Long-time Syzygy listener Jack asks: "Hey Emily — what's the deal with quasi-stars?" (We're paraphrasing). Quasi-stars are hypothetical, enormous stellar-object-thingies that might have formed shortly after the Big Bang. They're so huge they might have formed with black holes at their cores. If they existed at all, it would explain why astronomers keep finding intermediate-mass black holes in gravitational wave experiments. And as a bonus for you, Jack, Emily presents Hawking stars: otherwise ordinary stars that could be hiding a tiny black hole deep in their core. Could the Sun be a Hawking star? The mind boggles.

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Syzygy is produced by Chris Stewart and co-hosted by Dr Emily Brunsden from the Department of Physics at the University of York.

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Things we talk about in this episode:

• Quasi-stars

• (… as opposed to Quasars)

• Types of black hole

• Intermediate-mass black holes and LIGO

• Hawking stars

• The research paper that seeded this episode

• Asteroseismology, the music of the stars