May 16, 2018 - Science

Astronomers find 13 billion-year-old signs of early stars

An image of the galaxy cluster MACS J1149.5+2223 taken with the Hubble Space Telescope. Inset image is the galaxy MACS1149-JD1 observed with ALMA. Oxygen detected with ALMA is depicted in green.

Galaxy cluster MACS J1149.5+2223 with galaxy MACS1149-JD1 inset. Oxygen is depicted in green. Image: ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, W. Zheng (JHU), M. Postman (STScI), the CLASH Team, Hashimoto et al.

Astronomers have detected oxygen in a galaxy more than 13 billion light years away — a direct measurement of stars forming and dying in the early universe.

The big picture: The time when stars first formed in the universe is of intense interest to researchers. It is the epoch when matter began clumping together into stars and galaxies, heavy elements started to form, and our universe began to look like it does today.

"We have a theory for why that all happened but precious few observations of when it all started to take shape."
Rob Simcoe, astronomer, MIT

How they did it: Using the Atacama Large Millimeter/submillimeter Array (ALMA) in the Chilean desert, astronomers at Osaka Sangyo University detected a signature of oxygen in light from galaxy MACS1149-JD1.

  • Based on how much the light stretched due to the expansion of the universe, they determined the galaxy was 13.28 billion light years away, or from about 500 million years after the Big Bang, they report in Nature on Wednesday.
  • Researchers at the University College London then used the optical Very Large Telescope, also in Chile, to look for hydrogen emissions that supported the distance they observed.
  • "They brought to bear multiple assets from around the globe that, taken collectively, paint a pretty convincing case," says Simcoe, who was not involved in the research.

What it might mean: Oxygen is formed in stars and released when they die, so its detection indicates MACS1149-JD1 was old enough at the time to be home to stars that had already cycled through life.

  • When the researchers looked at infrared data of the galaxy from the Hubble and Spitzer telescopes, their model — which they acknowledge in their report is "somewhat speculative" — suggested many stars there were 300 million years old.
  • The team proposes that stars in the galaxy began to form just 250 million years after the Big Bang, then became inactive before another round of formation that the researchers detected with ALMA.
  • The first stars in the universe therefore may be older than expected, but Simcoe says "time will tell whether that holds up" because their formation is difficult to measure.

What's next: Studies like this one show it's "actually possible to identify, detect and study galaxies from the earliest times," Simcoe says. Researchers hope Hubble's successor, the James Webb Space Telescope (JWST), can be used to observe them with more resolution.

  • It won't launch until at least 2020 (it has been delayed multiple times), but in the meantime look for more studies about potential targets for JWST as researchers jockey for precious time on the telescope.
Go deeper