ALMA observes light from ionised oxygen in SXDF-NB1006-2

Using Atacama Large Millimeter/submillimeter Array (ALMA), astronomers from Japan, Sweden, the United Kingdom and ESO have observed one of the farthest galaxies known. SXDF-NB1006-2 is present at a redshift of 7.2.

In the high-sensitivity observations with ALMA, they have discovered light from ionised oxygen in SXDF-NB1006-2. The detection has become the farthest unambiguous discovery of oxygen ever obtained.

The team was looking forward to detect the heavy chemical elements existing in the galaxy, as they can shed light on the level of star formation, and thus give clues regarding the period in the history of the Universe called cosmic reionisation.

The research paper’s lead author Akio Inoue of Osaka Sangyo University, Japan, said, “Seeking heavy elements in the early Universe is an essential approach to explore the star formation activity in that period. Studying heavy elements also gives us a hint to understand how the galaxies were formed and what caused the cosmic reionisation”. The paper has been published in the journal Science.

There was a time when there were no objects in the Universe, and it was packed with electrically neutral gas. But when the first objects started shining, some hundred million years following the Big Bang, they released strong radiation that began breaking down the neutral atoms for the gas ionization.

During that time period, called cosmic reionisation, the entire Universe met a dramatic change. But the debate is still on over what type of objects exactly resulted into the reionisation. Astronomers can get an answer to this question by studying the conditions in very distant galaxies.

Prior to the study of far away galaxy, the researchers conducted computer simulations to estimate that how easily they may come across a proof of ionized oxygen with ALMA. They also noted the observations of similar galaxies that are quite neared to Earth, and said that the oxygen emission must be detectable, even at distant places.

According to a story published on the topic by Space, “Astronomers have discovered signs of oxygen in one of the universe’s first galaxies, which was born shortly after the cosmic “Dark Ages” that existed before the universe had stars, a new study finds.”

Previous research suggested that, after the universe was born in the Big Bang about 13.8 billion years ago, the universe was so hot that all of the atoms that existed were split into positively charged nuclei and negatively charged electrons. This soup of electrically charged ions scattered light, preventing it from traveling freely.

Details about the epoch of reionization are extremely difficult to glean because they happened so long ago. To see light from such ancient times, researchers look for objects that are as far away as possible — the more distant they are, the more time their light took to get to Earth. Such distant objects are only viewable with the best telescopes available today.

“This galaxy — which we’re observing as it was just 700 million years after the birth of the universe — shows the oldest signs of oxygen scientists have ever seen. That’s a big deal: In the immediate aftermath of the Big Bang, only the lightest elements — helium, lithium and hydrogen — existed. Heavier elements, such as carbon and oxygen, are necessary for the formation of life as we know it. But these elements didn’t form until the first stars had aged enough to produce them by way of fusion,” according to a news report published by Washington Post.

For starters, it could help us get a handle on the dark ages. Not the time period on Earth, but the one that happened on a universal scale. After the Big Bang, everything was hot and exciting. But after a few hundred thousand years, things cooled and calmed down. The gas that had held particles with electric charges became neutral hydrogen. Enter the dark ages, when the universe had nothing to do but slowly bring its neutral hydrogen gas into gravity-gathered clumps.

Fast-forward a few hundred million years, and you finally get enough hydrogen in one place to form the very first star. Stars ionized the gas around them — meaning they made the neutral particles charged again — in a phenomenon known as cosmic reonization. Eventually the universe hit a critical mass of hydrogen-processing stars, and it started to look like the incredible star factory we know and love. We can’t actually see the birth of these first stars, because all that hydrogen was pretty opaque, so scientists are always trying to push further and further back in time.

A report published in NewsLedge said, “Before planets, stars and galaxies began to take shape; the Universe was filled with electrically neutral gas. Several hundred million years after the Big Bang, the first stellar objects began to shine. This phase is known as cosmic reionization. And it broke up neutral atoms and ionized the gas.”

When SXDF-NB1006-2 was first discovered in 2012, it set the record for the most distant galaxy ever observed. That record didn’t stand long and continues to be broken each year. But the galaxy was still a great candidate to search for heavy elements such as oxygen and carbon.

Observing SXDF-NB1006-2 with ALMA brought its own non-traditional challenges. Astronomers from across the world vie for time with the best telescopes. Inoue and the rest of the team turned to computer simulations to predict how easily an oxygen detection would be for ALMA to see. The results showed the oxygen emission should be easily detected.

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