Transcript Slides from Lecture19 - Department of Physics & Astronomy

ASTR 1102-002
2008 Fall Semester
Joel E. Tohline, Alumni Professor
Office: 247 Nicholson Hall
[Slides from Lecture19]
Chapter 23: Our Galaxy
and
Chapter 24: Galaxies
Schematic Illustration
of
Our (Milky Way) Galaxy
Real ‘All Sky’ Images
of
Our (Milky Way) Galaxy
Aside:
• Atomic transition that gives rise to 21-cm
radiation, which is used by astronomers to
map out the distribution of neutral
hydrogen throughout our Galaxy (and
other galaxies), is also the physical
principle underlying the MRI (magnetic
resonance imaging) diagnostic tool in
modern medicine.
Medical MRI
Determining Size of MW Galaxy
• We have not always known that the
diameter of our Galaxy is ~ 50 kpc (as
illustrated in following slide)
• Herschel’s map of our Galaxy (1785)
based on star counts
– Thin disk not much more than 1 kpc across
– Sun approximately at center of disk
Determining Size of MW Galaxy
• We have not always known that the
diameter of our Galaxy is ~ 50 kpc (as
illustrated in following slide)
• Herschel’s map of our Galaxy (1785)
based on star counts
– Thin disk not much more than 1 kpc across
– Sun approximately at center of disk
Determining Size of MW Galaxy
• We have not always known that the
diameter of our Galaxy is ~ 50 kpc (as
illustrated in following slide)
• For example, Herschel’s map of our
Galaxy (1785) based on star counts …
– Thin disk not much more than 1 kpc across
– Sun approximately at center of disk
Herschel’s Map of MW Galaxy
Determining Size of MW Galaxy
• We have not always known that the
diameter of our Galaxy is ~ 50 kpc (as
illustrated in following slide)
• For example, Herschel’s map of our
Galaxy (1785) based on star counts …
– Thin disk not much more than 1 kpc across
– Sun approximately at center of disk
• Herschel’s map grossly distorted by
interstellar extinction
Prominent and Obscured Objects
Shapley’s View of MW Galaxy
• Look out of the plane of the MW disk to
minimize obscuration due to interstellar
extinction
• Distribution of Globular Clusters not
symmetric about Sun’s location
• Distances to GCs obtained using RR
Lyrae variable stars as “standard candles”
Shapley’s View of MW Galaxy
• Look out of the plane of the MW disk to
minimize obscuration due to interstellar
extinction
• Distribution of Globular Clusters not
symmetric about Sun’s location
• Distances to GCs obtained using RR
Lyrae variable stars as “standard candles”
Shapley’s View of MW Galaxy
• Look out of the plane of the MW disk to
minimize obscuration due to interstellar
extinction
• Distribution of Globular Clusters not
symmetric about Sun’s location
• Distances to GCs obtained using RR
Lyrae variable stars as “standard candles”
Shapley’s View of MW Galaxy
• Look out of the plane of the MW disk to
minimize obscuration due to interstellar
extinction
• Distribution of Globular Clusters not
symmetric about Sun’s location
• Distances to GCs obtained using RR
Lyrae variable stars as “standard candles”
Determining Distances in Astronomy
• Stellar parallax
• Spectroscopic parallax (main-sequence
fitting):
– Remember distance modulus:
(m – M) = 5 log(d) – 5
– If you know “M” for a certain type of star, then
a measurement of “m” gives you “d”
• Standard candles: Identifiable stars for
which you know “M”
Determining Distances in Astronomy
• Stellar parallax
• Spectroscopic parallax (main-sequence
fitting):
– Remember distance modulus:
(m – M) = 5 log(d) – 5
– If you know “M” for a certain type of star, then
a measurement of “m” gives you “d”
• Standard candles: Identifiable stars for
which you know “M”
Determining Distances in Astronomy
• Stellar parallax
• Spectroscopic parallax (main-sequence
fitting):
– Remember distance modulus:
(m – M) = 5 log(d) – 5
– If you know “M” for a certain type of star, then
a measurement of “m” gives you “d”
• Standard candles: Identifiable stars for
which you know “M”
Determining Distances in Astronomy
• Stellar parallax
• Spectroscopic parallax (main-sequence
fitting):
– Remember distance modulus:
(m – M) = 5 log(d) – 5
– If you know “M” for a certain type of star, then
a measurement of “m” gives you “d”
• Standard candles: Identifiable stars for
which you know “M”
Determining Distances in Astronomy
• Stellar parallax
• Spectroscopic parallax (main-sequence
fitting):
– Remember distance modulus:
(m – M) = 5 log(d) – 5
– If you know “M” for a certain type of star, then
a measurement of “m” gives you “d”
• Standard candles: Identifiable stars for
which you know “M”
Determining Distances in Astronomy
• Stellar parallax
• Spectroscopic parallax (main-sequence
fitting):
– Remember distance modulus:
(m – M) = 5 log(d) – 5
– If you know “M” for a certain type of star, then
a measurement of “m” gives you “d”
• Standard candles: Identifiable stars for
which you know “M”
Example Standard Candles
• RR Lyrae variables
– Pulsation period of about ½ day
– Luminosity is 100 x solar luminosity
• Sun: M = +4.8; let’s call it M = +5 for simplicity
• RR Lyrae: M = 0
• “Population I” Cepheid variables
– Luminosities range up to 10,000 solar (M = - 5)
– (Pulsation) period-luminosity correlation
• Type Ia supernovae
– Luminosity 3 x 109 solar !
