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The Supermassive Podcast · The Royal Astronomical Society

BONUS - Double Yolker Galaxies

·13 min·1 clip
Why do supermassive black holes seem to defy physics by not merging due to the final parsec problem?
In this bonus listener Q&A episode, Izzy Clark facilitates while Dr Becky Smethurst and Dr Robert Massey field questions submitted via email and Instagram. Massey addresses Ewan from Newcastle's question about orbital resonance, explaining that resonances occur when orbital periods share neat mathematical ratios, giving examples including the Galilean moons of Jupiter and the Neptune-Pluto 2:3 resonance. He notes that resonances can both stabilize and destabilize systems, as seen in the gaps of the asteroid belt, and that only about 1% of known exoplanet systems show obvious resonances. Smethurst answers a question about why gas giants cannot be seen through to their rocky cores, explaining that dense gas is opaque -- like steam or dry ice clouds -- and the intense pressure of a gas giant's atmosphere packs molecules so tightly that light cannot penetrate. Massey tackles Emily's question about the night sky during the first dinosaurs 250 million years ago, noting that while this roughly equals one galactic orbit of the solar system, all individual stars move at different speeds, making the ancient sky effectively unknowable. The episode's most technically rich segment comes from Smethurst responding to Brian's question about black hole mergers in merging galaxies. She introduces 'double yolker galaxies' -- galaxies with two simultaneously active supermassive black holes glowing as they grow post-merger. She then explains the 'final parsec problem': mathematical models suggest supermassive black holes stall when they are about three light years apart and cannot lose enough energy to complete the merger, yet correlations between galaxy and black hole mass suggest mergers do occur. She discusses pulsar timing arrays that detected evidence of spiraling supermassive black hole pairs, and the future LISA space-based gravitational wave detector -- a triangle of sensors the size of the solar system -- as the instrument that may finally resolve this mystery. The episode is a compact, accessible science Q&A suited for general audiences curious about astronomy and astrophysics.

As heard by us

Two astronomy questions, handled with patience, clear analogies, and a little useful wandering.

The Supermassive Podcast turns a listener question into two astronomy puzzles: why gas giant atmospheres stay opaque, and what the night sky may have looked like when the first dinosaurs appeared.

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Why you'd press play

Want a relaxed astronomy Q&A that ranges from dark matter to dinosaurs?

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