Billions of years from now, when our star, the Sun, reaches the end of its life,The helium core at the center of the sun will begin to fuse. Subsequently,The sun expands rapidly and becomes a red giant. When it swallows Mercury, Venus and the Earth with ease, it will expand so huge that it will no longer be able to retain the outermost layers of gas and dust.
In a glorious ending,The Sun ejects its outermost layers of gas and dust into space, creating a beautiful neon-like curtain of light that continues to shine for thousands of years before gradually extinguishing..
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The Milky Way is dotted with thousands of these radiant gem-like monuments, viz.planetary nebula. The masses of these dying stars range from half to eight times the mass of the Sun.The death process of stars with greater mass will be more violentforming what we callsupernova explosion. Planetary nebulae come in an astonishing variety of shapes, as the names of the Southern Crab Nebula, Cat's Eye Nebula and Butterfly Nebula imply. Although these nebulae are beautiful and dazzling, they have always been an unsolved mystery in the minds of astronomers. So, how does a gorgeous cosmic butterfly emerge from its cocoon from an ordinary red giant star?
Both observations and computer models point to the same explanation, which might have seemed absurd 30 years ago: that most red giant starsThere is a companion star much smaller than itself hidden within the gravitational field.. It is this companion star that shapes the planetary nebula into its bizarre shapes, like a potter shaping his pottery on a pottery wheel.
The main previous theories about the formation of planetary nebulae werearound a single star, only the red giant stars themselves were studied. Because the red giant's gravitational pull on its outer material is weak, in the final stages of its demise,Red giant stars lose mass rapidly, losing as much as 1% of their total mass every hundred years.. Under the surface of the red giant star, it is like a pot of boiling water, flowing and surging, causing its outermost layer to pulsate, shrink and expand. Astronomers speculate that the shock waves generated by these pulsations can eject gas and dust into space, forming what is often called a “stellar wind.” However, it would take a lot of energy to completely expel this material before it falls back into the star. Starwind has the power of a rocket jet and is by no means a gentle breeze.
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The outer layers of a red giant star escapeEventually, its smaller inner layers will collapse into a white dwarf. The white dwarf formed after the collapse is even hotter and brighter than the original red giant. The white dwarf continues to illuminate and heat the escaping gas until the gas itself glows, forming the planetary nebula we normally see. By astronomical standards, the entire process is actually very fast; but by human standards, this process is very slow, usually taking centuries or even thousands of years.
Until the launch of the Hubble Space Telescope in 1990, astronomer Bruce Balick of the University of Washington said, “We had a pretty good shot at understanding this whole process.” Then he and his colleague Adam from the University of Rochester in New York・Adam Frank attended a conference in Austria and saw the first photos of planetary nebulae taken by the Hubble Space Telescope. “As soon as we saw these pictures when we went out for coffee, we knew something had completely changed,” Balik said.
Astronomers once believed thatRed giant stars are spherically symmetrical. So, it stands to reason that a round star should produce a round planetary nebula. But what the Hubble Space Telescope captured was quite different. “Many planetary nebulae apparently have unusual axial symmetry. ” said astronomer Joel Kastner from the Rochester Institute of Technology. The Hubble Space Telescope captured strange petal-like, wing-like and other shaped structures. These structures are not round, but Symmetrical around the nebula's main axis, it looks like it was spun on a potter's wheel.
In 2002, Bruce Balik and Adam Frank published an article in the Annual Review of Astronomy and Astrophysics to document the debate among scientists at the time about the origin of the above structure. . Some scientists believe that this axial symmetry is caused by the way the red giant spins or its magnetic field, but neither idea stands up to some basic testing. Because when a star expands, both its rotation and magnetic field should weaken simultaneously. However, the rate at which red giants lose mass becomes increasingly faster in the final stages of their demise.
Another hypothesis is:Most planetary nebulae are formed not from one star, but from a pair of stars. Astronomer Orsola De Marco from Macquarie University in Sydney calls it the “double star hypothesis.” In this case, the second star is much smaller and thousands of times dimmer than the red giant, and shines as far from the Earth as Jupiter. Because the distance between the two is far enough, the second star can interfere with the red giant without being swallowed up. (Other possibilities exist, of course, such as the subduction orbit hypothesis, in which a second star approaches the red giant every few hundred years and strips away a layer of material.)
The binary star hypothesis nicely explains the first transition phase of a dying star, which is:When the companion star sucks dust and gas away from the main star, the material is not immediately sucked into the companion star, but forms a rotating disk made of material, which is an accretion disk formed on the orbital plane of the companion star.. This accretion disk is like a potter's wheel. If there is a magnetic field in the disk, any charged gas can be pushed out of the disk and pushed in the direction of the axis of rotation. However, even if the accretion disk does not have a magnetic field, the material in the disk will hinder the outward flow of gas on the orbital plane, causing the gas to exhibit a double-lobed structure and speeding up the flow of gas to the poles. That's exactly what the Hubble Space Telescope sees in images of planetary nebulae. “If the hypothesis of a companion star is sufficient to explain this phenomenon, why should we look for a more complicated explanation?” DeMarco said.
