2024-04-08 08:11:18
[비즈한국] Approximately 5 billion years from now, a terrible fate will befall our descendants. As the embers of nuclear fusion slowly die out, the sun swells into a huge red giant, and eventually the blazing surface of the sun reaches right in front of the Earth. This is something that is bound to happen unless the laws of the universe change. Even if our descendants are really lucky and survive on Earth for nearly 5 billion years without a major fight, this fate cannot be avoided. All you can do is look at the surface of the sun slowly approaching in the sky and pray.
There is only one survival strategy. They are running away from the huge bulging sun to a planet outside the solar system. For example, we can think of humanity migrating to the orbits of Jupiter and Saturn. If the Sun swells significantly into a red giant, then the orbits of Jupiter and Saturn may enter the Goldilocks zone, where they receive a moderate amount of sunlight. I have a vague expectation that in 5 billion years, we will be in an era where it will be easy to travel to the outskirts of the solar system. May astronomical luck be with our descendants… .
However, for the migration plan to Jupiter and Saturn to be successful, one important prerequisite is needed. Even if the Sun passes through a red giant and disappears in a huge explosion, leaving behind only a white dwarf, Jupiter and Saturn must survive without being completely destroyed. A rocky planet orbiting the inner solar system will be eaten by the giant bulging surface of the sun. In comparison, the fate of gas planets orbiting the outer solar system is difficult to guarantee. Will the gas planets be destroyed by the powerful explosion of the sun, or will they survive the storm and firmly hover around the sun, which eventually became a white dwarf? .
Recently, James Webb discovered an interesting site that may provide a little hope for our descendants. They captured a surviving gas-type exoplanet, steadily orbiting next to a white dwarf that disappeared in an explosion a long time ago! It shows the amazing possibility that even if the central star explodes, the surrounding planets can survive without being destroyed. We introduce James Webb’s latest observation results, which may provide a glimmer of hope for future generations.
New observations have been published showing the ‘hopeful’ possibility that in the distant future, even if the sun explodes leaving behind only a white dwarf, the entire planetary system orbiting around it will not disappear.
It is very difficult to find exoplanets next to white dwarfs. White dwarfs are the ‘dead bodies’ of stars that can no longer undergo nuclear fusion and glow with the warmth they had left just before death. It gradually loses heat to outer space and cools down. So, when observed using normal visible light, it is very dark. It is almost drowned out by the light of other ordinary stars shining around it. Instead, because the temperature is lukewarm, more energy is emitted in the long-wavelength infrared region. This is where James Webb can play an important role.
James Webb is a space telescope that observes the universe in infrared light. To the human eye and a general telescope that looks at the universe in visible light, white dwarfs appear to be hiding in the dark, but to James Webb, white dwarfs may be an easier target to find.
A common way to find an exoplanet orbiting another star is to use a transit, in which the brightness of the starlight slightly dims when the exoplanet passes in front of the central star. This is the method used by the Kepler Space Telescope, an exoplanet hunter that was active from 2009 to 2018 and helped humanity discover more than 5,000 exoplanets, and the TESS Space Telescope, which went up into space and is still actively observing. Until recently, the majority of exoplanets were discovered this way.
There is a method of exoplanet search that may seem the most intuitive at first glance, but is actually the least preferred by astronomers. Direct imaging is a method of taking the authentication shot itself. Simply using a high-performance telescope and camera, you can capture the image of an exoplanet hidden next to a star, faintly reflecting starlight and shining. But usually this method is rarely used. This is because the exoplanets orbiting the sides are very dark and small compared to the very bright star at the center. Because the blurry image of an exoplanet is buried in the starlight that spreads out in all directions, it is very difficult to confirm its existence through direct imaging alone unless it is a fairly large exoplanet.
However, James Webb is able to utilize this hunting method thanks to his outstanding performance. Astronomers observed white dwarfs WD 1202-232 and WD 2105-82 in February and April 2023, respectively, using James Webb’s MIRI instrument, which takes images in the relatively long wavelength mid-infrared band. The first white dwarf, WD 1202-232, was originally a light star with only 1.3 times the mass of the Sun, but it stopped nuclear fusion a long time ago and has been cooling for 900 million years. The star itself is estimated to be about 5.3 billion years old. The second white dwarf, WD 2105-82, was about 2.5 times the mass of the sun, but it also stopped nuclear fusion and has been cooling for 800 million years. This star is about 1.6 billion years old. They are all white dwarfs that have completed their evolution early and are slowly cooling down, relying on the heat that remained immediately after the explosion.
In general observation, white dwarfs are very difficult celestial bodies. This is because it is buried among the brightly shining stars and is difficult to see. However, paradoxically, white dwarfs had an advantage in the direct imaging that James Webb attempted to determine the existence of nearby exoplanets. White dwarfs do not shine too brightly. It glows very darkly. So the form of emitting light is not complicated. In the case of white dwarfs, which radiate heat only lukewarmly compared to other dazzlingly large stars, the distribution of light emitted by the star can be modeled more easily. It is much simpler and neater to find the components of starlight mathematically.
Astronomers subtracted each white dwarf’s brightness distribution, which was relatively easily modeled, from images observed by James Webb. Just like erasing a pimple you want to erase with the Photoshop app, only the light component of the lukewarm glowing white dwarf star in the center of the photo is removed. Then, the small speck that had been vaguely visible around it became clearer.
