The James Webb Space Telescope (JWST) has discovered a tiny galaxy in the early universe that is rapidly expanding as it forms stars at a breakneck pace, revealing more about the ancestors of galaxies such as ours.
THE galaxycalled RX J2129-z95, is seen at a red shift of 9.51. This number, which refers to the extent to which the galaxy’s light has been stretched by the expansion of the universemeans that we see it as it existed barely 510 million years after the big Bang.
Because it is so far away, RX J2129-z95 is exceptionally weak. However, his light received a boost from the gravitational lens effect of a massive foreground galaxy cluster called RX J2129.6+0005, which is located about 2.5 billion light-years from Earth along the same line of sight. The gravity of the 150 trillion solar mass cluster amplified the light from RX J2129-z95, while splitting it into three images.
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The galaxy’s redshift has been confirmed by JWSTfrom the NIRSpec (Near-Infrared Spectrometer) instrument, which also detected strong cloud emission of hydrogen and oxygen gas in RX J2129-z95. These emission lines in the spectrum of the galaxy revealed some of the extraordinary properties of RX J2129-z95.
For example, RX J2129-z95 is only 105.6 light-years in diameter, which is tiny compared to the 100,000 light-year diameter of our milky way galaxy or even modern dwarf galaxies that span thousands of light-years. Yet despite being a thousand times smaller in volume than the Milky Way, RX J2129-z95’s star formation rate is the same as that of our galaxy, which means it’s much more intense.
JWST finds that such high star formation rates are a fairly typical trait of galaxies in the early universe, but RX J2129-z95 is extreme even when it comes to high redshift galaxies.
“The star formation rate is similar to other high redshift galaxies confirmed by NIRSpecbut the radius of the galaxy is at least three times smaller than these other galaxies,” said Hayley Williams, a PhD student at the University of Minnesota who led the research, in an interview with Espace.com. “That means a ton of star formation is packed in a very small volume.”
The fact that all of these early galaxies were small, despite their high luminosity, supports the popular hierarchical galaxy formation model, which predicts that small galaxies formed first, before merging and expanding into larger galaxies such as the Milky Way.
Williams’ team also found no evidence of activity. a supermassive black hole in the center of RX J2129-z95. This could be significant, since RX J2129-z95 exists towards the end of the “Cosmic Dark Age”, when radiation ionized most of the vast ocean of neutral hydrogen gas that filled the universe. One of the greatest questions in cosmology has been what led to the end of the Dark Ages – was it the radiation of greedy growth? black holes, or massive star formation episodes? If RX J2129-z95 is typical, then the absence of an obvious black hole could indicate radiation from many hot young stars as the main driving force behind the end of the dark ages.
So far, the amount of ionizing radiation produced by RX J2129-z95 has not been quantified. However, “if there is a substantial population of similar galaxies, then perhaps they play a key role in the ionizing photon budget,” Williams said.
More observations of galaxies at similar redshifts are needed, but with a handful of very high redshift luminous galaxies already confirmed by the JWST and many more such discoveries likely to follow, astronomers will have soon from a large sample.
Until then, “it’s hard to draw conclusions about these things with such a small sample size,” Williams said.
The results (opens in a new tab) were published April 13 in the journal Science.
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