SIRIUS
Brightest Star in
the night sky
Alpha Canis Majoris
The Dog Star
Sirius b –
faint companion
Deneb
Deneb = Alpha Cygni
Distance: ~ 1500 LY
Diameter: ~20 x Sun
Mass: ~20 x Sun
Luminosity: 60,000 x
Sun
1 LY =
9,460,528,400,000 Km
Most Distant Star
(that you can see!)
Distance:
150 million Km
The Closest Star
Our Sun is a typical,
middle-aged star
Diameter:
1.4 million Km
= 100 x Earth
Temperature:
6,000 C (outside)
15 million C (inside)
Mass:
Age:
4.6 billion years
2 x 1030 kg
= 300,000 x Earth
A Range of Size and Mass
MASS
0.08 MSun
~200 MSun
DIAMETER
0.1 MSun
~1000 MSun
Only certain combinations of size and mass
are stable
Stars will shrink or expand to reach stability
A Range of Temperature
TEMPERATURE
200,000 C
2000 C
Cool stars
are reddish
in color
The Sun is
about 6000 C
Hot stars
are bluish
in color
A star’s brightness depends on its
temperature and radius
Allowed Temperature & Luminosity
A Range of Ages
AGE
~13 Billion Years
Brand New Stars
The Sun formed 4.6
billion years ago
Stars have been forming continuously since the
Universe began 13.7 billion years ago
Some old stars are still around; other stars are
brand new
Birth of the Sun
BIRTH
Middle Age
BIRTH
H
The Sun Today
Inside the Sun: Energy and Motion
The energy
comes from
nuclear fusion
reactions in the
Sun’s core
Energy flows
slowly from the
inside to the
surface
The Visible “Surface” of the Sun
Sunspots
• cooler regions
• magnetic fields
• prominences originate
from active regions
5
The Sun
in Time
Brightness
4
3
Luminosity of the Sun
2
1
0
0
2
4
6
8
10
Time since Formation (Billions of Years)
12
The Sun is
gradually growing
brighter over
time, as it
converts
hydrogen into
helium
Eventually…
As the Sun Grows Old
He
BIRTH
H
NOW
Future
Sun
The Sun
today
The Sun as
a red giant
The orbit of Venus
Astronomers aren’t sure how big the
Sun will grow when it becomes a red
giant, Perhaps as large as the orbit of
Venus, or even the orbit of the Earth
The Sun’s Final Glory
He
BIRTH
H
NOW
What’s Left?
A White Dwarf
12,000 Km
Mass: 50% Sun
Density: 1-2 tons per cc3
Composition: C & O, the
Sirius B
“ashes” of nuclear fusion
Cools & fades slowly
Nearest
White Dwarf
Star
Sirius b
Diameter: 1/100 Sun
Mass: 98% Sun
Distance: 8.6 LY
The
BIGGEST
Credit: NASA/ESA/R Humphreys/U Minnesota)
A red “hypergiant” star
Diameter: 2000 x Sun
Mass: 30-40 x Sun
Luminosity: 500,000 x Sun
5,000 light-years away
The Sun
VY Canis
Majoris
BRIGHTEST & MOST MASSIVE
Mass = 265 Suns (probably
320 Suns at birth!)
Luminosity = 8-9 million x
Sun
Diameter: 35 x Sun
Located in the Large
Distance: 165,000 LY
Magellanic
Cloud
Future hypernova?
R136A*
The HOTTEST STARS NGC 2440 (central star)
are tiny, dim, new
Distance: 4500 LY
white dwarfs
T=200,000 C
NGC 6302 (central star)
Distance: 3800 LY
Hidden by central dust ring
KPD 0005+5106
Only 2200 years “old”
Distance: 2500 LY
The
WISE
COLDEST
Brown Dwarfs!