However, some astronomers do not accept the binary star hypothesis because the companion star cannot be detected. In 2020, Leen Decin, an astronomer at the University of Leuven in Belgium, wrote that a famous astrophysicist told her: “You know, Leen, this all looks so dreamy, the observations are so unreliable. Fascinating. The current state-of-the-art models are doing a good job of interpreting the data, but at the end of the day, we should just trust the actual observations, right?”
Over the past 10 to 15 years, however, the situation has steadily reversed. A new innovative telescope reveals what a red giant star looks like before it becomes a planetary nebula. Telescope images captured images showing swirling structures and accretion disks surrounding some red giant stars. This is as expected from the hypothesis that there is a second star sucking material from the red giant.In some detections, astronomers may even have alreadyThe companion star itself is detected.
Deshin and her colleagues relied in particular on Chile's Atacama Large Millimeter/submillimeter Array (ALMA), which began operating in 2011. ALMA consists of 66 radio telescopes that work together to present images of celestial objects. “ALMA provides images that not only cover a wide range but also have very high spectral resolution, so they help people understand astronomical dynamics and velocities,” Dexin said. For scientists, speed is the key to unraveling the difficult problems of stellar winds and accretion disks. .
ALMA has observed spiral or arc-shaped structures around more than a dozen red giant stars. It is almost certain that this is the material emitted by the red giant stars, and that these materials are spiraling towards the companion stars. These vortex structures are in good agreement with computer simulations and cannot be explained by old stellar wind models. In the 2020 issue of Science, Dexin published preliminary research results. A year later, Dexin further discussed this result in the Annals of Astronomy and Astrophysics.
In addition, Dexin's team discovered in ALMA's imagesTwo previously undetectable companions to red giant stars, namely P1 Gruis and L2 Puppis. To confirm the discovery, she will need to monitor them over time to see if these newly discovered objects orbit the host star. “If they are indeed orbiting the primary star, then I believe what we have found is the companion star,” Dexin said. The discovery may convince those who doubt the binary star hypothesis.
Like crime scene detectives, astronomers collected snapshots of the planetary nebula before and after it formed. But they still lack a piece of evidence like CCTV footage. So, do astronomers hope to capture the entire process of a red giant turning into a planetary nebula?
So far, computer models are the only tool capable of showing this centuries-long process from start to finish. The model helps astronomers understand this dramatic process:The companion star orbits the main star for a long time, then approaches under the influence of tidal forces, and is eventually sucked into the main star. “As the companion star spirals toward the core of the red giant, it releases huge amounts of gravitational energy,” Frank said. Computer models show that gravitational energy greatly accelerates the process of shedding material from the star's outer layers, shortening the entire process to one to ten years. If this process is true, and astronomers know where the observing points are, then they can witness the death of a star and the birth of a planetary nebula in real time.
One candidate observation that deserves attention is V Hydrae. The red giant star is extremely active, spewing bullet-like clumps of plasma toward the poles every 8.5 years. And, in the last 2100 years, it has erupted six large rings on the equatorial plane. In April, astronomer Raghvendra Sahai of NASA's Jet Propulsion Laboratory published findings about these rings. He believes that this red giant star has not just one companion star, but two. A companion star located near the red giant may have rubbed into the red giant's envelope, causing a plasma eruption. At the same time, another companion star slightly farther away erupted in subducting orbital motions, creating a ring structure. If this is true, then V Hydrae may be about to swallow its closer companion star.
So,How will our sun eventually come to an end?The study of binary stars seems to have nothing to do with the fate of the sun, which is a lonely star. Dexin estimates,Stars with companions lose mass approximately 6 to 10 times faster than stars without companionsthis is because the companion star can effectively help the red giant star peel off its outer shell much faster than a single red giant star can peel off its outer shell on its own.
This means that data measured by scientists on stars with companions cannot reliably predict the fate of stars without companions, such as the Sun. About half of all stars about the same size as our sun have companions. Dexin believes that the companion star affects the shape of the stellar wind from beginning to end. And if the companion star is close enough to the star, it will greatly accelerate the star's mass loss rate. Compared with other stars, the Sun is most likely to eject its outer shell more slowly and stay in the red giant stage several times longer.
but,Exactly what the sun does when it dies is still a mystery.For example, even though Jupiter is not a star, it may still be heavy enough to attract material from the Sun and form an accretion disk. “I think we're going to see Jupiter form a very small spiral structure,” DeSing said. “Even in our computer simulations, you can see Jupiter's influence on the solar wind.” If that's the case, then our Sun There may also be a dazzling ending.
Author: Dana Mackenzie
Translation: Bian Ying
Reviewer:K. Collider(
Original link:A dying star's last hurrah