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New Knowledge About the Fate of the Sun

A planetary nebula is a region of cosmic gas and dust formed from the cast-off outer layers of a dying star. Despite their name, planetary nebulae have nothing to do with planets.

After the cold weather for a while from the end of 2013 to the beginning of 2014, now the weather is starting to heat up. The sun was bright and the sky was so clear that some people started to dislike it. But it’s hot like this, it’s not comparable to what the world in the 5th era, 000 million years from now will meet At the end of the lifespan of the sun (If anyone could live that long, they would have experienced it firsthand), at which time the Earth would be inside the Sun. Because the Sun will expand in size and mass a lot. Let’s say the size of the Sun today is comparable to a soccer ball.

In the future, it will expand to the size of a football field. before being reduced to the size of an ant walking on that football field Many people wonder how they know. which the answer is We speculate on the answer by observing the evolution of other stars similar to the Sun in the Milky Way. These studies give us clues to predict the fate of the Sun. So let’s learn what happens to the stars. I really want to know how it ended.

Stellar life cycle

about a century ago Danish scientist Ejnar Hertzsprung and American astronomer Henry Norris Russell each made remarkable observations while analyzing them. Many stars closest to the Sun found that some stars of the same color Stars that are about the same distance from Earth differ widely in brightness. Then, in December 1913, Russell presented the first chart of what we now call the Hertz Sprung-Russell chart. (Hertzsprung- Russel diagram) or H-R chart. This chart compares a star’s brightness (on the vertical axis) with the color of the star or spectrum (on the horizontal axis).

Based on data from observations of stars in the sky in the 20th century, some of the earliest observations of stellar physics emerged, believing that stellar mass and brightness were related. At that time, astronomers began to wonder how stars evolved and thought it might be possible for them to evolve and move on the H-R chart. For decades we have learned that a star’s mass dictates its life. It also determines the brightness and temperature of the star. We now summarize all stages of stellar evolution in this important chart.

Astronomers use powerful telescopes both on the ground and in space to measure color brightness. For example, the Hubble Space Telescope was able to observe a sun-like star 25 million light-years away in the Andromeda Galaxy. Those stars are 10 billion times less bright than the brightest stars that humans can see with the naked eye.

In the final stages of stellar evolution, The outer shell of a star The sun (like the Sun) is blown out into the surrounding interstellar medium, leaving only a hot, unshrouded core. This image represents a planetary nebula. The ultraviolet rays emitted from the core illuminate the expelled gas and dust. forming the shape which is the origin of the name In the future, this nebula will only be the core of the hydrogen-burning progenitor star. which we call white dwarfs.

We know that long periods of calm last most of a star’s life after the formation of new stars. Its core reaches temperatures in the tens of millions of degrees. which is hot enough to fuse hydrogen together to form helium and power During the nuclear “burning” phase, the star’s appearance remains relatively stable, with slight variations in brightness, magnitude, and temperature late in life. Most stars with masses less than 10 times the mass of the Sun.

Nuclear fuel will be used up. The star swells and sheds its outer layers. The core cools over time to become a “white dwarf,” a carbon-oxygen remnant. (Because these elements are products of nuclear fusion of hydrogen. and helium in the star’s core) and a thin layer of hydrogen on its surface. and since there is no nuclear power source It thus cools over time and radiates away the stored heat.

What’s missing??

We already have a clear understanding of the hydrogen combustion stage. and white dwarf stages in stellar evolution. But tracing what happened in the middle remains a great mystery. It was during these times that the star went through a lot of changes. It can change size tens of thousands of times faster. Begins to burn hydrogen, the outer envelope of the star begins to scatter and expand. which we call red giants At this stage the star becomes much brighter than a white dwarf of the same temperature due to the greater emission of energy from its surface area.

When stars evolve further in The “Red Giant Path” as it is called on the H-R chart. It grows brighter over time. The stellar wind 1 can eject the outer layers away from the star and dump it into the surrounding environment. Red directly determines the future of a star.

After the red giant stage The star burns helium in its core and changes in temperature and size again as the star moves along. “Asymptotic giant branch” and burns up the surrounding helium. The lifespan of a star along this path depends on how long it takes to completely eject its envelope and how bright it reaches.

If a star loses its enveloping material rapidly, the evolutionary phase is over. and form a white dwarf But if the star slowly loses its matter, it will live longer on the asymptote along the giant star’s path. and continued until it grew brighter and puffed up. Knowing how much matter a star has lost help us understand the later stages of stellar evolution

We can use it to observe the color and brightness of the stars. They also use models that predict the effect of physical changes on the emergent spectrum to learn about properties such as age, chemical composition, and chemistry. and the birth rate of stars of galaxies inhabited by those stars

Kalirai and colleagues studied stars at different stages of evolution in order to piece together the process. To figure out how much matter a star has lost in evolution We need to know the initial and final masses of the same star, but the timescale over millions to billions of years is too long to watch a single star evolve. We have no way of inferring the final properties of white dwarfs. From the hydrogen-burning stars that glow in the night sky. likewise We have no way of inferring the stellar mass. in the early stages of a nearby white dwarf

In fact, we have a laboratory to deal with the problem. That is, different star clusters, the surroundings of thousands of stars all coming from the same source. All stars within the cluster formed at the same time and had the same composition. But there are different masses. Each cluster provides information on stars of a certain age, so we can directly see the impact that stellar evolution has on stars of different masses.

