Tag Archives: stars

The Threat of Cool Star’s Strong Winds to Exoplanets

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Artist’s illustration of a stellar planetary system. You can clearly see the stellar wind orbiting the star and its effect on the planet’s atmosphere.Credit: AIP/ K. Riebe/ J. Fohlmeister, editor

A groundbreaking study reveals that cold stars with strong magnetic fields generate powerful stellar winds, providing important information for assessing the habitability of exoplanetary systems.

A study led by scientists at the Potsdam Leibniz Institute for Astrophysics (AIP) uses cutting-edge numerical simulations to systematically characterize the properties of stellar winds in a sample of cold stars for the first time. Ta. They found that stars with stronger magnetic fields generate stronger winds. These winds create unfavorable conditions for the survival of planetary atmospheres, thus affecting the habitability of these systems.

Cool star classification

The Sun is one of the most abundant stars in the universe, known as “cool stars.” These stars are divided into four categories (F-type, G-type, K-type, and M-type) that differ in size, temperature, and brightness. The Sun is a fairly average star and belongs to category G. Stars that are brighter and larger than the Sun belong to category F, while K stars are slightly smaller and cooler than the Sun. The smallest and faintest star is the M star, also known as a “red dwarf” because of the color in which it emits most of its light.

Solar wind and its effects

Satellite observations have revealed that, apart from light, the sun continuously emits a stream of particles known as the solar wind. These winds travel through interplanetary space and interact with the planets of our solar system, including Earth. The beautiful displays of the Northern Lights near the North and South Poles are actually produced by this interaction. But these winds can also be harmful, as they can erode Earth’s stable atmosphere. Mars.

We know a lot about the solar wind, thanks in part to missions like Solar Orbiter, but the same isn’t true for other cool stars. The problem is that we can’t see these stellar winds directly, so we’re limited to studying their effects on the thin gas that fills the cavities between stars in galaxies. However, this approach has some limitations and can only be applied to a small number of stars. This has encouraged the use of computer simulations and models to predict various properties of stellar winds without the need for astronomer observations.

Pioneering research on the properties of stellar winds

In this regard, in collaboration with Cecilia Garaffo of the Harvard University Center for Astrophysics, doctoral student Judy Chevely of AIP’s Stellar Physics and Exoplanet Division, and scientist Julián D. Alvarado Gomez Dr. Katja Poppenhager, head of the department, assisted. The Smithsonian Institution conducted the first systematic study of the expected stellar wind properties for F, G, K, and M stars.

To this end, they performed numerical simulations using one of the most sophisticated models currently available, driven by the observed large-scale magnetic field distributions of 21 well-observed stars. I used it. The simulations were performed at the AIP and Leibniz-Rechenzentrum (LRZ) supercomputing facilities.

The research team investigated how star properties such as gravity, magnetic field strength, and rotation period affect the properties of the wind in terms of velocity and density. The results include a comprehensive characterization of stellar wind properties across spectral types and, in particular, challenge previous assumptions about stellar wind speeds when estimating associated mass loss rates from observations. This indicates that it needs to be reconsidered.

In addition, the simulations can predict the expected size of the Alfvén surface, the boundary between the stellar corona and the stellar wind. This information is the basis for determining whether planetary systems are affected by strong magnetic star-planet interactions. This interaction can occur when a planet’s orbit enters or is completely embedded in the Alfvén surface of its host star.

Impact on planetary systems

Their findings show that stars with magnetic fields larger than the Sun have faster winds. In some cases, stellar wind speeds can be up to five times faster than the average solar wind speed (typically 450 km/s). The study revealed how strong these stars’ winds are in their so-called “habitable zone,” defined as the orbital distance at which a rocky exoplanet can maintain liquid water on its surface and provide an Earth-like atmospheric pressure. It was evaluated as being strong. They found milder conditions around F- and G-type stars, comparable to those experienced by Earth around the G-type Sun, and increasingly harsh wind environments around K- and M-type stars. discovered. Such intense stellar winds have a strong impact on any atmosphere a planet might have.

Broader implications for exoplanet research

This phenomenon is well documented in heliophysics between rocky planets and the Sun, but not in exoplanetary systems. This requires estimates of stellar winds to assess processes similar to those seen between the solar wind and planetary atmospheres. This study is important from the perspective of habitability, as no information on stellar winds has been known for main-sequence stars F to M until now.

Although the study presented in this paper was performed on 21 stars, the results are general enough to apply to other cool main sequence stars. This study paves the way for future studies of stellar wind observations and their effects on planetary atmosphere erosion.

References: Judy J Chebly, Julián D Alvarado-Gómez, Katja Poppenhäger, and Cecilia Garraffo, “Quantifying the wind properties of cool main-sequence stars,” July 19, 2023. Royal Astronomical Society Monthly Notices.
DOI: 10.1093/mnras/stad2100

Source: scitechdaily.com

A spectacular first photo of a snow leopard captured under the stars

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Looking for ghosts requires special patience. The chances of finding it are low, but doubting means giving up, so keep looking.

This is a technique for tracking snow leopards. Morap Namgair learned that early. He was five years old when he first saw the animal in his remote village of Ulay in Ladakh, India. The area is full of wildlife and is a paradise for aspiring photographers like Molap and his younger brother Stanzin. These big cats are called locally. Shanimmortalized in the BBC series Planet Earth II They were mainly grateful to their father, Norbu, who followed them as a crew member.

Ladakh had just become famous for its sightings, but everything was shut down due to the pandemic. That’s when the brothers vowed to photograph something no one had ever photographed before: a snow leopard under the stars. They hoped the image would highlight the beauty of this mountain region and its apex predator, thereby spurring efforts to conserve both. The region is warming twice as fast as the rest of the world, threatening landscapes and wildlife. The brothers believed that if the outside world could only see what was at stake, that would influence the government’s actions.

