Look into the tur­bu­lent heart of a Scor­pion and you’ll find so much more than mere ra­di­ance.

Australian Geographic - - Contents - FRED WAT­SON is an as­tronomer at the Aus­tralian As­tro­nom­i­cal Ob­ser­va­tory.

Ex­plor­ing a star

HAVE YOU EVER looked at stars through a tele­scope? Chances are you have, be­cause it’s the most ob­vi­ous thing to do with a tele­scope at night after you’ve taken in the Moon and plan­ets.What you saw might, how­ever, have dis­ap­pointed.

Cer­tainly, stars ap­pear brighter through a tele­scope and, when grouped in a clus­ter, can be ra­di­antly beau­ti­ful. You might even be able to de­tect dif­fer­ing colours among them.

But what you won’t see is any de­tail in the stars them­selves. And that goes not just for back­yard view­ing, but for most of the world’s big tele­scopes.The fact is that, with the ex­cep­tion of the Sun, stars are sim­ply too far away to be seen as any­thing other than points of light.They are ‘un­re­solved’, as we say in the trade.

What would be re­quired to am­plify star im­ages into de­tailed discs of light is a big­ger tele­scope.To­day’s largest op­ti­cal tele­scopes have dished mir­rors of about 10m in di­am­e­ter, but you would need one per­haps 20 times big­ger to see features on the sur­face of a star. Such tele­scopes do not ex­ist, yet. But there is a tech­nique known as in­ter­fer­om­e­try that al­lows the wave prop­er­ties of starlight to be used to mimic the ef­fect of a sin­gle big mir­ror by com­bin­ing the light from sev­eral smaller ones.

At the Euro­pean South­ern Ob­ser­va­tory’s Very Large Tele­scope in north­ern Chile, there is a fa­cil­ity known as VLTI (the I is for in­ter­fer­om­e­ter) that works in ex­actly this way.

VLTI has re­cently been used to make the first de­tailed im­age of a star other than the Sun.The tar­get ob­ject was the red su­per­giant star Antares, fa­mil­iar to south­ern stargaz­ers as the heart of the Scor­pion. Antares is known to be los­ing mass and, by mak­ing care­ful mea­sure­ments of its rain­bow spec­trum,VLTI re­searchers have also been able to chart the tur­bu­lent mo­tion of gas in Antares’ ex­tended at­mos­phere.

This ex­tra­or­di­nary achieve­ment paves the way for a com­pletely new branch of as­tron­omy that will ex­plore the sur­faces of stars.

This artist’s im­pres­sion of the star Antares is based on im­ages of un­prece­dented de­tail, con­structed by as­tronomers us­ing the Very Large Tele­scope In­ter­fer­om­e­ter fa­cil­ity.

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