White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:&...

55
White Dwarfs: The most interes2ng boring objects in the universe F.M. Walter 3 March 2017

Transcript of White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:&...

Page 1: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

White  Dwarfs:  The  most  interes2ng  boring  

objects  in  the  universe  

F.M.  Walter  3  March  2017  

Page 2: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Sirius  (α  CMa),  the  brightest  star  in  the  sky,  is  a  main  sequence  A  star.    Visual  magnitude  -­‐1.5                    

The  Discovery  of  Sirius  B  ñ  

Page 3: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

The  Discovery  of  Sirius  B  

             

•  1844:  Friedrich  Bessel  notes  “wobble”  in  proper  mo2on,  deduces  unseen  companion  

 

Page 4: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

•  1862:  Alvan  Clark  sees  Sirius  B  while  tes2ng  18.5”  telescope  for  Dearborn  Observatory.  Visual  magnitude  8.4  

 

Sirius  A  and  B  have  a  common  proper  mo2on  

The  Discovery  of  Sirius  B  

HST  image  

Page 5: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Aside:  Magnitudes  

Sirius  A  is  9.9  magnitudes  brighter  than  Sirius  B.  What  does  this  mean?  •  Magnitudes  are  propor2onal  to  the  logarithm  of  the  brightness  

•  1  magnitude  is  a  factor  of  2.512  in  brightness  •  5  magnitudes  -­‐>  a  factor  of  100  in  brightness  •  10  magnitudes  -­‐>  a  factor  of  10,000  (104)  

Sirius  A  is  9100  :mes  brighter  than  Sirius  B.  

Page 6: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

What  determines  the  brightness  of    a  

star?  •  How  fast  they  fuse  Hydrogen  into  Helium  

•  The  Sun:  – Absolute  magnitude:  4.8  

–  Luminosity:          4  x  1033  erg/s  

Page 7: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

•  1915:  Walter  Adams  obtains  spectrum  with  Mt  Wilson  60”;  shows  it  is  spectra  type  A,  like  Sirius  A  

•  The  stars  have  about  the  same  temperature  –  about  twice  a  hot  as  the  Sun  

Sirius  B  

Page 8: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

A  White  Dwarf  

¢  

¢  

Page 9: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

How  Big  is  Sirius  B?  •  Stars  can  be  approximated  as  black  bodies:  L  =  4πr2σT4  –  r:  stellar  radius;  4πr2  is  surface  area  – T:  stellar  temperature  – σ: Stefan-­‐Boltzmann  constant  

Page 10: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

How  Big  is  Sirius  B?  Stars  can  be  approximated  as  black  bodies:              L  =  4πr2σT4    

(rA/rB)2  =  (LA/LB)(TB/TA)4    Plugging  in:  •  TB/TA  ~  1  •  LA/LB  ~  104  

•  è  rA/rB  ~  100  •  rA  ~  2  R¤,  so  rB  ~  0.02  R¤, or 2 Earth radii

•  More accurately, rB = 0.0084 R¤,  or  0.92  R⊕    

Page 11: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Mass  of  Sirius  B  

MA/MB  =  aA/aB  =  2.07;    a  is  semi-­‐major  axis  of  orbit  è  MB  =  0.98  M¤  

Page 12: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Evolu2on  of  White  Dwarfs  

Page 13: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Evolu2on  of  White  Dwarfs  

Exposed  core  of  a  low  mass  star  (<8  M¤)

Page 14: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Ring Nebula - M 57

Page 15: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Catseye Nebula

Page 16: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Hourglass Nebula MyCn 18

Page 17: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&
Page 18: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Evolu2on  of  White  Dwarfs  

Exposed  core  of  a  low  mass  star  (<8  M¤) •  Composition:

– C + O (if solar mass) – O + Ne + Mg (if more massive) – He (if less massive)

•  Inert: no nuclear fusion •  Cool with time •  Crystalize at T~4000K  

Page 19: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

40  Eri  

Source:  University  of  Alabama/SARA    

Page 20: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Density  of  Sirius  B  •  Density  (ρ) =  mass/volume  •  ρ =  4.7  x  106  gm/cm3  

•  ρ confirmed  by  gravita2onal  redshii  in  1925  

•  Reference  densi2es  (gm/cm3):  – Water:  1.0  –  Sun:  1.4  –  Rock:  3.3  –  Earth:  5.5  – Osmium:  22.6  

Page 21: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Theory  of  White  Dwarfs.  I.  

