Understanding Massive Stellar Death

Michigan State Professor Fascinates Crowd with Core-Collapsed Supernovae

On March 3, 2020, Embry-Riddle Aeronautical University hosted Professor Sean Couch from Michigan State University. He came to the Jim and Linda Lee Planetarium to give a talk on core-collapsed supernovae. He spoke to a rather full planetarium about massive stellar death and ways that it can be simulated.

Professor Couch started with showing a picture of Cassiopeia A, a supernova remnant, or collapsed star, from 300 years ago. He then went on to start speaking of the topic of the presentation: core-collapsed supernovae. 

It appears to be that neutron stars and black holes are born from these core-collapsed supernovae. These strange phenomena play a major role in the feedback of their universe and regulate star creation. Stars are “born” in the collapsed cores of these supernovae. 

They also drive cosmic chemical evolution. Without the chemicals that are synthesized in these supernovae, planets would not exist. Neither would life on these planets because life needs the oxygen that is created by the star and then spread throughout the universe by supernovae. 

An important attribute of core-collapsed supernovae is that they emit neutrinos and gravitational waves. This was discovered when physicists were studying the SN 1987A, a star that exploded in our own universe. 

Core-collapsed supernovae are caused by the deaths of massive stars in the universe. In this process, the core actually collapses under its own weight, releasing large kinetic energies.  This explosion causes a neutrino star to form. An interesting aspect of these explosions is that they are three-dimensional but not spherically symmetrical. 

Massive stars follow an interesting series of stages leading up to their collapse. As they grow, they will burn successively heavier and heavier elements, with iron being the last element burned due to its tightly bound nucleus. This process is an endothermic reaction. When it is roughly 1.5 times the mass of our sun, the massive star becomes gravitationally unstable as electrons are being stolen from its core. This causes it to start to collapse. However, then a strong nuclear force stops the collapse. It launches strong shock waves into the outer limits of the star, but then eventually stalls due to loss of energy and neutrino cooling. 

Professor Couch then moved on to efforts to simulate this process, announcing, “We did it. Probably.” For a long time, the three-dimensional simulation technology needed to simulate a core-collapse supernova was infeasible. However, with the invention of such technology, physicists are able to more accurately model such explosions, or predict if such an explosion will occur. They discovered that the presence of perturbations causes explosions because it pushes the star beyond the stability threshold. 

“Every star has a magnetic field,” Professor Couch explained to the audience. Rotation and magnetic fields play an interesting role in the explosions of supernovae because they have an effect on gravitational waves. Professor Couch says that “inclusion of rotation can mute gravitational waves,” but it can also make gravitational waves much, much louder. Physicists have yet to explain this phenomenon, although research in the field is being done. 

Overall, the group seemed engaged and interested in the presentation. There was audience participation at all times, and Professor Couch did his best to make the presentation fascinating and informative. Department of Physics Chair Dr. Bailey said, “It was a great comprehensive presentation on supernova and how we can simulate them…It is great to have visitors who end up working with our students on these research projects.” Freshman Braedon Steuer commented, “I think it’s pretty cool stuff…It’s pretty cool how we are pushing technology.”

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