the universe, astronomers often talk about “voids.” What are voids?

A

Volumes of space hundreds of millions of light-years across that contain almost no galaxies

15
Q

The primary evidence for the expanding universe concept is

A

the redshift of light from distant galaxies, which increases with distance of the galaxy from the Earth.

16
Q

What is the Local Group?

A

A cluster of 49 galaxies of which the Milky Way is a member

16
Q

Who first showed that the recessional speeds of galaxies increase with increasing distance from the Earth?

A

Edwin Hubble

16
Q

Which single major problem perhaps puzzles astronomers the most as they attempt to interpret the properties and behavior of clusters of galaxies?

A

The missing-mass problem, where the amount of mass needed for galactic cluster stability is estimated to be at least 10 times more than the observed visible mass

17
Q

What is the most outstanding feature of a quasar compared to other objects in deep space?

A

Its prodigious output of energy

17
Q

What is the Hubble flow?

A

Distant galaxies are all moving away from us, with speed increasing with increasing distance.

18
Q

The mathematical form of the Hubble law for the expanding universe concept relates the velocity of recession v to the distance of the observed object d (with H0 the Hubble Constant) as follows:

A

v = H0 d

18
Q

The energy output of a typical quasar per second is equal to that emitted by the Sun in

A

200 years.

19
Q

Quasars all appear to be

A

moving away from us at very high speeds, up to about 90% of the speed of light.

19
Q

The distance to the bright quasar 3C 273 is estimated to be

A

2 billion ly.

19
Q

Quasars in our Universe are

A

relatively common, with over 100,000 identified so far.

20
Q

In the expansion of the universe, the expansion takes place

A

only between objects separated by vacuum; as a result, our bodies do not expand, but the Earth-Moon system does.

21
Q

Which scientist discovered that the equations he had derived predicted an expanding universe, then modified his equations to eliminate this expansion?

A

Albert Einstein

22
Q

In 2004 a blazar of 10 billion solar masses was discovered at a distance of 12.5 billion ly. What was particularly intriguing about this discovery?

A

This blazar must have been formed very early in the history of the universe—too early, presumably, to have that much mass concentrated together.

23
Q

What is it that keeps localized regions of space, such as things on the Earth, planetary systems, star clusters, and whole galaxies, from participating in the general expansion of the universe?

A

The mutual gravitational attraction between objects in these systems

23
Q

The cosmic background radiation is

A

the flux of visible radiation in empty space, contributed by all visible stars in the universe.

24
Q

How many fundamental forces are there in nature at the present time under normal conditions?

A

Four: strong, weak, electromagnetic, and gravitational

25
Q

What is the range of the electromagnetic force (the maximum distance over which it acts)?

A

Infinity

25
Q

Knowing Luminosity Classes of stellar objects – how far is the closet object with these properties: G2V, 1LO, 1MO, 1RO

A

1AU

26
Q

Our view of the universe is a limited one because of what fundamental fact?

A

The cosmological redshift has moved the light from very distant objects out of our detectable range, making these objects invisible to us.

27
Q

What is the difference between dark matter and dark energy?

A

Dark matter is attractive and slows the universal expansion, whereas dark energy is repulsive and accelerates the universal expansion.

28
Q

Starburst galaxies

A

are often associated with a galaxy that is colliding with another galaxy.

28
Q

In the late 1990’s, it was discovered from distances of ______in distant galaxies that the expansion of the universe is ___________

A

supernovae; accelerating

28
Q

If the absolute magnitude, M, of a supernova is -19 and a galaxy is found that contains a supernova with an apparent magnitude, m, of 16. What is the distance to the galaxy? Hint: dpc = 10(m - M + 5)/5 using a scientific calculator.

A

100 Mpc

28
Q

A ____ generally contains well over 1000 galaxies and is quite dense. They often contain many giant elliptical galaxies.

A

rich cluster

28
Q

If the red shifts of quasars arise from the expansion of the universe yet they have brighter magnitudes than galaxies with the same red shifts, the quasar must be

A

emit a very large amount of energy per second.

28
Q

The letters AGN stand for _____.

A

an active galaxy nucleus

29
Q

We suspect that quasars are the active centers of galaxies because

A

“fuzz” around the central luminous regions produces spectra like a collection of normal stars..

29
Q

What was the first evidence that quasars were different from astronomical objects before they were observed in visual wavelengths?

A

Quasars emitted radio energy like active galaxies, but appeared to be point sources in radio wavelengths.

30
Q

Galaxies may contain a supermassive black hole at their center but _____ an active nucleus because of _______ into the black hole

A

show; mass inflow

31
Q

Evidence that supports quasars being the nuclei of very distant galaxies includes

A

all of the above

31
Q

How are astronomers able to determine that quasars are so small?

A

They are variable over a short period of time.

32
Q

How does the study of quasars reveal information of the history of the universe?

A

Typical quasars are very distant so we can view how galaxy evolution occurred in the past.

33
Q

Measured ages of globular clusters suggests that the universe is about …

A

14 billion years

33
Q

The ____ view of the universe is that it is eternal and unchanging.

A

static

34
Q

The cosmological principle states that any observer in any galaxy will see the same general features of the universe.

A

True

Intro Astronomy (4 decks)

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