This is a Neutron Star. Pulsating NS's called pulsars were the first to be detected by Jocyln Bell in the 1960's. Story time in class!



They are small - the size of Manhattan.




The pulses from pulsars are very regular.




The crab nebular contains a pulsar. Young ones are rotating quickly and are found near supernova remnants.




See pulsar cos of the lighthouse effect they have. The beam of radiation points out from the NS.




See them in other wavebands now.









X-ray to radio.














This is what they look like - have very odd properties.




Pulsation period slows down with time - see some glitches - quakes on the surface




Pulsars can eat their companions.




Here see Doppler shift at work - the pulses from the NS are more frequent when the pulsar is towards us.




NS accreate mass from neighbouring stars if in binary systems. This can change the periods of an NS. Young ones rotate fast and are often seen near SN remnants. However, some fast pulsars appear isolated. They are 'spun up' by material hitting them at a specific angle.




Accretion onto a NS can also cause an explosion. As mass travels towards NS T is raised and it stars to burn - burster if onto a NS. Similar effect with WD's, called nova but not supernova as whole WD doesn't explode.




Nova - long (ish) period




Burster - short period




This is the Black holes part but first a review of relativity! This is how you add velocities according to Newton's Law's. Fine until




you get to high velocities. Einstein's theory of relativity is that nothing travels faster than the speed of light. Newtonian mechanics wrong at high speeds.




Leeds to strange effects such as time dilation and length contraction. Time runs slower if you are moving fast.









Next bit is general relativity. Einstein argued that is in an elevator, cannot tell if apple moving down or elevator moving up. Principle of equivalence - doesn't matter.




Large masses can warp space.




The more mass that is put their - the more space is warped - can detach itself and not appear to be there.




Why do we believe this - it explains the precession of mercury.




And the position of stars appears to change if the light passes by the sun - seen in a total eclipse.




Why do we care? There are some high mass and high density objects out there. Black holes are objects where the velocity to escape the NS is higher than the speed of light.




Light that is emitted outside the Schartschild radius experiences a gravitational redshift - hard work climbing out of the potential well the BH creates.




This is what a BH looks like.




Some rotate though.




Cannot see them but can infer their presence. This object twinkles on a period t< 1/100th second. Nothing travels faster than c => size of object as light has to cross it. The orbits of stars around it give a clue to the mass. Fine M > 7 Msun in a space size of Earth => black hole.




Some are fed by accretion of mass and grow to large mass. 10^8 Msun Black holes are detected now.




Science fiction - maybe they are connected?




Worm holes? Mathematically possible but i'm not going o try it - speghetification as you enter a BH.




Can cause an event called lensing. The light is bent - see numerous objects




Famouse lensing picture.




Another




Simulation




If perfectly aligned get an Einstein cross




Believe many galaxies (including our own) contain a BH. Sometimes we see evidence for them. These objects are called Quasar's or AGN (active galactic nuclei).




See radio jets emitted from the center of a galaxy














Accretion disk and often round it, a dusty torus. The unified model of AGN.