E treme Stars Caty Pilachowski Mini-University June 2012

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

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

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

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

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

Allowed Temperature & Luminosity

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

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 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 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

The Sun’s Final Glory He BIRTH H NOW

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

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

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: 30-40 x Sun Luminosity: 500,000 x Sun 5,000 light-years away VY Canis Majoris

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

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 0005+5106 Distance: 2500 LY Only 2200 years “old”

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

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

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 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

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

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 This star smokes!

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

Extreme Spots! Artist Conception HD 12545 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.

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!

Crab Pulsar MORE EXTREME ROTATION 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! Extreme Neutron Stars SGR 1900+14 Magnetars! 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?

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

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

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

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