The Fate of Stars - Physics and Astronomy and more! Fate of Stars.pdf · The Fate of Stars...
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8/15/2014 1 The Fate of Stars Spectacular Endings One Quality to Rule Them All The single quality of a star that most determines its existence and its fate is its mass, both initially and at the end of its life cycle – A reminder: when we talk about the life and death of a star, we are not talking Hollywood; our stars have more character but are not alive Initial Mass Function How many stars of each mass category form from a GMC-not the auto company From the HR diagram, there are many more low mass stars than high mass stars – 80% in Milky Way We see mostly high mass or enormous stars at night because they tend to be the brightest
Transcript of The Fate of Stars - Physics and Astronomy and more! Fate of Stars.pdf · The Fate of Stars...
8/15/2014
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The Fate of Stars
Spectacular Endings
One Quality to Rule Them All
The single quality of a star that most determines its existence and its fate is its mass, both initially and at the end of its life cycle– A reminder: when we talk about the life and
death of a star, we are not talking Hollywood; our stars have more character but are notalive
Initial Mass Function
How many stars of each mass category form from a GMC-not the auto company
From the HR diagram, there are many more low mass stars than high mass stars– 80% in Milky Way
We see mostly high mass or enormous stars at night because they tend to be the brightest
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But counter-intuitively, high mass stars are the shortest-lived
They do have the most fuel to begin with, but high mass stars burn it at vastly higher rates than low mass stars
We can see some relatively low-mass stars with the naked eye, but this is because they have puffed up in their post Main Sequence stages, providing more surface area to shine
Low Mass Endings (M, L)
For stars less massive than our Sun, say <50% Msun, the end is rather anticlimactic– The star remains convective for all of its MS
years, longer than the age of the Universe
– It has insufficient mass to move onto the CNO cycle
Brown dwarfs barely fuse heavy hydrogen, much less p+-p+
– It will ultimately become a helium white dwarf, then presumably a helium black dwarf
Sun-like stars ( K, G, and F)
We’ve seen this before:
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Mass/Temperature Line
0.085Msol 0.80Msol 1.5Msol
BrownDwarf
RedDwarf
YellowDwarf
Giants
3000K 6000K 10,000K 30,000K400K
Coolest BD yet discovered, 30-40 Jupiter masses!
Mass/Lifetime Line
BrownDwarf
RedDwarf
YellowDwarf
Giants
0.085Msol 0.80Msol 1.4Msol
Chandrasekhar Limit
~3Msol
12 Tyr 20Gyr 5Gyr 10Myr
The Mass Cut (A, B, and O)
The real fun begins for stars that have MS masses > 1.5Msun
– Or, for white dwarfs or neutron stars > 1.4Msun
– Chandrasekhar limit
CNO cycle– C is a catalyst for H He
Two paths you can go by*:– Supernova– Black Hole
*But in the long run…
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Subrahmanyan Chandrasekhar
1910-1995
If the WD > 1.4Msol, degenerate electron gas pressure can be overcome (!!)– A consequence of SR
– The WD collapses
Author: "Truth and Beauty: Aesthetics and Motivation in Science" (1987)
The Novae Family
Nova– Outbursts fueled by degenerate hydrogen ignition on WD
Not enough H before ignition to drive WD > 1.4 Msun
Type Ia: thieving white dwarfs!– Found in galactic bulges, halos, elliptical galaxies
Population II starsType 1b, 1c– Similar to Type II– No evidence of hydrogen
Lost its H envelope in earlier ‘wind’ or companion actionIb, Ic show signs of ionized Fe, Ca, etc.
Type II: supermassive stars– Core collapse– Hydrogen evident– Found in regions of star formation (disks)
Population I stars– Expel more mass than Type Ib, Ic but at a lower velocity
Binary and Trinary Systems
By a small majority (53%), most stars are not solitary but gravitationally bound to a companion star (or two)Dwarf-dwarf, giant-dwarf, giant-giant
– 75% of O-type stars have a companion
– Maybe 33% of these will merge, creating hypermassive stars too massive to have formed ‘normally’
– The rest may share atmospheres…
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Nova Mechanism
When the massive companion to a dwarf expands beyond its Roche lobe, accretion occursThe small star’s H layer increases in mass (but not height) causing compression and heating until there’s a surface explosion 1045 ergs of energy released, only1038 in the optical
The white dwarf survives the explosion to nova again
Thousands to millions of years in the cycle
Nova vs. Type 1a
It would seem that the same accretion process produces two different results
Not so! Here’s the difference:– If the WD is initially close to the Chandrasekhar
limit the additional mass from the companion will push it over the edge. Type 1a
– If the WD is somewhat less than the limit the surface H will ignite before the total exceeds the limit. Nova
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Type 1a
Supernovae in general
The death of a star ~ 1sec– Type I: critical density of 2X109 g/cc
Merging white dwarfs (more common) or accretion (more powerful)
– Type II: at least 10 Msol
1053 ergs released in SN 1987A– More than Type 1a because C -> Fe fusion is less
energetic than UG release in Type IINeutrino precursorMaterial ejected at 1000’s km/secBetelgeuse (427 LY) a candidate– We’re safe!– Closer than 26 LY to affect the ozone layer
Layers
H, He, C, Ne, O, Si, Fe-Ni
Less and less energy in fusion of heavier elements
Hydrostatic equilibrium fails
Fe core for about 1 day, then BOOM!