Example Standard Candles
• RR Lyrae variables
– Pulsation period of about ½ day
– Luminosity is 100 x solar luminosity
• Sun: M = +4.8; let’s call it M = +5 for simplicity
• RR Lyrae: M = 0
• “Population I” Cepheid variables
– Luminosities range up to 10,000 solar (M = - 5)
– (Pulsation) period-luminosity correlation
• Type Ia supernovae
– Luminosity 3 x 109 solar !
Example Standard Candles
• RR Lyrae variables
– Pulsation period of about ½ day
– Luminosity is 100 x solar luminosity
• Sun: M = +4.8; let’s call it M = +5 for simplicity
• RR Lyrae: M = 0
• “Population I” Cepheid variables
– Luminosities range up to 10,000 solar (M = - 5)
– (Pulsation) period-luminosity correlation
• Type Ia supernovae
– Luminosity 3 x 109 solar !
Example Standard Candles
• RR Lyrae variables
– Pulsation period of about ½ day
– Luminosity is 100 x solar luminosity
• Sun: M = +4.8; let’s call it M = +5 for simplicity
• RR Lyrae: M = 0
• “Population I” Cepheid variables
– Luminosities range up to 10,000 solar (M = - 5)
– (Pulsation) period-luminosity correlation
• Type Ia supernovae
– Luminosity 3 x 109 solar !
Example Standard Candles
• RR Lyrae variables
– Pulsation period of about ½ day
– Luminosity is 100 x solar luminosity
• Sun: M = +4.8; let’s call it M = +5 for simplicity
• RR Lyrae: M = 0
• “Population I” Cepheid variables
– Luminosities range up to 10,000 solar (M = - 5)
– (Pulsation) period-luminosity correlation
• Type Ia supernovae
– Luminosity 3 x 109 solar !
Example Standard Candles
• RR Lyrae variables
– Pulsation period of about ½ day
– Luminosity is 100 x solar luminosity
• Sun: M = +4.8; let’s call it M = +5 for simplicity
• RR Lyrae: M = 0
• “Population I” Cepheid variables
– Luminosities range up to 10,000 solar (M = - 5)
– (Pulsation) period-luminosity correlation
• Type Ia supernovae
– Luminosity 3 x 109 solar !
Example Standard Candles
• RR Lyrae variables
– Pulsation period of about ½ day
– Luminosity is 100 x solar luminosity
• Sun: M = +4.8; let’s call it M = +5 for simplicity
• RR Lyrae: M = 0
• “Population I” Cepheid variables
– Luminosities range up to 10,000 solar (M = - 5)
– (Pulsation) period-luminosity correlation
• Type Ia supernovae
– Luminosity 3 x 109 solar !
Example Standard Candles
• RR Lyrae variables
– Pulsation period of about ½ day
– Luminosity is 100 x solar luminosity
• Sun: M = +4.8; let’s call it M = +5 for simplicity
• RR Lyrae: M = 0
• “Population I” Cepheid variables
– Luminosities range up to 10,000 solar (M = - 5)
– (Pulsation) period-luminosity correlation
• Type Ia supernovae
– Luminosity 3 x 109 solar !
NOTE:
Transient Events (in time) also occur
NOTE:
Transient Events (in time) also occur
NOTE:
Transient Events (in time) also occur
Example Standard Candles
• RR Lyrae variables
– Pulsation period of about ½ day
– Luminosity is 100 x solar luminosity
• Sun: M = +4.8; let’s call it M = +5 for simplicity
• RR Lyrae: M = 0
• “Population I” Cepheid variables
– Luminosities range up to 10,000 solar (M = - 5)
– (Pulsation) period-luminosity correlation
• Type Ia supernovae
– Luminosity 3 x 109 solar !
Distance Ladder
Shapley’s View of MW Galaxy
• Look out of the plane of the MW disk to
minimize obscuration due to interstellar
extinction
• Distribution of Globular Clusters not
symmetric about Sun’s location
• Distances to GCs obtained using RR
Lyrae variable stars as “standard candles”
Stellar Populations
• Pop I
• Pop II
• Pop III
Prominent and Obscured Objects