AstroTalk Episode October 19, 2017

Collision of Neutron Stars

3:08pm - 3:38pm

Light cannot escape a black hole, so when astronomers at LIGO detected the collision of 2 black holes a few years ago, LIGO detected gravitational waves only. But when 2 neutron stars (that were 130 million light years away, in the galaxy NGC 4993) collided, and their signal was received on Earth on August 17, 2017, gravitational waves, and a whole array of electromagnetic radiation was detected. Astronomers were able to confirm their theories on many aspects about neutron stars from the collision. The newspaper, the Independent, claims that " the event has kickstarted a "new chapter in astrophysics" and confirmed theories about the origin of the mysterious neutron stars". Astronomers detected the formation of many precious and heavy metals from the collision. This kilonova, which was apparently 1000s of times stronger than a mere nova, flung out a whole host of knowledge, along with gravitational waves, electromagnetic radiation, gold, plantinum and lanthanides, among a host of other heavy elements. The mass of the colliding neutron stars was 1.4 and 1.6 solar masses. This was the first detection of gravitational waves from anything other than black holes. The neutron stars stretched and warped space-time as they approached each other, and then collided. A burst of short gamma ray bursts, short GRBs, was detected 2 seconds after the detection of the gravitational waves. The event also was detected for 100 seconds, whereas in the collision of black holes, the 4 previous detections lasted at most only 2 seconds. When the event, called GW170817, occurred, dinosaurs roamed the Earth. The findings were published in the journals, Nature, Nature Astronomy, and Physical Review Letters. The collision answered 3 questions about neutron stars: (1) What happens when neutron stars merge (2) What causes the short duration gamma ray bursts, short GRBs (3) Where are heavy elements like gold made. Astronomers feel this is a new chapter in astrophysics.
Dr. BS Sathyaprakash from Cardiff University remarked that the 12 hours following the collision of the 2 neutron stars was the most exciting period of his entire scientific life. The collision also helped astronomers more accurately measure the expansion rate of the universe. The explosion will help explain the inner workings of neutron stars, as well as confirming the theories in general relativity. 15:08:33 15:38:38