The Milky Way is home to one of the oldest objects known in the universe.
A densely packed ball containing stars, approximately 27,000 lights-years away from Earth. About 13.8 billion years agoResearchers report in a June 3 paper submitted to arXiv.org. This cluster of stars is now estimated to be nearly as old as the entire universe, thanks to a newly refined age estimation.
The age of the Universe can be limited by refining the age of clusters such as M92. It can also solve cosmic conundrums regarding how the Universe evolved.
The age is “on the edge of the age of the universe, as estimated by other groups,” says astronomer Martin Ying of Dartmouth College. “It helps us set the lower bound of the age of the universe. We don’t expect M92 to be born before the universe, right?”
Globular clusters, like M92, are believed to be tight knots of starry stars that all formed simultaneously. It makes it easier to find. astronomers to measure the stars’ ages (SN: 7/23/21). Stars born at different masses will have different fates. The large stars use up their fuel rapidly and die young while the smaller ones remain. Figuring out how many of the cluster’s stars have aged out of the main parts of their fuel-burning years gives a sense of when the whole cluster was born.
However, these estimates rely upon assumptions about the way stellar evolution operates. Ying and his colleagues were looking for a way to measure age that did not rely on these assumptions.
The team used a computer to create 20,000 synthetic star populations for M92. Each population was created for a possible age of the cluster. The team compared Hubble Space telescope observations of M92 with the colors and brightnesses of each of these stellar populations and calculated the best age for the collection.
This isn’t the first time astronomers have measured M92’s age, but previous estimates relied on just one synthetic collection of stars. The uncertainty created by assumptions in each model was reduced when thousands of them were compared. Ying claims that the new technique has reduced the uncertainty in the cluster age by 50 percent. The cluster was found to be 13.8 billions years old. This is a range of 750-750 million years. That’s strikingly close to the best estimate of the age of the universe: a smidge over 13.8 billion years, plus or minus 24 million years, according to the Planck satellite’s measurement of the first lightAfter the Big Bang.SN: 12/20/13).
The age of clusters, like M92, is important in part because of the growing tension regarding how fast the universe grows. Astronomers know since the 1990s the universe is growing at a rapid rate. a mysterious substance dubbed dark energy (SN: 8/25/22). Recent measurements of this expansion rate, called the Hubble constant. It is not acceptable to disagree with one another (SN: 7/30/19).
Mike Boylan Kolchin of the University of Texas at Austin, coauthor of the study and a cosmologist, believes that accepting a new age for the Universe is one way of resolving this tension.
“We often think about it as, Moses came down from Mount Sinai with ‘13.8 billion years’ written on some tablets or something, but it’s not quite like that,” he says. “If one takes the Hubble tension seriously, then one also has to say we don’t know the age of the universe that well.”
That’s where M92 comes in. Before spacecraft measured the cosmos’ earliest light, globular cluster ages were the best way to place limits on the age of the universe. This practice has been out of style for some time, according to Wendy Freedman, a cosmologist at the University of Chicago who wasn’t involved in the work.
The new technology, the theory and the measurements of distances between clusters, like M92, make it worthwhile to try again.
“The Hubble tension itself is a really challenging nut to crack,” Freedman says. This measurement alone isn’t precise enough to settle the debate. But “the more kinds of constraints we have, the better,” she says. “It’s showing a way for the future.”
