It would seem that a star cluster in the Milky Way is as ancient as the cosmos itself.

• Rating

• cosmological mysteries
• astronomer
• Martin Ying
• Dartmouth College
• globular clusters
• star development
• artificial star populations
• Hubble Space Telescope
• uncertainty

The Milky Way is now being traversed by one of the most ancient things currently known to exist in the cosmos.

In a document that was posted to arXiv.org on June 3, researchers reported that star cluster M92, which is a tightly packed ball of stars located around 27,000 light-years from Earth, is approximately 13.8 billion years old. According to the most recent and accurate revision of the age estimate, this cluster of stars is almost exactly the same age as the universe.

The age of the cosmos itself can be constrained by more accurately determining the ages of galaxy clusters like M92. Additionally, it may assist in the resolution of cosmological mysteries about the development of the cosmos.

The age is "on the edge of the age of the universe, as estimated by other groups," according to astronomer Martin Ying of Dartmouth College. "It assists us in establishing a lower limit for the age of the cosmos. We don't think that M92 will come into being before the universe, do we?

Globular clusters, such as M92, are dense groups of stars that are considered to have come into existence at the same moment. Astronomers will have an easier time determining the ages of the stars as a result of this (SN: 7/23/21). Stars that are born at various masses have varied destinies: the massive ones burn up their fuel rapidly and perish young, whilst the little ones live for a long time. Getting a notion of when the entire cluster was created requires first determining how many of the cluster's stars have aged out of the primary sections of their fuel-burning years.

These estimations, however, are based on a number of presumptions about the process of star development. Ying and her coworkers intended to establish an alternative method of measuring age that would avoid making such assumptions.

The group constructed twenty thousand artificial star populations for M92 on a computer, each one representing a distinct probable age for the cluster. After that, they compared the colors and brightnesses of each of these populations with the observations of M92 made by the Hubble Space Telescope, and they computed the age that was the most appropriate for the collection.

Despite the fact that this is not the first time scientists have determined the age of M92, earlier estimations were based on just a single artificial grouping of stars. By comparing thousands of them, we were able to minimize the amount of uncertainty caused by the baked-in assumptions in each one. According to Ying, the use of the new methodology cut the amount of ambiguity associated with the cluster age by around fifty percent. According to the findings of the scientists, the age of the cluster is around 13.8 billion years old, give or take 750 million years. According to the Planck satellite's measurement of the first light emitted after the Big Bang (SN: 12/20/13), this is startlingly near to the best estimate of the age of the universe, which is a little over 13.8 billion years, plus or minus 24 million years. This is an astonishingly accurate estimate of the age of the universe.

There is an increasing sense of unease over the rate at which the universe is expanding, and one reason why the age of clusters like M92 is crucial is because of this. Because of a mysterious material known as dark energy, astronomers have known since the 1990s that the universe is expanding at an ever-increasing pace (SN: 8/25/22). However, recent assessments of the pace at which that expansion is occurring, a quantity known as the Hubble constant, conflict with one another (SN: 7/30/19).

Mike Boylan-Kolchin, a cosmologist at the University of Texas at Austin and a collaborator on the paper, suggests that one method for resolving this conflict is to acknowledge the possibility of an alternative age for the universe.

"We often think about it as Moses coming down from Mount Sinai with '13.8 billion years' written on some tablets or something, but it's not quite like that," he adds. "We often think about it as Moses coming down from Mount Sinai with '13.8 billion years' written on some tablets or something." If one accepts seriously the Hubble tension, then one must also admit that we do not have a very good understanding of the age of the universe.

Here is where the M92 comes into play. Before satellites were able to determine the age of the universe's first light, the best approach to impose limitations on the age of the universe was to use the ages of globular clusters. According to cosmologist Wendy Freedman of the University of Chicago, who was not engaged in the current investigation, this method has been out of style for some time now.

However, given the advancements that have been made in computation, theory, and measurements of the distances to clusters such as M92, it seems worthwhile to do it once again.

"The Hubble tension itself is a really challenging nut to crack," adds Freedman. "It's a tough nut to crack." This measurement, on its own, is not accurate enough to put an end to the discussion. On the other hand, "the more kinds of constraints we have, the better," according to what she says. "It's illuminating a path for the years to come."

CITATIONS

J. Ying et al. The absolute age of M92. arxiv:2306.01280. Submitted June 3, 2023.