# Presentation: 096881

## THE FIRST STARS III

*CONFERENCE SUMMARY*
*JULY  20, 2007*
*Chris McKee*

## Donald Rumsfeld’s Contribution to Science:

- “There are known knowns...

- There are known unknowns...

- There are also unknown unknowns.”

## The study of the first stars is a new field

- There are almost no “known knowns,” except for the background cosmology and an increasing set of data on abundances of very metal poor stars

- Until recently, the effect of dark matter annihilation on the first stars was an “unknown unknown”

## Conjecture: The number of unknown unknowns---i.e., the discovery potential---in a field is proportional to the ratio of the number of known unknowns to known knowns:

- UU  KU / KK

- If true, the study of the First Stars is an excellent field for young people--as evidenced by the youth of the organizers and of the audience!

## OUTLINE

- BIRTH

- What are the masses of the first stars?

- LIFE AND DEATH

- What elements do they produce?

- What kind of supernova?

- Can they be observed--SNe, GRBs, at low z, CIB?

- AFTERLIFE

- Reionization of the universe

- Stellar archaeology

- PROPOSED CLASSIFICATION

- Black holes--see paper

## PROPOSED CLASSIFICATION OF THE FIRST STARS

- Population II: (Z > Zcr ) Metals affect formation

- Population III.1: First generation--determined by cosmology

- (Population II.5 ?? Rapidly rotating stars with Z~10-6Zsun have much greater mass loss than Z=0 stars (Meynet) and could form a separate class if Zcr>> 10-6Zsun)

## Mass of the First Stars (III.1)

- Robust theoretical prediction: first stars were massive

- (Norman)

- Consistent with observed absence of Z=0 stars

- No angular momentum barrier

- No evidence for fragmentation. Abel has suggested term “Russian-doll fragmentation” to describe case in which T(n) suggests fragmentation, but none occurs.

- Weak turbulence => no Salpeter IMF

## Pop III.1

**Schaerer (2002)**
**primordial stars**

**O’Shea & Norman (2007a)**

- Masses

- M. Norman

- Accretion rate estimated prior to formation of expansion wave => lower limit to actual value prior to onset of feedback

## BREAKTHROUGH SIMULATION: FORMATION OF THE FIRST PROTOSTAR (Yoshida)

- A new born proto-star
- with T* ~ 20,000K

- r ~ 10 Rsun!

- Protostellar mass 0.01 Msun, density 1021

- See also simulations of Turk to densities above 1018

## ADVANCING INTO “TERRA INCOGNITA:”

- Rotation leads to accretion disk, crucial for feedback

## HEATING BY DARK MATTER ANNIHILATION?

- Chen & Kamionkowski 2004; Ripamonti ea. 2007; Spolyar ea. 2007; A.Natarajan & Tan 2007

- Main uncertainties: DM(r<10-3pc), m, <v>, ftrap
- Could potentially delay/halt collapse

- --A new “known unknown”

- (Tan)

## POPULATION III.2: MASS AFFECTED BY FEEDBACK

- Dominant effect: HD cooling (Bromm; Glover; Bryan)

- E01(HD)  (1/4)E02 (H2) => HD can cool to ~ 50 K

- HD fractionation since formation exothermic

- HD cooling important only for T<150K

- Requires high H2 abundance due to photo- or

- collisional ionization

- Reduces characteristic stellar mass to a few 10’s Msun

- Lower T => supersonic turbulence => poss. Salpeter-like IMF

## POPULATION II (Z > Zcr)

- Zcr for gas phase metals ~ 10-4 Zsun (Bromm; Shull)

- Gas phase metals ~ HD: cooling can exceed H2

- but ineffective at high density => minimum fragment mass >10 Msun at z > 20 (Omukai)

- But grain nucleation theory very uncertain, requires efficient dust formation in SNe, in contrast to SN 87A

## THE LIFE AND DEATH OF THE FIRST STARS

- Pop III stars are more compact and bluer, and they have much lower mass loss than Pop I stars

- (the most important “known unknown”--Woosley)

## The uncertain role of magnetic fields in stellar rotation:

- In the absence of an effective dynamo in massive stars, surface can rotate subcritically and no significant mass loss

- If dynamo is efficient, then large mass loss at late times for rapid rotation (vrot/vcrit = 0.56) --star can lose more than half its mass (Ekstrom)

