Mysterious clumps of matter around star

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Re: Mysterious clumps of matter around star

Unread postby allynh » Tue Aug 09, 2016 8:45 am

Here's another arxiv paper from August 2016

Triple signal of ‘alien megastructure’ star baffles astronomers ... tronomers/
Comet swarm
Comet swarms: just one suggested explanation for strange signals from the “alien megastructure” star
By Shannon Hall

The mystery of the so-called “alien megastructure” star just deepened.

KIC 8462852, as it is more properly known, flickers so erratically that one astronomer has speculated that nothing other than a massive extraterrestrial construction project could explain its weird behaviour. A further look showed it has been fading for a century. Now, fresh analysis suggests the star has also dimmed more rapidly over the past four years – only adding to the enigma.

“It seems that every time someone looks at the star, it gets weirder and weirder,” says Benjamin Montet at the California Institute of Technology, who led the study.

This space oddity was first spotted by NASA’s Kepler space telescope, which continually monitored 100,000 stars from 2009 to 2013. Any dip observed in a star’s light is a sign that an exoplanet has passed in front of it. These dips, which occur regularly, block at most 1 per cent of the star’s light and have revealed thousands of exoplanets.

But KIC 8462852, also known as Tabby’s star after its discoverer Tabetha Boyajian of Yale University, was an outlier. Its light dipped by as much as 20 per cent and didn’t conform to any regular time intervals – so the signature couldn’t have been caused by a planet.

Astronomers came up with an array of potential explanations, from the mundane to the bizarre. The star made headlines when Jason Wright, an astronomer at Pennsylvania State University, announced that an advanced extraterrestrial civilization could be responsible for the signal.

Curiouser and curiouser

But the plot thickened when Bradley Schaefer, at Louisiana State University in Baton Rouge, probed the star’s behaviour over the past century by looking at old photographic plates from 1890 to 1989. More than 1200 images revealed that Tabby’s star gradually dimmed by as much as 15 per cent over the course of a century.

Schaefer’s work was immediately called into question. However, with so few astronomers who have an expertise in these plates, no one seemed able to settle the debate. That is until Montet and his advisor Josh Simon realised that an answer might be hidden within the Kepler data.

They found that for the first 1000 days of the Kepler mission, Tabby’s star decreased in brightness at roughly 0.34 per cent a year – twice as fast as measured by Schaefer. What’s more, over the next 200 days, the star’s brightness dropped another 2.5 per cent before beginning to level out. It was a much more rapid change than before.

That means the star undergoes three types of dimming: the deep dips that first made it famous, the relatively slow decline observed by Schaefer and verified by Montet and Simon, and the intermediate rapid decline that occurred over a few hundred days.

“We can come up with scenarios that explain one or maybe two of these, but there’s nothing that nicely explains all three,” says Montet.

And the team doesn’t want to resort to creating three separate scenarios. “It would be much more satisfying to think of a single physical cause that could be responsible for all of the brightness variations that we observe,” says Simon. “But we’re still struggling to come up with what that might be.”

And Wright couldn’t be more thrilled. “I was always worried that the mystery would be solved with some really mundane explanation, like some overlooked instrumental effect, and that it would turn out to be a wild goose chase,” he says.

Explanations range from a swarm of comets orbiting the star to an intervening cloud in the interstellar medium – but none fit all the data.

An alien concept

What about that advanced alien megastructure? “Once you’re invoking arbitrary advanced aliens doing something with technology far beyond ours, then there isn’t very much that can’t be explained,” says Simon. “But we don’t really want to resort to that until we exhaust all of the possible natural explanations we can think of.”

Even Wright, the astronomer who postulated the alien megastructure in the first place, admits that it’s a last resort.

In the meantime, astronomers will continue to monitor the star. A successful crowdfunding campaign earlier this year raised over $100,000, allowing astronomers to secure time at the Las Cumbres Observatory Global Telescope Network, where they can observe the star for a year.

The hope is that Tabby’s star will soon drastically dim and they will be able to swing different ground-based and space-based observatories towards it. Catching a transit in as many wavelengths as possible should help pin down what is interfering with the star – be it a swarm of comets, an alien megastructure, or something else entirely.

