-
-
---------------------------- 2399 - RED DWARF STARS - win the survival race
-
- Scientists think that 20 out of the 30 stars near Earth are red dwarfs. The closest star to the sun, Proxima Centauri, we know that it is a red dwarf.
-
- The term "red dwarf" does not refer to a single kind of star. It is frequently applied to the coolest objects, or, brown dwarfs, often referred to as "failed stars" because they do not sustain hydrogen fusion in their cores.
-
- Red dwarfs form like other main-sequence stars. First, a cloud of dust and gas is drawn together by gravity and begins rotating. The material then clumps at the center, and when it reaches the critical temperature, fusion begins.
-
- Red dwarfs include the smallest of the stars, weighing between 7.5% and 50% the mass of the sun. Their reduced size means that they burn at a lower temperature, reaching only 3,500 degrees Celsius. The sun, by comparison, has a temperature of 5,500 C. The low temperatures of red dwarfs mean they are far, far dimmer than stars like the sun.
-
- Their low temperature also means that they burn through their supply of hydrogen less rapidly. While other, more massive stars burn through only the hydrogen at their core before coming to the end of their lifetimes, red dwarfs consume all of their hydrogen, inside and outside their core. This stretches out the lifetime of red dwarfs to trillions of years; far beyond the 10-billion-year lifetime of sun-like stars.
-
- Scientists occasionally have difficulty distinguishing a red dwarf star from a brown dwarf. Brown dwarfs are cool and dim, and likely form the same way red dwarfs do, but brown dwarfs never reach the point of fusion because they're too small, and therefore, they're not considered stars.
-
- To figure out whether a celestial object is a brown or red dwarf, scientists measure the temperature of the object's atmosphere. Fusion-free brown dwarfs are cooler than 1,727 C, while hydrogen-fusing stars are warmer than 2,427 C. In between, a star could be classified as a red dwarf or brown dwarf.
-
- Sometimes, chemicals in the object's atmosphere can reveal clues about what's happening at its heart. The presence of molecules like methane or ammonia, which can only survive at cold temperatures, suggests that an object is a brown dwarf. Lithium in the atmosphere also suggests that a red dwarf is a brown dwarf rather than a true star.
-
- But scientists may still use the term red dwarf to describe how a celestial object looks, small and dim, even if the object is actually a brown dwarf.
-
- Brown dwarfs mix features of stars and planets, but they are their own unique entities.
Planets form from the material left over in a disk after their star has been created. Many red dwarfs have been found with planets surrounding them, though enormous gas giants are rare.
-
- Because red dwarfs are dimmer than stars like the sun, it is easier to find small planets that may surround these dimmer objects, making red dwarfs a popular target for planet hunting.
-
- Since the planets examined are near bright stars that tend to be close to Earth, it's easier for ground telescopes to follow up on the observations. In April 2019, investigators announced they had found the first Earth-size planet, although its conditions are not ideal for life as we know it.
-
- For a long time, scientists thought red dwarfs were uninhabitable. Their limited light and heat meant that the habitable zone , or the region where liquid water could form on planets around a red dwarf, would be very close to the star, putting the planets in range of harmful radiation from the star.
-
- Other planets may be tidally locked to the star, with one side constantly facing their sun, causing one side to be too warm, and the other to be too cold.
-
- In 2016, a potentially habitable planet was found orbiting Proxima Centauri (Earth's closest star). And in 2019, astronomers announced the possibility of a second planet orbiting far outside that star's habitable zone.
-
- At least seven Earth-size planets orbit the red dwarf TRAPPIST-1, and many studies suggest at least some of those planets could host life.
-
- Astronomers have found that 6 percent of all red dwarf stars have an Earth-sized planet in the habitable zone, which is warm enough for liquid water on the planet’s surface. Since red dwarf stars are so common, then statistically the closest Earth-like planet should be only 13 light-years away.
-
- Tiny red dwarfs may have an extended lifetime, but like all other stars, they'll eventually burn through their supply of fuel. When they do, the red dwarfs become white dwarfs. White dwarfs are dead stars that no longer undergo fusion at their core. Eventually, the white dwarfs will radiate away all of their heat and become black dwarfs.
-
- But unlike the sun, which will become a white dwarf in a few billion years, red dwarfs will take trillions of years to burn through their fuel. This is significantly longer than the age of the universe, which is less than 14 billion years old.
-
- Red dwarfs may be a bit dim, but, they slowly but surely win the survival race.
-
- June 10, 2019
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ----
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
- https://plus.google.com/u/0/ -- www.facebook.com -- www.twitter.com
--------------------- Monday, June 10, 2019 --------------------
-----------------------------------------------------------------------------------------
No comments:
Post a Comment