The Mysterious, Unknown and Strange things of the day.
This thread is about all unknown thing that fascinate you or you are interested about them. Space, different places, strange humans...anything.
Ok, here is the thing to discuss this day.
Mu Cephei, The Garnet Star.
The star of the month this month is the famous, interesting and extremely bright red supergiant in the constellation Cepheus, Mu Cephei. This star may be the largest star visible to the naked eye - it is roughly 2.4 billion miles across! If it replaced our Sun, it would extend beyond the orbit of Saturn. Mu Cep is a slow semiregular variable that is easily visible to the unaided eye in suburban skies when at its maximum brightness of magnitude 3.4, but may be a little more challenging at its minimum of 5.1. The color of the star is quite magnificent and has been the source of some discussion. It is most often described as "a deep red" or "reddish orange" but has sometimes been noted as "orange" and even having "a purplish tint". The most famous observation of Mu Cep comes from Sir William Hershel who commented on its "garnet" color, an observation that lead to the popular name "Herschel's garnet star". William Herschel (1738-1822) was probably the most famous astronomer of the 18th century. He discovered the planet Uranus, many new nebulae, clusters of stars and binary stars, and was the first person to correctly describe the form of our Galaxy, The Milky Way. While writing about the proper motions of the Sun and Solar System in 1783, Herscel noted some stars not listed in Flamstead's well-known star catalogue -- one of which was the bright Mu Cephei. Herschel's "garnet star observation" can be found in the Philosophical transactions of the Royal Astronomical Society of London (1783), in the section called, "Stars newly come to be visible" on page 257 William Herschel writes:A very considerable star, not marked by Flamstead, will be found near the head of Cepheus. Its right ascension in time, is about 2'19" preceding Flamstead's 10th Cephei, and it is about 2o20'3" more south than the same star. It is of a very fine deep garnet colour, such as the periodical star o ceti was formerly, and a most beautiful object, especially if we look for some time at a white star before we turn our telescope to it, such as a cephei, which is near at hand.
Mu Cephei is really big. It is so big that it is one of the largest stars known; estimated to be the third largest star in the sky after its neighbor VV Cephei and the even larger Epsilon Aurigae (both are eclipsing binaries). If you were so inclined, you could fit one billion suns inside mu cephei and have room to spare. It is three times as large as Mira (omi ceti) and much more luminous than the sun. A star of this grandeur deserves no other name than that of supergiant. It is a red supergiant that probably started its life at a substantial 20 to 25 solar masses (a high mass star is considered to be 10 solar masses or more) and has evolved "quickly" (high mass stars burn energy faster than lower mass stars). The life expectancy of a star like Mu Cephei is only around a few million years - short for astronomical time scales.
The evolution of Mu Cephei is probably similar to other high mass stars which Kaler (1997) explains in the following way. It starts by burning hydrogen in its core until there is no more left, it then expands to its current supergiant status. Now helium burning takes place in the core while hydrogen burning continues in the outer shells. Since it is so big, the gravitational energy on the core is great and further nuclear burning can take place. Carbon will be burned to form magnesium then magnesium to silicon and finally silicon to iron. Iron is the end of the road, however, and no energy can be generated by additional fusion. Once the iron core develops, fusion stops. The outward push of hot gases from the interior can no longer counteract the inward pull of gravity so gravity wins. The core collapses, releasing a vast amount of energy in a few seconds. As the core collapses, it first rebounds, sending a shock wave out into the surrounding envelope. The shock wave and a huge number of nearly massless particles called neutrinos push the envelope outward, creating a cataclysmic explosion - a supernova - that can be seen across vast reaches of the universe. The iron atoms break down ultimately to protons and electrons, which merge, producing a ball of neutrons that squeezes to 30 kilometers across: called a neutron star. This is the predicted future of Mu Cephei, it will eventually explode in a huge supernova explosion leaving a supernova remnant with a neutron star or a black hole (Kaler 1997).
Wouldn't you like to help keep the coverage of this star complete? Mu Cep is a relatively easy-to-find variable star located in the jaw area of Cepheus, the King. You can locate it with the naked eye or, in really bad light pollution by working toward it from Alpha with a finderscope. There is an 'a' scale AAVSO Chart for delta cep that has the location of Mu Cep on it.
"According to some observers" writes Burnham, "the star varies in color as well as in light. It usually appears a deep orange-red but on occasion seems to take on a peculiar purple tint. Since human eyes vary in color sensitivity, and since color is affected by atmospheric and instrumental factors, it is still uncertain whether such changes are real." In particular a star's color tends to be most vivid in a small telescope, assuming the aperture is large enough to collect the light necessary for color to be perceived at all. So, in order to fully realize the peculiar tint of the "Garnet Star", use a small telescope or binoculars and take Herschel's advice by comparing the light with a white star such as Alpha Cephei at the time.
Big read, but I can put it short.
That's an really fricking big star.
Discuss.
Mu Cep-Our Sun
Damn, space is interesting.
🙂