### Question --- What is the historical significance of the Hulse-Taylor binary radio pulsar to physics? ### Answer --- The Hulse-Taylor was the first binary [[Neutron Star#Pulsar|pulsar]]-[[Neutron Star|NS]] system discovered (Hulse + Taylor, 1974) - Won Nobel Prize in 1993 for being the first discovered binary with a [[Neutron Star#Pulsar|pulsar]] - Due to the [[Binary Stars|binary]] orbit, the radio pulses of the pulsar exhibited a periodic effect (timescale $\sim 8$ hours) of arriving "a little early" and then "a little late" - This implied the existence of the non-visible companion in the binary. With large [[Binary Stars#For a Spectroscopic Binary|radial velocity amplitudes]], they were able to get a mass estimate $\implies$ [[Neutron Star|neutron star]] This system is also very important as a test of general relativity and gravitational waves. - Two compact objects in a close binary should be losing orbital energy and angular momentum to [[Gravitational Waves]]. - [[Gravitational Waves#Gravitational Radiation]] carries away energy from the system, such that to conserve energy, the overall energy of the binary must also decrease. - For a [[Kepler's Laws of Planetary Motion|Keplerian Orbit]], the energy of the binary is roughly $E_{\rm binary} \simeq -\frac{G M_{1} M_{2}}{2 a}$ such that if the energy decreases, so must $a$. By comparing the change in period ($\dot{P}$) and comparing general relativity predictions, we found incredible agreement between the theory and data for over 30 years: ![[hulse_taylor_binary.png|align:center|450]] This was one of the first pieces of evidence for the existence of [[Gravitational Waves#Gravitational Radiation|gravitational radiation]].