•  Normal  gas:  PV=nkT    (or  P  ~  ρT)  –  Pressure  from  thermal  energy  (kT)  

•  Gas  law  breaks  down  at  high  pressure  – High  pressure  dislodges  electrons  from  atoms:  a  sea  of  ions  and  electrons  

•  Pauli  Exclusion  Principle:  no  two  iden2cal  fermions  can  have  exactly  the  same  posi2on  and  momentum.  –  Sets  a  minimum  pressure  independent  of  temperture  

•  degenerate  electron  pressure  

Page 22: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Theory  of  White  Dwarfs.  II.  •  Non-­‐rela2vis2c  electrons:    

– Radius  ~  mass  -­‐1/3  

– As  mass  increases,  star  gets  smaller!  •  Rela2vis2c  electrons:  

– Radius  independent  of  mass.  –  Implies  maximum  mass          ~  1.4  M¤ – This is called the Chandrasekhar limit  

Page 23: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Single  White  Dwarfs  

•  Generally  boring  •  Stra2fied  atmospheres  (heavy  elements  sink)  •  They  make  good  calibrators  

Page 24: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

White  Dwarfs  in  the  Field  

20  WDs  show  debris  disks/evidence  of  accre2ng  asteroids  

Page 25: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

White  Dwarfs  in  Binary  Systems  

V471  Tau:  K2V  +  DA                                        Period  =  12.5  hours  

Page 26: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

V471  Tau:  Egress  13  March  1998  

Page 27: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

White  Dwarfs  in  Binary  Systems  

WDs  have  a  strong  gravita2onal  poten2al  Dropping  something  onto  the  surface  releases  a  lot  of  energy!  •  E  =  GMm/R  •  184  g  (0.4lb)  falling  on    

– Sirius  B:  1  kiloTon;    – Earth:  0.000003  ktons  

Page 28: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

WDs  in  Binaries:  I.  Cataclysmic  Variables  

•  Dwarf  novae  

Page 29: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&
Page 30: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

SS  Cygni  –  a  dwarf  nova  Disk  accre:on  •  Maper  inspirals  •  Under  certain  

condi2ons  disk  becomes  unstable,  and  collapses  onto  star  

•  Rapid  release  of  gravita2onal  poten2al  energy  heats  maper  and  disk  brightens  

Page 31: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

EF  Eri  –  a  Polar  •  Accre2on  directly  onto  surface.  •  Accre2on  flow  channeled  by  strong  magne2c  field  –  no  disk  forms  

•  Outbursts  from  instabili2es  in  donor  star?  

Page 32: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

WDs  in  Binaries:  II.  Classical  Novae  

What  happens  to  the  maper  that  reaches  the  surface  of  the  WD?  –  It  is  ini2ally  non-­‐degenerate  –  It  is  in  hydrosta2c  equilibrium  –  Pressure  and  temperature  build  up  at  the  base  of  the  accreted  layer  –  The  base  of  the  layer  becomes  degenerate  

•  Degenerate  H  is  unstable  to  exploding  –  Nuclear  reac2on  rates  are  propor2onal  to  Tn,  where  4  <  n  <  16  –  Reac2on  release  energy  hea2ng  the  material  and  causing  T  to  rise  –  A  thermo-­‐nuclear  runaway  ensues  

Page 33: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

WDs  in  Binaries:  II.  Classical  Novae  

What  happens  to  the  maper  that  reaches  the  surface  of  the  WD?  –  It  is  ini2ally  non-­‐degenerate  –  It  is  in  hydrosta2c  equilibrium  –  Pressure  and  temperature  build  up  at  the  base  of  the  accreted  layer  –  The  base  of  the  layer  becomes  degenerate  

