{"id":30845,"date":"2022-04-08T07:51:25","date_gmt":"2022-04-08T07:51:25","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=106864"},"modified":"2022-04-08T08:05:15","modified_gmt":"2022-04-08T08:05:15","slug":"a-guide-to-star-betelgeuse","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/a-guide-to-star-betelgeuse\/","title":{"rendered":"A guide to star Betelgeuse"},"content":{"rendered":"

<\/p>

By Anton Vamplew\n \t\t<\/p>

Published: Friday, 08 April 2022 at 12:00 am<\/p>

\n\n

Betelgeuse is one of the most well-known stars in the night sky, and is in fact one of the more massive stars in our part of the Universe.<\/span><\/p>\n

Its Bayer designation \u03b1 Orionis, or Alpha Orionis, most stargazers know the star as its Arabic name, Betelgeuse, translated affectionately into English as \u2018the armpit of the giant\u2019.<\/span><\/p>\n

This definition gives a hint of its location if you know the pattern of the stars in the constellation of Orion<\/a>, the Hunter.<\/span><\/p>\n

Although most English-speaking astronomers today would more likely refer to Betelgeuse as being the shoulder of Orion.<\/p>\n

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Betelgeuse. Credit: Decin Herschel<\/span><\/figcaption><\/div>\n

How to pronounce Betelgeuse<\/strong><\/h2>\n

There is some debate in astronomy circles as to how the star Betelgeuse\u2019s name should be pronounced.<\/p>\n

Many people prefer to pronounce Betelgeuse as \u2018Beetlejuice\u2019, like the titular character played by Michael Keaton in Tim Burton\u2019s 1988 horror comedy.<\/p>\n

But astronomers are most likely to pronounce Betelgeuse with a soft \u2018G\u2019 like BEH-TEL-GUHZ or with a hard \u2018G\u2019 like BEH-TEL-JUHZ.<\/p>\n

How to find Betelgeuse in the night sky<\/strong><\/h2>\n
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Orion\u2019s Belt by Davy Cannon, Hamilton, Scotland, UK.<\/span><\/figcaption><\/div>\n

Even if you are unfamiliar with Orion, you may have heard of Orion\u2019s Belt.<\/span><\/p>\n

This is made up of three stars close together, of roughly equal brightness, in a line. Once you\u2019ve found Orion\u2019s Belt, it\u2019s easy to star-hop<\/a> to Betelgeuse.<\/span><\/p>\n

If you look a short way above the top left of the Belt stars, your gaze will settle upon a particularly bright and reddish star. This is Betelgeuse.<\/span><\/p>\n

Betelgeuse is the main star of Orion, which is why its technical designation is Alpha Orionis.<\/span><\/p>\n

Depending on how dark your location is (the darker the better) you should be able to make out that reddish colour to Betelgeuse. This is because Betelgeuse is a red giant star.<\/span><\/p>\n

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Betelgeuse and Rigel. Credit: iStock<\/span><\/figcaption><\/div>\n

To appreciate Betelgeuse\u2019s reddish colour you can compare it with another star in Orion. <\/span><\/p>\n

This star is called Rigel and it has a bluish tinge. You can find it by looking to the lower-right of the Belt.<\/span><\/p>\n

If you flip your gaze between these two stars, the colours may be more apparent. Find out more about the colour of stars<\/a> with our guide on why some stars are red and some stars are blue<\/a>.<\/span><\/p>\n

Betelgeuse\u2019s dimming<\/strong><\/h2>\n

Words: Emily Cannon<\/em><\/p>\n

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ESO\u2019s Very Large Telescope images of Betelgeuse. Left: January 2019, before dimming. Right: December 2019, during dimming. Credit: ESO\/M. Montarg\u00e8s et al.<\/span><\/figcaption><\/div>\n

\u00a0<\/p>\n

Arguably the most famous of the red supergiants, Betelgeuse continues to give us a unique insight into the workings of the largest stars in the Universe.<\/span><\/p>\n

On 7 December 2019 an Astronomer\u2019s Telegram (which these days is announced via email and Twitter) claimed that Betelgeuse was dimming, followed by news in February 2020 that Betelgeuse was brightening again<\/a>.<\/span><\/p>\n

As Betelgeuse is a variable star<\/a> it is not unusual to see variations in its brightness.<\/span><\/p>\n

However, on this occasion the brightness of Betelgeuse was continuing to fall far below that of what was expected and the dimming became so apparent that it was even noticeable by eye in the night sky.<\/span><\/p>\n

