stellar evolution: outline - academic computer...

Stellar Evolution: Outline

● Interstellar Medium (dust)– Hydrogen and Helium– Small amounts of Carbon

Dioxide (makes it easier to detect)

– Massive amounts of material between 100,000 and 10,000,000 solar masses

● Gravitational Collapse of dust– Competing forces of pressure

and gravity where gravity “wins”

– Collapse “ignites” nuclear fuel

– Causes stellar birth and stellar death

Stellar Evolution: Outline part 2

● Contraction of the cloud– Slow gravitational pull on

particles (million years or so)– Collapsing cloud becomes

opaque and heats up– Temperature increases

therefore pressure increase● Slows contraction● Several million years● Shines in IR (is not

ignited yet)● Eventually core gets hot

enough to initiate hydrogen fusion

Proto-star

● Proto-star– The beginnings of a star– 10,000,000 K at which point

hydrogen fuses to helium● Star is ignited● Burns due to nuclear fusion

– Star reaches an equilibrium with gravity● Pressure and gravity are

equal● Will stay equal until gravity

wins again – death– When star transitions into a

“real” star the star is called a Zero Age Main Sequence (ZAMS) star.

Fusion produces a star

● Hydrogen fusion– Hydrogen does NOT burn into helium– Hydrogen fuses together to form

helium

– This reaction has a mass loss (the right side has less mass then the left side)

– Mass loss is converted into energy– Mass loss is mostly due to binding

energy● The two protons and two neutrons in the

helium atom weights less when then they individually due when “binded” into a helium atom

● That mass loss is converted to energy

4 H11+4 e→2 He2

4+2e

Young Star

● http://hubblesite.org/newscenter/newsdesk/archive/releases/2006/07/image/a+zoom

● Young star– Many different types– Hot and blue– Cool and red– Low mass, high mass– On the main sequence now

(H-R diagram)● Off main sequence in

birth and death● In galaxy at right young

blue stars are in the arms and older yellowish stars are in the center

Energetic Young Star and Jets

● Young Star– Energetic outflows associated

with young stars● In this picture your star

responsible is not seen on the top of the picture

● Magnetic fields of collapsing rotating clouds are responsible

● Jets– Used to dissipate excess

angular momentum (important so the star doesn't tear itself apart)

Middle-aged Star

● Middle-aged Star– On main sequence– Many different types– Generally 0.8 to 8 solar

mass– No more jets, just a

“normal” star

Mature Star

● Mature Star– Hydrogen is used up– Nuclear process

ceases and gravity starts to win again

● Inner core compresses

● Outer layers expand

Red Giant● Red Giant

– Outer layer expands– Our Sun: passes Earth– Hydrogen “shell” still burns– Will fuse helium slowly

● Triple fusion into carbon● Some less massive stars fuse

helium fast– Helium flash

● Temperatures rise● Helium burns

– 100,000,000 K allows this fusion to take place

– ~ 500000 years– Blue stars

● Off main sequence

Red Giant example

Planetary Nebula

● Planetary Nebula– Eventually the star

(assuming a “normal star”) will eject material

– This material will spread out into the Universe and will be used again

Death of a star● Death of a star

– Low-mass stars● Universe isn't old enough

to know– Medium-mass stars

● Red Giant for 1 billion years

● Planetary nebula star to form from instabilities

● Core is a white dwarf– Radiates heat, but

has no fuel– Eventually turns to a

black dwarf– Massive stars

● Fusion goes to heavier elements

Supernova

● Massive stars– Fusion goes to iron– Iron absorbs energy but

cannot fuse...boom– Supernova

● Supernova– Neutron stars

● Electrons go into protons to form neutrons

● Rapidly rotating● Very very dense● Size of a city● Pulsars

– Black holes● Light does not escape● Event horizon● Wormhole?

Evolution of stars from Alpha to Omega

● Alpha to Omega– On the edges dark clouds

where formation of stars begin

– As we go into the picture stellar nurseries in pillars of dust

– In the middle young blue stars whose stellar winds blow away the interstellar gas

– Somewhat right of the cluster is the ring typical of supernovas (like 1987A)

FYI: Our Sun

Why different wavelengths?

● Molecular – Emission in microwave, then infrared● Young star – Emission in IR, note jets● Disk – Emits in the IR● Mature star – Emits in X-ray and UV

● Molecular Young Star Disk Mature Star

Black Holes

● Theorized in Newtonian times, but not like the modern black hole idea

● Forms into a singularity– Zero volume– Not allowed by Quantum

Mechanics...● Types

– Not spinning● Event horizon

– Spinning ● Kerr-Newman black hole● All mass in a singularity● Will have an event

horizon plus● Kerr solution leads to

possible “wormhole” to a negative universe

Black Hole Formation

● Black Hole Formation– Stellar– Accumulation of extra mass

from a companion as in a binary system

– Stellar remains (like white dwarf or neutron stars) merging

● Likely will form super massive black holes

● Galaxies with bulges seem to have super massive black holes – NEW EVIDENCE suggests black holes from before the galaxies...

● Image: Wikipedia

Black Hole Eating a Star

Black Holes colliding (will merge)

Black Holes in Merging Galaxies

Micro Black Holes

● Black Hole Formation– Mini-black holes? Have been

reported in particle accelerators = fireballs

● Not a gravitational object however; so...

● Some believe there were many micro black holes formed at the beginning of the universe and the “zip” through Earth even today...still needs to be proved….