Milky Way star cluster as old as the universe

One of the oldest known celestial bodies in the universe wanders around the Milky Way.
Cluster M92 is a dense ball of stars about 27,000 light-years distant from Earth and is about 13.8 billion years old, researchers report in a paper submitted to ArXiv.org. Newly refined age estimates show that the star cluster is nearly as old as the Universe.
Accurately determining the age of star clusters like M92 will help us put a limit on the age of the universe itself. It could also help solve cosmic conundrums about how the universe evolved, Science News reported.
Dartmouth College astronomer Martin Ying says its age is “on the edge of what other groups have estimated for the universe.” “It helps set a lower bound on the age of the universe. You wouldn’t expect M92 to predate the universe, would you?”
Globular clusters like M92 are dense clusters of stars that are thought to have all formed at the same time. This makes it easier for astronomers to determine the age of stars. Stars born with different masses have different destinies. Large stars quickly run out of fuel and die young, while smaller stars survive. Knowing how many of the cluster’s stars have aged out of the main part that continued to burn fuel can tell us when the entire cluster was born.
But those estimates rely on assumptions about how stellar evolution works. Ying et al. wanted to find an age measurement method that circumvents these assumptions.
Using a computer, the researchers created a synthetic cluster of 20,000 stars for M92, each corresponding to a different possible star cluster age. They then compared the color and brightness of each of these populations to her Hubble Space Telescope observations of M92 and calculated the ages that best fit the collection.
It’s not the first time astronomers have determined the age of M92, but previous estimates have relied on just one synthetic star cluster. Comparing thousands of them mitigated the uncertainty introduced by the assumptions built into each.
“The new technique has reduced the uncertainty of cluster age by about 50%,” Yin says.
The researchers found the cluster to be 13.8 billion years old, with an error of 750 million years. This is surprisingly close to the most accurate estimate of the age of the universe, just over 13.8 billion years plus or minus 24 million years, according to the Planck satellite’s measurements of the first light emitted after the Big Bang.
The importance of the age of star clusters like M92 is partly due to the growing tensions over the growth rate of the universe. Astronomers have known since the 1990s that the universe is expanding at an accelerating rate thanks to a mysterious substance called dark energy. But recent measurements of its expansion rate, a number called the Hubble constant, don’t agree with each other.
“One way around this tension is to embrace different ages of the universe,” says cosmologist and study co-author Mike Boylan-Colchin of the University of Texas at Austin.
“We often think that Moses came down from Mount Sinai with ‘13.8 billion years’ written on a tablet or something, but that’s not the case at all,” he says. “If we take Hubble tension seriously, we have to say that we know very little about the age of the universe.”

https://ift.tt/NLs813h Milky Way star cluster as old as the universe

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