High Mass and Binary System Stellar Evolution LACC §: 22.1, 22.2, 23.5 • High Mass (>~10 M solar ) Stars • Binary Systems • Enrichment of the ISM An attempt to answer the “big questions”: What is out there? Where did I come from? 1 Thursday, April 29, 2010
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High Mass and Binary System Stellar Evolution
LACC §: 22.1, 22.2, 23.5
• High Mass (>~10 Msolar) Stars
• Binary Systems
• Enrichment of the ISM
An attempt to answer the “big questions”: What is out there? Where did I come from?
The stellar wind causes mass loss for AGB stars. This loss is around 10-4 solar masses per year, which means that in 10,000 years the typical star will dissolve, leaving the central, hot core (the central star in a planetary nebula).
If the star is larger than 8 solar masses, then the core continues to heat. Carbon and oxygen fuse to form neon, then magnesium, then silicon. All forming into burning shells surrounding an iron ash core.
Novae and Type-Ia SupernovaeSpectacular explosions keep occurring in the binary star system named RS Ophiuchi. Every 20 years or so, the red giant star dumps enough hydrogen gas onto its companion white dwarf star to set off a brilliant thermonuclear explosion on the white dwarf's surface. At about 2,000 light years distant, the resulting nova explosions cause the RS Oph system to brighten up by a huge factor and become visible to the unaided eye. The red giant star is depicted on the right...while the white dwarf is at the center of the bright accretion disk on the left. As the stars orbit each other, a stream of gas moves from the giant star to the white dwarf. Astronomers speculate that at some time in the next 100,000 years, enough matter will have accumulated on the white dwarf to push it over the Chandrasekhar Limit, causing a much more powerful and final explosion known as a supernova.
the iron core collapses in just a few seconds to a neutron star (or black hole).
when the stellar core becomes solid iron, there is no fusion reaction available to produce energy to keep the core hot and maintain the pressure that resists gravity
Gas is recycled in the Galaxy. It goes into forming stars and is returned during the death throws of stars enriched with heavy elements for the next generation of stars. It is a giant cycle of life.
Neutron Stars / PulsarsWhat a star becomes when it dies depends on the mass left when all possible nuclear fuels are exhausted and the star has lost some of its original mass by ejecting it:
M <= 1.4 M -----> white dwarf (planetary nebulae)
1.4 M <M < ~3 M --> neutron stars/pulsars (type II supernova)
M > ~ 3 M ----> supernovae/black holes (type II supernova)
This picture shows a time sequence for the pulsar in the Crab nebula, shown in context against an image.... Both the nebula and its central pulsar were created by a supernova explosion in the year 1054 A.D. The enlarged region is a mosaic of 33 time slices, ordered from top to bottom and from left to right. Each slice represents approximately one millisecond in the period of the pulsar.
“A (simulated) Black Hole of ten solar masses as seen from a distance of 600 km with the Milky Way in the background (horizontal camera opening angle: 90°).”
Gamma-Ray BurstsJames Annis, an astrophysicist at Fermilab, near Chicago, has speculated that such events could sterilize entire galaxies, wiping out life-forms before they had the chance to evolve to the stage of interstellar travel. 1 "If one went off in the Galactic center," he wrote, "we here two-thirds of the way out of the Galactic disk would be exposed over a few seconds to a wave of powerful gamma rays." It would be enough, according to Annis, to exterminate every species on Earth. Even the hemisphere shielded by the planet's mass from immediate exposure would not escape, he claimed, since there would be lethal indirect effects such as the demolition of the entire protective ozone layer. The rate of GRBs in the universe today appears to be about one burst per galaxy per several hundred million years.
into it forming an even tighter binary system. The core of the massive star produces a supernova and leaves behind a neutron star. The neutron star's companion eventually begins to lose mass and forms an accretion disk around the neutron star. The accretion of material onto the neutron star causes it to spin faster and faster, eventually reaching a spin period of a few milliseconds. The accreted material produces X-rays which in turn can begin vaporizing the companion. All that remains at the end is a highly compact, rapidly rotating neutron star which produces a pair of radio beams and may be observable as a millisecond radio pulsar. http://heasarc.gsfc.nasa.gov/docs/
xte/Snazzy/Movies/millisecond.html
Millisecond PulsarsThis animation attempts to condense the billion year evolutionary history of such a binary system into a few tens of seconds. It begins with two stars, one more massive than the other, in a tight orbit. The massive star evolves first and swallows up its companion, which spirals
• solar phenomena (solar magnetic field): granules sunspots, flares, prominence/filaments, coronal mass ejection, aurora and geomagnetic storms (on Earth)
(red-shift vs. blue shift), composition, cluster age (main sequence turn-off)
• determining distances: (radar (closest planets/asteroids only)), stellar parallax, standard candles--e.g. main sequence fitting, RR Lyrae and Cepheid variables
• other properties: proper motion, luminosity, apparent brightness/magnitude vs. absolute brightness/magnitude, spectroscopic or eclipsing binaries to determine mass
[10 pts] Stellar Evolution• HR Diagram: x-,y-axes, evolutionary tracks• low mass evolution: Hayashi track, main sequence (H
• high mass evolution: similar to low mass stars, but keep fusing elements up to iron, type-II supernova (gamma ray burst), neutron star (pulsar) or black hole
[10 pts] Nebulae, Binary Systems & Stellar Remnants • nebulae: molecular clouds, HII regions (star forming
• nova and type-I supernova: binary system with a white dwarf, light curves; X-ray binaries and X-ray bursters: binary system with a neutron star or black hole; accretion disks
• stellar remnants: masses, sizes, densities of white dwarfs vs. neutron star vs. black holes; pulsars; black holes (singularity, Schwarzschild radius, event horizon)
[10 pts] Identify from an Image or Chart• solar surface features: sun spots (umbra, penumbra),
granules, prominence, flare, coronal mass ejection; nebulae: molecular clouds, star forming HII region, planetary nebulae, reflection nebulae
• HR Diagram: regions--main sequence, white dwarfs, giants, supergiants, spectral class, luminosity class; axes--x-axis = temperature, spectral class; y-axis = luminosity, absolute magnitude; mass & age & main sequence--high mass at top left, short lifetimes; low mass at lower right, long lifetimes; main sequence turn-off point gives a star cluster’s age
• Make use of a chart containing the following stellar data: apparent magnitude (mv), absolute magnitude (Mv), spectral class, luminosity class