Astronomers find evidence for stars forming just 250 million years after Big Bang

The galaxy cluster MACS J1149.5+2223 taken with the
NASA/ESA Hubble Space Telescope and the inset image is the
galaxy MACS1149-JD1 located 13.28 billion light-years away
observed with ALMA. Here, the oxygen distribution detected
with ALMA is depicted in green. Credit: ALMA
(ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, W. Zheng
(JHU), M. Postman (STScI), the CLASH Team, Hashimoto et al.

Not long after the Big Bang, the first generations of stars
began altering the chemical make-up of primitive galaxies,
slowly enriching the interstellar medium with basic elements
such as oxygen, carbon, and nitrogen. Finding the earliest
traces of these common elements would shed important light on
the chemical evolution of galaxies, including our own.


New observations with the Atacama Large
Millimeter/submillimeter Array (ALMA) reveal the faint,
telltale signature of oxygen coming from a galaxy at a
record-setting distance of 13.28 billion light-years from
Earth, meaning we are observing this object it as it appeared
when the universe was only 500 million years old, or less than
4 percent its current age.

For such a young galaxy, known as MACS1149-JD1, to contain
detectable traces of oxygen, it must have begun forging
even earlier: a scant 250 million years
after the Big Bang. This is exceptionally early in the history
of the universe and suggests that rich chemical environments
evolved quickly.

“I was thrilled to see the signal of the most distant oxygen,”
explains Takuya Hashimoto, the lead author of the research
paper published in the journal Nature and a researcher
at Osaka Sangyo University and the National Astronomical
Observatory of Japan.

“This extremely distant, extremely young galaxy has a
remarkable chemical maturity to it,” said Wei Zheng, an
astronomer at Johns Hopkins University in Baltimore, who led
the discovery of this galaxy with the Hubble Space Telescope
and estimated its distance. He also is a member of the ALMA
research team. “It is truly remarkable that ALMA detected an
emission line—the fingerprint of a particular element—at such a
record-breaking distance.”

The galaxy cluster MACS J1149.5+2223 taken with the NASA/ESA
Hubble Space Telescope; the inset image is the very distant
galaxy MACS1149-JD1, seen as it was 13.3 billion years ago
and observed with ALMA. Here, the oxygen distribution
detected with ALMA is depicted in red. Credit: ALMA
(ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, W. Zheng
(JHU), M. Postman (STScI), the CLASH Team, Hashimoto et al.

Following the Big Bang, the chemical composition of the
universe was starkly limited, with not even a trace of elements
like oxygen. It would take several generations of star birth
and supernovas to seed the young cosmos with detectable amounts
of oxygen, carbon, and other elements forged in the hearts of
stars.

After they were liberated from their stellar furnaces by
supernovas, these made their way into
interstellar space. There they became superheated and were
ionized by the light and radiation from massive stars. These
hot, ionized atoms then “glowed” brightly in infrared light. As
this light traveled the vast cosmic distances to Earth, it
became stretched by the expansion of the universe, eventually
changing into the distinct millimeter-wavelength light that
ALMA is specifically designed to detect and study.

By measuring the precise change in the wavelength of this
light—from infrared to millimeter—the team determined that this
telltale signal of oxygen traveled 13.28 billion light-years to
reach us, making it the most distant signature of oxygen ever
detected by any telescope. This distance estimate was further
confirmed by observations of neutral hydrogen in the galaxy by
the European Southern Observatory’s Very Large Telescope. These
observations independently verify that MACS1149-JD1 is the most
distant galaxy with a precise distance measurement.




Computer graphics movie of the star formation history in the
galaxy MACS1149-JD1. The self-gravity of matter creates
filamentary structures and the density at the intersections
of the filaments increases. Around 200 million years after
the Big Bang, active star formation ignites in the high
density regions, which leads to the formation of galaxies.
The gas in the galaxy is blown off by active stellar wind and
supernovae, then the gas returns to the galaxy and causes
another burst of star formation. Credit: ALMA (ESO/NAOJ/NRAO)

The team then reconstructed the star formation history in the
galaxy using infrared data taken with the NASA/ESA Hubble Space
Telescope and NASA’s Spitzer Space Telescope. The observed
brightness of the galaxy is well explained by a model where the
onset of star formation was another 250 million years ago. The
model indicates that the star formation became inactive after
the first stars ignited. It was then revived at the epoch of
the ALMA observations: 500 million years after the Big Bang.

The astronomers suggest that the first burst of star formation
blew the gas away from the galaxy, which would suppress the
star formation for a time. The gas then fell back into the
galaxy leading to the second burst of star formation. The
massive newborn stars in the second burst ionized the oxygen
between the stars; it is those emissions that have been
detected with ALMA.

Microwave spectrum of ionized oxygen in MACS1149-JD1 detected
with ALMA. Originally emitted as infrared light with a
wavelength of 88 micrometers, the ALMA detection was made
with an increased wavelength of 893 micrometers due to the
expansion of the universe over 13.28 billion years. Credit:
ALMA (ESO/NAOJ/NRAO), Hashimoto et al.

“The mature stellar population in MACS1149-JD1 implies that
stars were forming back to even earlier times, beyond what we
can currently see with our telescopes. This has very exciting
implications for finding ‘cosmic dawn’ when the first galaxies
emerged,” adds Nicolas Laporte, a researcher at University
College London/Université de Toulouse and a member of the
research team.

“I am sure that the future combination of ALMA and the James
Webb Space Telescope will play an even greater role in our
exploration of the first generation of stars and ,” said Zheng.

ALMA has set the record for the most distant oxygen several
times. In 2016, Akio Inoue at Osaka Sangyo University and his
colleagues found the signal of oxygen at 13.1 billion
light-years away with ALMA. Several months later, Nicolas
Laporte of University College London used ALMA to detect oxygen
at 13.2 billion light-years away. Now, the two teams merged
into one and achieved this new record. This reflects both the
competitive and collaborative nature of forefront of scientific
research.

“With this discovery we managed to reach the earliest phase of
cosmic star formation history,” said Hashimoto. “We are eager
to find in even farther parts of the
universe and expand the horizon of human knowledge.”

This research is presented in a paper “The onset of 250 million years after the Big
Bang,” by T. Hashimoto et al., to appear in the journal
Nature.

Explore further:
Ancient
stardust sheds light on the first stars

More information: The onset of star formation 250
million years after the Big Bang, Nature (2018).
nature.com/articles/doi:10.1038/s41586-018-0117-z

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