After University of Minnesota researchers found the farthest star from Earth ever recorded last year, they recently found a second star to add to their "x-ray image" of distant galaxies.
The star recorded last year, named Icarus, remains the oldest recorded star at over 9 billion years old. In a paper submitted in February, the newly discovered star named Warhol is estimated to be around 6 billion years old. The team who discovered the two blue supergiants are studying them to gain insights into further star observation, dark matter and the universe's rate of expansion.
“The models we’re constructing now and the tests of magnification will allow us to basically use galaxy clusters as more powerful tools, so we can learn more about stars floating around in them,” said Patrick Kelly, a University astrophysics professor who discovered Icarus.
The researchers are using the galaxy clusters, described as “natural magnifying glasses,” to pioneer their own set of gravitational lensing techniques for continued analysis of stars. Gravitational lensing is when the gravity of space matter bends light, and researchers use it to more closely view other stars.
“We do not expect to directly detect a single star. But if we have this lensing that we have got the cluster in between the source and us, then we have the chance to see this extremely magnified event,” said post-doctorate astrophysics researcher Wenlei Chen, who discovered Warhol.
Evan Skillman, director of the Minnesota Institute for Astrophysics, said discoveries like these could create a new field by inspiring new questions from the research community. The team hopes the data they will collect from observing the galaxy clusters will help further discussion about the expansion rate of the universe, which is currently under debate because of recent data from the Hubble Space Telescope.
“The contrast that it's highlighting is between the measurement of the cosmic expansion rate from nearby supernovae and from that measured from the cosmic microwave background,” Kelly said. “And so this measurement, which we're working on now, will complement those because it's entirely independent, a completely different kind of technique."
After less than a year working with the team, Chen discovered Warhol in December — possibly opening a new window into the cosmic search for dark matter.
While current methods can observe dark matter through events such as two merging black holes releasing gravitational waves, the discovery of stars such as Warhol points to their ability to more acutely observe isolated black holes. Researchers believe this could lead to improved dark matter discovery in the future.
“I think it is one of very few avenues to probe the population of this single, compact dark matter object,” he said.
The examination of distant stars can be used for comparing the mass distribution of stars in the universe from over 9 billion years ago to today.
“We can learn about how stars may have formed differently in different environments when the universe was a lot younger,” Kelly said. “In some galaxies, you can see now there seems to be far more really low-mass stars than there are in other environments. And so it's kind of a big mystery at the moment.”
University researchers recently received a National Science Foundation award worth more than $400,000, which will allow them to use the Large Binocular Telescope Observatory in Arizona this fall to better study the stars they discovered.
The researchers did not expect to find a similar star in the galaxy cluster as quickly as they did.
“This is enabling us to have a much more detailed view of the stars. You know, hopefully, eventually, most of the way back to the Big Bang,” Kelly said. "So it's kind of an entirely new window on the universe.”