Stellar Evolution: Outline - Academic Computer...
Transcript of 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….