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The variability of Betelgeuse is seen in this image captured by Amanda Cross: a composite showing Betelgeuse\u2019s apparent movement across the sky. Credit: Amanda Cross.<\/span><\/figcaption><\/div>\n

Within two weeks of the telegram, our team, led by Dr Miguel Montarg\u00e8s, submitted a proposal and was granted time to observe Betelgeuse with the SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument, among others, at the European Southern Observatory\u2019s Very Large Telescope in Chile\u2019s Atacama Desert.<\/span><\/p>\n

The high angular resolution capabilities of SPHERE allow us to resolve the surface of Betelgeuse, which means that the star no longer looks like a point source and we can distinguish surface features.<\/span><\/p>\n

It was clear from the images we obtained on 27 December 2019 that there was a drop in brightness in the southern part of the star when compared to observations from January 2019.<\/span><\/p>\n

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A view of Chile\u2019s famous Very Large Telescope, located in the Atacama Desert of northern Chile. Image Credit: Y. Beletsky (LCO)\/ESO<\/span><\/figcaption><\/div>\n

But what could have caused this dramatic change in Betelgeuse\u2019s brightness? Much of the physics of red supergiants is still uncertain, so multiple causes are being explored.<\/span><\/p>\n

The fact that part of the surface is at a cooler temperature could be due to the convective activity of the star, or because a clump of dust has been ejected in our direction.<\/span><\/p>\n

This dust theory would not be too unexpected as Betelgeuse has already been observed to have a clumpy outer wind, just like many other red supergiants.<\/span><\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Betelgeuse can be seen as the left shoulder of the winter constellation Orion. Credit: Bernhard Hubl \/ CCDGuide.com<\/span><\/figcaption><\/div>\n

Does this dimming mean Betelgeuse is about to go supernova<\/a>? It is unlikely.<\/span><\/p>\n

The final nuclear reaction sequences that happen within the star have such short timescales that their light would not reach the surface before the explosion occurred, so we don\u2019t expect to see changes in brightness pre-supernova.<\/span><\/p>\n

As we watch Betelgeuse regain brightness it is important to note that without the help of amateur astronomers in observing and documenting this star each day, much of this science would not be possible and events like this could be missed.<\/span><\/p>\n

Could Betelgeuse go supernova and explode?<\/strong><\/h2>\n

Words: Paul Cockburn<\/em><\/p>\n

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Multiwavelength composite image (x-ray, radio and optical) of supernova remnant Cassiopeia A. Credit: X-ray: NASA\/CXC\/SAO; Optical: NASA\/STScI; Radio: NSF\/NRAO\/VLA<\/span><\/figcaption><\/div>\n

All stars are powered by fusion, initially the \u2018burning\u2019 of hydrogen into helium.<\/p>\n

Once the supply of hydrogen runs out a star continues to shine by burning helium into heavier, denser elements, such as carbon and oxygen.<\/p>\n

As this process continues, the energy generated by the fusion begins to lose a long-standing battle against the star\u2019s own gravity, drawing in material to the core.<\/p>\n

The final point of collapse happens in a matter of seconds, leading to a massive explosion as matter rebounds off the core. The result can outshine a galaxy, but generally don\u2019t last for long.<\/p>\n

What\u2019s left behind largely depends on how large the star originally was: it can be a neutron star<\/a>, which is extremely dense, or even a black hole<\/a>\u2014so dense that not even light can escape from its gravity.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Tycho is an example of a supernova remnant; what\u2019s left after a star goes supernova. Credit: Chandra X-ray Observatory, Sloan Digital Sky Survey<\/span><\/figcaption><\/div>\n

Astronomers believe that supernovae not only help spread heavier elements throughout the Universe, but the pressure from the explosion can even encourage new star formation elsewhere.<\/p>\n

For more on this, listen to our podcast interview with supernova scientist Or Graur<\/a>.<\/p>\n

\u201cProbably everything below 20 solar masses makes a neutron star,\u201d says Dr Matt Nicholl<\/a>, a Royal Astronomical Society Research Fellow.<\/p>\n

Betelgeuse, which is estimated to be around 15 solar masses, is one of the most prominent stars in the night sky, clearly visible from both the northern and southern hemispheres.<\/p>\n

\u201cThe radius of Betelgeuse is probably about 900 times the radius of the Sun,\u201d says Matt Nicholl about the red supergiant star, \u201cwhich means that, if you stuck it in the middle of our Solar System, its surface would extend out beyond Jupiter<\/a>!<\/p>\n

\u201cWe know the distance to Betelgeuse is around 650 lightyears \u2013 plus or minus 50 \u2013 but the big uncertainty in all of this is the distance, because it\u2019s very hard to measure distance in space.<\/p>\n

