So, no, prob­a­bly not a mega-gi­ant alien space­ship

The Washington Post - - POLITICS & THE NATION - BY BEN GUAR­INO ben.guar­ino@wash­post.com

Four­teen hun­dred light-years sep­a­rate Earth from the strangest star in the sky. The light from this star flick­ers, like a gi­ant neon sign drift­ing through the con­stel­la­tion Cygnus. The star dims for days or weeks, then bright­ens again.

Now a 200-strong team of sci­en­tists says it has ar­rived at an ex­pla­na­tion for the strange be­hav­ior, thanks to an as­tron­omy project crowd­funded on Kick­starter. It’s not aliens, as some peo­ple have spec­u­lated, but prob­a­bly a cloud of dust.

In 2015, as­tro­physi­cist Ta­betha Boy­a­jian pub­lished a pa­per de­scrib­ing the starlight dips. The bright­ness di­min­ished by 20 per­cent, ac­cord­ing to ob­ser­va­tions from the Ke­pler Space Tele­scope. Plan­ets block starlight when they pass across stars, like a hand waved in front of a flash­light. But even an ob­ject as huge as Jupiter can re­duce a star’s bright­ness by just 1 per­cent.

“It truly is some­thing ex­tra­or­di­nary,” said Tyler El­lis, a PhD stu­dent who, along with Boy­a­jian, works at Louisiana State Univer­sity and stud­ies this star and oth­ers.

The star, a yel­low-white dwarf la­beled KIC 8462852, was un­usual enough to get a nick­name, “Tabby’s Star,” af­ter Boy­a­jian. It earned its own Red­dit fo­rum.

And the star was so cu­ri­ous that Ja­son Wright, an as­tronomer at Penn­syl­va­nia State Univer­sity, floated the most ex­otic ex­pla­na­tion avail­able to as­tronomers — aliens. Per­haps ex­trater­res­tri­als had con­structed a ti­tanic ar­ray of so­lar pan­els around the star.

But when as­tronomers with the SETI In­sti­tute aimed their ra­dio tele­scopes at Tabby’s Star, they heard no signs of life.

Mean­while, Boy­a­jian and her col­leagues wanted to go be­yond the Ke­pler data and watch the star dip in real time. They pre­dicted the star would dim on a 750-day cy­cle. But, to be sure, they needed to con­tin­u­ously col­lect images each night, in a va­ri­ety of ranges across the light spec­trum.

A public Kick­starter cam­paign col­lected $100,000 to pur­chase tele­scope time at a pri­vate fa­cil­ity called Las Cum­bres Ob­ser­va­tory, and the hunt be­gan through the lens of the Cal­i­for­nia tele­scope.

The star be­gan dim­ming in May. As­tronomers nick­named the event Elsie (a pun on “L-C,” for “light curves,” as well as the tele­scope ob­ser­va­tory’s ini­tials). Be­tween May and De­cem­ber, the star's bright­ness dimmed three other times, each dip last­ing sev­eral days to weeks.

The sci­en­tists probed the Elsie se­quence in mul­ti­ple color bands. “We had blue light, red light and yel­low light,” Boy­a­jian said, a broader range of light than Ke­pler’s ob­ser­va­tions.

What­ever sub­stance ex­ists be­tween us and Tabby’s Star blocks more blue light than red light, as Boy­a­jian, El­lis, Wright and other re­searchers re­ported in the Astro­phys­i­cal Jour­nal Let­ters on Wed­nes­day. Plan­ets would be un­likely to cre­ate the dips. “If you have some­thing that is com­pletely opaque like a planet, you would ex­pect all the colors of the light to be blocked out at the same lev­els,” Boy­a­jian said. Like­wise, the dis­cov­ery also rules out alien in­dus­try.

“The se­lec­tive ab­sorp­tion of blue light has to point to dust,” El­lis said. Very small par­ti­cles could block blue light’s shorter wave­lengths while al­low­ing red light, which has longer wave­lengths, to es­cape.

If it is dust, the cloud has not spread far be­yond its point of ori­gin, the au­thors noted in the pa­per. A ring of dust around the star would con­stantly block starlight rather than dim light in bouts. And the amount of dust needed is more than Tabby’s Star should pro­duce.

So even with a nat­u­ral cause for its dips, Tabby’s Star is still mys­te­ri­ous.

“We are not done,” El­lis said. “We are cer­tainly not done with this star yet.”

More at wash­ing­ton­post.com/ news/ speak­ing-of-sci­ence

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