One Of The First Galaxies Has Been Discovered In the Distant Universe

Artist's impression of a very young galaxy. NRAO/AUI/NSF/S. Dagnello

Astronomers have made an incredible discovery of a galaxy that’s thought to originate from the dawn of the cosmos, when the universe was just 2 percent of its current age.

The discovery, published in Nature, was led by Takuya Hashimoto from Osaka Sangyo University in Japan. The team used the Atacama Large Millimeter Array (ALMA) and the Very Large Telescope (VLT), both in Chile, to study this distant galaxy called MACS1149-JD1, first spotted in 2012.

The galaxy is seen today at a distance of 13.28 billion light-years as it was 500 million years after the Big Bang. But the team detected a signature of oxygen in the galaxy, the most distant such detection ever seen, which means it must have been forming stars earlier in order to produce it.

“The galaxy was already forming stars 250 million years after the Big Bang,” Nicolas Laporte from University College London, one of the study's co-authors, told IFLScience. “Thanks to the oxygen, we can look at the star formation history in this galaxy.”

The oxygen signature of the galaxy is shown here in red. ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, W. Zheng (JHU), M. Postman (STScI), the CLASH Team, Hashimoto et al.

MACS1149-JD1 is small, containing about 1 billion stars compared to the 100 billion or so in the Milky Way. It’s thought to be similar in size to the Magellanic Cloud dwarf galaxies that orbit our galaxy.

The first stars were composed of hydrogen and helium, producing heavier elements like oxygen via fusion in their cores, and releasing them when they went supernova. Thus, the detection of oxygen in the galaxy – made using ALMA – allowed the researchers to date the process of star formation, as the galaxy already has a population of mature stars.

Using infrared data from the Hubble and Spitzer telescopes, they noted that the brightness of the galaxy today is consistent with a model where it started forming stars 250 million years ago. This would make it one of the first galaxies in the cosmos.

“I was thrilled to see the signal of the distant oxygen in the ALMA data,” Hashimoto said in a statement. “This detection pushes back the frontiers of the observable universe.”

Using the VLT, the team were also able to detect a weaker signal of hydrogen coming from the galaxy too. These two measurements allowed them to measure the distance of 13.28 billion light-years, which makes it the most distant galaxy with a precise distance measurement.

Note that these are not the first stars in the universe. In fact, in February this year we actually spotted the hydrogen signal from stars dating to just 180 million years after the Big Bang. However, it dramatically pushes back our understanding of the first galaxies.

The team think the galaxy is going through a high rate of star formation, producing about five stars every year compared to just one in the Milky Way. However, there’s something quite unusual about it, as they think the galaxy was brighter in the past; normally galaxies should get dimmer.

The earliest galaxies ionized the gas between stars, known as the Epoch of Reionization or Cosmic Dawn. NRAO/AUI/NSF; S. Dagnello

“From the star formation history we can see this object was brighter in the past,” Laporte said. “We know the first galaxies were merging, so there’s a possibility we could find more such bright objects in the past.”

And that’s quite important because it means future telescopes like the James Webb Space Telescope (JWST) could find more galaxies like this. If they were brighter in their youth, then at greater distances closer to the Big Bang they may be possible to spot.

Next up the team hope to work out if there’s a supermassive black hole at the center of this galaxy, like we see in more modern galaxies. For now, though, it’s giving us a fascinating insight into how our universe first started to take shape.

“With these new observations of MACS1149-JD1 we are getting closer to directly witnessing the birth of starlight!” Richard Ellis, also from UCL and a co-author on the paper, said in a statement. “Since we are all made of processed stellar material, this is really finding our own origins.”

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