47 Tuc X9 A black hole consuming a white dwarf Ross Church - - PowerPoint PPT Presentation

47 Tuc X9 A black hole consuming a white dwarf

Ross Church Department of Astronomy and Theoretical Physics Lund University Collaborators: Melvyn B. Davies & Alexey Bobrick (Lund) Jay Strader (Michigan State)

Talk summary

47 Tuc X9 is a black hole devouring the remnants of a carbon-oxygen white dwarf Systems like 47 Tuc X9 do not form in the field, but can form dynamically in dense clusters

Bahramian et al. (2017) MNRAS 467 2199 Bobrick, Davies & RC (2017) MNRAS 467 3556 Church et al. (2017) ApJL 851 4

The dynamical formation channel requires a third body and we might have seen a signal of its presence

30" NuSTAR extraction region

NuSTAR 3-78 keV

X-rays from 47 Tuc

NuSTAR extraction region

AKO 9

30" NuSTAR extraction region

Chandra 6-10 keV

30" NuSTAR extraction region

Chandra 0.3-10 keV

NuSTAR 3-78 keV

~30"

X-ray images from Bahramian et al. (2017) MNRAS 467 2199 Visual image: J Mack &

• G. Piotto, via Wikimedia

Commons

X9 X9 X9 is the brightest X-ray source in 47 Tucanae

Ultra-compact X-ray binaries (UCXBs)

MWD ≈ 0.01 M Observed as bright X-ray sources; e.g. 4U 1820-30 Recap from Alexey's talk!

Properties of 47 Tuc X9

No lines of H or He visible in spectrum

Tudor et al. (2018) MNRAS 476 1889

28-minute periodicity in X-rays: orbital period?

Bahramian et al. (2017) MNRAS 467 2199

7-day "super-orbital" period in X-ray and UV

Bahramian et al. (2017), Tudor et al. (2018)

Implies that 47 Tuc X9 is an ultra-compact X-ray binary with a carbon-oxygen white dwarf donor

But...

COWD-NS binaries do not form UCXBs!

Specific angular momentum lost in mass transfer Stable Unstable WD mass SPH result

Bobrick, Davies & RC (2017) MNRAS 467 3556

X-ray vs radio emission

1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1-10 keV X-ray luminosity (erg s−1) 1025 1026 1027 1028 1029 1030 1031 5-GHz radio luminosity (erg s−1)

VLA J2130+12 M22 M62 47Tuc X9 AE Aqr SS Cyg PSR J1023+0038 XSS J12270-4859 V404 Cyg

Quiescent/hard state BHs Candidate BHs identified via radio/X-ray flux ratio Hard state NSs AMXPs tMSPs CVs

Bahramian et al. (2017) MNRAS 467 2199

5 10 15 20 M•/M 0.2 0.4 0.6 0.8 1 MWD,crit/M Defaults fEdd = 10 fEdd = 10, RCE = 3 a fEdd = 10, RCE = 3 a, NCE = 108 fEdd = 100 Stable Unstable NWD

WD-BH mass transfer stability

Moderately efficient accretion permits WD-BH UCXBs

RC et al. (2017) ApJL 851 4

But...

BH-WD UCXBs don't form in the field

This mass transfer stage is stable: WD progenitor BH The orbit widens Form a non-interacting BH-WD binary

Making WD-BH binaries in clusters

Collision-induced common-envelope evolution

Rate and properties calculation

Γ = 2πGfpfsegv−1

∞

X

i

ni Z

t

[Mi(t) + M•] R?,i(t)dt,

Fraction of BHs undergoing collision with an evolved star Tidal capture out to fp ≈ 3 giant radii Mass segregation increases rate by fseg ≈ 2 af = R? αCEλ 2 M• M? M?,core M?,env take the common-envelope efficienc Assume a common-envelope-like process after collision

Ivanova et al. (2010) ApJ 717 948 RC et al. (2017) ApJL 851 4

Collisionally-formed COWD-BH binaries

AGB

0.3 0.4 0.6 1 Mcore/M 1 10 100 1000 rperi/R

HB Merge Need help merging

RC et al. (2017) ApJL 851 4

1 2M?σ2 ≈ GM•MWD 2ahard ⇒ ahard ≈ GM•MWD M?σ2 ≈ 7000 R

Help with merging

Binaries are "hard" if encounters with single stars do not disrupt them. Exchange into wider binaries can drive Kozai-Lidov cycles and bring the binary into contact. Our binary has so will be hardened by encounters and exchange into binaries. a ≈ 20 R

Rates: expect about one in Milky Way globular system

A possible cousin

• 47 Tuc X9

RZ 2109

And finally...

What about the mystery seven-day period? Post Lidov-Kozai, expect coplanar triple Inner UCXB orbit (much smaller than shown) Outer perturber

• rbit (properties

unknown) Black hole

3-body model

Outer binary pericentre passages RWD∆e ≈ hρ

Talk summary

47 Tuc X9 is a black hole accreting stably from a carbon/oxygen white dwarf in an ultra-compact binary BH + COWD UCXBs like 47 Tuc X9 do not form in the field, but can form dynamically in dense clusters

Bahramian et al. (2017) MNRAS 467 2199 Bobrick, Davies & RC (2017) MNRAS 467 3556 Church et al. (2017) ApJL 851 4

The third body needed in the dynamical formation channel might be responsible for the 7-day periodicity