stellar evolution a look at the stars from their birth to their death
TRANSCRIPT
Stellar Evolution
A look at the stars from their birth to their death
Nuclear Fusion !
At 15 million degrees Celsius in the center of the star, fusion ignites !
4 (1H) --> 4He + 2 e+ + 2 neutrinos + energy
Where does the energy come from ?
Mass of four 1H > Mass of one 4He
E = mc2
Our sun is currently burning Hydrogen
Larger stars (8M) have the capability to burn larger elements:
Hydrogen
Helium
Carbon
Oxygen
Neon
Magnesium
Silicon
Iron
Most of the universe is made of Hydrogen and Helium, all of the heavier elements that make up the Earth came from nuclear fusion reactions within stars.
A Balancing Act
Energy released from nuclear fusion counter-acts inward force of gravity.
Throughout its life, these two forces determine the stages of a star’s life.
Stage 1: An Interstellar Cloud
•A very large interstellar cloud of gas and dust provides the initial stage of star formation.
•The cloud might contain thousands of times the Sun's mass.
Stars form in gas nebulas
They collect gas from their surroundings
They enter the main sequence at various points depending on how much mass they collect
Cat’s Paw Nebula
• Resembling a huge paw print, the Cat's Paw Nebula is a star-formation region, with stars of close to 10 solar masses produced there in the past several million years. Its color is due to ionized hydrogen.
Photo: T.A.Rector/University of Alaska Anchorage
Pillars of Creation
• The renowned Hubble Space Telescope rendition of the "Pillars of Creation" in the Eagle Nebula, using more accurate color data. Ionized molecular hydrogen can be seen evaporating from the tips of these star-forming columns of gas and dust, under pressure of ultraviolet light from the nebula's central blue giant stars.
Photo: Jeff Hester and Paul Scowen/Hubble Space Telescope
Bok Globules
• Eerily suspended Bok Globules -- the larva-like clouds of molecular hydrogen, helium and silicate dust visible throughout the Carina Nebula -- have been sculpted by radiation from the nebula's giant star, Eta Carina, which is not visible here.
Photo: Michael Benson/Hubble Space Telescope, ESA, NASA
Witch Head Nebula• Basking in the glow of the bright supergiant star Rigel, the Witch Head Nebula trails like a puff of smoke through the Eridanus constellation about 700 light years away.
Photo: Davide De Martin/Palomar Observatory
Carina Nebula
• Distinctive cloud formations in the Carina Nebula. At the tips of the dust and gas protrusions, excellent examples of Herbig-Haro objects can be seen. These high-speed jets of gas are the byproduct of the birth of new stars, still hidden in the clouds.
Photo: Hubble Space Telescope/NASA, ESA, Michael Benson
Cone Nebula• A startling interplay
of blue and red colors characterizes NGC 2264, the region surrounding and including the Cone Nebula, which is at the bottom of the image. The region features immensely powerful blue stars, which light interstellar dust grains, producing the blue part of the glow. The red is from ionized hydrogen.
Photo: Davide De Martin/ESO
Crab Nebula• The sea-sponge-like
Crab Nebula is a 6-light-year-wide remnant of a supernova that exploded in 1054 Earth time. It is mostly made of ionized hydrogen and helium, though carbon, oxygen, nitrogen and other atoms are present, producing the complex color blend visible here. Photo: Hubble Space Telescope/NASA, ESA
HorseheadNebula
• The spectacular Horsehead Nebula is actually a projection of cold gas and dust extending from the dense Orion Molecular Cloud.
Photo: J.C Cuillandre (Canada France Hawaii Telescope) and Giovanni Anselmi (Coelum Astronomia)
Pelican Nebula
• The seemingly sculpted formations in its upper area are the result of the erosion of gas and dust by young, energetic stars. A long tendril of colder gas and dust extends many light years into the void from the receding ionization front.
Photo: Charles Shahar/Palomar
Snake Nebula• The Snake Nebula,
silhouetted against ancient stars massed near the nucleus of our galaxy, which is about 25,000 light years away. A classic dark nebula, the Snake is a tendril of interstellar gas and dust about 650 light years away.
Photo: J.C Cuillandre (Canada France Hawaii Telescope) and Giovanni Anselmi (Coelum Astronomia)
Rosette Nebula
• The center of the Rosette Nebula, which glows with the red light of ionized hydrorgen, is fueled by a central cluster of powerful giant stars. 3,000 cubic light years of gas have been heated to a temperature of over 10 million degrees Fahrenheit here -- about half the temperature of the Sun's core.
Photo: J.C Cuillandre (Canada France Hawaii Telescope) and Giovanni Anselmi (Coelum Astronomia)
NG 6559• NGC 6559 provides
a perfect demonstration of the first parts of the stellar life cycle. In a kind of star assembly line, interstellar molecular clouds collapse, producing new stars, which then gradually push back the remaining gas and dust.
