AaS! 255: How Do the Biggest Stars Get So Big?

Ask a Spaceman!

Paul M. Sutter

Astrophysics, Science, Cosmos, Holes, Black, Astronomy, Natural Sciences, Universe, Cosmology, Space, Physics

4.8 • 853 Ratings

🗓️ 9 September 2025

⏱️ 32 minutes

🔗️ Recording | iTunes | RSS

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Summary

How do we measure the sizes of stars? What are the biggest ones today, and how big could stars have gotten in the past? Is there any way for a star to cheat and get even bigger? I discuss these questions and more in today’s Ask a Spaceman!

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Transcript

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0:00.0	The largest star in the known universe.
0:09.1	Bigger than any other star by a factor of 20,000.
0:14.4	It's a true beast.
0:16.8	Is the sun?
0:18.5	Thank you for listening.
0:19.5	And I'll see you next time for more. Complete knowledge of
0:22.0	wait, wait, wait, wait, wait, hold up. That really can't be the end of the episode, can it?
0:27.1	No, it's not. But just like that professor in college who always asked rhetorical questions
0:32.6	seemingly just for the sake of annoying you, I'm about to ask a rhetorical question seemingly just for the sake of annoying you.
0:39.5	And that question is, what does it mean for a star to be big?
0:44.4	The sun is by far the biggest star on our sky.
0:49.3	And I know you're thinking, Paul, come on.
0:51.2	It's big because it's close, not big because it's, you know, big.
0:55.4	It looks big on our sky, the same way an ant can look huge if you hold it up to your eye,
1:00.9	but when you put it back on the ground, it looks small again.
1:03.9	But let me ask you this.
1:05.9	So what?
1:07.0	So what if it's only big because it's close?
1:10.6	Sure, the sun may not have the largest physical diameter of any star in the universe,
1:15.6	but to us it's big.
1:18.2	And that means something.
1:20.1	The sun gives us heat and light and gravity in a way that no other star does.
	...

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