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Astronomie - Hat Kepler bei Exoplanet KIC 8462852 eine Alien Megastruktur entdeckt?

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15.10.2015

Has Kepler revealed evidence for a technologically advanced civilization around a star only 1500 light-years away? That's one exciting, if unlikely, interpretation of recent transit data.
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NASA’s Kepler Space Telescope is tasked with finding small, rocky worlds orbiting distant stars. However, exoplanets aren’t the only thing Kepler can detect — stellar flares, star spots and dusty planetary rings can also pop up in the mission’s observations.
But there’s also been speculation that Kepler may have the ability to detect more than natural phenomena; if they’re out there, Kepler may also detect the signature of artificial structures orbiting other stars. Imagine an advanced civilization that’s well up on the Kardashev scale and has the ability to harness energy directly from its star. This hypothetical alien civilization may want to construct vast megastructures, like supersized solar arrays in orbit around their host star, that could be so big that they blot out a sizable fraction of starlight as they pass in front.
When Kepler detects an exoplanet, it does so by sensing the very slight dip in starlight from a given star. The premise is simple: an exoplanet orbits in front of star (known as a “transit”), Kepler detects a slight dimming of starlight and creates a “lightcurve” — basically a graph charting the dip in starlight over time. Much information can be gleaned from the lightcurve, such as the physical size of the transiting exoplanet. But it can also deduce the exoplanet’s shape.
Normally the shape of an exoplanet isn’t particularly surprising because it’s, well, planet-shaped. It’s round. The physics of planetary formation dictate that a planetary body above a certain mass will be governed by hydrostatic equilibrium. But say if Kepler detects something that isn’t round. Well, that’s when things can get a bit weird.
For the most part, any dip in star brightness can be attributed to some kind of natural phenomenon. But what if all possibilities are accounted for and only one scenario is left? What if that scenario is this object appears to be artificial? In other words, what if it’s alien?
In a chilling article written by Ross Andersen of The Atlantic, at first glance, it seems we may be at this incredible juncture.
A star, named KIC 8462852, has been found with a highly curious transit signal. In a paper submitted to the journal Monthly Notices of the Royal Astronomical Society, astronomers, including citizen scientists from the Planet Hunters crowdsourcing program, report: “Over the duration of the Kepler mission, KIC 8462852 was observed to undergo irregularly shaped, aperiodic dips in flux down to below the 20 percent level.”
The research paper is thorough, describing the phenomenon, pointing out that this star is unique - we’ve seen nothing like it. Kepler has collected data on this star steadily for four years. It’s not instrumental error. Kepler isn’t seeing things; the signal is real.
“We’d never seen anything like this star,” Tabetha Boyajian, a postdoctorate researcher at Yale University and lead author, told The Atlantic. “It was really weird. We thought it might be bad data or movement on the spacecraft, but everything checked out.”
The Planet Hunters volunteers are depended on to seek out transits in Kepler’s stars in the direction of the constellation Cygnus. This is a huge quantity of data, from over 150,000 stars in Kepler’s original field of view, and you can’t beat the human eye when identifying a true dip in starlight brightness. The Planet Hunters described KIC 8462852 as “bizarre,” “interesting” and a “giant transit.” They’re not wrong.
Follow-up studies focus on two interesting transit events at KIC 8462852, one that was detected between days 788 and 795 of the Kepler mission and between days 1510 to 1570. The researchers have tagged these events as D800 and D1500 respectively.
The D800 event appears to have been a single transit causing a star brightness drop-off of 15 percent, whereas D1500 was a burst of several transits, possibly indicating a clump of different objects, forcing a brightness dip of up to 22 percent. To cause such dips in brightness, these transiting objects must be huge.
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The transit data for KIC 8462852, featuring the obvious transit features D800 and D1500.
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The researchers worked through every known possibility, but each solution presented a new problem. For example, they investigated the possibility of some kind of circumstellar disk of dust. However, after looking for the infrared signal associated with these disks, no such signal could be seen.