Photo: J.C Cuillandre (Canada France Hawaii Telescope) and Giovanni Anselmi (Coelum Astronomia)
Picture of interstellar cloud
At this phase the cloud is very diffuse (not compacted), so heat is not trapped (except near the center) and temperature does not build much ( except at the center)
Stage 2: Collapsing cloud fragment
Several tens of thousands of years after the stage 2 fragment began to collapse, it becomes opaque at the center, and the central temperature rises significantly.
•Cloud has now shrunk to region the size of our Solar System•Protostar (early star) appears at the center of the fragment
Stage 3: Fragmentation Ceases
•The collapsing cloud heats as it contractsStage 4: Protostar
Low temperature, but very bright
Stage 5: Protostellar evolution
•As the protostar moves beyond stage 4, it moves toward the main sequence•Central temperature is still not hot enough for thermonuclear fusion
•Nuclear fusion begins •Energy is emitted
Stage 6: Newborn Star
•Star contracts a bit and reaches equilibrium.
Stage 7: The main sequence
Reprise: the Life Cycle
Sun-like Stars Massive Stars
•Stars of different masses from the Sun follow different tracks on the H-R digram.•Arrive at different points on the main sequence•Star "stays put" on the main-sequence, spending most of its life in one place
Big star, small star
An artist's comparison of a blue supergiant with the Sun and Jupiter:
Blue Supergiant
A blue supergiant is a very large, very hot, and very luminous star
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, Kinetic energy of collapse converted into
heat.
This heat expands the outer layers.
• Meanwhile, as core collapses, Increasing Temperature and Pressure ...
Red Giant
The picture above illustrates the relative sizes of main sequence stars like the Sun and Spica as compared to a Red Giant. The sun will eventually turn into a Red Giant, billions of years from now.
Represents a late stage in stellar evolution, it occurs after the star has burned through most of its hydrogen and the temperature begins to decrease and the star gets larger.
Red Dwarfs, the smallest Main Sequence stars have about 10% the radius of the Sun. Low mass Main Sequence stars don't have as much weight pushing them down in the center so don't have fusion at such high temperatures as the Sun.
White dwarf. Our Sun will one day leave behind a white dwarf as a corpse.
Small stars
Here is an example of a Red Supergiant
This is Betelgeuse, the first star after the sun whose surface was imaged in photographs
There are several kinds of exploding stars:
• Planetary Nebulae- when sun-size stars die
• Novas---100,000 times the energy output (luminosity) as our Sun.
• Supernovas--one million times brighter than novas!
Star DeathSometimes stars die and blow up. This is a good thing for the following reasons:1. When a massive star blows up, it releases the heavy
elements its made by fusion back into space--those elements can then go into making up beings like ourselves (calcium in our bones, iron in our blood cells, zinc, copper, etc.)
2. When stars fuse, it takes energy to make elements heavier than Iron. So how are those elements made at all? Many are made in the explosion that blows up a star (very powerful).
3. Star explosions can lead to the birth of other stars.
Life Cycle of Stars – Depends upon their original mass
• After they spend their life as main sequence star ….
• Sun size > expand to red giant in about 5 billion years > white dwarf > black dwarf
• Super giant > supernova >
very high mass – black hole
high mass – neutron star
The end for solar type stars
Planetary Nebulae
After Helium exhausted, outer layers of star expelled
Planetary Nebula
•Planetary Nebulae mark the death of sun-like stars (billions of years old)
•Nebulae last ~10,000’s years
•Top one is the closest to the sun (400 light years away)
•Bottom is 1000 light years away
Star Dies – Star casts off shell . It creates nebula that can take a variety of shapes – Ant Nebula
More p. nebula
bug nebula
Helix nebula
Cool Hubble pictures
cont
White dwarfs
At center of Planetary Nebula lies a White Dwarf.
• Size of the Earth with Mass of the Sun “A ton per teaspoon”
• Inward force of gravity balanced by repulsive force of electrons.
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.
The End of the Line for Massive Stars
Massive stars burn a succession of elements.
Iron is the most stable element and cannot be fused further. Instead of
releasing energy, it uses energy.
What’s Left After the Supernova
Neutron Star (If mass of core < 5 x Solar)
• Under collapse, protons and electrons combine to form neutrons.
• 10 Km across
Black Hole (If mass of core > 5 x Solar)
• Not even compacted neutrons can support weight of very massive stars.
SupernoSupernova!va!
The intense explosion forces the gases outward, away from the core…creating a NEW NEBULA
Elements from Supernovae
All X-ray Energies Silicon
Calcium Iron
NEUTRON STAR:
Tiny and dense remains of the a star’s core. Left behind after the outer layers were blown off.
Black Holes - Up Close and Personal
Jet(not always present)
Accretion DiskEvent Horizon
Singularity(deep in center)
Star’s Life Cycles