However, it is not immediately possible to be certain that the spots around the white dwarf that have been identified in this way are really exoplanets orbiting it. It may be that images of background galaxies in the much more distant background of the universe coincidentally overlap with each other in similar directions. In fact, looking at previous observations, the probability that the spots identified around the star are not exoplanets but just another celestial body in the background is about 1 in 3,000. Not very low. Therefore, further analysis is needed to verify whether this is truly an exoplanet.
To achieve this, astronomers modeled and removed the speckled light remaining in the image after previously subtracting the components of the central white dwarf. If this blob is indeed a dimly glowing ball-shaped exoplanet reflecting the light of the central white dwarf, the light should have been observed as a simple spherical object emits light. By applying the light brightness distribution modeled in this way, the remaining stains were once again removed from the photo. As a result, it was confirmed that the stains were almost completely erased in both white dwarf photos.
This shows that there is a high possibility that this celestial body actually shines in a round shape, reflecting the light of the central star. If it had been a background galaxy much further away rather than an exoplanet, the stain would not have been erased so cleanly. Unlike exoplanets where a single celestial body emits light alone, galaxies where hundreds of billions to trillions of stars are gathered together to shine in the distance, this is because the brightness is distributed in a much more spread and complex manner. If this object was a background galaxy, there would have been more dirty stains left that could not be removed.
After further careful analysis, astronomers suggested that the two blobs seen in James Webb’s image were candidates for gaseous exoplanets orbiting white dwarfs. Of course, it is still difficult to say 100% that it is an exoplanet. In order to judge more clearly, we need to observe the same area again after some more time. If it is indeed an exoplanet orbiting a white dwarf, the location of this spot should shift slightly when observed again later. Of course, it takes a very long time for an exoplanet to orbit. It can take anywhere from a few years to as long as several decades. Therefore, it takes a very long time to determine whether it is an exoplanet based on direct imaging observations alone. This is another limitation that prevents astronomers from using direct imaging techniques in the field.
James Webb’s performance is excellent, but because the exoplanet itself appears so dark and blurry, it is difficult to determine the exact mass of the exoplanet candidate corresponding to this speck based on this observation alone. However, the masses of the two exoplanets estimated through this first observation are approximately 1 to 7 times the mass of Jupiter. It is estimated to be a giant gas planet about the size of Jupiter or relatively larger. The two candidate objects appear to be approximately 11 to 35 AU away from the central white dwarf. This is similar to the distance Jupiter and Saturn are from our Sun.
This observation provides a glimpse into the future that will occur in our solar system 5 billion years from now. Interestingly, gas-type planets located at a distance of 10 to 30 AU from the central star are able to stay by their side without being completely destroyed or thrown out of the orbit even when the central star explodes, leaving behind a white dwarf. Jupiter and Saturn may follow similar fates. If so, wouldn’t it be possible for our distant descendants to dream of a future in which they live far away on the icy moons of Jupiter and Saturn, away from the sun that swells and then explodes?
Meanwhile, this new possibility that a giant gas planet can survive around a white dwarf provides an important astronomical clue. As I have emphasized several times before, the white dwarf itself is the corpse of a dead star that can no longer undergo nuclear fusion. However, sometimes white dwarfs appear to contain a fairly high content of heavy metal elements. As if it were not dying and was continuously producing heavier metal elements by continuing the nuclear fusion reaction inside it!
However, it is difficult to believe that the nuclear fusion reaction that fills the white dwarf with new metal elements continues continuously. To explain the existence of white dwarfs with such high levels of metallic elements, astronomers focused on the role of giant planets that may be orbiting them. It is conceivable that the giant planets orbiting nearby may influence the orbits of various comets and asteroids spread out further away, and that some of them may fall headlong into the central white dwarf. As a result, the white dwarf is replenished with various metal elements contained in asteroids and comets, and can show a fairly high metal content even when nuclear fusion has stopped. The white dwarf is literally polluted with metals contained in asteroids and comets.
This discovery also shows the possibility of the existence of a giant planet that may be disrupting the orbits of asteroids and comets next to the white dwarf. It is expected that this will be a new clue to explain the existence of white dwarfs that are ‘contaminated with metallic elements’, which have remained a mystery for a long time.
In a way, the stars in the universe may live an eternal life that never dies ever since they were born. On the surface, it appears as if the entire nuclear fusion process has stopped and disappears in a huge explosion, but even after that solemn moment of death, the star does not stop and continues to change its appearance. From the perspective of astronomy, which defines the change in appearance over time as ‘evolution’, a white dwarf that changes its chemical composition by continuously replenishing metal elements from surrounding asteroids and comets is also not dead, but continues to evolve. G is a living being.
Long ago, ancient philosophers said, “The universe does not allow a vacuum.” However, the universe shown by 21st century astronomy seems to show that ‘the universe does not allow death.’ Could it be that the true identity of the ‘vacuum’ that the universe was afraid of meant ‘death, stopping’?
reference
https://iopscience.iop.org/article/10.3847/2041-8213/ad2348
What about the writer Ji Woong-bae? He loves cats and space. As a child, he watched ‘Galaxy Railroad 999’ and had a dream to publicize the beauty of the universe. He is currently researching evolution through the interaction of galaxies at Yonsei University’s Galactic Evolution Research Center and Near Cosmology Laboratory, and is engaged in various science communication activities such as lecturing and writing. He wrote books such as ‘Astronomical Observatory’, ‘Thinking about the Universe All Day’, and ‘The Science of Stars and Light’.
Ji Woong-bae, science columnist writer@bizhankook.com
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