March 3, 2024

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Detection of “ancient smoker” stars in the heart of the Milky Way

Detection of “ancient smoker” stars in the heart of the Milky Way

Philip Lucas/University of Hertfordshire

The artist's illustration depicts an old smoky star, or an old red giant star emitting a thick cloud of smoke and dust.

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A decade-long survey of the night sky has revealed a mysterious new type of star that astronomers refer to as an “ancient smoker.”

These previously hidden stellar objects are ancient, giant stars located nearby The heart of the Milky Way Galaxy. Stars remain inactive for decades, fading until they are almost invisible before spewing out clouds of smoke and dust, which astronomers believe could play a role in the distribution of elements across the universe.

Four studies Details of the observations were published on January 25 in the Monthly Notices of the Royal Astronomical Society.

Astronomers observed ancient smoky stars for the first time during a survey that included observing nearly a billion stars in infrared light, which is invisible to the human eye.

The observations were made using the Visible and Infrared Survey Telescope, located at a vantage point high in the Chilean Andes at the Cerro Paranal Observatory.

The team's initial goal was to search for newborn stars, which are difficult to detect in visible light because they are obscured by dust and gas in the Milky Way. But infrared light can penetrate high concentrations of dust in the galaxy to pick up hidden or faint objects.

Philip Lucas, professor of astrophysics at the University of Hertfordshire, said that while two-thirds of the stars were easy to classify, the rest were more difficult, so the team used the European Southern Observatory's Very Large Telescope to study individual stars. Lucas was the primary author of One study and co-author of the other three.

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Philip Lucas/University of Hertfordshire

This illustration shows an eruption occurring in the swirling disk of matter around a newborn star.

While astronomers were observing hundreds of millions of stars, they tracked 222 stars that experienced noticeable changes in brightness. The team found that 32 of them were newborn stars at least 40 times brighter, and some up to 300 times brighter. A large percentage of explosions are ongoing, so astronomers can continue to monitor how stars evolve over time.

“Our main goal was to find rarely seen newborn stars, also called protostars, as they undergo a massive explosion that can last for months, years, or even decades,” said Dr. Chen Guo, a Fondecyt Postdoc Fellow at UCLA. Valparaiso, Chile, in a statement. It was Guo Lead author Of two studiesand co-authored the other two.

Philip Lucas/University of Hertfordshire

Astronomers used an infrared telescope to observe a star that gradually brightened 40 times over the course of two years, and has remained bright since 2015.

“These explosions occur in the slowly rotating disk of matter that forms a new solar system. They help the newborn star in the center grow, but make it difficult for planets to form. We don't yet understand why the disks are unstable in this way,” Guo said.

During their observation of stars near the galactic center, the team identified 21 red stars that experienced unusual changes in brightness that puzzled astronomers.

“We weren't sure if these stars were protostars starting to explode, recovering from a drop in brightness caused by a disk or shell of dust in front of the star — or if they were older giant stars shedding matter in the late stages,” Lucas said. Of their lives.”

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The team focused on seven of the stars and compared the new data they collected with data from previous surveys to determine that the stellar objects are a new type of red giant star.

Philip Lucas/University of Hertfordshire

Infrared images show a red giant star located 30,000 light-years away near the center of the Milky Way. The star faded and then reappeared over several years.

Red giants form when stars exhaust their stores of hydrogen needed for nuclear fusion and begin to die. In about 5 or 6 billion years, our Sun will become a red giant, inflating and expanding as it releases layers of material and likely vaporizes the inner planets of the solar system, although Earth's fate remains unclear, according to NASA.

But the stars observed during the survey are different.

“These old stars sit quietly for years or decades and then spew out clouds of smoke in a completely unexpected way,” said Dante Minniti, a professor in the Department of Physics at Andres Bello University in Chile and co-author on three of the studies. a permit. “They look so dull and red for several years, that sometimes we can't see them at all.”

The stars are found largely in the innermost nuclear disk of the Milky Way, where stars are more concentrated in heavy elements. Understanding how ancient smokers released elements into space could change the way astronomers think about the way these elements are distributed across the universe.

Astronomers are still trying to understand the process behind stars giving off thick smoke, and what happens next.

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“Material ejected from ancient stars plays a key role in the life cycle of elements, helping to form the next generation of stars and planets,” Lucas said. “This was thought to occur mainly in a well-studied type of star called a Mira variable. However, the discovery of a new type of star that sheds matter could have greater significance for the spread of heavy elements in the nuclear disk and metal-rich regions in other galaxies.”