ASTR101 Chapter 15 Flashcards

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Questions and Answers

A spherical galaxy, like M87, which looks like a monster globular cluster, is type?

ES1

E0 (correct)

S0 (correct)

The flattest of the ellipticals are class?

SBF

SBO

E7 (correct)

The Large and Small Magellanic Clouds fall into Hubble's class?

Irr I (correct)

SBc

Pec

When mass is accreted into a black hole, how much total mass-energy can be radiated away?

20% Signup and view all the answers

The Milky Way is often considered to be an intermediately wound, barred spiral, which would be type ________ according to Hubble.

SBb Signup and view all the answers

The greatest variation in size, mass, and luminosity occurs in?

elliptical galaxies Signup and view all the answers

Which of the following is NOT one of Hubble's types of galaxies?

Seyfert spirals Signup and view all the answers

Within the boundaries of the constellations Coma and Virgo are found?

the largest nearby super-clusters of galaxies Signup and view all the answers

Most of the galaxies in the Local Group are?

small irregulars and ellipticals like the SMC and the companions to M31 in Andromeda Signup and view all the answers

What is the nearest huge cluster of galaxies to our Local Group?

Virgo Cluster Signup and view all the answers

The Tully-Fisher relation exists between the galaxy's luminosity and its?

rotation Signup and view all the answers

What is the nearest huge cluster of thousands of galaxies, to which the Local Group may belong?

Virgo Cluster Signup and view all the answers

Why does the Cepheid 'standard candle' have limited usefulness beyond 20 Mpc?

Cepheids are too faint to be seen beyond that distance, even with HST. Signup and view all the answers

Which of the following paraphrases Hubble Law?

The greater the distance to a galaxy, the greater its redshift. Signup and view all the answers

What is true of spiral galaxies?

They are relatively rare in regions of high galaxy density. Signup and view all the answers

For finding the distance to M31 (the Andromeda galaxy at 0.78 Mpc), Hubble relied upon?

Cepheid variables in its spiral arms. Signup and view all the answers

According to Hubble's Law, the greater a galaxy's redshift, the?

farther it is from us. Signup and view all the answers

While examining the spectrum of a galaxy you find all the hydrogen lines are shifted to longer wavelengths. This galaxy is?

moving away from us. Signup and view all the answers

Quasars usually have their distances measured by what technique?

Hubble's Law Signup and view all the answers

That quasars were at cosmological distances yet appeared like ordinary faint stars meant?

they must be producing such large quantities of energy that even fusion could not explain their output. Signup and view all the answers

Quasar's spectral lines are?

emission lines with large red shifts. Signup and view all the answers

Why is the energy source for active nuclei like Seyferts thought to be compact?

The light can vary over short time intervals. Signup and view all the answers

In what sense are the quasars 'quasi-stellar'?

In short time exposures, their images looked stellar. Signup and view all the answers

If we are directly in the line of a jet coming out of the lobe galaxy's core, we see a?

blazar. Signup and view all the answers

The huge lobe radio galaxy at the center of the Virgo Supercluster is?

M-87, a giant elliptical galaxy. Signup and view all the answers

The quasars with the largest presently known redshifts are close to?

6 Signup and view all the answers

A billion solar mass black hole would still have a radius of only?

20 AU Signup and view all the answers

Which of the following does the intensity of synchrotron radiation NOT depend on?

temperature Signup and view all the answers

The type of radiation coming from active nuclei due to electrons spiraling in very strong magnetic fields at relativistic speeds is?

synchrotron radiation. Signup and view all the answers

Synchrotron radiation produces a ________ spectrum.

continuous non-thermal Signup and view all the answers

The energy radiated by a typical quasar requires that its black hole accrete about?

one solar mass a year. Signup and view all the answers

Not only does the central engine of active galaxies and quasars require a black hole, but also ________ to provide the radiated energy.

an accretion disk of in-falling matter Signup and view all the answers

Study Notes

Galaxy Types and Classifications

M87 is classified as a spherical galaxy, resembling a globular cluster, identified as type E0.
The classification of elliptical galaxies ranges from E0 (flattest) to E7; E7 is the flattest elliptical.
Hubble's classification places the Large and Small Magellanic Clouds under Irr I, indicating irregular galaxies.
The Milky Way is categorized as an intermediately wound, barred spiral galaxy, specifically type SBb.

Mass and Energy in Black Holes

About 20% of total mass-energy can be radiated away when mass is accreted into a black hole.
The phenomenon of black holes is influential in understanding the dynamics of immense regions of space.

Local Group and Galaxy Clusters

The Virgo Cluster represents the nearest huge cluster of galaxies to our Local Group, containing thousands of galaxies.
Local Group galaxies predominantly consist of small irregulars and ellipticals, including companions of M31 in Andromeda.
Regions within the constellations Coma and Virgo comprise the largest nearby super-clusters of galaxies.

Distance Measurement Techniques in Astronomy

The Tully-Fisher relation correlates a galaxy's luminosity with its rotation speed.
Cepheid variables in the spiral arms of M31 (Andromeda) were key to determining its distance by Hubble.
Quasars' distances are typically measured using Hubble's Law, which relates redshift to distance.

Observations and Theories of Active Galaxies

The spectral lines of quasars exhibit emission lines with large redshifts, indicative of their significant distances and energy outputs.
Active nuclei sources, like Seyfert galaxies, are considered compact due to rapid light variability.
Quasars create the appearance of being stellar because they are extremely bright over vast distances.

Black Holes and Synchrotron Radiation

A billion solar mass black hole has a surprisingly small radius of only 20 AU.
Synchrotron radiation arises from electrons spiraling in strong magnetic fields and produces a continuous non-thermal spectrum.
The intensity of synchrotron radiation is independent of temperature, influenced instead by electron speed and magnetic field strength.

Quasars and Their Characteristics

Quasars may require their black holes to accrete about one solar mass per year to emit their immense energy.
They are observed as ordinary faint stars, but their luminosity greatly exceeds that of typical stars due to enormous energy outputs.
Quasar jets result in observable features like blazars when viewed along the jet direction.

Redshift and Cosmic Expansion

According to Hubble's Law, a greater redshift indicates a galaxy is farther from us, reflecting the universe's expansion.
Distant galaxies show redshifts in hydrogen lines, indicating they are moving away from the observer.

Conclusion

Understanding these concepts is essential for grasping galaxy classification, distance measurement, the dynamics of black holes, and the nature of cosmic entities such as quasars and active galactic nuclei.

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Description

Test your knowledge of elliptical galaxies and Hubble's classification system with these flashcards from ASTR101 Chapter 15. This quiz includes a variety of questions focusing on types of galaxies and their characteristics. Perfect for any astronomy student looking to reinforce their understanding of the topic.