Light from Infant Stars in the Early Universe

Big questions require big answers. Nowhere is this truer than in astronomy. Take, for example, the questions about the birth of the universe. What happened at the beginning? When did the first infant stars appear? People have heard of the Big Bang, for sure. Based on media reports and stories in science magazines, most folks have this idea of a giant explosion at the beginning. It sent the infant universe into a headlong expansion of space and time. That’s essentially what happened, but as usual, the devil is in the details.

It’s important to remember that the universe didn’t spring into being fully formed with all the stars and galaxies rushing out. I see illustrations sometimes that seem to imply that. But, in reality, the infant universe was a soup of quarks. As it expanded and cooled, those quarks combined to create larger particles. Eventually, they formed atoms of hydrogen and traces of helium and a little lithium. That all happened fairly quickly. If you’ve ever read the famous book, The First Three Minutes, it gives a good idea of what happened.

After the Big Bang

The past decades of cosmological research have focused on what happened after the Big Bang before the first stars existed. As part of their work, astronomers search for the earliest stars and galaxies, in an effort to figure out just how early they existed.

So, what happened before the first infant stars and galaxies shone out? Let’s go back almost to the beginning. After the Big Bang, the universe expanded and cooled for about 380,000 years. Electrons and protons combined into the first atoms (mostly hydrogen).

Eventually, this gas formed the first stars and galaxies. They were giant behemoths made entirely of hydrogen and helium. However, there was still a lot of hydrogen gas around and the stars existed in this fog of hydrogen. Essentially, it blocked their radiation. So, even though there were stars, the earliest universe was in a “cosmic Dark Age” that went on for about half a billion years.

Eventually, as the universe continued its expansion, it also cooled. The ultraviolet and visible starlight from the first stars and galaxies could “punch through” the cosmic fog and begin to clear it out. We see that early light today in the infrared part of the spectrum. That’s because its wavelengths have been stretched by their trip across an expanding universe. That first propagation of light from the infant star population began the “Epoch of Reionization” which ended the cosmic Dark Ages.

Probing the Early Universe and Infant Stars

The Cosmic Dark Ages provide a barrier that light cannot pass. So, astronomers look at the “most recent” early epochs. That would be a time when light was starting to propagate from the first stars and galaxies. To see “back” that far, astronomers use every instrument they can. Hubble Space Telescope and ground- and space-based infrared-enabled telescopes are their main tools. They let observers look across billions of years of time. Such telescopes can peer back to the moments when the first stars started to light up the infant universe. When the James Webb Space Telescope is launched and comes online, the “look-back” ability will improve.

“Bubbles” Made by Infant Stars in Early Galaxies

So, what did it look like “way back when”? As the first stars dissipated the fog, they created large “ionized bubbles” around their galaxies. For the first time, astronomers have found these bubbles. How did they do it? A team led by Arizona State University researcher Vithal Tilvi developed an observing program to look for evidence of the first stars in the earliest galaxies. They used the Mayall telescope at Kitt Peak National Observatory to study the galaxy cluster EGS77. Thir data provided evidence of three overlapping “bubbles” around the cluster at the beginning of the Epoch of Reionization. That’s when the galaxies’ hot young stars began to heat up their environment.

This is a pretty important find because there’s so little observational data from that period of time in the universe. First of all, it has been difficult to observe, even with some very good telescopes. However, we live in an era of technological advancement, and that includes higher-resolution instruments for astronomy. The Kitt Peak Mayall telescope was outfitted with an infrared imager called NEWFIRM. It dissects light signals from that distant epoch. That has opened up the era of reionization for study.

In addition, measurements of the ionized bubbles around EGS77 show that it’s the most distant galaxy group ever observed. (You can read more details about the observations here.)

Continuing Probing of the Infant Universe

It will probably never be possible to look all the way back to the Big Bang. That cosmic fog I talked about earlier is an impassable barrier. But, now astronomers can chip away at the first moments when light could traverse the newborn universe.

“Cosmic dawn” presents interesting possibilities for further research. It has always been part of theories about the evolution of the early universe, and that will continue to be true.

Also, I think it’s pretty exciting that astronomers use existing observatories with new-generation instruments to probe this epoch of cosmic history. Now that the technique for doing is successful, I think we can expect more observations like the ones done at Kitt Peak. Of course, these bubbles could be rarer than we expect. That makes it doubly important to do follow up studies in all directions. More data will helps astronomers better understand the earliest epochs of the universe.

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