Stars, Their Lives, And The Stuff In Between Sarah Silva Program Manager Sonoma State University NASA Education and Public Outreach

Stars, Their Lives, And The Stuff In Between

Sarah SilvaProgram Manager

Sonoma State University NASA Education and Public Outreach

The NASA E/PO Program at Sonoma State University

• A group of seven people working collaboratively to educate the public about current and future NASA high energy astrophysics/astronomy missions.

• Led by Prof. Lynn Cominsky Swift

GLAST

XMM-Newton

What do we know about stars?

Life Cycles of Stars

Classifying Stars

Hertzsprung-Russell diagram

Stars spend most of their lives on the Main Sequence

Stars and Balloons

• Volunteers Please

Stars and Balloons

• Imagine we have:• 12 - Red Balloons • 12 - Yellow Balloons• 4 - White Balloons• 2 - Blue Balloons

OR• Roughly 80% red and yellow, 15% white,

and 5% blue.

Preparation:

• Place 1 wooden bead inside each red and yellow balloon.

• Place 1 marble inside each white balloon.

• Place 1 ball bearing inside each blue balloon.

Stars and Balloons

• Red Balloons ↓0.4 Solar Mass (2/5 the mass of our Sun): Red stars

• Yellow Balloons 1 Solar Mass (the mass of our Sun): Yellow Stars

• White Balloons 3 Solar Masses (3 times the mass of our Sun): White Stars

• Blue Balloons 9 Solar Masses (9 times the mass of our Sun): Blue Stars

• Please blow up your balloon until it has a 3 inch diameter.

5 Million Years

Red Balloons Yellow Balloons White Balloons Blue Balloon

↓0.4 Solar Mass (2/5 the mass of our Sun): Red stars

1 Solar Mass (the mass of our Sun): Yellow Stars

3 Solar Masses (3 times the mass of our Sun): White Star

9 Solar Masses (9 times the mass of our Sun): Blue Stars

Wait. Do not change diameter of balloon.



Blow slightly more air into balloon.

10 Million Years






Wait. Wait. Blow up a little more Blow up star as fast and as much as you can. When star is fully inflated, -a supernova.

500 Million Years






Wait Wait (note: planets are forming)

Continue to slowly inflate star. As it gets bigger, star cools, so color it yellow and red (make squiggles on surface with markers).

This popped star has become a black hole; all of the super nova remnants can be thrown out into space.

1 Billion Years






Wait Blow up a little bit. Quickly blow up star until fully inflated; pop balloon. Make sure to catch marble

Still black hole!

8 Billion Years






Wait Blow up more. The star is getting cooler, so color it red with marker. It is now a supergiant.

This star has exploded. Holding on to neutron star (marble), throw supernova remnants into space. Place remnants in a recycle bin to demonstrate stellar gas is recycled into new star matter.

Still black hole

10 Billion Years






Wait Blow up a little more. Outer envelope dissolves, so cut up balloon. The inside bead becomes a white dwarf, and the bits of balloon represent the planetary nebula.

Neutron star Still black hole

Reprise: the Life Cycle

Sun-like Stars Massive Stars

Molecular clouds and protostars

• Giant molecular clouds are very cold, thin and wispy– they stretch out over tens of light years at temperatures from 10-100K, with a warmer core

• They are 1000s of time more dense than the local interstellar medium, and collapse further under their own gravity to form protostars at their cores

BHR 71, a star-forming cloud(image is ~1 light year across)

Protostars• Orion nebula/Trapezium stars (in the sword)• About 1500 light years away

HST/ 2.5 light years Chandra/10 light years

Stellar nurseries

• Pillars of dense gas

• Newly born stars may emerge at the ends of the pillars

• About 7000 light years away

HST/EagleNebula in M16

HR Diagram again as a reminder

Main Sequence Stars

• Stars spend most of their lives on the “main sequence” where they burn hydrogen in nuclear reactions in their cores

• Burning rate is higher for more massive stars - hence their lifetimes on the main sequence are much shorter and they are rather rare

• Red dwarf stars are the most common as they burn hydrogen slowly and live the longest

• Often called dwarfs (but not the same as White Dwarfs) because they are smaller than giants or supergiants

• Our sun is considered a G2V star. It has been on the main sequence for about 4.5 billion years, with another ~5 billion to go

Pro Fusion or Con Fusion?

