1. E treme Stars
Caty Pilachowski
Mini-University
June 2012

2. Brightest Star in the night sky
SIRIUS
Alpha Canis Majoris
The Dog Star
Sirius b –
faint companion

3. Most Distant Star (that you can see!)
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

4. The Closest Star Our Sun is a typical, middle-aged star Age: Distance:
150 million Km
The Closest Star
Diameter:
1.4 million Km
= 100 x Earth
Our Sun is a typical, middle-aged star
Temperature:
6,000 C (outside)
15 million C (inside)
Mass:
2 x 1030 kg
= 300,000 x Earth
Age:
4.6 billion years

5. A Range of Size and Mass 0.08 MSun ~200 MSun 0.1 MSun ~1000 MSun
DIAMETER
0.1 MSun
~1000 MSun
Only certain combinations of size and mass are stable
Stars will shrink or expand to reach stability

6. Cool stars are reddish in color
A Range of Temperature
TEMPERATURE
200,000 C
2000 C
The Sun is about 6000 C
Hot stars are bluish
in color
Cool stars are reddish in color
A star’s brightness depends on its temperature and radius

7. Allowed Temperature & Luminosity

8. The Sun formed 4.6 billion years ago
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

9. Birth of the Sun
BIRTH

10. Middle Age
BIRTH H
The Sun Today

11. 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

12. The Visible “Surface” of the Sun
Sunspots
cooler regions
magnetic fields
prominences originate from active regions

13. The Sun in Time
The Sun is gradually growing brighter over time, as it converts hydrogen into helium
Eventually…

14. As the Sun Grows Old He
BIRTH H
NOW

15. Future Sun The Sun as a red giant The Sun today 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 today
The Sun as a red giant
The orbit of Venus

16. The Sun’s Final Glory He
BIRTH H
NOW

17. What’s Left? A White Dwarf
Mass: 50% Sun
Density: 1-2 tons per cc3
Composition: C & O, the “ashes” of nuclear fusion
Cools & fades slowly
12,000 Km
Sirius B

18. Sirius b Nearest White Dwarf Star Diameter: 1/100 Sun Mass: 98% Sun
Distance: 8.6 LY
Sirius b

19. BIGGEST VY Canis Majoris The The Sun A red “hypergiant” star
Credit: NASA/ESA/R Humphreys/U Minnesota)
A red “hypergiant” star
Diameter: 2000 x Sun
Mass: x Sun
Luminosity: 500,000 x Sun
5,000 light-years away
VY Canis Majoris

20. BRIGHTEST & MOST MASSIVE
Mass = 265 Suns (probably 320 Suns at birth!)
Luminosity = 8-9 million x Sun
Diameter: 35 x Sun
Distance: 165,000 LY
Future hypernova?
R136A*
Located in the Large Magellanic Cloud

21. The HOTTEST STARS are tiny, dim, new white dwarfs T=200,000 C
NGC 2440 (central star)
Distance: 4500 LY
NGC 6302 (central star)
Distance: 3800 LY
Hidden by central dust ring
KPD
Distance: 2500 LY
Only 2200 years “old”

22. COLDEST Stars The Brown Dwarfs! WISE 1828+2650 Temperature ~25 C
About 27 LY
Mass < 0.1 Suns
Too small for nuclear fusion

23. The Oldest Stars! HE 1523-0901 13.2 billion years old Mass: 0.8 Suns
Distance: ~7500 LY
A red giant star
Today
13.2 billion
Years ago

24. The Youngest Stars
Stars are forming today in the “empty” regions of interstellar space.

25. Stages of Star Formation

26. Stars on the Weird Side!

27. The Famous Pleiades Distance: 1300 LY Brightest Star Cluster
Formed about 115 million years ago
The blue glow is dust!

28. 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 The “expanding shell” is actually an expanding light echo

29. V838 Monocerotis – The Light Echo
To Earth
Arrives first
Arrives later

30. A Real Shooting Star! 13 LY tail 291,000 mph Mira = Omicron Ceti
An unstable red giant
Losing mass
Distance: 400 LY
Mass: 1.2 Suns
13 LY tail
291,000 mph
GALEX
GALEX
As seen by Hubble

31. Epsilon Aurigae Dust Disk 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

32. 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

33. 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
This star smokes!

34. More R Corona Borealis Extreme helium star
Very little hydrogen
Lots of carbon
Origin: merger of two white dwarfs?

35. Extreme Spots! Artist Conception
HD holds the record for the largest “starspot”
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.

36. Extreme Rotation! Rotates every 16 hrs! Other stars, too!
Regulus
Regulus = Alpha Leo
Distance: 78 LY
Mass: 3.8 Suns
Radius: 3-5 Suns
Altair
Vega
Rotates
every 16 hrs!
Other stars, too!

37. Crab Pulsar MORE EXTREME ROTATION Distance: 6500 LY
Mass: ~ Suns
Remnant of 1054 Supernova
Density: 100,000,000 tons
per thimbleful
Spins 30 times per second

38. Magnetars! Extreme Neutron Stars
SGR
Magnetars! Extreme Neutron Stars
SGR
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

39. Supernova 1987a

40. Supernova 1987a Detected in 1987 Exploded 170,000 years ago
Originally about 18 solar masses
Where is the neutron star?

41. Black Holes Closest candidate: Best candidate: V616 Mon
Distance: 3000 LY
Star mass: ~0.5 Suns
BH mass: ~6 Suns
BH Diameter: ~40 km
Orbit period: 7.75 hrs
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

42. The Universe is Full of Surprises!
And that’s what makes astronomy so much fun!

43. Kirkwood Observatory Open Tonight, 10:30-11:30PM
Weather permitting! Kirkwood Observatory is located at the west end of Dunn’s Woods, behind Bryan Hall

44. Happy Summer Solstice! On the handout:
URL for this presentation on the Web
Related websites
Kirkwood Observatory open tonight