Which Stars form Neutron
Stars and Black Holes?
Michael Muno (Caltech)
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
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.
The Collapse Causes an
Explosion
Supernova 1987A, before and during.
(D. Malin, Anglo-Australian Telescope)
Leaving Behind a Compact
Object Chandra: X-rays
ESO VLT: Optical
Crab Remnant and Pulsar from the SN of 1054 AD
• Stars between 8 and 25 solar masses leave
neutron stars:
– M~1-2 Msun, R~10 km, r~1015 g cm-3
• More massive stars leave black holes:
– M>3 Msun, RSchw~3M km
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.
The Collapse Tests the
Frontiers of Physics
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Burrows et al. 2D simulation; see
also Mezzacappa et al., Woosley,
Fryer, et al. . .
During collapse, the core
has T > 109 K,
P > 1025 erg cm-3,
and r ~ 109 - 1015 g cm-3.
Models require:
• (Magneto)hydrodynamics
• Nuclear dissociation
• Neutrino opacities
3-D models only explode if
there is some asymmetry.
Understanding Supernovae
Observationally
(D. Malin, Anglo-Australian Telescope)
Hubble Space Telescope
SN 1987A
We want to know
• What star exploded,
• What the explosion looked like, and
• What it left behind.
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.
Finding the Compact Remnants:
Neutron Stars and Black Holes
Crab Nebula and Pulsar
with Chandra
Illustration of an X-ray binary
One Solar Radius
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 >3 Msun
• Only some tentative
measurements of spin
The Tools: from Radio to g-Rays
Radio
Infrared Optical
X-ray
Spitzer Space Telescope
Green Bank Telescope
Chandra X-ray
Observatory
MeV - g-ray - TeV
GLAST
HESS
The Tools: from Radio to g-Rays
Finding Pulsars
Spitzer Space Telescope
Green Bank Telescope
Chandra X-ray
Observatory
GLAST
HESS
The Tools: from Radio to g-Rays
Finding X-ray Binaries
Spitzer Space Telescope
Green Bank Telescope
Chandra X-ray
Observatory
GLAST
HESS
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).
– G292.0+1.8 : 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).
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.
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).
Finding the Star Clusters that
Produce Supernovae
100 lt-yr
Blue image from the Digitized Sky Survey
Finding the Star Clusters that
Produce Supernovae
100 lt-yr
Near infrared image from the Palomar Sky Survey
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
The Most Massive Young
Galactic Star Cluster
Westerlund 1
5 lt-yr
VRI from 2.2m MPG/ESO+WFI
Clark et al. (2005)
• 150 stars with M>35 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!
Chandra Observations to
Identify Compact Objects
pulsar
VRI from 2.2m MPG/ESO+WFI
Clark et al. (2005)
Chandra ACIS
(Muno et al. 2006)
5 lt-yr
The brightest X-ray source is a 10.6 s pulsar!
Pulsar CXO J164710.2-455216
Muno et al. (2006)
• 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
K<20.0 (not an X-ray
binary)
• Spin-down: 4x10-5 s yr-1
• B ~ 1014 G
This pulsar is a magnetar.
(Spin down measured by Woods et al. 2006; Israel et al. 2006)
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
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
The Pulsar Had a >50 Msun
Progenitor
pulsar
VRI from 2.2m MPG/ESO+WFI
Clark et al. (2005)
Chandra ACIS 5 lt-yr
(Muno et al. 2006)
35 solar mass stars in Wd 1 are still burning Hydrogen;
more evolved stars were initially 40-50 solar masses.
Other Magnetars with
>30 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 1900+14).
Heger et al. 2003
White Dwarf
metal-free
Metallicity solar
Which Stars Form Black Holes?
9
25 40
100 140 260
Initial Mass (Solar Masses)
9
25 40
100 140 260
Initial Mass (Solar Masses)
Heger et al. 2003
White Dwarf
Wd 1
metal-free
Metallicity solar
Which Stars Form Black Holes?
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).
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).
Gamma-Rays Provide a New
Window to Search for Compact
Objects
HESS TeV map (Aharonian et al. 2005)
Spitzer/GLIMPSE
image (8.0, 5.8, and
3.6 mm).
At least one cluster has a
counterpart at TeV
energies: is it a pulsar too?
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
What Are the X-ray Sources?
WR 124;
HST/WFPC
QuickTime™ and a
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~10,000 accreting
white dwarfs.
~100 pulsars.
(see Muno et al. 2004, 2006)
~100 massive stars in
colliding-wind binaries.
~100 black hole and
neutron star X-ray
binaries.
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.
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).
Progress is Being Made!
• I have found a neutron star in Westerlund 1
with an unexpectedly massive progenitor.
– The neutron star is highly magnetized (B~1014 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.