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)

Bri

gh

tne

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

The Sun’s Final Glory

BIRTH

NOWH

He

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

GAL

EX

As seen by Hubble

GALEX

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

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