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Starts With A Bang

Starts With A Bang podcast #91 — Hypermassive neutron stars

Somewhere out there in the Universe is the heaviest neutron star, and elsewhere lies the lightest black hole. Where’s the line between them?
hypermassive neutron star
This image shows the illustration of a massive neutron star, along with the distorted gravitational effects an observer might see if they had the capability of viewing this neutron star at such a close distance.
Credit: Daniel Molybdenum/flickr and raphael.concorde/Wikimedia Commons
Key Takeaways
  • Black holes and neutron stars form by the same mechanism: the collapse of the core of a very massive star.
  • But neutron stars can also merge together, producing either a neutron star (below some threshold), a black hole (above it), but there is a third option, too.
  • Sometimes, neutron star mergers make a hypermassive neutron star: that exists for under a second before becoming a black hole. This “edge case” is ultra-interesting.

When stars are born, they can come with a wide variety of masses. But there are only a few ways that stars can die, and only a few types of remnants that can be left behind: white dwarfs, neutron stars, and black holes. Neutrons stars and black holes are most frequently created from core-collapse supernova events: the deaths of massive stars. Somewhere, even though we’re not sure exactly where it is, there’s a dividing line between “what makes a neutron star?” and “what makes a black hole?” Somewhere out there, there’s a heaviest neutron star, and someplace else a lightest black hole.

But the dividing line might not be so clean, after all. It turns out that when neutron stars merge, they can form another neutron star, a black hole, or a third case: an in-between scenario. In this third case, you can temporarily form a hypermassive neutron star: a neutron star that’s too massive to be stable, but that collapses in short order to a black hole, but only after persisting as a neutron star for a detectable amount of time.

To help guide us through the science of hypermassive neutron stars, I’m so pleased to welcome Dr. Cecilia Chirenti to the show, a joint scientist at NASA Goddard and the University of Maryland, College Park. There’s a whole lot of cutting-edge science right at (and even over) the horizon of what we know today, and you won’t want to miss this information-rich episode!


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