Astronomers Use Massive Galaxy Cluster to ‘Peer Back in Time’

Astronomers recently used a giant cluster of galaxies as an X-ray magnifying lens to spot a tiny, star-forming dwarf galaxy for the first time.

The team, which was able to “peer back in time” to approximately 9.4 billion years ago, detected the tiny dwarf galaxy, which was experiencing its first, high-energy stages of star formation, MIT said in a press release. While galaxy clusters have been previously leveraged to magnify objects at optical wavelengths, this is the first time scientists have used galaxy clusters to examine distant, X-ray emitting phenomena in space.

About 1/10,000 the size of our Milky Way, the dwarf galaxy appears as a blue speck and it’s churning out its first stars. Researchers detected these short-lived objects in the form of a bright blue arc, according to MIT. The team published their findings on the tiny dwarf galaxy in the journal Nature Astronomy.

“It’s this little blue smudge, meaning it’s a very small galaxy that contains a lot of super-hot, very massive young stars that formed recently,” says Matthew Bayliss, a research scientist in MIT’s Kavli Institute for Astrophysics and Space Research. “This galaxy is similar to the very first galaxies that formed in the universe … the kind of which no one has ever seen in X-ray in the distant universe before.”

Galaxy clusters emit a large amount of X-rays, so it could be hard to detect objects, such as single galaxies, behind them without the proper equipment. However, the team was able to move past this challenge with the X-ray magnifying lens.

“If you’re trying to see an X-ray source behind a cluster, it’s like trying to see a candle next to a really bright light,” Bayliss explains. “So we knew this was a challenging measurement to make.”

The team wondered if they could extract the X-ray emissions coming from the galaxy cluster to see what was behind the massive galaxy cluster. They tested the idea with observations from NASA’s Chandra X-ray Observatory, specifically of the Phoenix cluster, a galaxy cluster that’s located 5.7 billion light-years away from our planet with gravitational effects.

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Bayliss and his colleagues examined the Phoenix cluster observations that were taken continuously by Chandra for more than 30 days. They also analyzed images taken by the Hubble Space Telescope and the Magellan telescope in Chile.

After sourcing different views, the team built a model to characterize the galaxy cluster’s optical effects. This enabled them to precisely measure X-ray emissions from the galaxy cluster and subtract it from the data. The team discovered two similar patterns of X-ray emissions positioned around the cluster, which they said were gravitationally bent by the cluster. While “going back in time,” they found that the X-ray emissions came from a distant source: the tiny dwarf galaxy that was hiding behind the galaxy cluster.

“We’re catching this galaxy at a very useful stage, where it’s got these really young stars. Every galaxy had to start out in this phase, but we don’t see a lot of these kinds of galaxies in our own neighborhood,” Bayliss adds. “Now we can go back in time, look in the distant universe, find galaxies in this early phase of their life, and start to study how star formation is different there.”

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