Which Stars form Neutron Stars and Black Holes?

1
Which Stars form Neutron Stars and Black Holes?
Michael Muno (Caltech)
2
Star Clusters Galactic Center
J. S. Clark F. Baganoff
P. Crowther G. Bower
S. Dougherty W. N. Brandt
D. Figer P. Broos
R. de Grijs A. Burgasser
C. Law G. Garmire
S. McMillan J. Mauerhan
I. Negueruela M. Morris
D. Pooley S. Park
S. Portegies Zwart E. Pfahl
S. Ransom
3
The Life and Death of a Massive Star
At least 8 times the mass of the sun

• It will burn hydrogen for a few million years.
• As heavier elements are burned, it will swell up
  and produce powerful winds that carry away many
  solar masses of materials.
• Once the core is made of iron, fusion is no
  longer exothermic, and the core collapses.

4
The Collapse Causes an Explosion
Supernova 1987A, before and during. (D. Malin,
Anglo-Australian Telescope)
5
Leaving Behind a Compact Object
ESO VLT Optical
Chandra X-rays
Crab Remnant and Pulsar from the SN of 1054 AD

• Stars between 8 and 25 solar masses leave neutron
  stars
• M1-2 Msun, R10 km, r1015 g cm-3
• More massive stars leave black holes
• Mgt3 Msun, RSchw3M km

6
Why are the Supernovae Important?

• Any part of a star that does not end up in a
  compact remnant will return to space, energizing
  it and populating it with metals.
• We want to know what fractions of old galaxies
  are composed of compact objects.
• The observed types of compact objects provide
  crucial constraints on supernova models.

7
The Collapse Tests the Frontiers of Physics
During collapse, the core has T gt 109 K, P gt
1025 erg cm-3, and r 109 - 1015 g cm-3.

• Models require
• (Magneto)-hydrodynamics
• Nuclear dissociation
• Neutrino opacities

Burrows et al. 2D simulation see also Mezzacappa
et al., Woosley, Fryer, et al. . .
3-D models only explode if there is some
asymmetry.
8
Understanding Supernovae Observationally
Hubble Space Telescope
(D. Malin, Anglo-Australian Telescope)
SN 1987A

• We want to know
• What star exploded,
• What the explosion looked like, and
• What it left behind.

9
How to Approach the Problem
There are few observations linking the compact
object to the star that left it, so I

• Identify individual black holes and neutron stars
  in star clusters, to determine the masses of the
  stars that produced them.
• Assemble a large sample of binary stars
  containing black holes and neutron stars.
• To measure masses for the compact objects.
• Constrain asymmetries in the supernova explosion.

10
Finding the Compact RemnantsNeutron Stars and
Black Holes
Crab Nebula and Pulsar with Chandra

• Neutron Star Pulsars
• Rotation 1 ms - 1 hour
• Spin down 10-3 to 10-13 s yr-1
• B-fields 109 to 1015 G
• Space velocities up to 1500 km s-1
• Black Hole X-ray Binaries
• Mass gt3 Msun
• Only some tentative measurements of spin

Illustration of an X-ray binary
One Solar Radius
11
The Tools from Radio to g-Rays
Radio
Infrared
Optical
X-ray
MeV - g-ray - TeV
Spitzer Space Telescope
GLAST
Chandra X-ray Observatory
Green Bank Telescope
HESS
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The Tools from Radio to g-Rays
Finding Pulsars
Spitzer Space Telescope
GLAST
Chandra X-ray Observatory
Green Bank Telescope
HESS
13
The Tools from Radio to g-Rays
Finding X-ray Binaries
Spitzer Space Telescope
GLAST
Chandra X-ray Observatory
Green Bank Telescope
HESS
14
The Scant Connections to Progenitors

• Model the initial masses of supernovae known to
  have produced compact objects.
• Crab best estimate is 8-10 Msun (Nomoto et al.
  1982).
• G292.01.8 a 25 Msun progenitor to a fast X-ray
  pulsar (Hughes Singh 1994 Hughes et al. 2004).
• Cas A a 20-25 Msun progenitor (Laming Hwang
  2003), or a 15-25 Msun star in a binary (Young et
  al. 2006).

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The Scant Connections to Progenitors

• Model the initial masses of supernovae known to
  have produced compact objects.
• Model individual high mass X-ray binaries (Ergma
  van den Heuvel 1998 Wellstein Langer 1999).
• Cyg X-1 14 Msun black hole and 35 Msun donor.
• GX 301-2 neutron star (pulsar) with 40 Msun
  donor.
• The technique has problems, but these systems do
  provide the masses of compact objects.

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The Scant Connections to Progenitors

• Model the initial masses of supernovae known to
  have produced compact objects.
• Model individual high mass X-ray binaries.
• Search for associations between compact objects
  and star clusters for which we know the masses of
  stars that died (Pellizza et al. 2005 Fuchs et
  al. 1999 Vrba et al. 2000).

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Finding the Star Clusters that Produce Supernovae
100 lt-yr
Blue image from the Digitized Sky Survey
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Finding the Star Clusters that Produce Supernovae
100 lt-yr
Near infrared image from the Palomar Sky Survey
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Finding the Star Clusters that Produce Supernovae
Westerlund 1, discovered in the 1960s, neglected
for 35 years
100 lt-yr
Near infrared image from the Palomar Sky Survey
20
The Most Massive Young Galactic Star Cluster
Westerlund 1

• 150 stars with Mgt35 Msun
• Mass 105 Msun
• Extent 20 lt-yr across
• Age 4 /- 1 Myr
• The cluster is coeval, and old enough to have
  produced supernovae.
• Est. rate 1 per 10,000 years!

