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Astronomers routinely provide the ages of the stars they study. But the methods of measuring ages aren’t 100% accurate. Measuring the ages of distant stars is a difficult task.

The Nancy Grace Roman Space Telescope should make some progress.

Stars like our Sun settle into their main sequence lives of fusion and change very little for billions of years. It’s like watching middle-aged adults go about their business during their working lives. They get up, drive to work, sit at a desk, then drive home.

But what can change over time is their rotation rate. The Sun now rotates about once a month. When it was first formed, it rotated more rapidly.

But over time, the Sun’s rotation rate, and the rotation rate of stars the same mass or lower than the Sun’s, will slow down. The slowdown is caused by interactions between the star’s magnetic fields and the stellar wind, the stream of high-energy protons and electrons emitted by stars. Over time, these interactions reduce a star’s angular momentum, and its rotation slows. The phenomenon is called “magnetic braking,” and it depends on the strength of a star’s magnetic fields.

When the Sun rotates, the magnetic field lines rotate with it. The combination is almost like a solid object. Ionized material from the solar wind will be carried along the field lines and, at some point, will escape the magnetic field lines altogether. That reduces the Sun’s angular momentum. Image Credit: By Coronal_Hole_Magnetic_Field_Lines.svg: Sebman81Sun_in_X-Ray.png: NASA Goddard Laboratory for AtmospheresCelestia_sun.jpg: NikoLangderivative work: Aza (talk) – Coronal_Hole_Magnetic_Field_Lines.svgSun_in_X-Ray.pngCelestia_sun.jpg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8258519

The more rapidly a star initially spins, the stronger its magnetic fields. That means they slow down faster. After about one billion years of life, stars of the same age and mass will spin at the same rate. Once astronomers know a star’s mass and rotation rate, they can estimate its age. Knowing stars’ ages is critical in research. It makes everything astronomers do more accurate, including piecing together the Milky Way’s history.

The problem is that measuring rotation rates is challenging. One method is to observe spots on stars’ surfaces and watch as they come into and out of view. All stars have star spots, though their characteristics vary quite a bit. In fact, stars can have dozens of spots, and the spots change locations. Therein lies the difficulty. It’s extremely difficult to figure out the periodicity when dozens of spots change locations on the star’s surface.

This is where the Nancy Grace Roman Space Telescope (the Roman) comes in. It’s scheduled for launch in May 2027 to begin its five-year mission. It’s a wide-field infrared survey telescope with multiple science objectives. One of its main programs is the Galactic Bulge Time Domain Survey. That effort will gather detailed information on hundreds of millions of stars in the Milky Way’s galactic bulge.

This is a simulated image of what the Roman Space Telescope will see when it surveys the Milky Way’s galactic bulge. The telescope will observe hundreds of millions of stars in the region. Image Credit: Matthew Penny (Louisiana State University)

The Roman will generate an enormous amount of data. Much of it will be measurements of how the brightness of hundreds of thousands of stars changes. But untangling those measurements and figuring out what those changes in brightness mean for stellar rotation requires help from AI.

Astronomers at the University of Florida are developing AI to extract stellar rotation periods from all that data.

Zachary Claytor is a postdoc at the University of Florida and the AI project’s science principal investigator. Their AI is called a convolutional neural network. This type of AI is well-suited to analyzing images and is used in image classification and medical image analysis, among other things.

AI needs to be trained before it can do its job. In this case, Claytor and his associates wrote a computer program to generate simulated stellar light curves for the AI to process and learn from.

“This program lets the user set a number of variables, like the star’s rotation rate, the number of spots, and spot lifetimes. Then it will calculate how spots emerge, evolve, and decay as the star rotates and convert that spot evolution to a light curve – what we would measure from a distance,” explained Claytor.

Claytor and his co-researchers have already tested their AI on data from NASA’s TESS, the Transiting Exoplanet Survey Satellite. The longer a star’s rotation period is, the more difficult it is to measure. But the team’s AI demonstrated that it could successfully determine these periods in TESS data.

The Roman’s Galactic Bulge Time Domain Survey is still being designed. So astronomers can use this AI-based effort to help design the survey.

“We can test which things matter and what we can pull out of the Roman data depending on different survey strategies. So when we actually get the data, we’ll already have a plan,” said Jamie Tayar, assistant professor of astronomy at the University of Florida and the program’s principal investigator.

“We have a lot of the tools already, and we think they can be adapted to Roman,” she added.