They spent months blanketing the area with cameras. However, halfway through the project, Stanzin died of heart disease. Although it was difficult, Morap pushed forward on his own.

Last August, on a 33°C (91°F) day, he climbed a ridge at 4,900 meters above sea level. “What I found on camera was a dream come true,” Morap says. He was bittersweet though. “Buddhism believes in reincarnation. I always look at snow leopards and often think, ‘What would happen if Stan Jin was reincarnated as a snow leopard?’ Perhaps he will stop for a photo or perhaps say hello. Maybe he did.”

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Source: www.newscientist.com

Three new young stars found in the central region of the Milky Way galaxy by astronomers

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According to some researchers, the oldest of these stars is 1.5 billion years old, while the youngest is only 100 million years old. paper Published in Astrophysics Journal Letter.

This infrared image from Hubble shows the Milky Way Core Cluster, the densest and most massive star cluster in our galaxy. Image credit: NASA / ESA / Hubble Heritage Team / STScI / AURA / T. Do & A. Ghez, UCLA / V. Bajaj, STScI.

The center of our Milky Way galaxy is located about 27,000 light-years away in the constellation Sagittarius and is a crowded place.

This region is so dense that it’s equivalent to a million stars crammed into the space between the Sun and Alpha Centauri, 4.3 light-years away.

This nuclear cluster surrounds Sagittarius A*, a 4.3 million solar mass black hole at the center of the galaxy.

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In general, many nuclear star clusters coexist with supermassive black holes, which are found in more than 70% of galaxies with masses greater than 100 million to 10 billion solar masses.

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“In previous work, we hypothesized that these particular stars in the middle of the Milky Way may be unusually young,” said Lund University astronomer Rebecca Forsberg.

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“Now we can confirm this. Our study shows that three of these stars are relatively young, at least as far as astronomers are concerned, ranging in age from 100 million years to about 1 billion years. We were able to determine the age.”

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“This is equivalent to the age of the Sun, which is 4.6 billion years old.”

This panorama shows the central region of the Milky Way galaxy. It builds on previous surveys by NASA’s Chandra X-ray Observatory and other telescopes, and extends Chandra’s high-energy field of view further up and down the galactic plane than previous imaging campaigns. The X-rays from Chandra are orange, green, and violet, indicating different X-ray energies. Radio data from MeerKAT is gray. Image credits: NASA / CXC / UMass / QD Wang / NRF / SARAO / MeerKAT.

In this study, Dr. Forsberg and colleagues used high-resolution data from the Keck II telescope in Hawaii. This Keck II telescope is one of the largest telescopes in the world with a 10 meter diameter mirror.

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For further verification, they measured the amount of iron, a heavy element, in the stars

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This element is important in tracking the development of galaxies. This is because astronomers’ theories about star formation and galaxy development show that the formation of heavy elements increases over time in the Universe, so younger stars contain more heavy elements.

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To determine iron levels, astronomers looked at the star’s spectrum in infrared light. Infrared light is a part of the light spectrum that can more easily illuminate dust-dense parts of the Milky Way compared to optical light.

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Researchers say there is considerable variation in iron levels.

“The very wide spread in iron levels could indicate that the innermost parts of the galaxy are incredibly heterogeneous, or unmixed,” said Dr. Brian Thorsbro, an astronomer at Lund University. Stated.

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“This is something we didn’t expect, and it tells us something not only about what the center of a galaxy looks like, but also about what the early universe looked like.”

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“Personally, I think it’s very exciting that we can now study the galactic center itself at such a detailed level,” Dr. Forsberg said.

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“While these types of measurements have been standard for observations of our own galactic disk, they have been an unattainable goal in more remote and exotic parts of the galaxy.”

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“Studies like this can teach us a lot about how our home galaxy formed and developed.”

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B. Thorsbro other. 2023. The range of old metallicities of stars in nuclear clusters is wide. APJL 958, L18; doi: 10.3847/2041-8213/ad08b1

Source: www.sci.news

The Revealed True Nature of Magellan’s Stars After 50 Years of Exploration

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An artist’s rendition of the Magellanic Star Stream, depicting the Small and Large Magellanic Clouds, the Milky Way’s nearest neighbors, is shown in the diagram. The gaseous Magellanic Stream swirls behind the galaxies, spreading across the southern sky as they move, with 13 red giant stars discovered within the stream.

Astronomers from the Center for Astrophysics at Harvard University and the Smithsonian University have solved a 50-year-old mystery by identifying stars within the Magellanic Stream. The discovery helps reveal the distance to the stream, providing new insights into the history and characteristics of our galaxy and its neighbors.

The study, published in the Astrophysical Journal, showcases the discovery of 13 stars within the stream and their unique characteristics that place them precisely within the mysterious structure. The stars’ distances and chemical compositions offer clues to the formation of the Magellanic Stream and the interactions of the Magellanic Clouds with the Milky Way.

By conducting a spectroscopic analysis of distant Milky Way stars, researchers were able to determine their chemical makeup and velocity, ultimately allowing them to identify stars within the Magellanic Stream. This discovery also sheds light on the origin and gravitational pull of the stream, as well as its potential role in the future formation of new stars within the Milky Way.

The Magellanic Stream, which acts as a supplier of cold neutral gas for the formation of Milky Way stars, also holds valuable insights into the composition of galaxies and the distribution of dark matter. Further study of the stream and additional discoveries of stars are expected to provide more surprises and lead to a deeper understanding of our galaxy’s outer reaches.

Source: scitechdaily.com