Tag: megastructure

The Ever More Puzzling, And Intriguing, "Tabby’s Star."

Star debris illustration

Did Tabby’s star going through periodic and deep dimmings because of dust and debris clouds that pass edbetween it and the mirror of the Kepler Space Telescope?  That was an earlier explanation for the highly unusual behavior of the star, but new research makes that answer less likely. Artist drawing by NASA/JPL-Caltech/T. Pyle

Substantial, sun-like stars are not supposed to dim.  They start with gravity and pressure induced nuclear reactions, and then they burn brighter and brighter until they either explode (go supernova) or burn all their fuel and become small, enormously dense, and not very bright “white dwarfs.”

Of course, the transit technique of searching for exoplanets looks precisely for dimmings — of stars caused by the passage of an exoplanet.  But those are tiny reductions in the star’s brightness and short-lived.  So if a star is dimming significantly over a much longer period of time, something unusual is going on.

And that is apparently exactly what is happening with the current poster child for mysterious stars — KIC 8462852 or “Tabby’s star,” named after the Yale University postdoc who, with the help of citizen scientists, discovered it,  Tabetha Boyajian.

First written up last fall, the big news was data from the Kepler Space Telescope showed that the star had experienced two major and dissimilar dips in brightness — a highly unusual and perplexing phenomenon.  The dips appeared much too large to represent the passage of an exoplanet, so explanations tended towards the baroque — a swarm of comets, a vast dust cloud, even an alien megastructure (proposed as a last possible explanation.)  The observation was first identified by citizen planet hunters working with Boyajian, making it an even more compelling finding.

Now the mystery has grown stranger still.  A paper made public last week based on a different kind of Kepler imaging (full-frame imaging) found not two but one enormous dip in the light curve, as well as a surprising and significant dimming the of star over the four year observing period of the space telescope.  The paper has been submitted for publication in American Astronomical Society journals.

Benjamin Montet of Caltech and Joshua Simon of the Observatories of the Carnegie Institution of Washington, analyzed the full-field images taken by Kepler every three months (rather than the hourly images studied by Boyajian et al,) and concluded that something strange was indeed going on.

Their conclusion: “No known or proposed stellar phenomena can fully explain all aspects of the observed light curve.”… Read more

The Still Mysterious "Tabby’s Star"

Artist rendering of star xxx, and the unexplain ed objects close to it. KNown as "Tabby's" star

Artist rendering of dusty comets approaching star KIC8462852, an interpretation of the mysterious objects that periodically block out substantial amounts of the star’s light. Known informally as “Tabby’s” star, it was discovered by citizen scientists using Kepler Space Telescope data, and they are looking for ways to continue their work. (NASA/JPL-Caltech)

It’s been eight months since citizen “Planet Hunters”  working with Yale postdoc Tabetha Boyajian announced the discovery of a most unusual star, or rather a star where something most unusual was intermittently and erratically happening.

The puzzle began with some light curve data, taken over a four year period, by the Kepler Space Telescope  The citizen planet hunters pored through reams of data sent back by Kepler looking for signals of planetary transits — the ever-so-slight dimmings of the star caused by the crossing or an orbiting exoplanet.

But the light curve for KIC 8462852 showed dimmings that were anything but slight, and anything but regular.  The Planet Hunters flagged the star for Boyajian’s groups attention, and the mystery star was born.

Theories on what was causing the very large dips ranged from a host of enormous comets, to a violently exploding planet, to an asteroid belt or the presence of close by stars, from an artifact of Kepler’s camera to, finally, an alien megastructure.  (The last was offered by Penn State astronomer Jason Wright as a kind of “Hail Mary” explanation if and when the others are found wanting.  But that’s what got the press.)

Despite years of concerted observing, theorizing and analyzing, Boyajian, Wright the citizen planet hunters and others intrigued by the mystery say they are no closer to an explanation for whatever is passing in front of the star (now informally called “Tabby’s star.”)  NASA has ruled out a technical glitch in the Kepler data, and a range of astronomers have found fault with all the explanations put forward.

But while the quite tantalizing mystery remains, efforts to learn more about the star may have to wind down soon.  The primary Kepler mission is over, so it will provide no more data for this star.  Other space telescopes will not be looking, nor will the major ground-based observatories.  And  the first SETI searches for signals coming from the star has found nothing unusual.

So with options dwindling to learn more, Boyajian, her citizen astronomers and others have begun a grassroots effort to raise $100,000 to buy time at a network of smaller ground-based telescopes around the world.… Read more

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