Artist’s impression of the Nancy Grace Roman Space Telescope, named after NASA’s first Chief of Astronomy. When launched later this decade, the telescope will measure the rotational periods of hundreds of thousands of stars and, with the help of AI, will determine their ages. Credits: NASA

Measuring stellar ages is difficult, yet age is a key factor in understanding any star. Astronomers use various methods to measure ages, including evolutionary models, a star’s membership in a cluster of similarly-aged stars, and even the presence of a protoplanetary disk. But no single method can measure every star’s age, and each method has its own drawbacks.

If the Roman can break through this barrier and accurately measure stellar rotation rates, astronomers should have a leg-up in understanding stellar ages. But there’s still one problem: magnetic braking.

This method relies on a solid understanding of how magnetic braking works over time. But astronomers may not understand it as thoroughly as they’d like. For instance, research from 2016 showed that magnetic braking might not slow down older stars as much as thought. That research found unexpectedly rapid rotation rates in stars more evolved than our Sun.

Somehow, astronomers will figure this all out. The Roman Space Telescope should help, as its vast trove of data is bound to lead to some unexpected conclusions. One way or another, with the help of the Roman Space Telescope, the ESA’s Gaia mission, and others, astronomers will untangle the problem of measuring everything about stars, including their ages.

The post Roman Will Learn the Ages of Hundreds of Thousands of Stars appeared first on Universe Today.

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Expedition 70 NASA astronaut Loral O’Hara gives a thumbs up inside the Soyuz MS-24 spacecraft after she, Roscosmos cosmonaut Oleg Novitskiy, and Belarus spaceflight participant Marina Vasilevskaya, landed in a remote area near the town of Zhezkazgan, Kazakhstan, Saturday, April 6, 2024. O’Hara is returning to Earth after logging 204 days in space as a member of Expeditions 69-70 aboard the International Space Station and Novitskiy and Vasilevskaya return after having spent the last 14 days in space.NASA/Bill Ingalls

NASA astronaut Loral O’Hara returned to Earth after a six-month research mission aboard the International Space Station on Saturday, along with Roscosmos cosmonaut Oleg Novitskiy, and Belarus spaceflight participant Marina Vasilevskaya.

The trio departed the space station aboard the Soyuz MS-24 spacecraft at 11:54 p.m. EDT on April 5, and made a safe, parachute-assisted landing at 3:17 a.m., April 6 (12:17 p.m. Kazakhstan time), southeast of the remote town of Dzhezkazgan, Kazakhstan.

O’Hara launched Sept. 15, 2023, alongside Roscosmos cosmonauts Oleg Kononenko and Nikolai Chub, who both will remain aboard the space station to complete a one-year mission. Novitskiy and Vasilevskaya launched aboard Soyuz MS-25 on March 23 along with NASA astronaut Tracy C. Dyson, who will remain aboard the orbiting laboratory until this fall.

O’Hara spent a total of 204 days in space as part of her first spaceflight. Novitskiy has logged a total of 545 days in space across four spaceflights and Vasilevskaya has spent 14 days in space as part of her first spaceflight.

Supporting NASA’s Artemis campaign, O’Hara’s mission helped prepare for exploration of the Moon and build foundations for crewed missions to Mars. She completed approximately 3,264 orbits of the Earth and a journey of more than 86.5 million miles. O’Hara worked on scientific activities aboard the space station, including investigating heart health, cancer treatments, and space manufacturing techniques during her stay aboard the orbiting laboratory.

Following post-landing medical checks, the crew will return to the recovery staging city in Karaganda, Kazakhstan. O’Hara will then board a NASA plane bound for her return to the agency’s Johnson Space Center in Houston.

With the undocking of the Soyuz MS-24 spacecraft with O’Hara, Novitskiy and Vasilevskaya, Expedition 71 officially began aboard the station. NASA astronauts Michael Barratt, Matthew Dominick, Tracy C. Dyson, and Jeannette Epps, as well as Roscosmos cosmonauts Nikolai Chub, Alexander Grebenkin, and Oleg Kononenko make up Expedition 71 and will remain on the orbiting laboratory until this fall.

Learn more about space station activities by following @space_station and @ISS_Research on X, as well as the ISS Facebook, ISS Instagram, and the space station blog.

-end-

Joshua Finch / Julian Coltre / Claire O’Shea
Headquarters, Washington
202-358-1100
joshua.a.finch@nasa.gov / julian.n.coltre@nasa.gov / claire.a.o’shea@nasa.gov

Sandra Jones
Johnson Space Center, Houston
281-483-5111
sandra.p.jones@nasa.gov

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