|NASA’s GALEX ultraviolet satellite identified nearby starburst galaxies that made good analogs of early galaxies. Follow-up images taken by the Hubble Space Telescope revealed that the compact galaxy J0921 allowed a large fraction of its radiation to escape.
A compact galaxy some 3 billion light-years away is shedding light, shedding light on how stars formed during when our universe was young.
A densely packed star-forming galaxy is reproducing the events that brought light to the early universe.
The nearby compact galaxy named J0921+4509, which is rapidly producing stars, has many of the characteristics that would have been required to light up the early universe. Located approximately 3 billion light-years from the Milky Way, the star-forming regions of the tightly bound galaxy are surrounded by dense clouds of gas. Holes in the gas allow radiation to leak out, mimicking events that would have broken through the darkness that followed the birth of the universe.
J0921+4509 produces approximately 50 solar-masses’ worth of stars each year, more than 33 times the number of stars created by the Milky Way every year. While most stars in other locations remain swathed in the gas that forms them, trapping radiation inside, J0921 has holes that allow the radiation to escape, much as it might have in the early universe.
Only a few hundred thousand years after the Big Bang, hydrogen gas in the universe cooled and became neutral as protons and electrons paired up. Any radiation emitted was quickly absorbed, rendering the period unobservable, or “dark,” to astronomers. By the end of the first billion years, radiation known as Lyman continuum had reionized the hydrogen, scattering electrons and making the universe visible once again.
Events from the dark ages of the universe, including its reionization, cannot be directly studied. Instead, astronomers must search for similar processes in objects they can examine today, such as those found in the starburst galaxy J0921. The name “starburst galaxies” comes from the unusually high rate of stellar production in such locations…
A starburst studied
A handful of galaxies in the early universe are leaking radiation. Scientists are able to study these galaxies from the universe’s youth because of the correlation between the distance light travels and the time it takes to make the journey. Essentially, looking at objects in the distant universe is like looking back in time; astronomers see the light as it was when it left the object.
Two other nearby galaxies are suspected to be leaking radiation, but each has only a tenth as much radiation as J0921.
“This is the direct evidence of how the galactic feedback via winds can lead to conditions that allow Lyman continuum to escape,” Borthakur said. “This tells us about the physics of star formation and its feedback in the epoch of reionization, and solves the decades-old mystery of how Lyman continuum photons can escape through the cold cloud cocoon enveloping star-forming regions.”
The new research is published this week in the journal Science.