The discovery of ‘green pea’ galaxies could end the dark age of the universe

The findings, presented at the American Astronomical Society (AAS) meeting in Seattle, Washington, may explain reionization – A period in which powerful radiation exploded the “haze” of hydrogen atoms suspended over the universe, making stars and galaxies visible for the first time.

Immediately after the Big Bang, the universe was amazingly bright. The residual heat was so great that electrons could not combine with protons to form atoms. Instead, the universe was boiling with plasma – A dense glowing gas of electrically charged (or ionized) particles that scatters light, such as a fluorescent lamp.

After about 380,000 years, the expanding universe cooled enough to form hydrogen atoms. Some of these atoms eventually coalesced to form the first stars and galaxies. However, the layer of hydrogen around it absorbs its light – much like a thick fog can obscure a car’s headlights.

Finally, this cosmic dark age is over. The energetic radiation has smashed the hydrogen atoms between galaxies – and turned them back into individual protons and electrons – in a process called Partition.

Ionizing all intergalactic matter requires an enormous amount of energy, and astronomers have long argued about the exact factor. Starlight was probably one of the oldest galaxies. Or perhaps the event was caused by supermassive black holes that pull matter together and heat it up.

On July 11, 2022 — about six months after JWST launched — the observatory provided the deepest and sharpest picture of the distant universe seen to date. This image focuses on a group of galaxies called SMACS 0723. It contains thousands of previously observed faint galaxies.

JWST can catch it because it analyzes infrared light. As the universe expands, more distant galaxies appear to be moving from the visible part of the electromagnetic spectrum into the infrared. Among the thousands of galaxies in the SMACS 0723 image, the researchers decided to make more spectroscopic observations of three galaxies that appear very far away.

When James Rhodes, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and his colleagues saw the trio’s spectra for the first time, they realized that the galaxies looked like objects that would normally be nearby. They bore an uncanny resemblance to the “green pea” galaxies first spotted by a citizen science project called Galactic Zoo and reported in 2009.

The green pea galaxies are named because of their color and small size. It is only 5% of the Milky Way’s size and 1% of its mass. But don’t be fooled by its small size: it’s producing stars at an exponential rate—about 100 times faster than astronomers expected given its mass. They also appear to contain relatively few heavy elements. Their green color comes from the glow of ionized oxygen (a relatively light element) being heated by newborn stars.

The green pea has astounded astronomers because, although it was only observed in the nearby universe, its properties are similar to those of previous galaxies.
For example, the first galaxies are thought to contain only light elements because heavy elements take time to form. Sangeeta Malhotra, an astronomer at Goddard Space Flight Center, joked at the AAS meeting on January 12, They are “Peter Pan galaxies” because they haven’t matured.

That’s why Rhodes, Malhotra, and their colleagues were excited about the spectra of the three galaxies analyzed by JWST — The galaxies are from early space but look like neighboring green peas.

“We knew they looked like mock green peas the moment we saw them,” Rhodes said in an interview. nature. Like a green pea, the trio is small and has strong emission spectra — Which means it produces stars quickly. In addition, it contains a low percentage of elements heavier than hydrogen and helium. In fact, the outermost ones contain about 2% of the oxygen found in the Milky Way. This is probably the lowest amount of oxygen ever observed in the galaxy.

There is no doubt that they are things of the same kind. Before observing JWST, scientists measured green peas that formed ten billion years after the Big Bang. We can now suddenly study galaxies that formed only 700 million years after the Big Bang.

Another reason for excitement comes from 2016, when astronomers, including Thuan, reported that green peas sent a mass of ionizing photons into the intergalactic medium. Most galaxies observed in the nearby universe do not. With so many stars in such a small size, green peas may be able to channel through the interstellar medium, creating an escape route for energetic radiation.

This could mean that objects like the Trio from the early universe produced the energy needed to rid the universe of its dark age.

Source: nature.com