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Re: Mysterious clumps of matter around star

Unread postby allynh » Mon Jul 10, 2017 2:09 pm

Another Possibility for Boyajian’s Star ... ians-star/
Susanna Kohler7 July 2017
The unusual light curve of the star KIC 8462852, also known as “Tabby’s star” or “Boyajian’s star”, has puzzled us since its discovery last year. A new study now explores whether the star’s missing flux is due to internal blockage rather than something outside of the star.

Mysterious Dips

comets around a star

Most explanations for the flux dips of Boyajian’s star rely on external factors, like this illustrated swarm of comets. [NASA/JPL-Caltech]

Boyajian’s star shows unusual episodes of dimming in its light curve by as much as 20%, each lasting a few to tens of days and separated by periods of typically hundreds of days. In addition, archival observations show that it has gradually faded by roughly 15% over the span of the last hundred years. What could be causing both the sporadic flux dips and the long-term fading of this odd star?

Explanations thus far have varied from mundane to extreme. Alien megastructures, pieces of smashed planets or comets orbiting the star, and intervening interstellar medium have all been proposed as possible explanations — but these require some object external to the star. A new study by researcher Peter Foukal proposes an alternative: what if the source of the flux obstruction is the star itself?

Analogy to the Sun

Decades ago, researchers discovered that our own star’s total flux isn’t as constant as we thought. When magnetic dark spots on the Sun’s surface block the heat transport, the Sun’s luminosity dips slightly. The diverted heat is redistributed in the Sun’s interior, becoming stored as a very small global heating and expansion of the convective envelope. When the blocking starspot is removed, the Sun appears slightly brighter than it did originally. Its luminosity then gradually relaxes, decaying back to its original value.
fig3-1-260x180.jpg (17.68 KiB) Viewed 792 times

Model of a star’s flux after a 1,000-km starspot is inserted at time t = 0 and removed at time t = ts at a depth of 10,000 km in the convective zone. The star’s luminosity dips, then becomes brighter than originally, and then gradually decays. [Foukal 2017]

Foukal recognized that this phenomenon may also provide an explanation for Boyajian’s star. He modeled how this might occur for Boyajian’s star, demonstrating that if its flux is somehow blocked from reaching the surface and stored in a shallow convective zone, this can account for the 20% dips seen in the star’s light curve.

In addition, these sporadic flux-blocking events would cause Boyajian’s star to constantly be relaxing from the post-blockage enhanced luminosity. This decay — which occurs at rates of 0.1–1% brightness per year for convective-zone depths of tens of thousands of kilometers — would nicely account for the long-term, gradual dimming observed.

What’s blocking the flux? Foukal postulates a few options, including magnetic activity (as with the Sun), differential rotation, sporadic changes in photospheric abundances, and simply random variation in convective efficiency.

Strangely Unique
fig4-260x186.jpg (12.79 KiB) Viewed 792 times

Boyajian’s star’s flux in May and June shows some brand new dips. Note that the team now names them! [Tabetha Boyajian and team]

So why have we only found one star with light curves like Boyajian’s? If these are inherently natural processes in the star, we would expect to have seen more than one such object. This may be selection effect — Boyajian’s star lies at the hot end of the range of stars that Kepler observes — or it may be that the star is reaching the end of its convective lifetime.
Until we discover more cases, the best we can hope for is more data from Boyajian’s star itself. Conveniently, it has continued to keep us on our toes, with new dips in May and June. Perhaps our continued observations will finally reveal the answer to this mystery.


Peter Foukal 2017 ApJL 842 L3. doi:10.3847/2041-8213/aa740f

Related Journal Articles

Kic 8462852 faded throughout the kepler mission doi: 10.3847/2041-8205/830/2/L39
Families of plausible solutions to the puzzle of boyajian’s star doi: 10.3847/2041-8205/829/1/L3
Magnetically modulated heat transport in a global simulation of solar magneto-convection doi: 10.3847/1538-4357/aa6d60
Sonneberg plate photometry for boyajian's star in two passbands doi: 10.3847/1538-4357/aa615d
Magnetic cycles in the sun: modeling the changes in radius, luminosity, and p-mode frequencies doi: 10.1086/522559
Global parameter and helioseismic tests of solar variability models doi: 10.1086/375484
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Re: Mysterious clumps of matter around star

Unread postby Lucien_Beckmann » Wed Aug 23, 2017 9:31 pm

the Hubble image (2010) seems to contain some interesting "ring-like" troughs, but there's not enough information in the images (or in the article) to enable a non-instructed interpretation.

