Scientists observe dwarf galaxy churning out its first stars 9.4 billion years ago using giant galaxy cluster as magnifying lens
The galaxy, about 1/10,000 the size of our Milky Way, is similar to the very first galaxies that formed in the universe, the kind that "no one has ever seen in X-ray in the distant universe before."
Astronomers have spotted a tiny dwarf galaxy in its very first, high-energy stages of star formation. The team from Massachusetts Institute of Technology (MIT) and other institutes made the observation by using a massive cluster of galaxies as an X-ray magnifying glass to look back in time, to nearly 9.4 billion years ago. The scientists observed a blue speck of an infant galaxy, about 1/10,000 the size of our Milky Way, while churning out its first stars - supermassive, cosmically short-lived objects that emit high-energy X-rays - which the researchers detected in the form of a bright blue arc.
According to Matthew Bayliss, a research scientist at MIT's Kavli Institute for Astrophysics and Space Research, the galaxy is similar to the very first galaxies that formed in the universe, the kind that "no one has ever seen in X-ray in the distant universe before."
"It is this little blue smudge, meaning it is a very small galaxy that contains a lot of super-hot, very massive young stars that formed recently," adds Bayliss.
Scientists have used galaxy clusters as cosmic magnifying glasses, with the help of a technique called "gravitational lensing," but this is the first time they have been used to zoom in on extreme, distant, X-ray-emitting phenomena, says the study published in Nature Astronomy.
Galaxy clusters, explain the research team, are the most massive objects in the universe, composed of thousands of galaxies, all bound together by gravity as an enormous force.
"Galaxy clusters are so massive, and their gravitational pull is so strong that they can distort the fabric of space-time, bending the universe and any surrounding light. Scientists have used galaxy clusters to magnify objects at optical wavelengths, but never in the X-ray band of the electromagnetic spectrum, mainly because galaxy clusters themselves emit an enormous amount of X-rays. Scientists have thought that X-rays coming from a background source would be impossible to discern from the cluster's own glare," says the study.
Accordingly, for the current study, the scientists decided to test an idea: if they could remove the X-ray emissions coming from the galaxy cluster to view the much fainter X-rays coming from an object, behind from the cluster and magnified by it.
The idea was tested with observations taken by NASA's Chandra X-ray Observatory. The scientists looked in particular at Chandra's measurements of the Phoenix cluster, a distant galaxy cluster located 5.7 billion light-years from Earth. The Phoenix cluster, which was discovered in 2012, is one of the most massive and luminous galaxy clusters in the universe. This cluster, says the study, is estimated to be about a quadrillion times as massive as the sun, with gravitational effects that should make it a powerful, natural magnifying lens.
"The idea is to take whatever your best X-ray telescope is (in this case, Chandra), and use a natural lens to magnify and effectively make Chandra bigger, so you can see more distant things," says Bayliss.
The researchers analyzed observations of the Phoenix cluster, taken continuously by Chandra for over a month. They also looked at images of the cluster taken by two optical and infrared telescopes -- the Hubble Space Telescope and the Magellan telescope in Chile.
The combination of Chandra and the Phoenix cluster's natural lensing power enabled the team to see the tiny galaxy hiding behind the cluster, magnified by about 60 times.
"With all these various views, a model was developed to characterize the cluster's optical effects, which allowed precise measurement of the X-ray emissions from the cluster itself, and subtract it from the data," the findings state.
The scientists were left with two similar patterns of X-ray emissions around the cluster. When the team traced the emissions backward in time, they found that they originated from a single, distant source: a tiny dwarf galaxy from 9.4 billion years ago, when the universe itself was roughly 4.4 billion years old - that is, about a third of its current age.
"We are 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. 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," says Bayliss.
According to the scientists, the detection of this single, distant galaxy is evidence that researchers can use galaxy clusters as natural X-ray magnifiers, to "pick out extreme, highly energetic phenomena" in the universe's early history.
"With this technique, we could, in the future, zoom in on a distant galaxy and age-date different parts of it - to say, this part has stars that formed 200 million years ago, versus another part that formed 50 million years ago, and pick them apart in a way you cannot otherwise do," says Bayliss.