When Did The First Stars And Galaxies Light Up?

  • A new study suggests that the Dark Ages completely ended around 12 billion years ago. 
  • This is when the first generation of stars and galaxies lit up the universe. 

It is estimated that our universe is 13.8 billion years old, with an uncertainty of 21 million years at the 68% confidence level.

The earliest generation of stars and galaxies formed about 500 million years after the Big Bang. The first generation of stars, called population III stars, was the first source of visible light in the universe.

They haven’t yet been observed but it is considered that they are non-metallic, 100 to 300 times more massive than Sun, and have relatively short lifetimes. As these stars emerged, the Dark Ages slowly ended.

Some theories indicate that a few of those stars are still burning today. The data, however, isn’t accurate: exact timings are still being researched. A new study suggests that the Dark Ages only completely ended around 12 billion years ago, as the universe took its present appearance.

The data gathered via Murchison Widefield Array (MWA) radio telescope has put scientists one step closer to detecting the ultra-faint signal from the earliest stages of the universe’s existence when the first stars lit up the cosmos.

Exploring the Epoch of Reionization (EoR) can reveal significant information about the evolution of the universe in the early stages, as well as X-ray and ultraviolet properties of the first galaxies.

The first type of molecule to form in the universe was helium hydride ions. Each of these charged molecules was made of a positively charged hydrogen atom and a neutral helium atom. They formed about 100,000 years after the Big Bang.

An artist’s impression of first-generation population III stars | Credit: Image: Wise, Abel, Kaehler (KIPAC/SLAC)

Positively charged hydrogen atoms reunited with their electrons (forming neutral hydrogen) as the universe cooled and expanded. About 12 billion years ago, atoms began clustering together to form stars and galaxies. The intense radiation from these objects reionized the neutral hydrogen, and thus most of the neutral hydrogen atoms disappeared from interstellar space.

Reference: arXiv:1911.10216 | Brown University 

MWA tries to spot these neutral atoms from the dark ages and determine how they evolved as the EoR unfolded. If successful, the observations could reveal important details about the first stars and galaxies. However, catching those signals is a tough task and requires extremely sensitive instruments.

Catching Neutral Hydrogen Signal

MWA is an array of 2,048 radio antennas operating in the frequency range from 70 to 300 MHz. It is used to detect neutral atomic hydrogen emission from the cosmological EoR.

An individual MWA-32T tile | Wikimedia

However, the signal researchers are trying to detect is too weak. Neutral hydrogen emits radiation at 21 cm wavelength, but over the course of 12 billion years, the signal from the EoR has stretched to 200 cm.

Millions of other sources (including man-made objects and natural sources like other galaxies) emit radiation at the same wavelength, which is why it’s hard to detect these signals.

To overcome this issue, researchers used hundreds of advanced processing methods while accounting for unique frequency responses of the instrument itself. MWA’s new configuration revealed some exciting information.

The findings set the lowest limit yet for the strength of the neutral hydrogen signal. It can help researchers accurately constrain the timing of when the first stars lit up the cosmos.

Read: 13 Different Types of Stars In The Universe

This is the 2nd consecutive best-limit-to-date data revealed by MWA. Researchers believe that such experiments will one day identify the hard-to-catch EoR signature.

Written by
Varun Kumar

Varun Kumar is a professional science and technology journalist and a big fan of AI, machines, and space exploration. He received a Master's degree in computer science from Indraprastha University. To find out about his latest projects, feel free to directly email him at [email protected] 

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