Review Neutron Stars(NSs) and SNR (Crab Nebula…) and then on to BHs…

1. Review Neutron Stars(NSs) and SNR (Crab Nebula…) and then on to BHs… • SN-II produce a NS for massive stars in approx. range 8-15Msun; and a black hole for progenitors >20Msun (approx.) • NSs discovered originally as Pulsars: NS with magnetic fields at their surface ~1012X that at surface of Sun (or Earth), and spinning at ~100X per second (when first born), are electric dynamo generators, accelerating enormous currents out along its magnetic field axis. • Pulsar drives off waves of energetic particles & synchrotron radiation (blue) in center of surrounding Supernova Remnant as best exemplified in Crab Nebula. See Movie Dec. 11, 2007

2. Supernova Remnants: Glowing Debris of exploded star • Crab Nebula (top fig) is remnant of SN-II that exploded in 1054AD (July 4!), leaving pulsar (33msec spin period) that energizes central nebula by its high energy electrons spiralling in nebula’s magnetic field: blue synchrotron radn. in central part of nebula. Reddish filaments are bright in emission line Hα(EL3) • Crab not typical SN-II; most do not have energetic pulsar, but expanding debris from the stellar envelope, as in Cas-A (LR image) • SN Ia (no H envelope and thus only heavy elements in nebula are qualitatively similar to Cas-A in appearance, though more iron-rich Dec. 11, 2007

3. Accretion onto NS remnant from binary companion: X-ray Binaries as Accretion-powered Pulsars or Bursters • Just as with SN-Ia when WD has binary companion, a NS with a binary companion will accrete gas from the companion (“normal” star) when the companion becomes a red giant (and fills its Roche Lobe), or when the companion is a lower mass star in very close orbit and then also fills its Roche Lobe. • NSs with higher mass star companions become High Mass X-ray Binaries (HMXBs) and are often detected as Accretion-powered Pulsars like CenX3 Dec. 11, 2007

4. NSs: X-ray Pulsars vs. X-ray Bursters… • If the NS has a strong magnetic field, the accretion is funneled onto the magnetic poles of the NS; the very hot poles come in/out of view: pulses of X-rays! • But if the NS has weak field, which occurs for very old NSs accreting for a long time when field is buried, then matter will “pile-up” on the NS surface and explosively “burn” (He  C, O) and produce an X-ray Burst: a ~100X increase in X-ray luminosity over a few seconds while entire surface of the NS “burns” (discovered by JEG…). Such “old NSs” live in globular clusters and in central bulge of our Galaxy and in turn evolve into Millisecond Pulsars…. Dec. 11, 2007

5. Chandra discovers “Nest” of accreting NSs and WDs in massive Globular Cluster 47 Tuc • X-ray binaries (accreting NSs or BHs) or Cataclysmic Variables (CVs; accreting WDs) are greatly enhanced in numbers (~100X more numerous) in dense cores of globular clusters, where “normal” binaries exchange a member star for a nearby-passing NS or WD. • The descendents of NS-LMXBs, the millisecond pulsars, are similarly over-abundant in globulars – e.g. 47Tuc: faint red sources vs. blue sources (CVs): Dec. 11, 2007 Ground based optical (left) vs. Space-based X-ray (Chandra; right) images of 47Tuc

6. Millisecond Pulsars (MSPs) in globulars can swap partners… • The MSP 47Tuc-W has exchanged its former partner star, which would have evolved to a WD, for a “fresh” M-S star, which “tries” to resume accretion onto the NS but is prevented by the “wind” of high energy particles (blue arc) from the MSP: Dec. 11, 2007

7. Now replace the NS with a Black Hole – even more powerful accretion source if in a binary or Galactic Nucleus! • Accretion power: the luminosity released by matter falling onto a very compact object (NS or BH): L = GM/R x (grams/sec of mass accreted) • X-ray binaries and ultimately Quasars are so luminous because M is large and R is very small: GM/R on a NS is 0.1mc2 – that is, 10% of rest mass energy of matter is released as radiation! Compared to 0.7% from nuclear burning! Accretion onto BHs produce the most luminous objects in Universe! • Accretion onto BHs makes them visible: • Very hot accretion disk is outside event horizon; emits mainly X-rays Dec. 11, 2007

8. X-ray Binaries with BHs • Cyg X-1 (near Deneb; EL1!) is prototype X-ray BH; discovered in 1971 but only confirmed as having BH by measuring its orbit in 1975 • Our Galaxy contains thousands of X-ray binaries with BHs as the accreting (primary) object. A “swarm” may exist around the central super-massive BH in our Galaxy Nucleus (see Chandra image around SgrA*) Dec. 11, 2007

9. Most massive “stellar mass” BH discovered in nearby Galaxy, M33 • Chandra X-ray telescope found an eclipsing BH in a binary in the nearby Galaxy, M33 • Eclipses mean orbit is edge-on, so mass of both BH and companion star can be measured “exactly”. The BH is most massive stellar BH yet: 15Msun! • The companion star feeding the BH is ~70Msun! So it, too, will form a BH – and make a BH-BH Binary – soon! Artist’s concept of most massive stellar BH accreting from disk fed by wind from its ~70Msun companion. Inset shows HST image of M33 stars near the X-ray source (blue). Dec. 11, 2007

10. “Stellar mass” BHs born in massive star core collapse (SNIb,c) about 1% of time are detected as Gamma-Ray Bursts! • Associated with SNIb or SNIc SNe (massive star core collapse) but only ~1% detected as GRBs due to beaming • GRBs mark the moment of birth of a stellar mass BH! • GRBs are most luminous cosmic sources yet detected: Etot ~1052 ergs which is ~1million times more energy output in ~100 keV X-rays and Gamma-rays as in all visible (thru X-ray) spectrum of Type II Supernovae! • Can thus be detected out to most distant universe… • These will be the tools to probe the most distant universe, back to time before Galaxies formed (stay tuned) Dec. 11, 2007