Astronomers say we may be witnessing a merger of two small galaxies just 400 million years after the Big Bang.
“Gravitational lensing by massive galaxy clusters magnifies distant objects,” said Dr. Dan Coe, an astronomer of AURA/STScI for ESA and the Johns Hopkins University, and his colleagues.
“Thanks to these cosmic telescopes, not only the luminosities of faint objects in the early Universe are boosted to the observable regime, they also enable us to study the small-scale structures.”
“Thus, lensing has enabled us to discover early galaxies and study their properties.”
In 2012, the astronomers discovered a small galaxy that existed 13.3 billion years ago.
The gravity of the massive galaxy cluster MACS J0647+7015 (MACS0647 for short) triply lensed the galaxy, which was named MACS0647-JD, causing its image to appear in three separate locations.
“I discovered MACS0647-JD 10 years ago with the NASA/ESA Hubble Space Telescope,” Dr. Coe said.
“At the time, I’d never worked on high redshift galaxies, and then I found this one that was potentially the most distant at redshift 11, about 97% of the way back to the Big Bang.”
“Due to the gravitational lensing of MACS0647, it’s lensed into three images: JD1, JD2, and JD3,” he added.
“They’re magnified by factors of eight, five, and two, respectively.”
In a new study, the researchers observed MACS0647-JD using the NASA/ESA/CSA James Webb Space Telescope.
They found that the object has two components that are either merging galaxies or stellar complexes within a single galaxy.
Both are very small, with stellar masses of around 100 million solar masses and diameters less than 200 parsecs (652 light-years).
The brighter larger component is intrinsically very blue, likely due to very recent star formation and no dust, and has a diameter of 140 parsecs (457 light-years).
The smaller component appears redder, likely because it is older (100-200 million years old), and a smaller diameter of 40 parsecs (130 light-years).
“With Hubble, it was just this pale, red dot. We could tell it was really small, just a tiny galaxy in the first 400 million years of the Universe,” Dr. Coe said.
“Now we look with Webb, and we’re able to resolve two objects!”
“We’re actively discussing whether these are two galaxies or two clumps of stars within a galaxy. We don’t know, but these are the questions that Webb is designed to help us answer.”
“You can also see that the colors between the two objects are so different. One’s bluer; the other one is redder,” said Tiger Yu-Yang Hsiao, a Ph.D. student at the Johns Hopkins University.
“The blue gas and the red gas have different characteristics. The blue one actually has very young star formation and almost no dust, but the small, red object has more dust inside, and is older. And their stellar masses are also probably different.”
“It’s really interesting that we see two structures in such a small system. We might be witnessing a galaxy merger in the very early Universe. If this is the most distant merger, I will be really ecstatic!”
The team’s new paper will be published in the journal Nature.
Tiger Yu-Yang Hsiao et al. 2022. JWST reveals a possible z~11 galaxy merger in triply-lensed MACS0647-JD. Nature, in press; arXiv: 2210.14123
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