Astronomers find stars forming just 250 million years after Big Bang

Astronomers find stars forming just 250 million years after Big Bang

Pinning down the star formation history of the Universe is a challenging task, but astronomers studying the very distant galaxy MACS1149-JD have detected the most distant oxygen ever detected from stars that had begun forming a mere 250 million years after the Big Bang. When ALMA's antennas (which range from 7 to 12 meters in diameter) are configured in different ways, the array is capable of zooming in on some of the most distant cosmic objects in the universe, as well as capturing images that are clearer than those produced by the Hubble Space Telescope.

Titled "The onset of star formation 250 million years after the Big Bang", the paper, involving a large global team of researchers, was published online Wednesday in the journal Nature. They measured the frequency of a peak in the galaxy's spectrum that comes from ionized oxygen gas. It's this light signal that ALMA has picked up some 13 billion years later, although in that time the expansion of the universe has stretched the light into the millimeter wavelength.

The new details revealed that light from a galaxy dubbed MACS1149-JD1 was 13.28 billion lightyears old, an worldwide team reported in the scientific journal Nature.

The ionised oxygen from stars in MACS1149-JD1 therefore means that there must have been an even earlier generations of stars before these ones.

"I was thrilled to see the signal of the distant oxygen in the ALMA data". "This detection pushes back the frontiers of the observable Universe".

In 2016 and 2017, a team of astronomers took another look using the Atacama Large Millimeter/submillimeter Array (ALMA), a collection of 64 radio telescopes in Chile. The distance to the galaxy determined from this observation is consistent with the distance from the oxygen observation.

The oxygen signal was observed from an ancient galaxy, MACS1149-JD1, which is the most distant galaxy observed yet.

Dr Nicolas Laporte, from University College London, who co-led the team, said: "This is an exciting discovery as this galaxy is seen at a time when the Universe was only 500 million years old and yet it already has a population of mature stars".

After figuring out the age of the signal, the astronomers worked backwards to determine when the galaxy's first stars fired up. To find out, the team reconstructed the earlier history of MACS1149-JD1 using infrared data taken with the NASA/ESA Hubble Space Telescope and the NASA Spitzer Space Telescope. But for the galaxy to have enough oxygen to be visible, it must have been creating stars for around 250 million years before that, making it one of the earliest known star-producing galaxies.

The maturity of the stars seen in MACS1149-JD1 raises the question of when the very first galaxies emerged from total darkness, an epoch astronomers romantically term "cosmic dawn".

"The mature stellar population in MACS1149-JD1 implies that stars were forming back to even earlier times, beyond what we can now see with our telescopes", said Laporte. Whether MACS1149-JD1 is just an outlier or the tip of an iceberg will have to wait for more observations. "Since we are all made of processed stellar material, this is really finding our own origins". "It is truly remarkable that ALMA detected an emission line - the fingerprint of a particular element - at such a record-breaking distance".

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