Betelgeuse
Betelgeuse, also called α Orionis, is a bright red supergiant star. It is found in the constellation Orion and is the ninth brightest star in the sky. Its characteristic color comes from the low temperatures of its surface (about 3000 K). The evolutionary state of the star is advanced: it has already passed the most important stage of its life, the main sequence, the fuel in its core that provided it with energy (by hydrogen fusion) has already been exhausted, after which it increased its size to today's enormous dimensions. Its luminosity variations are typical of its present as a giant star.
Betelgeuse's surface temperature is relatively low, yet as a supergiant star it is very bright. Although it is Orion's α star, it is not the brightest of the constellation in visible light, as Rigel (β Orionis) surpasses it in this regard; but in red and near-infrared light, Betelgeuse is the brightest.
Etymology
The original name is speculated to come from يد الجوزا, (transcribed as yad al-jawzā, that is, 'the hand of Jauza'), Jauza being a female mythological figure, initially identified by the ancient Arabs in the firmament with Gemini and later associated with the constellation of Orion, the hunter. During the Middle Ages, when the name of the star was transcribed into Latin, the initial Arabic character, "Ya" (ي) from the "y" sound, was misinterpreted as a "Ba" (ب), from a "b" sound, probably because the Arabic script allows "Ya" alter your spelling at word beginnings, and "Yad al-Jauza" became "Bedalgeuze" /ˈbɛtəldʒuːz, ˈbiːtəl-, -dʒuːs/.
In the 1492 Venetian edition of the Alphonse Tables —titled Tabule astronomice Alfonsi Regis— he appears as "Beldelgenze".
Later, during the Renaissance, it was speculated among Western scholars that the original name would have been "Bait al-Jauza," which was intended to mean "Jauza's shoulder" in Arabic, which led to the current form "Betelgeuse"; even so, the correct form of "shoulder" in Arabic it would be كتف (katf).
Pronunciation of the name "Betelgeuse"
It is pronounced, naturally, as it is written. Language specialists represent the pronunciation like this: /beteljéuse/. Other pronunciations originating from other languages belong to such foreign languages, and not to Spanish.
Main features
Betelgeuse is a very large, luminous but medium-temperature star classified as an M1-2 Ia-ab red supergiant. The letter "M" in this designation it means that it is a red star belonging to the star spectral class M and therefore has a relatively low photospheric temperature; The suffix "Ia-ab", in the Yerkes spectral classification scheme, indicates that it is an intermediate-luminosity supergiant, with properties halfway between a normal supergiant and a luminous supergiant. Since 1943, the Betelgeuse spectrum has served as one of the stable anchor points by which other stars are classified.
Betelgeuse was the first star whose diameter could be measured with any accuracy using interferometric techniques; its diameter is between 850 and 905 million kilometers. At its maximum size the star would extend beyond the orbit of Mars. Its mass is 20 times the mass of the Sun. Astrophysicists predict that Betelgeuse will explode as a type II supernova at the end of its life. Some of them affirm, based on the variability shown by the star, that such an explosion could take place in a very close period of time (in the next few thousand years). Other astrophysicists are more conservative and think that it could continue with its current activity for a much longer period.
Recent studies show that, during the last fifteen years, the diameter of Betelgeuse has shrunk by 15%, the reasons for this phenomenon being unknown. Others show that it has a somewhat oval shape.
The Betelgeuse disk has been resolved using the VLT telescope, showing the best image of the star to date. Unlike stars like our Sun, in which the surface of the star is Covered by a multitude of granules (convective cells), in red giant and supergiant stars such as Betelgeuse there are only a small number of them, these structures being responsible for the brightness variations that can be observed in these types of stars.
Betelgeuse is surrounded by a complex-looking nebula made of silicates and dust ejected by the star in stellar flares and convection in its atmosphere, and extends up to a distance of 400 astronomical units.
Betelgeuse, finally, is a runaway star that has been kicked out of the Orion OB1 stellar association.
It is still debated which part of the electromagnetic spectrum (visible, near-infrared (NIR), or mid-infrared (MIR)) produces the most accurate angular measurement. In 1996, Betelgeuse was shown to have a uniform disk of 56.6 ± 1.0 mas. In 2000, the SSL team produced another measurement of 54.7 ± 0.3 mas, ignoring any possible contribution from critical points, which are less noticeable in the mid-infrared. A theoretical allowance for limb darkening was also included, yielding a diameter of 55.2 ± 0.5 plus. The above estimate equates to a radius of about 5.6 AU or 1200 R☉, assuming the Harper 2008 distance of 197.0 ± 45 pc, a figure about the size of the Jovian orbit of 5.5 AU, published in 2009 in Astronomy Magazine and a year later in NASA's Astronomy Image of the Day.
