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Science story useful for daily lessons tochildren

 

 

    No more Betelgeuse existing?

 

  

At the shoulder of the constellation Orionwhich is called as the king in winter, a first magnitude, orange star isshining.  That is Betelgeuse, one of manyfirst magnitude stars in winter.  It hasbeen known that the star, red and enormously large, belongs to a type calledthe red supergiant star.  How big is theBetelgeuse?  If we place the star intothe Sun of our solar system, its surface reaches beyond the orbit of theJupiter.  Its diameter is more than 500times that of the Sun, that is beyond our imagination!  By the way, orbit of the Earth isapproximately 100 times the diameter of the Sun.

 

       orion-k2

        ・Orion

 

The modern science began when GalileoGalilei gazed at stars with his invented telescope.  About 400 years since then, now we can tell acourse scenario of the life of stars.

 

 

It is thought that a new star is born wheregas and/or dust are accumulating in the Universe.  Firstly, I talk about the life of a starsimilar to size of the Sun.  The lifespan of a star like the Sun is said to be around ten billion years.  The Sun, that spontaneously emit light calledas a fixed star, generates heat (energy) by nuclear fusion reaction.  At the center of the Sun, four hydrogen atomschange into one helium atom, a reaction called as nuclear fusion, iscontinuously occurring.  Through thereaction, a subtle amount of mass disappears, which is changed into enormousamount of energy.  Ultimately, such astar goes into a stage called as the red giant star, and the fuel isexhausted.  The center of the starshrinks to form a white dwarf star while the dispersed outer part forms aplanetary nebula, which will be scattered around the Universe.  The current age of the Sun is likely to besame as the Solar system that is 4.6 billion years.  Hence, the Sun is middle-aged if it is inhuman life.

 

 

Secondly, as to the star whose initialweight is more than eight times that of the Sun, the nuclear fusion reaction isfacilitated because of the huge mass of the star, therefore the star burns outwithin shorter time, i.e. some ten million years.  Ultimately, such a star becomes the redsupergiant star.  Antares in the Scorpionand Betelgeuse in the Orion are thought to be at this stage. Different from theSun that will burn out gently, the entire red supergiant star explodes that iscalled as the supernova explosion.

 

 

Then, what will happen next?  Our curiosity is limitless, however, let metouch upon the nuclear fusion reaction taking place in a star.  Formerly, I stated that, under the high pressureand high temperature status, four hydrogen atoms get together and form a heliummolecule.  As the helium accumulates atthe center, helium gets together to form a carbon atom.  Furthermore, molecules such as nitrogen,oxygen, neon, silicon are formed and the star will look like an onion.  However, the reaction will not carry oninfinitely.  Finally, iron isformed.  However, energy cannot be takenout from iron.  Once the core of the staris changed to iron, the pressure in the center disappears, and the vast amountof materials forming the star shrinks towards the center of the star, like awaterfall.  Collisions occur at thecenter of the star, and the reactive shock wave is conducted throughout theentire star body, which blows up the star: this is the supernova explosion.

 

 

Hydrogen is the simplest element, followedby helium.  When the universe began,there were only these two element existing in the Universe.

 

I formerly mentioned that a variety ofelements are formed in the star, which ends up with iron.  However, there are many elements heavier thaniron in the Universe.  It is thought thatelements heavier than iron are formed on the occasion of supernova explosionand they will be scattered around the Universe. One of the purpose of the observation of supernova explosion is toconfirm such theory.

 

 

What will happen after the supernovaexplosion?  There are two cases dependingon the initial weight of the star.  Ifthe weight is relatively light, a neutron star, which is extremely dense, isformed.  The neutron star emits highfrequency electric wave because of the rapid revolution.  This phenomenon is called as the pulsar, andthe neutron star was discovered from this phenomenon.  When the heavier star causes the supernovaexplosion, it eventually forms the black hole. Due to the very strong gravity, even the light, i.e. every information,cannot escape from the black hole.

 

     betelgius-1

       ・Betelgeuse

 

Betelgeuse has a mass (weight) 20 timesthat of the Sun and is a great red supergiant star.  Ordinarily, the fixed stars are so far awaythat we cannot measure their apparent diameter. However, there are some exceptions such as Betelgeuse.  Among such exceptional stars, Betelgeuse hasthe largest apparent diameter.  It isalso observed that the brightness of the star is changing semi-regularly, whichis called as the pulsating variable light. This means that the star is unable to emits light with the constantbrightness any longer.

According to NASA’s observation in 2010,Betelgeuse was deformed.  This may meanthat the surface of the star has become rough and a part is draining from thestar.  In other words, such phenomenonmay indicate the prelude of the supernova explosion.  It may be possible that Betelgeuse hasexploded already.

Since the Universe is extensively large, ittakes time for the light of explosion of a faraway star to reach theEarth.  Although the light is the fastestin the Universe, running seven and a half times around the Earth surface persecond, the speed has a limit.  Forastronomical distance, we use a scale “light year”, that is the distance thelight travels for one year.  For example,if a star one light year away explodes, it will reach the Earth, i.e. we cansee, one year later.

 

 

The light travels approximately 0.3 millionkilometers per second in the vacuum space. The distance between the Earth and the Moon is about 0.38 millionkilometers, therefore it takes about 1.3 seconds for the light to travelbetween these two planets.  The Moon thatyou gaze at the night sky is about 1 second before.  Similarly, the Sun, which is 0.15 billion kmaway from the Earth, that we watch is about eight minutes before.

 

How far is it from the Earth to Betelgeusein light years?  According to the recentdata, it is approximately 640 light years. Hence, if the star abruptly causes the supernova explosion now, it can beobserved on the Earth 640 years later. Any person currently on the Earth will be unable to see the explosion.

 

 

However, we cannot deny a possibility thatthe star has exploded.  If this is thecase, the explosion will be about 400 years after the previous supernovaexplosion in our Galaxy.  It is said thatthe explosion is as bright as the full moon and lasts for about two months,however, since there are several different types in the supernova explosion, itis very interesting to see how it looks like. Although nobody knows when the supernova explosion occurs, it can betomorrow.

 

 

 

[Distance to Betelgeuse]

489 light years: Rika Nenpyo, 2018.

430 light years: Tenmon Nenkan, 2018.

642.53  146.77 light years: Wikipedia.

640 light years: A book edited by Prof.Katsuhiko Sato.

 

 

 

   fuji-1214-4

      Gekko Astronomical Observatory

 

 


       
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