About 5,000 light-years away, a dying star has made a cloud of gas colder than the afterglow of the Big Bang: about 1 degree above absolute zero. This is the Boomerang Nebula, the coldest natural place known. We explain how a star made something colder than space itself, and compare it with the coldest places on Earth, on the Moon and in our laboratories.

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Chapters

0:00 Colder than space

0:26 What "cold" means in space

0:56 The Boomerang (or Bow Tie) Nebula

1:27 A shadow on the Big Bang's light

2:01 The cosmic refrigerator

2:39 A star that swallowed its partner?

3:12 ALMA's view

3:34 The ladder of cold

4:20 The Universe is still cooling

4:44 A record, for now

Sources

• Sahai & Nyman 1997, ApJ 487, L155: https://iopscience.iop.org/article/10.1086/310897

• Sahai et al. 2013, ApJ 777, 92: https://arxiv.org/abs/1308.4360

• Sahai, Vlemmings & Nyman 2017, ApJ 841, 110: https://arxiv.org/abs/1703.06929

• ALMA 2013, the Boomerang Nebula: https://www.almaobservatory.org/en/press-releases/alma-reveals-ghostly-shape-of-coldest-place-in-the-universe/

• Fixsen 2009 (temperature of the cosmic microwave background): https://arxiv.org/abs/0911.1955

• NASA LRO, the coldest crater on the Moon: https://svs.gsfc.nasa.gov/10595

Labels: in the video every claim carries an on-screen label (FACT, THEORY, ESTIMATE, HYPOTHESIS, SPECULATION); in this audio edition the narration says out loud when something is an estimate or a thought experiment.

Narration: synthetic voice. Music: original.

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