Transcript The First Stars and Black Holes

The First Stars and Black Holes
Stars today
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Old and young populations (I and II)
Different histories
Different chemical makeup
Initial material (sampled between galaxies)
almost pure H/He
• No known stars so metal-poor
• So - where are the Old Ones?
Starbirth
• Interstellar gas/dust common
• Gas must cool to collapse
• Dust grains and heavy elements are
important in this (“coolants”)
• Hydrogen/helium stars would be different
Pure H/He starbirth
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Only very massive stars could collapse
Only minimal cooling from molecular H
Likely 80-300 solar masses, maybe more
One to a protogalaxy – they’re fratricidal
They blew up real good
• Up to 10x energy of type Ia supernova
• Up to 40% of mass released in O,C…
• Seeded future galaxies and gas between
(which we now see is slightly enriched)
• Enough heavy elements for normal star
formation to ensue
• But galaxy formation had to start twice!
Closest local analogs – the most
massive stars
Can we see them?
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Don’t come in clusters
Short-lived
High-redshift (pure infrared targets)
Don’t blow their mass away in winds
Their explosions bright enough to see… and
there should be one seen about every 8
seconds. Somewhere in the sky.
Have we already seen them?
• Gamma-ray bursts have finally been
associated with asymmetric supernovae
• Some bright bursts have no optical/nearinfrared afterglow
• Are these at still higher redshifts?
Digression – Gamma-ray bursts
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Discovered by Vela satellites
No pattern on sky
Compton: statistics indicate very distant
BeppoSAX+ground: fading afterglow in
optical, high redshift, host galaxy
• Later bursts: some have optical/X-ray
signature of fading supernova
• Collapsar picture
Fading afterglow
Of GRB 991216
(z=1)
Near-infrared bands
Collapsar model
• Hot neutron star or black holes forms in
center of explosion
• Temporary high-density surrounding disk
• Directs relativistic jets
• Gives stellar surface very rude surprise
• Boosted to gamma rays if we look along the
jet (so there are many more of these than we
see)
Finding Pop III (VMOs, SMOs)
• Look for their supernovae in IR (important in
JWST’s survey strategy)
• Look for deep-IR-only GRB afterglows
• Early ionization input seen by WMAP??
• Understand chemical prehistory of stars
• Look for their remnant black holes
• Read Stephen Baxter’s Vacuum Diagrams…
And speaking of black holes –
where did the first massive ones
come from?
The Problem(s)
• Most bright galaxies have a supermassive central
black hole
• Only some of these are now accreting and easy to
find
• Quasars are now known to redshift 6 (about t=800
million years)…
• Which have black holes just as massive as we see
later on. How did they do that?
• And have gas as metal-rich as we see later!
Nearby supermassive black holes
How could black holes jump-start?
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Direct formation from collapsing gas
Primordial objects
Dense “relativistic” star clusters
More exotic objects collapsing?
Are primordial stars even more massive
than we thought?
Gas around quasars – enriched!
• Spectra of quasars at all times show very
similar metal abundances
• Most heavy metals come from supernovae
• Are all quasars in sites of intense and early
starbirth (and stardeath)?
• Could the quasars have triggered this?
• We’re starting to look earlier than the age of
a type I supernova, should see iron decline
Composite of high-redshift quasars
H
N
Absorption by
intergalactic gas
Si