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The Sun's Close Relatives: What Are the Surprising Differences Between Solar-Type and Solar-Similar Stars?
The Sun is a unique star in our universe, but astronomers have discovered that there are several types of other stars that are very similar to it: "Solar-type stars," "Sun-like stars," and "Sun twins." These stars accurately reflect the degree of similarity to the Sun, with solar twins being the closest, followed by solar analogs, and finally solar-type stars. Observations of these stars will not only help us better understand the characteristics of our Sun, but will also provide insights into the habitability of planets.
Evolution of Similarity
The definitions of these three categories reflect the evolution of astronomical observation technology. Initially, only the definition of "solar-type stars" existed, based on the most basic similarity judgments. As instrumentation and observational techniques improved, astronomers could more accurately measure key characteristics of stars, such as temperature, leading to the creation of the category of "Sun-like stars." Eventually, continued refinement led to the creation of a category called "solar twins," stars that are identical to our sun in many respects.
The higher the similarity, the more an observer can use the Sun to test the derivatives of these stars.
Solar Type Stars
"Solar-type stars" are main-sequence stars that have broad similarities to the Sun. The B−V color index of these stars is typically between 0.48 and 0.80, compared to 0.65 for the Sun. Based on spectral type, Solar-type stars range from F8V to K2V, which accounts for about 10% of stars.
Sun-like stars
Compared to Sun-type stars, the requirements for "Sun-like stars" are more stringent. These stars must have temperatures within 500 K of the Sun (5278 K to 6278 K) and metallicity similar to that of the Sun, typically in the range of 50% to 200%. Furthermore, these stars cannot have close companions to avoid disrupting their activity. Such conditions are more limited than discovering planetary systems similar to the Sun.
For example, the galaxy HD 70642 is a G5V star with a temperature of 5533 K but is younger than the Sun, and there are other similar candidates such as HIP 11915.
Sun Twins
To date, no twin star identical to our Sun has been discovered. However, some stars are considered close to the criteria of "sun twins". The specific requirements for these stars include: the temperature must be within 50 K of the sun, the metallicity must be 89%-112% of the sun, and there must be no companion star. The age must be Within 100 million years of the Sun. These stringent conditions make true sun twins extremely rare.
Potential HabitabilityAnother way to define a sun twin is as a "habstar," a star that has the conditions necessary to support a planet with life. These conditions include a main sequence age of at least 50 million years, a habitable zone that can stably support Earth-like planets, and no close companion stars. These requirements make the search for stars suitable for life a challenging task.
Is it possible to find planets among these sun twins and similar stars that are suitable for life like ours?
As astronomy advances, studying these close relatives of the Sun will not only provide a deeper understanding of other star systems in the universe, but may also reveal the potential for life. This also raises another question: Is our solar system just a mineral vein, or is it part of the countless habitable galaxies in the universe?