• The core of the Sun is 15 million degrees Celsius

• Fusion occurs 1038 times a second• Sun has 1056 H atoms to fuse• 1018 seconds = 32 billion years• 2 billion kilograms converted every second• Sun’s output = 50 billion megaton bombs per

second

1018 seconds is a long time…

but it’s not forever.

What happens then?

Don’t Let the Sun Go Down on Me

The Beginning Of The End: Red Giants

After Hydrogen is exhausted in core...Energy released from nuclear fusion

counter-acts inward force of gravity.

Core collapses, and kinetic energy of collapse

converted into heat.

This heat expands the outer layers.

Meanwhile, as core collapses, Increasing Temperature and Pressure ...

More Fusion !

At 100 million degrees Celsius, Helium fuses:

3 (4He) --> 12C + energy

(Be produced at an intermediate step)

(Only 7.3 MeV produced)

Energy sustains the expanded outer layers of the Red Giant

Stellar evolution made simple

Stars like the Sun go gentle into that good night

More massive stars rage, rage against the dying of the light

Puff!

Bang!

BANG!

How stars die

• Stars that are below about 8 Mo form red giants at the end of their lives on the main sequence

• Red giants evolve into white dwarfs, often accompanied by planetary nebulae

• More massive stars form red supergiants

• Red supergiants undergo supernova explosions, often leaving behind a stellar core which is a neutron star, or perhaps a black hole

Red Giants and Supergiants

Hydrogen burns in outer shell around the core

Heavier elements burn in inner shells

Fate of high mass stars

• After Helium exhausted, core collapses again until it becomes hot enough to fuse Carbon into Magnesium or Oxygen.

12C + 12C --> 24Mg

OR 12C + 4H --> 16O

• Through a combination of processes, successively heavier elements are formed and burned.

Heavy Elements from Large Stars

• Large stars also fuse Hydrogen into Helium, and Helium into Carbon.

• But their larger masses lead to higher temperatures, which allow fusion of Carbon into Magnesium, etc.

Supernova !

Crab nebula and pulsar

X-ray/Chandra

Neutron Stars and Pulsars

Neutron Stars and Pulsars

If neutron stars are made of neutral particles, how can they have magnetic fields?

• Neutron stars are not totally made of neutrons-- the interiors have plenty of electrons, protons, and other particles.

• These charged particles can maintain the magnetic field. • Plus, a basic property of magnetism is that once a

magnetic field is made, it cannot simply disappear. • Stars have magnetic fields because they are composed

of plasma, very hot gas made of charged particles.

Magnetic Globe Demo

A Burst By Any Other Name…

• Neutron star: dense core leftover from a supernova

• Possess incredibly strong magnetic fields

• Soft Gamma Ray Repeater: violent energy release due to starquake

• Accretion: neutron star draws matter off binary companion

• Matter piles up, undergoes fusion: bang!

• Cycle repeats: X-Ray Burster

Flash!

The fading afterglow, seen for the first time in X-rays

Swift Mission

• Burst Alert Telescope (BAT)

• Ultraviolet/Optical Telescope (UVOT)

• X-ray Telescope (XRT)

Launched November 20, 2004

Swift Mission

• Will study Gamma-Ray Bursts with “swift” response• Survey of “hard” X-ray sky• Launched November 20, 2004• Nominal 2-year lifetime• Will see ~150 GRBs per year

Birth of a Black Hole

• Long bursts (>2 seconds) may be from a hypernova: a super-supernova

• Short bursts (<2 s) may be from merging neutron stars

• Both create nature’s vacuum cleaner: a black hole

Gamma-ray Bursts

Either way you look at it – hypernova or merger model

GRBs signal the birth of a black hole!

