Red dwarf stars

When you look up into the night sky, you never see red dwarfs. They re faint because of their small size and low temperature. Only the nearest red dwarf stars, up to about 90 light-years away, are visible to even the most powerful earth-based telescopes. Proxima Centauri, a member of the Alpha Centauri triple star system, is a red dwarf, and we ve discussed that it is the closest star to the Earth. Despite its proximity, it is a hundred times too faint to see with the naked eye. In contrast, we can see many larger stars using our eyes, even when these stars are thousands of light-years away. 

Astronomers have found about 450 young red dwarf stars within 80 light-years of the Earth. This means that there are more red dwarfs closer to Earth than all the other types of stars combined. Some astronomers suggest that red dwarfs are the most common type of star in the Universe.12 Others suggest that even cooler brown dwarfs are the most common star, but they are so dim they are more difficult to detect (figure 8.7). 

M Class Star The most common class of stars. These are red dwarf stars and are relatively small and cool. 

Barium stars were recognized as a distinct group of peculiar stars by [1], The objects initially included in this group were red giants of spectral type G and K, which showed strong lines of s-process elements, particularly Ba II and Sr II, as well as enhanced CH, CN and C2 bands. The discovery that HR 107, a dwarf star, shows a composition similar to that of a mild Barium giant by [6] has pushed the search for new Barium dwarfs. 

Dwarf Spheroidal galaxies are the smallest and faintest galaxies known. They are typically dominated by old stellar populations (e.g. Sculptor and Sextans), but some of them (e.g. Fornax) exhibit more recent star formation episodes (2-8 Gyr ago). Analysis of the horizontal branch morphology shows that Red HB stars are more centrally concentrated than Blue HB stars which could be interpreted either as an age or a metallicity gradient or both ([1]). Only spectroscopic observations can unambiguously separate metallicity gradients and make a link with the kinematics. 

To everyone s surprise, no event lasting less than two weeks has ever been observed. The mean mass inferred is half the solar mass, which rules out brown and red dwarfs but favours white dwarfs. However, too many of these remnants from intermediate-mass stars (1-8 Mq at birth) would contradict the traditional tenets of astrophysics. Indeed, it would imply a frenzied spate of nucleosynthesis during the formation of the galactic halo. The nature of the compact massive objects thus remains a mystery. 

A magnification of the H-R diagram in figure 5.3 can be quite instructive. Figure 5.8 shows the 50 nearest known stars to Earth, with the sizes of the stars indicated by the size of the circles. Looking at the plot, you can see that most of the Sun s nearest neighbors are relatively small stars, the slow-burning red dwarfs. 

Bob washes his faces and hands and returns to the chariot. This solar equilibrium almost seems to be a miracle. If gravity were much stronger or much weaker, this balance between gravitational force and the outward pressure of gas would be disturbed. For example, if the gravity was off by just a little bit, nature would tend to produce more extreme stars—hot blue giants or cool, dim red dwarfs— neither of which seem very conducive to the evolution of life. 2... 

My father had no idea, so I had to wait a few decades until 1 learned the answer. In about a hundred trillion years, the last generations of stars will have been born, and the few remaining red dwarfs will die. Let s digress for a moment and discuss red dwarfs before talking about the end of the Universe. We ve mentioned red dwarfs a few times in this book without giving a detailed description of what they are. 

Red dwarfs Small, cool, very faint, Main Sequence star. Surface temperature is less than 4,000 K. Some speculate that these are the most common type of star in the Galaxy. The nearest red dwarf is Proxima Centauri. Red dwarfs are not visible to the naked eye and are about 0.08 to 0.43 solar masses. 

There are also brown dwarfs to consider. Brown dwarfs are astronomical objects somewhat between a planet and a star and have a mass less than 0.08 times the mass of our sun and a surface temperature below 2,500 K. (As comparison, the cool red dwarfs are about 3,000-3,400 K). A large number of brown dwarfs would not change how bright the Galaxy appears in optical observations but would change its total mass quite substantially. 

Like many red dwarfs, Proxima or Alpha Centauri C is a flare star. Flare stars can brighten suddenly to many times their normal luminosity. The cause is thought to be a sudden and intense outburst of radiation on or above the star s surface. An increase in radio emission is often detected simultaneously with the optical outburst. 

A related question is this Which types of stars or supernova explosions produce the extinct radioactive nuclei thatare found in the solar system Here the reader is referred to the entry for each specific isotope. But this much must be appreciated first. Some radioactivities appear to be made primarily by the thermonuclear explosions of white-dwarf stars, called Type la supernovae. Others are created primarily in massive stars whose cores collapse to become neutron stars to initiate an explosive ejection (Type II supernovae). Type II supernovae occur three to five times more frequendy than do Type la supernovae. Some radioactive nuclei are made within differing portions of each event, some prior to the ejection, but some during the heat of the ejection process. And still other radioactive nuclei are created within evolved stars that do not become supernovae (red giants). This diversity of origin renders uncertain the identity of those extinct radioactivities that are to be attributed specifically to that supernova thatis supposed to have triggered the formation of the solar system. In recent scientific... 

The composition of the sun determines how the sun works and evolves over time, as composition influences the interior structure of the sun. Although the Sun is mainly composed of H and He, other heavy elements such as C, N, O, Ne, Fe, etc., are important opacity sources that influence the energy transport out of the sun through radiation and convection. The sun is a typical main sequence dwarf star and its composition is a useful baseline for comparison to abundances in other dwarf stars and to changes that appear in advanced stages of stellar evolution. For example, relative to the suns composition, red giant stars show observable abundance variations that are the result of... 

The solar system abundances are a useful local galactic abundance standard because many nearby dwarf stars are similar in composition however, in detail there are some stochastic abundance variations (e.g [1,2,3,5]). The term cosmic abundances should be avoided because abundances generally decrease with galactocentric distance. There are also abundance differences between our galaxy and galaxies at high red-shift hence there is no generic cosmic composition that applies to all cosmic systems. 

Reid N. and Hawley S.L. New Light on Dark Stars Red Dwarfs, Low-Mass Stars, Brown Stars. 2" edition. Springer Verlag Berlin, 2005. 

This small class of unique stars presents the opportunity to study the structure and behavior of matter in extremely strong magnetic fields. It is well known that these systems eonsist of eompact objects and red dwarfs. The general... 

He lifted his gaze above the flames darting out of the brazier. A vermillion sky was visible through the gaping rents in the broken window. Less than a dozen first magnitude stars twinkled above the wolds, the rest of the universe had been washed out in the red dwarf s sullied glow. The tiny blue-white lights seemed so delicate and pure. 

All of the elements heavier than Fe can only be formed in super massive stars as a result of nuclear fission, followed by neutron capture (smaller stars will eventually burn themselves out to form White Dwarfs, as shown in Figure 2.15). In these larger Red Supergiant stars, which have lifetimes of several million years, the heavier elements are formed gradually over thousands of years by the s-process (where the abbreviation s signifies slow). The s-process Increases A by a series of neutron... 

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