•  Degenerate  H  is  unstable  to  exploding  –  Nuclear  reac2on  rates  are  propor2onal  to  Tn,  where  4  <  n  <  16  –  Reac2on  release  energy  hea2ng  the  material  and  causing  T  to  rise  –  A  thermo-­‐nuclear  runaway  ensues  

Finally!  An  explosion  

Page 34: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

The  Nova  Phenomenon  

•  Thermonuclear  runaway  at  base  of  ejected  layer  

•  Overlying  gas  ejected  at  veloci2es  up  to  5000  km/s  (16%  of  c)  

•  Remaining  H  fuses  at  LEdd  (1038  erg/s;  105  L¤)  •  Ejecta  cools,  dust  forms  

Page 35: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

V1369  Cen      He  I  λ7065

High  velocity  ouslows  in  Helium,  up  to  4500  km/s  by  day  40  

Velocity  (km/s)  

Time  (days)                                                è

 

Page 36: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

V1369  Cen      Sodium  D  Time  (days)                                                è

 

Velocity  (km/s)  

Page 37: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Op2cal  Dips  •  Due  to  dust  absorp2on  on  line  of  sight  •  Cause  suggested  by  McLaughlin  in  1935  •  Occur  in  18%  of  light  curves  (Strope  et  al.  2010)  

Page 38: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

A  Big  Dust  Dip    

Page 39: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

GK  Per  (N  Per  1901)  

Source:  WIYN  

Page 40: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

T  Pyx  (N  Pyx  1890)  

Source:  HST  

Page 41: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Galac2c  Novae  

•  Are  a  surface  phenomenon  •  Do  not  destroy  the  star  •  Do  not  disrupt  the  binary  star  system  

•  Implica2on:  Novae  can  recur…  

Page 42: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

WDs  in  Binaries:  III.  Symbio2c  and  Recurrent  Novae  

Page 43: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

U  Scorpii  

Page 44: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Recurrent  Novae  

All  novae  repeat  •  Recurrence  2mes:  •  ~  1  year  (M31N  2008-­‐12a)  •  ~  1  decade  (U  Sco;  first  seen  in  1863)  •  ~  25  years  (T  Pyx)  •  ~  75  years  (YY  Dor)  •  …  

Page 45: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Nova  Theory  

Fujimoto  1982  ApJ,  257,  767  

Page 46: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Recurrent  Novae  

Do  white  dwarfs  gain  mass  during  a  nova  cycle?  •  Mass  ejected  ~  mass  accreted  •  If  Mej  >  Macc  then  WD  shrinks  •  If  Mej  <  Macc  then  WD  gain  mass    What  happens  when  MWD  approaches  the  Chandrasekhar  mass?  

Page 47: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

WDs  in  Binaries:  IV.  Type  Ia  Supernovae  

As  the  mass  approaches  the  Chandrasekhar  mass,  increasing  temperature  can  cause  carbon  can  ignite.  •  CO  core  detonates  •  Carbon  fusion  releases  about  1051  ergs,  enough  to  unbind  the  star.  

Complete  destruc2on  of  star  –  no  compact  remnant  

Page 48: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

SNe  IA  

•  Recycle  about  1  M¤ of Fe and Ni into the interstellar medium.

Page 49: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

SNe  IA  •  A standardizable candle useful for determining

cosmological distances.  

Page 50: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

SNe  Ia  

SN  2005cs  in  M51  

Page 51: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

SNe  Ia  

SN  2011dh  in  M51  

Page 52: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

Faint  SNe  from  HST  

Page 53: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

SNe  Ia  

Standardizable  candle:      Observed  light  curves  can  be  corrected  to  a  standard  template  because  width  depends  on  brightness  

Page 54: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

SNe  Ia  

Page 55: White&Dwarfs:& The&mostinteres2ng&boring& … · 2017. 3. 7. · White&Dwarfs:& The&mostinteres2ng&boring& objects&in&the&universe& F.M.&Walter& 3&March&2017&

All  because  white  dwarfs  are  the  only  stars  that  can  explode