When Does Does Star Start Again
Nosotros know quite a lot about stars. Afterward centuries of pointing telescopes at the nighttime sky, astronomers and amateurs akin can figure out key attributes of any star, like its mass or its limerick.
To calculate a star's mass, just look it its orbital period and do a chip of algebra. To determine what information technology's made of, look to the spectrum of light the star emits. But the one variable scientists oasis't quite cracked yet is time.
"The sunday is the just star we know the age of," says astronomer David Soderblom of the Infinite Telescope Science Institute in Baltimore. "Everything else is bootstrapped up from at that place."
Fifty-fifty well-studied stars surprise scientists every now then. In 2022 when the carmine supergiant star Betelgeuse dimmed, astronomers weren't sure if it was merely going through a stage or if a supernova explosion was imminent. (Turns out it was just a phase.) The sun besides shook things up when scientists noticed that it wasn't behaving similar other middle-anile stars. It's non every bit magnetically active compared with other stars of the aforementioned age and mass. That suggests that astronomers might non fully empathize the timeline of middle age.
Calculations based on physics and indirect measurements of a star's historic period can give astronomers ballpark estimates. And some methods work better for different types of stars. Hither are three means astronomers calculate the age of a star.
Hertzsprung-Russell diagrams
Scientists do take a pretty good handle on how stars are built-in, how they live and how they die. For instance, stars burn through their hydrogen fuel, puff upward and eventually expel their gases into infinite, whether with a blindside or a whimper. But when exactly each stage of a star's life cycle happens is where things get complicated. Depending on their mass, certain stars hit those points subsequently a unlike number of years. More massive stars die young, while less massive stars can burn for billions of years.
At the plough of the 20th century, ii astronomers — Ejnar Hertzsprung and Henry Norris Russell — independently came up with the idea to plot stars' temperature confronting their effulgence. The patterns on these Hertzsprung-Russell, or H-R, diagrams corresponded to where different stars were in that life cycle. Today, scientists use these patterns to decide the age of star clusters, whose stars are thought to have all formed at the aforementioned time.
The caveat is that, unless you practise a lot of math and modeling, this method can be used merely for stars in clusters, or past comparing a single star's color and brightness with theoretical H-R diagrams. "Information technology'due south not very precise," says astronomer Travis Metcalfe of the Space Scientific discipline Institute in Boulder, Colo. "Nevertheless, it'due south the best thing we've got."
Rotation rate
By the 1970s, astrophysicists had noticed a tendency: Stars in younger clusters spin faster than stars in older clusters. In 1972, astronomer Andrew Skumanich used a star's rotation rate and surface activeness to propose a simple equation to gauge a star's historic period: Rotation charge per unit = (Age) -½.
This was the go-to method for individual stars for decades, but new information accept poked holes in its utility. It turns out that some stars don't irksome downwards when they hit a certain age. Instead they keep the same rotation speed for the balance of their lives.
"Rotation is the best thing to use for stars younger than the sunday," Metcalfe says. For stars older than the dominicus, other methods are better.
Stellar seismology
The new data that confirmed rotation rate wasn't the best style to estimate an individual star's age came from an unlikely source: the exoplanet-hunting Kepler space telescope. Non simply a benefaction for exoplanet research, Kepler pushed stellar seismology to the forefront by only staring at the same stars for a really long time.
Watching a star flicker tin can give clues to its historic period. Scientists look at changes in a star'south brightness as an indicator of what'due south happening beneath the surface and, through modeling, roughly summate the star's historic period. To do this, one needs a really large dataset on the star's brightness — which the Kepler telescope could provide.
"Everybody thinks information technology was all about finding planets, which was truthful," Soderblom says. "But I like to say that the Kepler mission was a stealth stellar physics mission."
This approach helped reveal the sun'southward magnetic midlife crisis and recently provided some clues about the evolution of the Milky way. Effectually 10 billion years ago, our galaxy collided with a dwarf galaxy. Scientists have found that stars left behind by that dwarf milky way are younger or about the same age every bit stars original to the Galaxy. Thus, the Milky Way may have evolved more than quickly than previously thought.
As space telescopes similar NASA's TESS and the European Space Bureau's CHEOPS survey new patches of sky, astrophysicists will be able to learn more than about the stellar life cycle and come upward with new estimates for more than stars.
Bated from curiosity about the stars in our own lawn, star ages take implications beyond our solar arrangement, from planet formation to galaxy evolution — and even the search for extraterrestrial life.
"One of these days — information technology'll probably be a while — somebody'south going to claim they meet signs of life on a planet around another star. The first question people volition enquire is, 'How former is that star?'" Soderblom says. "That'due south going to be a tough question to reply."
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Source: https://www.sciencenews.org/article/star-age-calculation-astronomy-life-cycle
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