Galaxy Morphological Classification Flashcards

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Questions and Answers

How many galaxies are in the universe?

There are about $10^{11}$ (100 billion) galaxies in the observable universe.

What are the three major types of galaxies?

Irregular Galaxies (correct)

Spiral Galaxies (correct)

Elliptical Galaxies (correct)

Lenticular Galaxies

Describe the components of Spiral Galaxies.

Spiral Galaxies have a disk component with spiral arms containing gas, dust, and stars of all ages, and a bulge component with few young stars and red giants.

What defines Barred Spiral Galaxies?

Barred Spiral Galaxies have spiral arms that branch off from a straight bar of stars passing through the central bulge. Signup and view all the answers

Is the Milky Way Galaxy a Barred Spiral?

True Signup and view all the answers

Describe Elliptical Galaxies.

Elliptical Galaxies have no disk or spiral arms, are light dominated by red giants, and contain little gas and dust. Signup and view all the answers

What is the mass range of Elliptical Galaxies?

Ellipticals range from dwarf ellipticals, which are 10,000 to a million times less massive than the Milky Way, to giant ellipticals, which can be over 100 times more massive. Signup and view all the answers

Describe Irregular Galaxies.

Irregular Galaxies are chaotic systems with no disk or sphere, are rich in gas and dust, and are typically small with blue-white color lighting dominated by O and B-type stars. Signup and view all the answers

What is Hubble's Tuning Fork Diagram?

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What are the methods of measuring distance in astronomy?

The most reliable method is parallax; less reliable methods include spectroscopic parallax, Cepheid variables, and type Ia supernovae. Signup and view all the answers

Explain the concept of 'Standard Candles'.

Standard Candles are objects of known luminosities used to calculate distances by comparing their luminosities with their apparent brightnesses. Signup and view all the answers

Explain Spectroscopic Parallax.

Spectroscopic Parallax involves finding a star's luminosity from its position in the HR diagram based on its spectrum and estimating distance from apparent brightness. Signup and view all the answers

Describe Pulsating Variable Stars.

Pulsating Variable Stars experience substantial changes in luminosity due to pulsation of their outer layers. Signup and view all the answers

What is the Period-Luminosity Relationship?

This relationship states that by measuring the period of a Cepheid variable and determining its type, one can calculate its luminosity and thus distance using apparent brightness. Signup and view all the answers

Describe Cepheid Variables.

Cepheid Variables are stars found throughout the galaxy with pulsation periods ranging from 1 to 50 days, where luminosity is related to pulsation period. Signup and view all the answers

Describe RR Lyrae Variables.

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Study Notes

Galaxies in the Universe

Approximately 100 billion (10^11) galaxies exist in the observable universe, evidenced by Hubble's Extreme Deep Field.

Major Types of Galaxies

The three primary classifications of galaxies are:
- Elliptical Galaxies
- Irregular Galaxies
- Spiral Galaxies

Spiral Galaxies

Comprise a disk and a central bulge (sphere):
- Disk Component: Features spiral arms, gas, dust, and stars of various ages including young O/B-type and older Population II stars.
- Bulge (Sphere): Contains few young stars, predominantly red giants.
- An example is the Pinwheel Galaxy (M101), which constitutes 77% of observed galaxies.

Barred Spiral Galaxies

Characterized by spiral arms that emanate from a central bar of stars.
Up to two-thirds of spiral galaxies may have a bar structure.
Example: NGC 1300, a spiral galaxy featuring a central bar.

Milky Way Galaxy

Recognized as a barred spiral galaxy.
Spitzer Space Telescope detected a bar made of old, red stars, extending about 27,000 light-years across.

Elliptical Galaxies

Solely consist of a spherical component with no distinct disk or spiral arms.
Characterized by a yellow-red color with a scarcity of gas and dust and very few young stars.
Represent approximately 20% of observed galaxies.

Mass of Elliptical Galaxies

Exhibit a vast range of masses:
- Giant ellipticals can exceed 100 times the mass of the Milky Way.
- Dwarf ellipticals can be 10,000 to 1 million times less massive.

Irregular Galaxies

Display chaotic structures with no clear disk or spherical shape.
Often have a blue-white color and are dominated by O and B-type stars.
Typically rich in gas and dust; nearby examples tend to be small.
Example: The Large Magellanic Cloud, which is classified as irregular and constitutes about 3% of observed galaxies.

Measuring Distance to Galaxies

The most reliable method is parallax, effective for stars within ~150 pc.
Less reliable methods include spectroscopic parallax, Cepheid variables, and type Ia supernovae.

Standard Candles

Objects with known luminosities utilized to measure distances in the universe.
Their apparent brightness allows astronomers to calculate distances using the inverse square law.

Spectroscopic Parallax

This method estimates a star's luminosity and distance using its spectrum to locate it in the HR diagram.
Distance calculated (d) from apparent brightness (b) follows the formula: b = L / 4(pi)d².
The method's accuracy is limited, especially since stars of the same classification may not have identical luminosities.

Pulsating Variable Stars

These stars exhibit significant luminosity changes over short time frames.
Their pulsation results from the outer layers expanding and contracting, seen in types like Cepheid variables and RR Lyrae stars.

Period-Luminosity Relationship

A measure associating the pulsation period of Cepheid variables to their luminosity.
Discovered by Henriette Swan Leavitt, enabling determination of distances when combined with apparent brightness.
Types categorized as:
- Type I (metal-rich, more luminous)
- Type II (metal-poor, less luminous)

Cepheid Variables

Located throughout the Galaxy, exhibiting pulsation periods ranging from 1 to 50 days.
Luminosity is intrinsically linked to their pulsation periods.

RR Lyrae Variables

Characteristics and definition incomplete, requiring further detail.

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Description

Test your knowledge on galaxy classification with these flashcards. Explore the types of galaxies and their characteristics, including the major categories and components of spiral galaxies. Challenge yourself to remember key facts about the cosmos!