WISE 1828+2650
Temperature ~25 C
About 27 LY
Mass < 0.1 Suns
Too small for nuclear
fusion
Stars
The Oldest Stars! HE 1523-0901
13.2 billion years old
Mass: 0.8 Suns
13.2 billion
Years ago
Distance: ~7500 LY
A red giant star
Today
The Youngest Stars
Stars are forming today in the
“empty” regions of interstellar space.
Stages of Star
Formation
Stars on the Weird Side!
The Famous Pleiades
Distance: 1300 LY
Brightest Star
Cluster
Formed about 115
million years ago
The blue glow is
dust!
V838 MONOCEROTIS – THE LIGHT ECHO
V838 is a “central star” of a planetary nebula
Distance: 20,000 LY
Mass: 5-10 Suns
(originally much
more massive)
Outburst in 2002 The “expanding
shell” is actually an
expanding light
echo
V838 MONOCEROTIS – THE LIGHT ECHO
To Earth
Arrives first
Arrives later
A Real Shooting Star!
13 LY tail
291,000 mph
GALEX
Mira = Omicron Ceti
An unstable red giant
Losing mass
Distance: 400 LY
Mass: 1.2 Suns
As seen by Hubble
Epsilon Aurigae
Binary star (6 + 8 Suns)
27 year period
One star is invisible!
An unseen blue star hides
in a disk of dust that orbits
a yellow supergiant
When the blue star
passes in front of the
yellow star, the disk
blocks the light of
yellow star
8 AU
Dust Disk
Stellar Cannibalism
Binary stars that
orbit close together
often transfer mass
between the stars
Semi -Detached
Binary
Detached
Binary
Contact Binary
Warning: Artist’s Conceptions
R Corona Borealis – The “Fade Out” Star
Yellow supergiant star
Distance: 6000 LY
Mass: 0.8 Suns
Sometimes fades by
a factor of 1000 or
more in brightness!
Emits “puffs” of soot
that block the light of
the star
More
R Corona Borealis
Extreme helium star
Very little hydrogen
Lots of carbon
Origin: merger of
two white dwarfs?
HD 12545 holds
the record for
the largest
“starspot”
Artist Conception
Extreme
Spots!
Warning: Artist’s Conception
The rotation and revolution of
close binary stars are locked
together, forcing the stars to
rotate as fast as they orbit.
Fast rotation makes big spots.
Extreme
Rotation!
Regulus = Alpha Leo
Distance: 78 LY
Mass: 3.8 Suns
Radius: 3-5 Suns
Rotates
every 16 hrs!
Other stars, too!
Regulus
Altair
Vega
MORE EXTREME
ROTATION
Crab Pulsar
Distance: 6500 LY
Mass: ~ 1.4-2.0 Suns
Remnant of 1054 Supernova
Density: 100,000,000 tons
per thimbleful
Spins 30 times per second
Magnetars!
SGR 1900+14
Extreme Neutron
Stars
SGR 1900+14
Distance: 20,000 LY
Mass: ~ 2 Suns
Diameter: ~20 Km
7 LY
Most intense magnetic fields in the Universe
Hundreds of millions times stronger than the
strongest human-made magnets
Only 5 known
Sources of intense gamma ray bursts
Warning: Artist’s Conception
Supernova 1987a
Supernova
1987a
Detected in 1987
Exploded 170,000
years ago
Originally about 18
solar masses
Where is the
neutron star?
Closest candidate:
Best candidate:
V404 Cyg
Distance: 7,800 LY
Star mass: ~0.7 Suns
BH mass: ~12 Suns
BH Diameter: ~75 km
Orbital period: 6.5 days
V616 Mon
Distance: 3000 LY
Star mass: ~0.5 Suns
BH mass: ~6 Suns
BH Diameter: ~40 km
Orbit period: 7.75 hrs
The Universe is Full of Surprises!
And that’s what
makes astronomy so
much fun!
Weather permitting!
Kirkwood Observatory
is located at the west
end of Dunn’s Woods,
behind Bryan Hall
Happy Summer Solstice!
On the handout:
URL for this
presentation on the
Web
Related websites
Kirkwood
Observatory open
tonight
