When we look out across the Universe, we’re also peering back in time.
Light only travels at a finite speed across the vastness of space.
The light arriving now has already completed a multi-light-year journey.
Meanwhile, every star only lives for a finite amount of time.
The shortest-lived stars may live just 1 or 2 million years total, while others survive for billions to trillions of years.
Under ideal conditions on Earth, approximately 9,000 stars possess naked-eye visibilities.
The closest one is Alpha Centauri: 4.3 light-years away.
The farthest is V762 Cassiopeiae, some 16,000 light-years distant.
Overwhelmingly, most stars in existence are the lower-mass, longer-lived stars.
But the brightest ones are the easiest to see: the giants and supergiants.
Giant stars are late-stage stars, destined to die shortly in supernovae or planetary nebulae.
The supergiants are the shortest-lived stars, with total lifetimes under 10 million years.
Some compelling candidates for already dead stars are:
- Eta Carinae,
- Spica, and
- IK Pegasi.
But cumulative odds are slim that even one star has already died: below ~1%.
Every star we can see is almost certainly still alive, dispelling one of astronomy’s most popular myths.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.
Ethan Siegel is on vacation this week. Please enjoy this article from the Starts With A Bang archives!