The Universe is an enormous place, but we can’t see all the way back to the beginning. Here’s the latest record-breaker.
No matter how far back we look in the Universe, we cannot yet observe the first stars or galaxies directly.
The light they produce is too redshifted and blocked by too much intervening gas to be seen even by Hubble.
The most distant galaxy ever discovered is already late, dating back to 407 million years after the Big Bang.
But the very first stars should go back hundreds of million years further.
Sometime between the Cosmic Microwave Background, at 380,000 years, and that first galaxy, the first stars must have formed.
Owing to the second-most-distant galaxy ever found, MACS1149-JD1, we can understand when.
We see MACS1149-JD1 as it was 530 million years after the Big Bang, while inside, it has a special signature: oxygen.
Oxygen is only produced by previous generations of stars, indicating that this galaxy is already old.
MACS1149-JD1 was imaged with microwave (ALMA), infrared (Spitzer), and optical (Hubble) data combined.
The results indicate that stars existed nearly 300 million years before our observations.
The very first stars must have arisen no later than 250 million years after the Big Bang.
2021’s James Webb Space Telescope will image them firsthand.
Mostly Mute Monday tells the scientific story of an astronomical phenomenon or discovery in images, visuals, and no more than 200 words. Talk less; smile more.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.