- (However, SN determined by He core, which is affected much less)

## He Core            Main Seq. Mass     Supernova Mechanism

- Supernovae in non-rotating primordial stars (Woosley)

- (Fate determined by He core mass, not total mass)

- (significant metal ejection only in last event)

- (Mmetal ~ M, abundances violate observation)

## CAN POP III STARS BE OBSERVED?

## Three GRB-SNe = all Type Ic Hypernovae

- Rapidly rotating massive stars should produce GRBs

- Fraction predicted to increase from 0.1% to 3% between z=0 and 10 (Yoon)

- Three GRB-SNe = all Type Ic Hypernovae
-                                 E > 1052 erg (~10×normal SN)
-                                 Large Mms →Black Hole Forming SNe

- (Nomoto)

- (M~40 Msun)

- M(56Ni)/Msun ~ 0.35-0.55

## 3. Direct Observation of Pop III stars (Schneider)

- Chemical feedback due to

- -transport by outflows

- -”genetic propagation”--infall of enriched halo

- -Even at z=14, only 1% of stars are Pop III

- Model chemical evolution in simulation of 10 h-1 Mpc box

- Results:

- -Pop III stars form in outer low density regions

- PREDICTION: Non-negligible fraction of objects at z>3 may be powered by Pop III stars: by radiation (Lyman alpha emitters, Luminous Blue Galaxies) and/or by supernovae

## 4. Fluctuations in cosmic IR background

- Analysis of Spitzer data at near infrared bands shows fluctuations that are not correlated with ACS sources and are therefore attributed to high-z sources (Kashlinsky)

- Analysis of HST NICMOS data show fluctuations on scales where comparison can be made (<25 arcsec), but these are attributed to undetected galaxies at redshifts similar to the observed sources (Thompson)

- Both effects must contribute, but further observations are needed to determine which dominates

## AFTERLIFE

- REIONIZATION

- STELLAR ARCHAEOLOGY

- BLACK HOLES  (see paper)

## REIONIZATION

- Choudhury-Ferrara model (Ferrara):

- Ionization sources: Pop III stars with Salpeter IMF, Pop II stars, QSOs

- Follow evolution of HI, HII, and HeIII regions

- Radiative feedback suppresses SF in low mass halos

## HMP

**HMP**

**C-rich EMP**

**EMP**

**UMP**

- (K. Nomoto)

- STELLAR ARCHAEOLOGY: OBSERVATIONS

- Most or all in binaries => mass transfer may be important

- Not known if binary

- One detected

## Slide 24

## Direct measurements of stellar age by radioactive elements--U detected in two stars (Sneden)

- Lithium (Asplund): 7Li several times less than predicted by BBN; 6Li independent of [Fe/H]. Cleanest solution for both is processing by dark matter annihilation

## OBSERVATIONS OF GAS (Shull, Penprase)

- Lines of sight to QSOs and GRB afterglows allow measurement of mixing and metal evolution to high z, complementing stellar observations; GRBs probe host (generally) low-mass galaxies

- Very low metallicity damped Ly-a systems show rising C/O as O/H decreases

## INTERPRETATION OF ABUNDANCE OBSERVATIONS

- Key question: Are stars with very small metallicity contaminated by one SN (Nomoto) or many (Woosley)?

- A key “known unknown”: How effective is mixing?

## ROTATION AND NUCLEOSYNTHESIS

- Rapid rotation leads to tmix < tms => mixes H and He  (Yoon)

- Leads to efficient primary Nitrogen production--increase up to factor 200 (Chiappini)

## PAIR INSTABILITY SUPERNOVAE

- Pop III stars with 130 Msun < M < 260 Msun explode as pair instability SNe and eject all their mass as metals with an odd-even ratio ~ 0.01, far less than observed (Woosley, Qian)

- There is no known reason why such stars should not form in the first generation (III.1)-- (Tan)

- Rotation does not appear to lead to sufficient mass loss to change the initial mass  of the He core significantly (Maynet, Ekstrom)

- Hence, Pop III-1 must be rare and/or there must be substantial dilution of the nucleosynthesis products of such SNe in low mass stars

## FINALLY, A KNOWN KNOWN!

## Slide 31

## Metal-Poor Stars

***Metal-Poor Stars***

**HMP**

**C-rich EMP**

**EMP**

**UMP**

- (K. Nomoto)