properties of main sequence stars
DESCRIPTION
Properties of Main Sequence Stars. Masses Luminosities Lifetimes Distribution. How do we know the masses of stars?. •. Center of mass. By studying binary stars! “The mass of any central object can be determined if it has an observable orbiting satellite.”. - PowerPoint PPT PresentationTRANSCRIPT
Properties of Main Sequence Stars
•Masses
•Luminosities
•Lifetimes
•Distribution
•
How do we know the masses of stars?
By studying binary stars!
“The mass of any central object can be determined if it has an observable orbiting satellite.”
Center of mass
Main Sequence Stars
y = 0.0151x6 - 0.4107x5 + 4.5331x4 - 25.9297x3 + 80.9918x2 - 131.3942x + 88.6098
R2 = 0.9980
0.1
1.0
10.0
100.0
Spectral Type
Ma
ss
in
So
lar
Un
its
O B A F G K M
Stars have a fairly narrow range of masses.
Main Sequence Stars
y = 0.0151x6 - 0.4107x5 + 4.5331x4 - 25.9297x3 + 80.9918x2 - 131.3942x + 88.6098
R2 = 0.9980
0.1
1.0
10.0
100.0
Spectral Type
Ma
ss
in
So
lar
Un
its
O B A F G K M
Stars have a fairly narrow range of masses.
Sun-like stars are 1 solar mass
Main Sequence Stars
y = 0.0151x6 - 0.4107x5 + 4.5331x4 - 25.9297x3 + 80.9918x2 - 131.3942x + 88.6098
R2 = 0.9980
0.1
1.0
10.0
100.0
Spectral Type
Ma
ss
in
So
lar
Un
its
O B A F G K M
Stars have a fairly narrow range of masses.
Sun-like stars are 1 solar mass
O & B stars are a few 10’s of solar masses
Main Sequence Stars
y = 0.0151x6 - 0.4107x5 + 4.5331x4 - 25.9297x3 + 80.9918x2 - 131.3942x + 88.6098
R2 = 0.9980
0.1
1.0
10.0
100.0
Spectral Type
Ma
ss
in
So
lar
Un
its
O B A F G K M
Stars have a fairly narrow range of masses.O & B stars are a few 10’s of solar masses
M stars are a few 10’ths of a solar mass
Sun-like stars are 1 solar mass
How do we know the luminosity of stars?
1. From direct measurement of a star’s distance through stellar parallax and its apparent magnitude we can calculate the absolute magnitude: M = m - 5log(D) + 5
2. From theoretical nuclear fusion calculations the luminosity can be modeled as a function of spectral type with reasonable accuracy. (After all we make the best nuclear bombs!)
Main Sequence Stars
y = 0.0347x5 - 0.6105x4 + 4.23x3 - 14.575x2 + 26.982x - 20.282
R2 = 0.9871
-10.0
-5.0
0.0
5.0
10.0
15.0
20.0
Spectral Type
Ab
solu
te M
agn
itu
de
O B A F G K M
Stars have a HUGE range of luminosities.
Main Sequence Stars
y = 0.0347x5 - 0.6105x4 + 4.23x3 - 14.575x2 + 26.982x - 20.282
R2 = 0.9871
-10.0
-5.0
0.0
5.0
10.0
15.0
20.0
Spectral Type
Ab
solu
te M
agn
itu
de
O B A F G K M
Stars have a HUGE range of luminosities.
Sun-like stars are 1 solar luminosity
Main Sequence Stars
y = 0.0347x5 - 0.6105x4 + 4.23x3 - 14.575x2 + 26.982x - 20.282
R2 = 0.9871
-10.0
-5.0
0.0
5.0
10.0
15.0
20.0
Spectral Type
Ab
solu
te M
agn
itu
de
O B A F G K M
Stars have a HUGE range of luminosities.
