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The evolution and collapse of
BH forming stars
Chris Fryer (LANL/UA)
 Formation scenarios – If we form them, they
will form BHs.
 Stellar evolution: current issues
 Issues in collapse
 Neutrinos from Massive Stars
Formation Scenarios
• First stars: Without metals, it
is possible that the first
generation of stars is more
massive than later
generations (how different is
yet to be determined)
• Collisions of stars can build
up a massive star progenitor
(e.g. Portegies-Zwart 2004,
see next talk by Evghenii
Gaburov’s talk)
• Low metallicity scenarios
discussed by Marta Volunteri
• However such stars are
formed, the fate depends only
a few parameters – metals
(and winds) and final entropy
Explosions from stellar collapse – the fate depends on the
metallicity
The lower metallicity of the first star alters the winds and hence the
fate of these stars (but this also depends on the stellar model).
Mass Loss
depends
upon
prescription
used in
stellar model:
At solar
metallicity, a
120 Msun star
may end its
life as a 2-3
Msun star or
a >30 Msun
star
(depending
on code).
Limongi & Chieffi
Heger et al.
The lower metallicity of the first star alters the winds and hence the
fate of these stars (but this also depends on the stellar model).
Limongi & Chieffi massloss changes BH line and
BH masses
Heger et al. now working on stars from
1000Msun up to 1 million Msun
Mixing in Stars
•To construct a
single-star
progenitor for
GRBs, Yoon et al.
(2005,2006)
“discovered a new
rotationally induced
mixing algorithm
Mstar
Vinit
Mco
Mfinal
30
279
5.2
29.4
30
369
17.6
23.2
30
455
17.4
21.2
40
392
25.2
28.8
40
484
14.2
17.1
• Although this mechanism
increases the number of
stellar-mass black holes, it
tends to make smaller-mass
black holes
Stellar Evolution Issues
• The amount of mass-loss is still poorly determined and different groups
get different answers. For many models, the mass-loss has been scaled
to match Wolf-Rayet observations neglecting binary effects. Much of our
intuition may be flawed.
• The
treatment
for
convection
is the
source of
many
numerical
errors and is
still poorly
understood.
Modeling Collapse
• The Herant et al. (1994)
convective engine
seems to work. Most
groups produce
explosions in normalmassed (12-20 solar
mass) when they model
the instabilities above
the proto-neutron star.
• But this engine (and the
intuition we have gained
from it) is not valid for
massive stars.
Basic SN engine: the core collapses and
bounces; convection above the PNS
(perhaps SASI) revives explosion
Neutrino-Driven Supernova Mechanism: Convective Phase
Anatomy
Of the
Convection
Region
ProtoNeutron
Star
Upflow
Accretion
Shock
Downflow
Fryer & Warren 2002
Collapse of Massive Stars
• The evolution is
drastically altered
by higher entropy –
getting accurate
entropy
measurements
essential.
• Likely evolution
for these massive
stars predicts
massive protoblack holes (at
relatively low
densities) that then
collapse.
Collapse Calculations: Entropy of the Core
Critical
• Most of our intuition is based on black hole formation of stellar-massed
systems. But as we move up in stellar mass, the entropy in the core
increases. The intuition we’ve built up in the last decade may prove
useless.
Initial Entropy
105 solar mass star
After 1s
After 4s, just prior
to BH formation
Entropy differences alter the cooling, which in turn,
alters every phase of collapse.
For example, low entropy cores need to be quite
condensed to emit neutrinos. Only the inner core
cools, leading to a collapse of the inner ~1Msun. For
higher entropy, massive stars, a 40 solar mass protoblack hole forms.
280 ms
290 ms
Electron/positron pair annihilation (gamma-rays produce
positrons, positrons annihilate with electrons producing
neutrinos and anti-neutrinos) dominates the cooling at
higher entropies. The lepton fraction remains higher and
electron degeneracy pressure plays a stronger role at late
times.
Neutrino signals from massive stars
The neutrino signal from these
stars peaks higher than normal
supernovae (typically peaking at
1052 erg/s for 10ms) and the
luminosity remains high for several
seconds!
Both a 105 solar mass star (top) and
300 solar mass star (left) produce
strong neutrino signals with more than
104 times as much energy in the first
few seconds.
Neutrino Detection
• High fluxes, durations and energies may make these sources directly
detectable beyond the Virgo cluster (by IceCube or Dusel).
• But the most likely detection is through the diffuse neutrino background.
If they occur at low redshift, they will fit directly in the GADZOOKS energy
band.
GADZOOKS sensitivity
Preliminary results of a 105 solar
mass black hole : neutrino fluxes
(3 flavors) and gray energies.
Summary
• Massive star evolution plagued by a few key
uncertainties: mass loss from winds and stellar mixing.
It is possible that BHs above 100Msun can form with
metallicities above 0.1 solar.
• Although we seem to be converging on an engine for
“normal” supernovae, most of our intuition gained from
these low-entropy models is not so useful for BH
formation.
• The neutrino signal from these collapses may be
detectable. We need detailed spectra and details of
formation.
• We’re working on new models, requests taken.