Comets May Not Explain 'Alien Megastructure' Star's Strange Flickering
After All
By Shannon Hall, Space.com Contributor | February 3, 2016 07:30am ET
It's looking less likely that a swarm of comets or an "alien
megastructure" can explain a faraway star's strange dimming.
The star (nicknamed "Tabby's Star," after its discoverer, Tabetha
Boyajian) made major headlines last October when Jason Wright, an
astronomer at Pennsylvania State University, suggested that it could be
surrounded by some type of alien megastructure. A more likely idea — one
that's far less exciting — is that the star is orbited by a swarm of
comets. But scientists can't be sure either way.
Now, Bradley Schaefer, an astronomer at Louisiana State University, has
probed the star's behavior over the past century by looking at old
photographic plates. Not only does the star's random dipping date back
more than a century, but it also has been gradually dimming over that
period — a second constraint that makes it even harder to explain. [13
Ways to Hunt Intelligent Alien Life]
The first signs of the star's oddity came from NASA's planet-hunting
Kepler space telescope, which continually monitored the star (as well as
100,000 others) between 2009 and 2013. Astronomers, citizen scientists
and computers could then search for regular dips in a star's light — a
sign that an exoplanet has passed in front of that star. The largest
planets might block 1 percent of a star's light, but Tabby's star
dropped by as much as 20 percent in brightness. That, in and of itself,
would be weird. But the periodic dimmings didn't occur at regular time
intervals, either — they were sporadic. The signature couldn't be caused
by a planet, scientists said.
In September, a team led by Boyajian, a postdoctoral fellow at Yale
University, tried to make sense of the unusual signal. First, the
researchers looked into any angles that might mean there was something
wrong with the data itself. They even checked in with Kepler mission
scientists. But everything came out clean. "The data that we were
observing with Kepler is, in fact, astrophysical," Boyajian told Space.com.
Still, nothing about the observations indicated what might be causing
the extreme interference. After considering many possible scenarios,
Boyajian determined that dust from a large cloud of comets was the best
explanation. But she admits that "it's a bit of a stretch to have comets
that are large enough to block that much of the light from the star."
With her paper published, she hoped that other astronomers would jump in
with alternative solutions.
And they did. A month later, the star exploded into the public's eye
when Wright announced that an advanced extraterrestrial civilization
could be responsible for the signal, assuming this civilization built a
megastructure, like solar panels, around the star. And Boyajian thinks
the theory is definitely worth a follow-up.
"We have to look at every angle that we can — and that's one angle, as
wild and crazy as it seems," she said. Slate blogger and astronomer Phil
Plait, too, admitsthat "while it's incredibly unlikely, it does kinda
fit what we're seeing."
A follow-up looking for alien signals, however, turned up empty-handed.
So Schaefer turned to old photographic plates from the Harvard College
Observatory. Lucky for him, the star has been photographed more than
1,200 times as part of a repeated all-sky survey between the years 1890
and 1989. That many data points revealed that Tabby's star is acting
strangely in more than one way: It's flickering on short timescales, as
the Kepler and Harvard data show, and it's dimming over the course of a
century, as the Harvard data show.
"Occam's razor [the simplest explanation is likely the best one] needs
to be considered in a scenario like this," Boyajian said. A single
phenomenon must be causing both behaviors, she added. But what is it?
Well, the results don't look good for a family of comets. It would take
a vast number of comets to pass in front of the star for a century,
astronomers say.
"It would be more mass than what we have in the whole Kuiper Belt" [the
band of icy bodies in the vast region beyond Neptune], said Massimo
Marengo, an associate professor of astronomy at Iowa State University
who co-authored a paper supporting the comets theory in December.
"You can get out of that if you assume it's the same family of comets
passing in front of the star over and over," Marengo told Space.com. But
with the century-long dimming trend, too, that family of comets has to
get bigger every time it passes the star. "It's a difficult thing to
do," he said.
The results also change the requirements for the alien megastructure
hypothesis. Plait pointed out that the general fading is actually what
you'd expect to see if aliens were building a massive sphere around
their star. But before you get your hopes up, consider this: Plait
calculated that aliens would need to build a minimum of 750 billion
square kilometers (290 billion square miles) of solar panels to account
for the 20 percent drop in their star's brightness. "That's 1,500 times
the area of the entire Earth," Plait wrote. "Yikes."
So astronomers now have to hope that future observations might shed
light on this stellar oddity. "Nature can help us by creating another
one of these events," Marengo said. "But sometimes, we don't get lucky."
Follow Shannon Hall on Twitter @ShannonWHall. Follow us @Spacedotcom,
Facebook and Google+. Original article on Space.com.
- See more at:
http://www.space.com/31810-alien-megastructure-star-flickering-mystery-continues.html?cmpid=NL_SP_weekly_2016-2-03#sthash.VB7OwOca.dpuf
--
*================================================ Duane Whittingham -
N9SSN (ARES/RACES, EmComm, Skywarn & Red Cross)
http://www.radiodude.info ================================================*
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