Also, the star is a mature F-type star, approximately 1.5 times the size of our sun. Circumstellar disks are usually found around young stars.
The researchers also investigated the possibility of a huge planetary collision: could the debris from this smashup be creating this strange signal? The likelihood of us seeing a planetary collision is extremely low. There is no evidence in data taken by NASA’s Wide-field Infrared Survey Explorer (WISE) that a collision happened, creating a very tiny window of opportunity between WISE’s mission end and the beginning of Kepler’s mission (of a few years) for an astronomically unlikely cosmic event like this to occur.
The only natural explanation favored by the researchers seems to focus on an intervening clump of exocomets.
“One way we imagine such a barrage of comets could be triggered is by the passage of a field star through the system,” write the researchers.
Indeed, they argue, there’s a nearby star that might have tidally disturbed otherwise dormant comets in the outermost regions of the KIC 8462852 star system. This small star is located around 1,000 AU from KIC 8462852 and whether it’s a binary partner or an interstellar visitor, its presence may have caused some cometary turmoil. Like the other scenarios, however, the exocomet explanation still falls short of being fully satisfactory.
This research paper focuses only on natural and known possible causes of the mystery transit events around KIC 8462852. A second paper is currently being drafted to investigate a completely different transit scenario that focuses around the possibility of a mega-engineering project created by an advanced alien civilization.
This may sound like science fiction, but our galaxy has existed for over 13 billion years, it’s not such a stretch of the imagination to think that an alien civilization may be out there and evolved to the point where they can build megastructures around stars.
“Aliens should always be the very last hypothesis you consider, but this looked like something you would expect an alien civilization to build,” Jason Wright, an astronomer from Penn State University, told The Atlantic.
Indeed, hunting down huge structures that obscure the light from stars is no new thing. The Search for Extraterrestrial Technology (SETT) is one such project that does just this. Only recently, a survey of the local universe focused on the hope of detecting the waste heat generated by a technologically advanced civilization, specifically a Type II Kardashev civilization.
On the Kardashev scale, a Type II civilization has the ability to utilize all the available energy radiating from a star. Using a vast shell or series of rings surrounding a star, a Dyson sphere-like structure may be constructed. This has the effect of blotting out the star from view in visible wavelengths, but once the solar energy has been used by the alien civilization, the energy is shifted to longer wavelengths and likely lost as infrared radiation.
This recent search for aliens’ waste heat drew a blank, reaching the conclusion that as there appears to be no alien intelligence cocooning stars to harvest their heat, there’s likely no Type II civilization nearby.
But as KIC 8462852 is showing us, there may be something else out there — possibly an alien intelligence that is well on its way to becoming a Type II civilization, which is setting up some kind of artificial structure around its star.
Of course, these mystery transit events are nowhere near “proof” of an alien civilization. In fact, it’s barely evidence and a lot more work needs to be done.
The next step is to point a radio antenna at KIC 8462852, just to see whether the system is generating any artificial radio signals that could indicate the presence of something we’d define as “intelligent.” Boyajian and Wright have now teamed up with Andrew Siemion, the Director of the SETI Research Center at the University of California, Berkeley, to get a radio telescope to listen into the star and if they detect an artificial signal, they will request time on the Very Large Array (VLA) to deduce whether any radio signals from that star are the chatter of an alien civilization.
It might be a long shot, and the phenomenon is more likely a clump of comets or some other natural phenomenon that we haven’t accounted for blocking star light from view, but it’s worth investigating, especially if there really is some kind of alien intelligence building structures, or perhaps, ancient structures of a civilization long-gone, around a star only 1,500 light-years away from Earth.
Quelle: D-News
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Update: 18.10.2015
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Sehnsucht nach Aliens

