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?
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?
Signup and view all the answers
Is the Milky Way Galaxy a Barred Spiral?
Signup and view all the answers
Describe Elliptical Galaxies.
Signup and view all the answers
What is the mass range of Elliptical Galaxies?
Signup and view all the answers
Describe Irregular Galaxies.
Signup and view all the answers
What is Hubble's Tuning Fork Diagram?
Signup and view all the answers
What are the methods of measuring distance in astronomy?
Signup and view all the answers
Explain the concept of 'Standard Candles'.
Signup and view all the answers
Explain Spectroscopic Parallax.
Signup and view all the answers
Describe Pulsating Variable Stars.
Signup and view all the answers
What is the Period-Luminosity Relationship?
Signup and view all the answers
Describe Cepheid Variables.
Signup and view all the answers
Describe RR Lyrae Variables.
Signup and view all the answers
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.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
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!