What Is A Black Hole?

– Not just a vacuum cleaner– If you take an object and squeeze it down in

size, or take an object and pile mass onto it, its gravity (and escape velocity) will go up.

Black Hole Structure

• Schwarzschild radius defines the event horizon

• Rsch = 2GM/c2

• Not even light can escape, once it has crossed the event horizon

• Cosmic censorship prevails (you cannot see inside the event horizon) Schwarzschild BH

Black Hole Space Warp

• Record the following questions based on your observations.

1. What do the moving balls represent?

2. What does the weight represent?

3. What happened to the balls?

4. What does the blue latex material represent?

5. What happens to the material when the bouncy balls roll around?

Masses of Black Holes

• Primordial – can be any size, including very small (If <1014 g, they would still exist)

• “Stellar-mass” black holes – must be at least 3 Mo

(~1034 g) – many examples are known• Intermediate black holes – range from 100 to 1000

Mo - located in normal galaxies – many seen

• Massive black holes – about 106 Mo – such as in the center of the Milky Way – many seen

• Supermassive black holes – about 109-10 Mo - located in Active Galactic Nuclei, often accompanied by jets – many seen

How Do Black Holes Form?

• Stellar-mass black holes – Supernova: an exploding star. When a star

with about 25 times the mass of the Sun ends its life, it explodes.

– called a “stellar-mass black hole,” or a “regular” black hole

– Stellar-mass black holes also form when two orbiting neutron stars – ultra-dense stellar cores left over from one kind of supernova – merge to produce a short gamma-ray burst.

Where Are Black Holes Located?

• Let’s think….

• They form from exploded stars…

• We have one at the center of the Milky Way….

• The nearest one discovered is still 1600 light years away

• Black holes are everywhere!

Evidence• This shows ten

years worth of Prof. Ghez’ data at 2.2 microns of the stars orbiting around a 4 million solar mass black hole at the center of the Milky Way.

• It also shows the star’s orbits extrapolated into the future Note: Stars S0-2 and S0-16 provide the

best data

Supermassive Black Holes

• Normal galaxy– A system of gas, stars, and

dust bounded together by their mutual gravity.

VS.

• Active galaxy– An galaxy with an intensely

bright nucleus. At the center is a supermassive black hole that is feeding.

Galaxies and Black Holes

• Zooming in to see the central torus of an Active Galaxy.

Jet

Accretion disk

Black Hole

Resources

• 1st Section – Stellar Cycle Balloon Activity– Adler Planetarium:

http://www.adlerplanetarium.org/education/teachers/plans/gravity/9-12_gq5-1.shtml

• 2nd Section – Supernova and Magnetic Globe– http://xmm.sonoma.edu/edu/supernova

• 3rd Section – Black Holes Space Time Warp– http://glast.sonoma.edu/teachers/blackholes

– My Email: [email protected]



http://xmm.sonoma.edu/edu/supernova

http://xmm.sonoma.edu/edu/supernova

http://glast.sonoma.edu/teachers/blackholes

http://glast.sonoma.edu/teachers/blackholes

• extra

The Supernova ConnectionThe Supernova Connection

GRB011121

Afterglow faded like supernova

Data showed presence of gas like a stellar wind

Indicates some sort of supernova and not a NS/NS merger

Iron lines in GRB 991216

Chandra observations show link to hypernova model when hot iron-filled gas is detected from GRB 991216

Iron is a signature of a supernova, as it is made in the cores of stars, and released in supernova explosions

Hypernova

• A billion trillion times the power from the Sun• The end of the life of a star that had 100 times

the mass of our Sun

movie

Catastrophic Mergers

• Death spiral of 2 neutron stars or black holes

Documents

Stars, Their Lives, And The Stuff In Between Sarah Silva Program Manager Sonoma State University NASA Education and Public Outreach