O & B stars are 10,000
solar luminosities
Sun-like stars are 1 solar luminosity
Main Sequence Stars
y = 0.0347x5 - 0.6105x4 + 4.23x3 - 14.575x2 + 26.982x - 20.282
R2 = 0.9871
-10.0
-5.0
0.0
5.0
10.0
15.0
20.0
Spectral Type
Ab
solu
te M
agn
itu
de
O B A F G K M
Stars have a HUGE range of luminosities.
O & B stars are 10,000
solar luminosities
M stars are a few 10,000’ths of a solar luminosity
Sun-like stars are 1 solar luminosity
How do we know stellar lifetimes?1. Again, theoretical nuclear modeling yields
estimates of main sequence lifetimes.
2. However, a simple estimate can be made based upon the mass of the star and its luminosity as shown below.
Spectral Type
Mass
M
Luminosity
L
Lifetime in Solar Lifetimes
O stars 30 30,000 30/30,000 = .001
M stars .3 .0003 .3/.0003 = 1,000
Main Sequence Stars
y = 8E+07x3.3742
R2 = 0.9873
y = 1E+07x5.2587
R2 = 0.9675
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E+11
1.E+12
1.E+13
Spectral Type
Lif
etim
e in
Yea
rs
O B A F G K M
Stars also have a HUGE range of
lifetimes.
Main Sequence Stars
y = 8E+07x3.3742
R2 = 0.9873
y = 1E+07x5.2587
R2 = 0.9675
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E+11
1.E+12
1.E+13
Spectral Type
Lif
etim
e in
Yea
rs
O B A F G K M
Stars also have a HUGE range of
lifetimes.
10 Billion Years for Sun-like stars
Main Sequence Stars
y = 8E+07x3.3742
R2 = 0.9873
y = 1E+07x5.2587
R2 = 0.9675
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E+11
1.E+12
1.E+13
Spectral Type
Lif
etim
e in
Yea
rs
O B A F G K M
Stars also have a HUGE range of
lifetimes.
10 Billion Years for Sun-like stars
A few Million Years for O stars
Main Sequence Stars
y = 8E+07x3.3742
R2 = 0.9873
y = 1E+07x5.2587
R2 = 0.9675
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E+11
1.E+12
1.E+13
Spectral Type
Lif
etim
e in
Yea
rs
O B A F G K M
Stars also have a HUGE range of
lifetimes.
10 Billion Years for Sun-like stars
A few Million Years for O stars
A few Trillion
Years for M stars
Main Sequence Stars
y = 8E+07x3.3742
R2 = 0.9873
y = 1E+07x5.2587
R2 = 0.9675
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E+11
1.E+12
1.E+13
Spectral Type
Lif
etim
e in
Yea
rs
O B A F G K M
Stars also have a HUGE range of
lifetimes.
10 Billion Years for Sun-like stars
A few Million Years for O stars
A few 10’s of Trillion
Years for M stars
The Age of the Universe is now
considered to be 13.8 Billion years ± 1%
Main Sequence Stars
y = 8E+07x3.3742
R2 = 0.9873
y = 1E+07x5.2587
R2 = 0.9675
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E+11
1.E+12
1.E+13
Spectral Type
Lif
etim
e in
Yea
rs
O B A F G K M
Stars also have a HUGE range of
lifetimes.
10 Billion Years for Sun-like stars
A few Million Years for O stars
A few 10’s of Trillion
Years for M stars
The Age of the Universe is now
considered to be 13.8 Billion years ± 1%
None of the first O through G stars exist anymore.
Main Sequence Stars
y = 8E+07x3.3742
R2 = 0.9873
y = 1E+07x5.2587
R2 = 0.9675
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E+11
1.E+12
1.E+13
Spectral Type
Lif
etim
e in
Yea
rs
O B A F G K M
Stars also have a HUGE range of
lifetimes.
10 Billion Years for Sun-like stars
A few Million Years for O stars
A few 10’s of Trillion
Years for M stars
The Age of the Universe is now
considered to be 13.8 Billion years ± 1%
Every M star ever created is still a main sequence M star.