In 2004, a team of astronomers working in the near infrared announced that the most accurate photospheric measurement was 43.33 ± 0.04 plus. The study also presented an explanation for why variable wavelengths from the visible to the mid-infrared produce different diameters: the star is seen through an extended thick, warm atmosphere. At short wavelengths (the visible spectrum) the atmosphere scatters the light, thus slightly increasing the diameter of the star. At near-infrared wavelengths (K and L bands), scattering is negligible, so the classical photosphere can be seen directly; in the mid-infrared, the scattering increases once more, causing the thermal emission from the warm atmosphere to increase the apparent diameter.
Studies with IOTA and VLTI published in 2009 provided strong support for Perrin's analysis, yielding diameters ranging from 42.57 to 44.28 mas with comparatively negligible margins of error. In 2011, a third near-infrared estimate that corroborates the 2009 numbers, this time showing an obscured disk diameter of 42.49 ± 0.06 mas. Consequently, if van Leeuwen's smaller Hipparcos distance of 152 ± 20 pc is combined with Perrin's angular measurement of 43.33 mas, a near-infrared photospheric estimate would be equivalent to about 3.4 AU or 730 R☉. A 2014 paper derives an angular diameter of 42.28 mas (equivalent to a 41.01 mas uniform disk) using H and K band observations made with the VLTI instrument. AMBER.
At the center of this discussion, in 2009 it was announced that the radius of Betelgeuse had shrunk from 1993 to 2009 by 15%, with the 2008 angular measurement equal to 47.0 mas, not far from the estimate by Perrin. Unlike most previous work, this study covered a period of 15 years at a specific wavelength. Previous studies have typically spanned a year or two by comparison and have explored multiple wavelengths, often yielding vastly different results. The decrease in the apparent size of Betelgeuse equates to a range of values between 56.0 ± 0.1 more seen in 1993 to 47 ± 0.1 more seen in 2008, a contraction of almost 0.9 AU in 15 years. What is not fully known is whether this observation is evidence of a rhythmic expansion and contraction of the star's photosphere as astronomers have theorized, and if so, what the periodic cycle might be, although Townes suggested that if a cycle exists It's probably a few decades. Other possible explanations are photospheric bulges due to convection or a star that is not spherical but asymmetric, causing the appearance of expansion and contraction as the star rotates on its axis.
Future of Betelgeuse
Astronomers predict that Betelgeuse will eventually become a Type II supernova, although its mass may be low enough to leave behind a rare oxygen-neon white dwarf, not a neutron star. Opinions are divided on how long it will take for this event to occur: although Betelgeuse is approximately 10 million years old, but due to its great mass it has evolved rapidly, some point out that the current variability of the star would indicate that it is in the "burning" (fusion) of the carbon of its life cycle and therefore will explode sometime in the next 100,000 years. Skeptics disagree with this calculation and believe that the star could survive much longer, around 10 million years..
As of 2014, the most recent theoretical studies suggest that Betelgeuse has recently begun fusing helium in its core and that, after fusing carbon, neon, oxygen, and silicon in this process, it will explode as a supernova within the next 100,000 years. The red supergiant, which would still be brightening and expanding as the branch of red giants ascends, would be between 8 and 8.5 million years old and have a mass of 20 +5
−3 M☉. Depending on its rotation rate at birth, models of stellar evolution for a star in that mass range suggest that Betelgeuse could either remain a red supergiant until exploding as a supernova, or become a red supergiant. before exploding into a luminous blue variable or yellow hypergiant star-like body. The stellar remnant it would leave behind would be a neutron star approximately 1.5M☉.
The event will be, in any case, spectacular, although it is not clear if it will have important effects for life on our planet since Betelgeuse is close to the distance limit at which cosmic rays can significantly affect the ozone layer.
At that time, Betelgeuse would shine at least 10,000 times brighter than an ordinary supernova, with the luminosity of the first quarter Moon. Some sources predict a maximum apparent magnitude to that of the full Moon for several months. It would be an extremely bright point in the sky, which could be observed even during the day. After this period, it would gradually fade away until, after months or perhaps years, it was invisible to the naked eye. Orion's right shoulder would disappear until, after a few centuries, a splendid nebula developed there.
Notably, in 1980, a team of archaeologists discovered first-century Chinese reports referring to the color of Betelgeuse as white or yellow. However, Ptolemy, in a writing from the year 150, classifies it as a red star (although he also classifies Sirius as red, despite the fact that it is white). Therefore, Fang Lizhi, a Chinese astrophysicist, proposes that Betelgeuse could have become a red giant during that period. Stars are known to change color by ejecting a surface layer of dust and gas (a layer that can even now be seen moving away from Betelgeuse). Thus, if this theory is true, it is unlikely that Betelgeuse will go supernova soon, as a star typically remains a red giant for tens of thousands of years.
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