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Collapse
Fe tightly bound, no more energy out from fusing into heavier elements
All the outer layers fall onto iron core at 43,000 miles/sec
A mass the size of Earth compresses to less that the size of Catalina Island
Density: a sugar-cube sized chunk of compressed core would weigh as much as the entire human race
Rebound
The infalling material rebounds off the superdense core, creating a shockwave that blasts outwards– The whole process takes < 1 second
The star explodes violently– Elements heavier than Fe are made in this explosion– The beginning of bling: Au, Ag, etc.
Type 1a’s make most of the Fe, not much else
Electrons in the Fe core are driven into protons creating neutrons and neutrinos– No more electrostatic repulsion; neutrons pack tightly
Crab Nebula, 1054. Type II
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Tycho Brahe’s 1572 SN: Type 1a
X-ray image
Johannes Kepler’s 1604 SN. Type Ia
X-ray image
Type 1a in M101 6Mpc, 8/24/2011
Credit: Bill Schlosser
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SN 2011fe
1987a: Before and After. Type II
Sanduleak in the LMC
B3I blue giant– 16-20Msol
– 100,000Lsol
Tarantula Nebula
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flux
Previous Planetary Nebula Illuminated
Artist’s rendering
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SN 2003jd
Type Ic – In the spiral galaxy IC
1065– Taken by the Subaru
Telescope in Hawaii.
So-called hypernova– Supermassive
(100Msol) star collapse
Gamma rays bursts– Jets not aligned with
Earth (good!)
Hypernova Theory
UC Santa CruzShowed that hypernovae last as stars < 1Myr, then gamma burst on their way to becoming a black hole while other stars in the cluster are still forming
Dr. Stanford E. Woosley
Nearest SN Candidate: HR8210
The binary system first spotted in 1993150 LY away in Pegasus: too close for comfort!Harvard student astronomer Karin Sandstrom examined it for a college paper Could take hundreds of millions of years before it exceeds the Chandrasekhar limit and supernovas
This is the culprit
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Another Candidate: Eta CarinaHeavy outgassing is a sign she’s ready to blow!
– From 1839 to 1857 Eta Carina was the second brightest star in our sky after Sirius
Rare Luminous Blue Variable class– 8000LY
SN RemnantsNeutron Star
Magnetar– Magnetic Field 100X normal NS
Pulsar
LGM-1
First detected by graduate student Jocelyn Bell and her advisor Anthony Hewish
Only 1/1,000,000 of their energy comes in radio bandwidth– 10% in gamma
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Crab Nebula Pulsar: shock wave time lapse next slide
MagnetarNeutron star with tremendous magnetic fieldPerhaps the early stage of a NS before it “pulses”Releases energy like a Tesla coil but as magnetic flaresImage is NASA artist’s rendering
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The Red Pill or the Blue Pill?
Edgar Allen Poe: Descent into the Maelstrom
“After a little while I became possessed with the keenest curiosity about the whirl itself. I positively felt a wish to explore its depths, even at the sacrifice I was going to make ; and my principal grief was that I should never be able to tell my old companions on shore about the mysteries I should see.”
How did he know?
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Frame Dragging
The Black Hole: M > 18* Msun
Degenerate Neutron Pressure (DNP)– Like degenerate electrons in a White
DwarfDNP overcome; matter falls in on itself, infinitely curving spaceGravitational Red Shift, time dilation
*Could be as little as 3 Msun, but 18 is safe.
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Also photon sphere @ 1.5Rs
Gravitational Lensing
Cygnus X1
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In motion
In The Extreme Case, A Complete Absorption
Black Hole eats Neutron Star
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Nearest Black HoleV4641 Sgr. (in Sagittarius), 1600 LY away
VLA pictures 30 minutes apart show radio jets
2.5 Million Discovered by WISE*
*Wide-field Infrared Survey Explorer
Maximum Black Hole10 billion Msol!Anything more massive and the radiation from the accretion disk blows ‘lunch’ away
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Wormhole
Formally known as an Einstein-Rosen tunnel
Requires a perfect solution to GR equations:– No rotation
– No charge
– Perfectly homogeneous
Time Travel and Causality
If such a phenomenon was ever found, time and space travel might be possible– IF you could withstand
the tidal forces!
But you might end up in another Universe!– No kidding