The HUGE range in stellar lifetimes is reflected in the
distribution of stars in the Milky Way Galaxy.
• Long lived K & M stars are most abundant.• Short lived O & B stars are very rare.• Other very luminous stars (Giants) will also be rare due to
their short lifetimes. • White dwarf stellar remnants have VERY long cooling
times but are very low luminosity. They may represent the most common object in the galaxy but are undercounted.
Note the high abundance of
M dwarfs.
Note the low abundance of O & B stars.
There are also very few giant
stars.
There are probably many
more white dwarf stellar remnants
that are too dim to see.
Number of Stellar Types in the Milky Way
0% 1% 0% 0% 1% 3%7%
13%
68%
9%
0%
20%
40%
60%
80%
O-M F-M O B A F G K M B-F
Supergiant(I & II)
Red Giant(III)
Main Sequence (V) WhiteDwarf
Num
ber
Number of Stellar Types in the Milky Way
0% 1% 0% 0% 1% 3%7%
13%
68%
9%
0%
20%
40%
60%
80%
O-M F-M O B A F G K M B-F
Supergiant(I & II)
Red Giant(III)
Main Sequence (V) WhiteDwarf
Num
ber
Only 7% of the stars in the Milky Way galaxy are Sun-like and half of them are in
multiple star systems. Thus, star and planetary systems like our own represent less than 3% of all the stars in
the galaxy.
Number of Stellar Types in the Milky Way
0% 1% 0% 0% 1% 3%7%
13%
68%
9%
0%
20%
40%
60%
80%
O-M F-M O B A F G K M B-F
Supergiant(I & II)
Red Giant(III)
Main Sequence (V) WhiteDwarf
Num
ber
The most common stars in the Milky Way Galaxy are of such low luminosity that they are difficult to see even when they are right “next
door”. These stars are utterly invisible in distant
galaxies.
Number of Stellar Types in the Milky Way
0% 1% 0% 0% 1% 3%7%
13%
68%
9%
0%
20%
40%
60%
80%
O-M F-M O B A F G K M B-F
Supergiant(I & II)
Red Giant(III)
Main Sequence (V) WhiteDwarf
Num
ber
The very rare short lived stars are the most luminous and are the easiest seen in the night sky and in other
distant galaxies
This Spiral Galaxy resembles our Milky Way Galaxy
This Spiral Galaxy resembles our Milky Way Galaxy
This is a more distant galaxy of a different type.
Hot O and B stars dominate
the luminosity in the Spiral Arms There are
very many low
luminosity K and M
stars in the apparently
empty space
between the spiral arms.
• In the following M101 galaxy images you will see the galaxy through a red filter and then through a blue filter. (Repeats once)
• Notice that the galaxy is dimmer and less defined in red light and brighter and sharper in blue light.
Only the most luminous stars show up distinctly in distance galaxies. The most
common stars in the galaxy are individually invisible.
Red Filter
Spiral Galaxy
M101
Blue Filter
Spiral Galaxy
M101
Red Filter
Spiral Galaxy
M101
Blue Filter
Spiral Galaxy
M101
The Milky Way
0
25
50
75
100
O-M F-M O B A F G K M B-F
Supergiant(I & II)
Red Giant(III)
Main Sequence (V) WhiteDwarf
Luminosity Class and Spectral Type
Percentage of Galactic LuminosityPercentage in Number Percentage of Galactic Stellar Mass
75% of the Milky Way’s luminosity
arise from the rarest stars.
K & M stars account for ¾’s of the stars in the galaxy but contribute less than 5% of its
luminosity.
The properties of O and M Main Sequence Stars
O Stars• Mass 25 M
• Radius 6 R
• Temperature 30,000K• Luminosity 80,000 L
• M -6• Main Sequence Lifetime
3 Million years
• Mass 0.1 M
• Radius 0.1 R
• Temperature 3,000K• Luminosity 0.0001 L
• M 15• Main Sequence Lifetime
10 Trillion years
M Stars
For the
Test