In order to explore both initial and final stages at the same time. and to measure how much mass a star has lost in its evolution We can use the following 3-step process:

Step 1 Find a needle in the ocean.

For the past decade, a team of researchers has measured the brightness and color of every star in one cluster. In this process, we study both brighter, hydrogen-burning stars. Including when it is a giant star in the process of stellar evolution. and traces of much less luminous white dwarfs. These white dwarfs have also burned hydrogen in their cores in the recent past. But it progresses faster than the other stars in the cluster due to its greater initial mass.

Calirai and colleagues recently used the Hubble Space Telescope to observe the globular cluster 47 Tucanae (NGC 104) in the constellation Tucana. To see the faintest white dwarf at nearly 30 calirai magnitude, et al. determined the positions of all stars on the H-R chart. From the chart, strict constraints can be placed on the basic properties of each cluster, e.g. Age of the cluster This is because stellar evolution is linked to the mass of the star at birth.

To determine the age of a cluster, one can see what mass of the stars in the cluster are still burning hydrogen. and what mass has evolved past that point Using this chart we can measure the population of brighter white dwarfs. This will be studied in more detail by other telescopes. Another team of astronomers worked with Kalirai’s group to create similar charts.

47 Tucanae (NGC 104) or 47 Tuc is a globular cluster in the constellation Tucana (Tucana), about 15,000 light-years from Earth, and has a width of The cluster, spanning 120 light years, contains thousands of white dwarfs. The globular cluster is visible to the naked eye with an apparent magnitude of 4.03.

A Hertz Sprung-Russell chart showing the brightness of the stars in the globular cluster 47 Tucanae along the Y-axis and the star color (corresponding to temperature) along the X-axis. Burning hydrogen in dwarf galaxies (Small Magellanic Clouds) in the background. This galaxy lies 200,000 light years behind 47 Tuc.

Step 2 Take advantage of the natural lab.

One of the most remarkable properties of white dwarfs is their density. The mass of a typical white dwarf is about half the mass of the Sun. But it’s about the size of the Earth. Therefore, the matter density of white dwarfs may be a million times higher than that of the Sun.

Because the density of white dwarfs is very high. We therefore refer to the remnants of a star as a natural condensed matter laboratory. The pressure at the surface of a white dwarf is very high due to its density. And this gives it a unique optical characteristics or a spectrum unlike that of any other star.

These spectra hold important clues about the properties of stars. For “normal” white dwarfs with temperatures between 20,000 and 30,000 K, the spectra show a common line of hydrogen. But these lines don’t look at all similar to those observed in the laboratory or even from more typical stars that burn hot and burn hydrogen, such as Sirius A. The pressure on the white dwarf’s surface. making the assimilation lines unclear That is, the width of the spectral line is 5-10 times greater than that of a normal star.

while the Sun shows dark bands of multiple absorption lines. Hotter stars have simple spectral lines that show only the “Balmer sequence” of hydrogen. The newly formed white dwarf has a temperature similar to that of a hot blue giant. Therefore, Balmer lines are also shown.

But due to the intense pressure on the white dwarf’s surface, These absorption lines are therefore “widened by pressure” and are much wider than those of hydrogen-burning stars. by observing these Balmer lines Scientists were able to accurately measure the temperature of the remains and the gravity on the surface.

In order to observe these broader spectral lines Calirai and his colleagues used a special instrument called a spectrograph to separate the light from the star. Specifically, multiple-object spectrographs on a 10-meter telescope, such as the Keck telescope in Hawaii, are used to measure the spectra of dozens of white dwarfs in a cluster at the same time.

They then compared computer models of those hydrogen spectral lines with the white dwarf’s spectra to measure surface pressure, temperature and gravity on its surface. correct It also knows how long a star has reached such a mass. Since the original star ejected its outer layer of gas and left only the core.

Step 3. Put it together (Collect)

age of each star cluster (found in step 1) is the same age as the age of all the stars in it. For a white dwarf, this value is The sum of cooling times that have been completed for each carcass. and the hydrogen-burning life span of the initial star. This means that we can calculate the lifetime of the initial star using the following equation.

Cluster age – white dwarf cooling time = initial star lifespan

We can determine the origin of the mass of the initial star. By using a well-tested theoretical model at that age The new method allows us to observe both the initial and final masses of the same star.