in these Moon shots, however, the material/plasma/Disc-Section linearities are reasonably clear, but that doesn't explain or account for anything beyond what is apparent ... so, some kind of [Plasma ?] BLOB and concentric rings-sections ?

given the context of other images (from relatively the same location), the persistence of the Discs-Sections is not aligned to a single cross-section of Moon and do not appear to be part of some discharge as with AU Microscopii ...
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Re: Mysterious clumps of matter around star

Unread postby comingfrom » Thu Aug 24, 2017 3:17 pm

Planets, dust, comets, clumps, even aliens, are more acceptable than electricity, for an explanation.

A variable power source is too simple and obvious an explanation, but would cause their stellar model to go into fusion meltdown.
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Re: Mysterious clumps of matter around star

Unread postby allynh » Mon Oct 09, 2017 2:14 pm

New Observations Deepen Mystery of "Alien Megastructure" Star ... dquo-star/
Artist's illustration depicting a hypothetical dust ring orbiting KIC 8462852, also known as Boyajian’s Star or Tabby's Star. Credit: NASA/JPL-Caltech
There's a prosaic explanation for at least some of the weirdness of "Tabby's star," it would appear.

The bizarre long-term dimming of Tabby's star—also known as Boyajian's star, or, more formally, KIC 8462852—is likely caused by dust, not a giant network of solar panels or any other "megastructure" built by advanced aliens, a new study suggests.

Astronomers came to this conclusion after noticing that this dimming was more pronounced in ultraviolet (UV) than infrared light. Any object bigger than a dust grain would cause uniform dimming across all wavelengths, study team members said. [13 Ways to Hunt Intelligent Aliens]

"This pretty much rules out the alien megastructure theory, as that could not explain the wavelength-dependent dimming," lead author Huan Meng of the University of Arizona said in a statement. "We suspect, instead, there is a cloud of dust orbiting the star with a roughly 700-day orbital period."

Strange brightness dips

KIC 8462852, which lies about 1,500 light-years from Earth, has generated a great deal of intrigue and speculation since 2015. That year, a team led by astronomer Tabetha Boyajian (hence the star's nicknames) reported that KIC 8462852 had dimmed dramatically several times over the past half-decade or so, once by 22 percent.

No orbiting planet could cause such big dips, so researchers began coming up with possible alternative explanations. These included swarms of comets or comet fragments, interstellar dust and the famous (but unlikely) alien-megastructure hypothesis.

The mystery deepened after the initial Boyajian et al. study. For example, other research groups found that, in addition to the occasional short-term brightness dips, Tabby's star dimmed overall by about 20 percent between 1890 and 1989. In addition, a 2016 paper determined that its brightness decreased by 3 percent from 2009 to 2013.

The new study, which was published online Tuesday (Oct. 3) in The Astrophysical Journal, addresses such longer-term events.

From January 2016 to December 2016, Meng and his colleagues (who include Boyajian) studied Tabby's star in infrared and UV light using NASA's Spitzer and Swift space telescopes, respectively. They also observed it in visible light during this period using the 27-inch-wide (68 centimeters) telescope at AstroLAB IRIS, a public observatory near the Belgian village of Zillebeke.

The observed UV dip implicates circumstellar dust—grains large enough to stay in orbit around Tabby's star despite the radiation pressure but small enough that they don't block light uniformly in all wavelengths, the researchers said.

Mysteries remain

The new study does not solve all of KIC 8462852's mysteries, however. For example, it does not address the short-term 20 percent brightness dips, which were detected by NASA's planet-hunting Kepler space telescope. (Kepler is now observing a different part of the sky during its K2 extended mission and will not follow up on Tabby's star for the forseeable future.)

And a different study—led by Joshua Simon of the Observatories of the Carnegie Institution for Science in Pasadena, California—just found that Tabby's star experienced two brightening spells over the past 11 years. (Simon and his colleagues also determined that the star has dimmed by about 1.5 percent from February 2015 to now.)

"Up until this work, we had thought that the star's changes in brightness were only occurring in one direction—dimming," Simon said in a statement. "The realization that the star sometimes gets brighter in addition to periods of dimming is incompatible with most hypotheses to explain its weird behavior."

You can read the Simon et al. study for free at the online preprint site

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