Blue stragglers areGlobular clusterCommon in the blue edge of the main sequence "breaking point"fixed star。Blue stragglers have attracted more and more attention because of their special observational characteristics.These stars do not conform to the standard stellar evolution theory. At the same time, because they are bright and blue, several blue discrete stars can greatly change the integrated spectral characteristics of a star clusterclusterIt is very important in the research, and their formation path plays a key role in their observation characteristics.
yesOpen clusterorGlobular clusterWith other members of the main sequence, it is a blue star with higher surface temperature and higher luminosity.Therefore, their positions are different from other members of the star cluster in the Herot chart of the star cluster.It is reasonable to say that stars with such high luminosity should have left the main sequence and entered evolution in globular clusters and old open clusters.Blue stragglers seem to violate the current standard theory of star evolution, because the stars born at the same time should be clearly located on the same curve line on the Herot chart, and their original masses can be measured according to their positions.Because blue discrete stars deviate from this curve, it shows that they have different experiences in stellar evolution.
The star clusters form in a relatively short time, which means that the stars in the clusters are roughly the same age.Because bright massive stars burn faster and globular clusters are very old, only low-quality stars may still emit light.However, that is not the case.Under certain conditions, the stars in the globular cluster will perform a second spring, obtain additional fuel, and greatly improve the brightness.This phenomenon can only occur when stars absorb neighboring materials or collide.The rejuvenated stars are called "blue discrete stars", and their main characteristics are large mass and high brightness.
As globular clusters age, massive stars begin to move toward the center of the cluster, a process similar to sedimentation.Blue stragglers with larger mass are more likely to "sink".Because of its high brightness, scientists can easily observe it.In order to further understand the aging process of globular clusters, the research team conducted mapping and other observations on the distribution of blue discrete stars in 21 globular clusters.hubble space telescope High resolution imaging was carried out for the crowded center of 20 star clusters, and ground telescopes were responsible for imaging the outer regions with low star density.
By analyzing the observation data, scientists found that some globular clusters looked very young, and blue discrete stars were widely distributed;More globular clusters appear old, and blue discrete stars are concentrated in the middle;Some star clusters are in the aging stage, and the star closest to the core begins to move towards the center.university of bologna Barbara Lanzoni said: "Although these star clusters were formed at about the same time, there are huge differences in the evolution speed. Specifically, for the rapidly aging globular clusters, we believe that the sedimentation process may be completed in hundreds of millions of years, while those globular clusters with the slowest aging speed may need several times the time of the current cosmic age to complete this process."
As the most massive star settles to the center, the core of the globular cluster eventually collapses, and the star density in the center of the cluster reaches an extreme degree.Scientists have a good understanding of the process leading to the collapse of the core. The main factors include the number, density and moving speed of stars.However, the speed of the whole process is still unknown.This study provides the first evidence of how different globular clusters age rapidly.[1]
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There are many explanations about blue discrete stars, mainly including single star theory and multi star interaction theory.At present, it seems that the "rejuvenation" of a single star is unlikely, and only the interaction of multiple stars is more likely.There are two main interpretation models: star collision and mass transfer.
1: Stellar collisionThe merger of two stars will only create a star with greater mass. The surface temperature of this star will be hotter and brighter than that of stars of the same age.If this theory is correct, blue stragglers will not become a theoretical problem of star evolution. The merged star will have more hydrogen in the core, making it behave like a younger star.There is evidence to support this view. The number of blue discrete stars in the cluster is obviously related to the star density. The more dense the stars are, the more the number is, especially in the core area of the globular cluster.Because the more stars in the unit volume, the higher the chance of collision and close contact, and the star cluster is more likely to occur than other regions.
One way to test this hypothesis is to study thePulsating variable star。In astroseismology, the pulsation characteristics of merged stars are different from those of ordinary stars, and the difference may be measured.Although blue discrete stars with small luminosity amplitude can often be found in crowded areas, it is very difficult to measure pulsations in the absence of obvious blue discrete pulsars.
2: Substance transport: A binary star system consisting of a large mass star and a small mass star. The large mass star first evolves into a super giant and fills its Roche radius (the allowable radius of the binary star), thus becoming a pair of half connected binary stars. The red giant star transports material to the small star that has not evolved, and the small star becomes larger in mass, higher in temperature (blue), and higher in luminosity, making it appear to be "left behind"The blue stragglers of.
Recent studies have shown that blue stragglers have less carbon and oxygen than other stars in the nearby region, which means that the heating and blueing of a star is caused by grabbing material from another star in orbit;The stars whose mass is stolen will expose the areas that originally contained heavy elements such as carbon and oxygen in the deep layer to the surface.
Blue stragglers rotate rapidly, usually more than 75 times the sun, and their mass is 2-3 times that of other members of the cluster.
Related reports
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2011.5.25: In the old stellar nuclear sphere of the Milky Way, NASAHubble Space TelescopeOur sharp eye has found a rare strange star - blue straggler.This is the first time that we have found such objects in the nuclear sphere of our galaxy.Blue stragglers are named because they seem to lag far behind the surrounding old stars in evolution (according to the usual evolutionary sequence, such blue stars should have becomeWhite dwarforneutron star).
This discovery is a by-product of a 7-day Hubble Sky Survey project in 2006 - Sagittarius Skylight Transit Extrasolar Planet Search (SWEEPS) project.Hubble gazed at the crowded core of the Milky Way 26000 light years away from us, and obtained the luminosity change information of 180000 stars[2]。