How much mass was lost? After applying this calculation to what has been observed for decades in white dwarfs in nearby clusters, Including results from Calirai et al.’s 47 Tuc study. This led to the discovery that hydrogen-burning stars lose a lot of their mass. in stellar evolution More massive stars lose a proportional amount of their mass.

For example, a star born with a mass five times the mass of the Sun loses 80 percent of its mass in its evolution and dies as a massive white dwarf. Its mass is approximately equal to the mass of the Sun (Sirius b, the closest white dwarf to the Sun). (This is consistent with this prediction, since it has approximately the same mass as the Sun.) Such large stars are less common. This is because nature produces far more low-mass stars than massive ones.

while the evolution of Sun-like stars leads to white dwarfs containing carbon and oxygen. which looks more typical An ancestor of such a massive white dwarf. may have evolved to much higher temperatures and densities in this extreme environment. Even the carbon and oxygen in the cores of stars can melt into heavier elements like neon and magnesium.

Therefore, astronomers believe that the cores of these massive white dwarfs. have a different composition than that of a star More “typical” for stars of medium size, namely Its mass is about two to three times the mass of the Sun. It will lose about two-thirds to three-fourths of its mass.

Comparing properties of white dwarfs in clusters and determining the relationship between the masses of white dwarfs and their hydrogen-burning progenitors.

The greater the initial mass of a Sun-like star, the greater its mass. The greater the proportion of matter that will be lost through stellar evolution. Calirai and colleagues compared the properties of white dwarfs in star clusters. and determine the relationship between the mass of the white dwarf and its hydrogen-burning precursor star.

The destiny of our Sun (and Earth’s)

Measurements of the star’s initial and final mass can be extended to nearby Sun-like stars. Therefore, it can be used to predict the fate of the sun. We know that our Sun will use up all the hydrogen in its core in approximately 6.5 billion years, when no hydrogen remains in its core.

Like a normal red giant, our Sun will begin to burn elements in its surrounding layers. This insignificant layer expands due to heat generated. and expanded to a radius of 200 times the current radius The Sun’s surface temperature will drop to about half its current value (about 3,000 K). Therefore, it will be 1,000 times brighter than today.

when the sun expands It will completely devour Mercury and Venus. on the contrary Earth will try to play “catch” with the sun. when the sun loses its mass This would have a gravitational effect, causing the Earth’s orbit to extend as far as about 50 percent of its present time. Unfortunately for Earth, the Sun loses mass rapidly as a red giant. and its outer layer will catch up with the Earth’s orbit. and the world will be cooked By then, the heat would dry up the oceans and burn the atmosphere.

After encountering gas particles in the Sun’s insignificant outer surface The Earth senses “resistance” and begins to decrease its orbital speed around the Sun. Eventually, the Earth’s orbit will spiral towards the center of the Sun.

according to the model of stellar evolution After the red giant phase, The sun loses its shield and leaves only its core. This core, which is a white dwarf, will be very hot at first but due to lack of nuclear fuel So it will cool down quickly. The fate of our sun will be as follows. After losing 46 percent of its mass (which Kalirai and colleagues calculated), it becomes a normal white dwarf. The weight is 54 percent of the current weight. Like the white dwarf ancestors in the globular cluster 47 Tuc, our Sun will ultimately be very small in mass compared to its original mass.

It may seem like it has a rather boring life. as it burns hydrogen in its core over billions of years The Sun enters another long-standing state in stellar evolution. As a white dwarf Our sun will gradually release stored heat into space. and dims over time. It will join the Milky Way’s stellar cemetery, the place where 98 percent of the stars in the galaxy die.

1 Stellar wind is the flow of matter (protons, electrons and metal atoms at a star) is the flow of matter (protons, electrons and heavy metal atoms) ejected from a star These winds are characterized by continuous outflows of matter moving at speeds between 20 and 2,000 kilometers per second.

Bibliography:

Australian Astronomical Observatory. (2010, 1 August).The Globular Cluster 47 Tucanae (NGC 104). Retrieved February 21, 2014, from http://www.aao.gov.au/images/captions/aat076.html

Frommert, Hartmut. (2006, 20 June). NGC 104. Retrieved February 21, 2014 from, http://messier.seds.org/xtra/ngc/n0104.html

Howell, Elizabeth. (2013, May 29). Why Are Dying Stars in 47 Tucanae Cooling Off So Slowly? Retrieved February 21, 2014, from http://www.universetoday.com/102482/why-are dying-stars-in-47-tucanae-cooling-off-so-slowly/

Kalirai, Jason. (2014, February). New light on our Sun’sfate. Astronomy, 42 (2), 44-49.

Swinburne University of Technology. Stellar Winds. Retrieved February 21, 2014, from http://astronomy.swin.edu.au/cosmos/S/stellar+winds