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E treme Stars
Caty PilachowskiMini-University
June 2012
Brightest Star in the night sky
Alpha Canis Majoris
The Dog Star
SIRIUS
Sirius b – faint companion
Most Distant Star (that you can see!)
Deneb = Alpha CygniDistance: ~ 1500 LY
Diameter: ~20 x SunMass: ~20 x Sun
Luminosity: 60,000 x Sun
1 LY = 9,460,528,400,000 Km
Deneb
The Closest StarOur Sun is a typical, middle-aged star
Distance:150 million Km
Diameter:1.4 million Km= 100 x Earth
Age:4.6 billion years
Temperature:6,000 C (outside)
15 million C (inside)
Mass:2 x 1030 kg
= 300,000 x Earth
0.08 MSun ~200 MSun
MASS
DIAMETER
0.1 MSun ~1000 MSun
A Range of Size and Mass
Only certain combinations of size and mass are stable
Stars will shrink or expand to reach stability
TEMPERATURE
200,000 C2000 C
A Range of Temperature
A star’s brightness depends on its temperature and radius
The Sun is about 6000 C
Hot stars are bluish
in color
Cool stars are reddish
in color
Allowed Temperature & Luminosity
AGE
~13 Billion Years Brand New Stars
A Range of Ages
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
The Sun formed 4.6 billion years ago
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
The Sun in Time
Luminosity of the Sun
0
1
2
3
4
5
0 2 4 6 8 10 12Time since Formation (Billions of Years)
Brig
htne
ss
The Sun is gradually growing brighter over time, as it converts hydrogen into helium
Eventually…
As the Sun Grows Old
BIRTH
NOWH
He
Future Sun
The Sun today
The Sun as a red giant
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 orbit of Venus
What’s Left? A White DwarfMass: 50% SunDensity: 1-2 tons per cc3
Composition: C & O, the “ashes” of nuclear fusion
Cools & fades slowly
Sirius B12,000 Km
Sirius b
Diameter: 1/100 SunMass: 98% SunDistance: 8.6 LY
Nearest White Dwarf
Star
VY Canis Majoris
A red “hypergiant” star Diameter: 2000 x Sun
Mass: 30-40 x SunLuminosity: 500,000 x Sun
5,000 light-years away
Credit: NASA/ESA/R Humphreys/U Minnesota) The Sun
The
BIGGES
T
BRIGHTEST & MOST MASSIVE Mass = 265 Suns (probably
320 Suns at birth!)Luminosity = 8-9 million x
SunDiameter: 35 x SunDistance: 165,000 LYFuture hypernova?
Located in the Large Magellanic Cloud
R136A*
The HOTTEST STARS are tiny, dim, new
white dwarfsT=200,000 C
NGC 2440 (central star)Distance: 4500 LY
NGC 6302 (central star)Distance: 3800 LYHidden by central dust ring
KPD 0005+5106Distance: 2500 LYOnly 2200 years “old”
COLDEST
Brown Dwarfs!WISE 1828+2650Temperature ~25 CAbout 27 LYMass < 0.1 SunsToo small for nuclear
fusion
The
StarsWIS
E
The Oldest Stars! HE 1523-090113.2 billion years oldMass: 0.8 Suns
Today13.2 billion Years ago
Distance: ~7500 LYA red giant star
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 PleiadesDistance: 1300 LYBrightest Star
ClusterFormed about 115
million years agoThe blue glow is
dust!
V838 MONOCEROTIS – THE LIGHT ECHO
V838 is a “central star” of a planetary nebula
Distance: 20,000 LYMass: 5-10 Suns (originally much more massive)
Outburst in 2002 - The “expanding shell” is actually an expanding light echo
V838 MONOCEROTIS – THE LIGHT ECHO
Arrives firstArrives later
To Earth
A Real Shooting Star!Mira = Omicron CetiAn unstable red giantLosing massDistance: 400 LYMass: 1.2 Suns
13 LY tail291,000 mph
GALE
X
As seen by HubbleGALEX
Epsilon AurigaeBinary star (6 + 8 Suns)27 year periodOne star is invisible!
8 AU
Dust Disk
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
Stellar Cannibalism Binary stars that
orbit close together often transfer mass between the stars
Warning: Artist’s ConceptionsContact Binary
Detached Binary
Semi -Detached Binary
R Corona Borealis – The “Fade Out” StarYellow supergiant starDistance: 6000 LYMass: 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
This star smokes!
MoreR Corona BorealisExtreme helium star
Very little hydrogenLots of carbon
Origin: merger of two white dwarfs?
Extreme Spots!
HD 12545 holds the record for the largest “starspot”
Artist 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.
Warning: Artist’s Conception
Extreme Rotation!Regulus = Alpha LeoDistance: 78 LYMass: 3.8 SunsRadius: 3-5 Suns
Rotates every 16 hrs!
VegaAltair
Other stars, too!
Regulus
Crab Pulsar
Distance: 6500 LYMass: ~ 1.4-2.0 SunsRemnant of 1054 Supernova
Spins 30 times per second
MORE EXTREME ROTATION
Density: 100,000,000 tonsper thimbleful
Magnetars!Extreme Neutron Stars
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
SGR 1900+14
7 LY
SGR 1900+14Distance: 20,000 LYMass: ~ 2 SunsDiameter: ~20 Km
Supernova 1987a
Supernova 1987a
Detected in 1987Exploded 170,000
years agoOriginally about 18
solar massesWhere is the
neutron star?
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
Closest candidate: V616 Mon Distance: 3000 LY Star mass: ~0.5 Suns BH mass: ~6 Suns BH Diameter: ~40 km Orbit period: 7.75 hrs
Black Holes
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
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