5 lt-yr
VRI from 2.2m MPG/ESOWFI Clark et al. (2005)
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Chandra Observations to Identify Compact Objects
pulsar
5 lt-yr
Chandra ACIS (Muno et al. 2006)
VRI from 2.2m MPG/ESOWFI Clark et al. (2005)
The brightest X-ray source is a 10.6 s pulsar!
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Pulsar CXO J164710.2-455216

• Period 10.6107(1) s
• LX 3x1033 erg s-1 (not a radio pulsar)
• Spectrum kT 0.6 keV (not a cooling NS)
• No IR counterpart with Klt20.0 (not an X-ray
  binary)
• Spin-down 4x10-5 s yr-1
• B 1014 G

Muno et al. (2006)
This pulsar is a magnetar.
(Spin down measured by Woods et al. 2006 Israel
et al. 2006)
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Magnetars are Particularly Violent

• In December 2004, the magnetar SGR 1806-20
  produced a burst of g-rays that for a few
  milliseconds was the largest flux received from
  outside the Solar System in the history of modern
  astronomy.

Palmer et al. 2005 Mereghetti et al. 2006
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Confirmation that the Wd 1 Pulsar is a Magnetar

• On September 21, 2006 a burst of 100 keV photons
  was detected from the Wd1 pulsar.
• Further X-ray observations revealed the source
  brightened by a factor of 100 in less than a week.

Muno et al., submitted
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The Pulsar Had a gt50 Msun Progenitor
pulsar
5 lt-yr
Chandra ACIS (Muno et al. 2006)
VRI from 2.2m MPG/ESOWFI Clark et al. (2005)
35 solar mass stars in Wd 1 are still burning
Hydrogen more evolved stars were initially 40-50
solar masses.
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Other Magnetars with gt30 Msun Progenitors
1E 1048.1-5937
Magnetar 1806-20

• Neutral H around 1E 1048.1-5937 was interpreted
  as the wind-blown bubble from a 30-40 Msun
  progenitor (Gaensler et al. 2005 but see, e.g.,
  Durant van Kerkwijk 2006).
• SGR 1806-20 is the member of a star cluster 3
  Myr old, and so had a 50 Msun progenitor (Figer
  et al. 2005 also Vrba et al. 2000 for SGR
  190014).

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Which Stars Form Black Holes?
solar
Heger et al. 2003
White Dwarf
Metallicity
metal-free
9
25
40
100
140
260
Initial Mass (Solar Masses)
28
Which Stars Form Black Holes?
Wd 1
solar
Heger et al. 2003
White Dwarf
Metallicity
metal-free
9
25
40
100
140
260
Initial Mass (Solar Masses)
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Massive Progenitors to Magnetars

• Massive stars can lose 95 of their mass
• Through winds (e.g., Heger et al 2003),
• Via binary mass transfer (Wellstein Langer
  1999),
• Or during supernovae (Akiyama Wheeler 2005).
• B-fields appear important
• Massive stars could produce rapidly-rotating
  cores (e.g., Duncan Thomas 1992 Heger et al.
  2005).
• Or magnetars could form from highly-magnetic
  progenitors (e.g., Ferrario Wickramasinghe
  2005).

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The Future Search for Compact Objects in
Newly-Discovered Star Clusters
Spitzer/GLIMPSE images (8.0, 5.8, and 3.6 mm),
with clusters of massive stars identified by
Figer et al. (2006).
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Gamma-Rays Provide a New Window to Search for
Compact Objects
HESS TeV map (Aharonian et al. 2005)
At least one cluster has a counterpart at TeV
energies is it a pulsar too?
Spitzer/GLIMPSE image (8.0, 5.8, and 3.6 mm).
32
Using High-resolution Chandra Images to Find
X-ray Binaries
The central 1000 light years of the Galaxy Wang,
Gotthelf, Lang 2002 NASA/Umass Deep (170
hour) survey in progress (PI Muno)!
100 lt-yr
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What Are the X-ray Sources?
WR 124 HST/WFPC
100 massive stars in colliding-wind binaries.
10,000 accreting white dwarfs.
100 black hole and neutron star X-ray binaries.
100 pulsars.
(see Muno et al. 2004, 2006)
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Looking for A Large Sample of X-ray Binaries
Illustration from Our Universe, National
Geographic Society (1980)

• The orbital parameters from a sample can be used
  to constrain
• The kicks given to compact objects at birth.
• The masses of neutron stars and black holes at
  birth.

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X-ray Binaries Have Bright Infrared Counterparts
Mauerhan, Muno, Morris, submitted

• We have identified 10 candidate X-ray binaries
  in initial observations, and expect to find 100
  by the end of our survey (Muno et al. 2005
  Mauerhan et al. submitted).

36
Progress is Being Made!

• I have found a neutron star in Westerlund 1 with
  an unexpectedly massive progenitor.
• The neutron star is highly magnetized (B1014 G),
  which suggests a relationship between magnetic
  fields and extreme mass loss.
• With radio, X-ray, and (soon) g-ray
  observatories, I will be able to expand the
  sample.
• Chandra observations of the Galactic center will
  double the number of known young X-ray binaries,
  which can be used to measure the masses of
  compact objects.