Pulsars and Supernovae II
8. PULSAR BIRTH AND EVOLUTION -- BINARY AND MILLISECOND PULSARS
association with supernova remnants evolution of binary systems recycled pulsars mass transfer and spin-up Hulse-Taylor pulsar and gravitational radiation globular cluster searches Close supernova remnants • There are ~50 supernova remnants (SNRs) within 5 kpc of us, from which we may hope to detect pulsars.
• Statistically, we expect: – about 10 to be type 1a SNRs and therefore probably not associated with neutron stars. We know about two for sure:
Tycho (Chandra) SN 1006 (Chandra)
2 8. Binary and millisecond pulsars Close supernova remnants G11.2-0.3 (Chandra)
– about 10 -- 15 to have formed black holes – about 5 to have lost their neutron stars due to high proper motion.
• There should therefore be about 15-20 associated with neutron stars.
• We see that 10 have either pulsars or pulsar wind nebulae. 65 ms X-ray pulsar RCW 103 (Chandra) • A further ~10 have X-ray point sources at the centre, e.g. RCW 103. This one seems to be rotating with a period of 6.7 h. These ‘central compact objects’ are probably neutron stars.
• About 10 are yet to be searched – the numbers seem to add up OK.
3 8. Binary and millisecond pulsars Close supernova remnants
• The youngest, brightest, supernova remnant, Cassiopeia A, also has a clear point source at its centre in X-rays, but no pulsar.
• The lack of a pulsar or pulsar wind nebula may indicate that the magnetic field is either too weak or (more likely) too strong to allow the particle acceleration to occur.
Cas A (Chandra)
4 8. Binary and millisecond pulsars Cas A (Chandra)
5 8. Binary and millisecond pulsars Cas A (VLA)
6 8. Binary and millisecond pulsars Radio pulsars and supernova remnants
• About 20 radio pulsars appear to be associated with supernova remnants, though only ~13 have supporting evidence that the association is real (rather than a chance alignment).
• We expect these all to be young pulsars, and to appear close to the top of the P-Pdot diagram.
• Radio pulsars have not been found in most of the ~300 known supernova remnants, due to a combination of statistics, surveying difficulties and the distances involved.
7 8. Binary and millisecond pulsars Evolution of binary systems
• Not all pulsars are born in a simple isolated supernova explosion. Binary systems can show a range of evolutions as the two stars age, interact and form compact objects.
• In the simplest scenario, a massive primary star evolves rapidly and undergoes a Type II supernova explosion. The mass-loss reduces the binding energy of the system. This, and the ‘rocket’ force on the resulting neutron star, can disrupt the binary.
• We are left with a runaway secondary star and an isolated, high velocity pulsar.
8 8. Binary and millisecond pulsars Evolution of binary systems
• If the binary system survives the collapse of the primary we get a binary pulsar, or a simple binary star/neutron star system.
• As the secondary evolves it will, if sufficiently massive, swell to a red giant phase and overflow its Roche lobe, spilling material onto the (now spun-down) neutron star.
• The accretion has two effects: – Orbital angular momentum is transferred to the neutron star, spinning it up, and forming a recycled pulsar. – An accretion disk is formed, and X- rays emitted as in-falling matter impacts the disk.
9 8. Binary and millisecond pulsars Mass transfer and spin-up
10 8. Binary and millisecond pulsars Recycled pulsars
• On the P-Pdot diagram, recycled pulsars are clearly associated with binary systems (circles/ellipses):
• The shortest period recycled pulsars have periods of a few milliseconds, and nearly circular orbits (circles on the diagram).
• Mildly recycled pulsars have had less time to spin-up and to circularise their orbits (shown as ellipses on the diagram).
• about 80% are in binary Lorimer 2001 systems.
11 8. Binary and millisecond pulsars Recycled pulsars
Lorimer 2008
12 8. Binary and millisecond pulsars Evolution of binary systems • The fate of this X-ray binary system depends on the mass of the companion star
• If the system is a low-mass X-ray binary (LMXB), the mass transfer continues for a greater length of time, and the recycled pulsar is spun-up to a very short (~ms) rotation period.
• Eventually, the companion sheds its outer envelope and becomes a white dwarf.
• Orbits are generally highly circular (eccentricity ≪ 0.01).
13 8. Binary and millisecond pulsars Evolution of binary systems • You can sometimes see the white-dwarf companion at the location of the radio pulsar, e.g. J0218+4232 (~10 known)
white dwarf ~8000 K ~0.2 solar masses
J0218+4232 (Bassa et al 2003)
14 8. Binary and millisecond pulsars Evolution of binary systems
• If the system is a high-mass X-ray binary (HMXB), the companion will quickly form a supernova.
• If the binary system survives, we have a double neutron star binary system. Eccentricity Is generally large.
• If the binary system is disrupted (as seems to be common) we have two free pulsars -- one young and the other mildly recycled.
15 8. Binary and millisecond pulsars Hulse-Taylor pulsar and gravitational radiation • This is a famous double neutron star system PSR B1913+16. Such systems can be quite relativistic, and need post-keplerian orbital parameters to describe the orbital evolution.
• Keplerian: – Orbital period – Projected semi-major axis – Orbital eccentricity – Longitude of periastron – Epoch of periastron passage
• Can’t determine individual masses or orbital inclination.
• Post-keplerian: – Advance of periastron – Gravitational redshift – Orbital decay rate
• These allow the determination of orbital inclination and individual masses.
16 8. Binary and millisecond pulsars Hulse-Taylor pulsar and gravitational radiation
• The ‘advance of periastron’ parameter was the first clear evidence of gravitational radiation – GR predicts this to be particularly sensitive to the effects of radiation reaction.
Weisberg & Huang 2016
17 8. Binary and millisecond pulsars Globular cluster searches
• Globular clusters are a rich hunting ground for recycled pulsars, due to the high probability of interaction. Currently 138, in 25 globular clusters.
Terzan 5 (B. Saxton (NRAO/AUI/NSF); GBO/AUI/NSF; NASA/ESA Hubble, F. Ferraro) Scott Ransom
18 8. Binary and millisecond pulsars Globular cluster searches
• There are 23 millisecond radio pulsars in 47 Tucanae:
Michael Kramer 19 8. Binary and millisecond pulsars