\u201cIf we knew exactly how far away it is, we\u2019d know almost exactly how luminous it was and therefore how massive it was.<\/p>\n

\u201cWe\u2019d have a better idea of when it will explode too, because if we knew the mass and luminosity more accurately, we\u2019d also know the age more accurately.\u201d<\/p>\n

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Betelgeuse, as seen by the Atacama Large Millimeter\/submillimeter Array (ALMA).<\/span><\/figcaption><\/div>\n

Much of Matt Nicholl\u2019s research focusses on a rare class of superluminous supernovae, but he\u2019s pretty pessimistic about Betelgeuse exploding any time soon.<\/p>\n

\u201cBetelgeuse is a known variable star,\u201d he says. \u201cIt has periodic variations; it has semi-random-looking non periodic variations, and it\u2019s probably at least three different things that cause these different variations.<\/p>\n

\u201cThese giant stars pulse; their envelope inflates and deflates in response to things that are happening at the core\u2014when it gets bigger it looks brighter, so that\u2019s one thing.<\/p>\n

\u201cThere\u2019s also a lot of convection in these big envelopes, so you get hotspots that come to the surface, so also look brighter.<\/p>\n

\u201cThey also eject a lot of material\u2014their stellar wind is much more powerful than our solar wind. The gas that gets away from the star can cool down and make dust which can obscure our view for a period of time.<\/p>\n

\u201cSo all these things, and probably other things we don\u2019t know about, cause the brightness to go up or down.<\/p>\n

I think the preferred interpretation from astronomers is that all the different processes that make it go up and down are all in the down state at the minute.\u201d<\/p>\n

Not that he believes dimming is a prelude to a supernova explosion.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
This mosaic of stars Rigel, Betelgeuse and Sirius was created by capturing images 60 seconds apart to compare the differences in colour, caused by Earth\u2019s atmosphere splitting the starlight and the process being picked up by the DSLR camera. Credit: Amanda Cross<\/span><\/figcaption><\/div>\n

\u201cAs these massive stars get towards the end of their lives, they\u2019re burning fuel in the core faster and faster, and producing more heat; I don\u2019t think there\u2019s any expectation that it should get fainter now.\u201d<\/p>\n

While Betelgeuse is certainly expected to go supernova at some point \u201csoon\u201d, this is a relative term.<\/p>\n

\u201cOur best guess is that Betelgeuse \u2013 based on what we think the distance is, and what we think the luminosity is \u2013 will have finished hydrogen burning and is now burning helium into carbon and oxygen, which takes a few hundred thousand years.\u201d<\/p>\n

That said, Matt would love Betelgeuse to explode during his lifetime.<\/p>\n

\u201cIf Betelgeuse did explode, it would be a star about as bright as the full Moon, so it would be pretty fantastic. The Moon is spread out over a disc; a point that bright would be really impressive.\u201d<\/p>\n

For Betelgeuse to explode \u2018now\u2019, the actual supernova would have to occur some 650 years ago, given the time needed by light to reach us.<\/p>\n

We would, however, at least get some warning: gravitational waves and neutrinos, unlike light, escape the star immediately.<\/p><\/body><\/html>\n

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By Anton Vamplew Published: Friday, 08 April 2022 at 12:00 am Betelgeuse is one of the most well-known stars in the night sky, and is in fact one of the more massive stars in our part of the Universe. Its Bayer designation \u03b1 Orionis, or Alpha Orionis, most stargazers know the star as its Arabic […]<\/p>\n","protected":false},"author":24,"featured_media":30846,"template":"","categories":[1],"acf":{"readingTimeMinutes":"9"},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/04\/a-guide-to-star-betelgeuse.jpg",1500,999,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/04\/a-guide-to-star-betelgeuse-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/04\/a-guide-to-star-betelgeuse-300x200.jpg",300,200,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/04\/a-guide-to-star-betelgeuse-768x511.jpg",768,511,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/04\/a-guide-to-star-betelgeuse-1024x682.jpg",800,533,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/04\/a-guide-to-star-betelgeuse.jpg",1500,999,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/04\/a-guide-to-star-betelgeuse.jpg",1500,999,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"By Anton Vamplew Published: Friday, 08 April 2022 at 12:00 am Betelgeuse is one of the most well-known stars in the night sky, and is in fact one of the more massive stars in our part of the Universe. Its Bayer designation \u03b1 Orionis, or Alpha Orionis, most stargazers know the star as its Arabic…","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed\/30845"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/types\/rss_feed"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/users\/24"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/30846"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=30845"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=30845"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}