Ein mysteriöser Stern befeuert Spekulationen über außerirdisches Leben. Vieles davon ist Unsinn. Zwei Dinge würden sich aber ändern, wenn es Außerirdische gäbe.
Ein Kommentar von Robert Gast
So könnte das Signal aussehen, auf das sie alle sehnsüchtig warten, die Fans des Raumschiffs Enterprise. Vor dem Stern KIC 8462852 ziehen immer wieder riesige Schatten vorüber. Eine Deutung für diese Beobachtung des Weltraumteleskops Kepler geistert seit Tagen durchs Internet: Extrem fortschrittliche Aliens haben in 1480 Lichtjahren Entfernung Unmengen von Solarzellen im Orbit ihres Sterns platziert. Irgendwoher muss eine Zivilisation, die Tausende Jahre älter ist als die Menschheit, ja schließlich ihren Strom beziehen.
Astronomen winken zwar ab: Vermutlich ziehe bloß eine Wolke aus Kometenstaub an KIC 8462852 vorüber. Weltraumenthusiasten fantasieren natürlich trotzdem. Sollte es Aliens geben, könnten sie verraten, wie man Überbevölkerung und Klimawandel überwindet. Stephen Hawking hingegen will jeden Kontakt vermeiden. Eine Super-Zivilisation könnte mit der Menschheit schließlich das machen, was der Homo sapiens mit Ameisen im Küchenabfluss anstellt.
Solche Überlegungen tragen maßgeblich zur Faszination für Außerirdische bei. Sie sind allerdings grober Unfug. Aliens wären schlichtweg zu weit weg, um mit Menschen in Kontakt zu treten. Ein Funkspruch fliegt so schnell wie das Licht; vom Stern KIC 8462852 zur Erde bräuchte er also 1480 Jahre. Eben mal zu Besuch kommen könnten Außerirdische auch nicht. Die Gesetze der Physik verbieten Reisen mit Überlichtgeschwindigkeit. Gerade noch vorstellbar sind Raumschiffe, die ein Zehntel des kosmischen Tempo-Limits erreichen. Von KIC 8462852 zur Erde bräuchten sie 14 800 Jahre. Intelligente Wesen würden so eine Reise wohl nicht auf sich nehmen.
Von der Krönung der Schöpfung zum unbedeutenden Zellhaufen
Die Existenz Außerirdischer hätte dennoch Folgen, allerdings vor allem für das Selbstbild der Menschheit. Wenn sich noch auf anderen Planeten Säugetiere mit Gehirnen entwickelt haben, purzelt der Homo sapiens vom Thron der Evolution. Vielleicht hat die Natur Lebewesen hervorgebracht, die klüger, fitter und friedfertiger sind. In jedem Fall wären Aliens eine Entdeckung, die zu Demut anstiften würde. Tausende Jahre lang glaubte der Mensch, er sei die Krönung der Schöpfung. Letztlich wäre er aber nur ein Zellhaufen wie andere im Universum.
Fortschrittliche Außerirdische hielten aber auch eine gute Nachricht bereit. Zivilisationen hätten keinen eingebauten Selbstzerstörungsmechanismus, der sie irgendwann zurück in die Steinzeit befördert. Diese düstere Prognose gilt als eine der wahrscheinlicheren Erklärungen dafür, dass Forscher bisher nicht auf Außerirdische gestoßen sind. Jedes Volk gräbt sich früher oder später sein eigenes Grab, besagt die Theorie - oder es wird irgendwann von kosmischen Naturkatastrophen ausgelöscht. Haben Lebewesen irgendwo so lange durchgehalten, dass sie riesige Bauwerke ins All setzen, heißt das: Auch die Menschheit hat eine Chance.
Quelle. Süddeutsche Zeitung
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Update: 18.09.2016
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Comet storm, not alien megastructures
This illustration shows a star behind a shattered comet. (Credit: NASA / JPL-Caltech)

 

That mysterious “alien megastructure” star is still a mystery, but the most plausible explanations appear to be dense patches of interstellar gas or dust that just happened to pass in front of the star.

That’s the upshot of analyses conducted by the astronomer who first raised the idea of an extraterrestrial construction project a year ago.

In the Astrophysical Journal Letters, Penn State’s Jason Wright and a co-author, Steinn Sigurdsson, run through a wide range of hypotheses for the behavior of a star called KIC 8462852, also known as Boyajian’s Star or Tabby’s Star.

Not even the alien hypothesis is ignored.

The mystery has to do with a strange pattern of erratic dimming and brightening that was observed by NASA’s Kepler space telescope. That pattern was noted last September in a study with Yale astronomer Tabetha Boyajian as principal author. (Hence the star’s nickname.)

 

Wright suggested that the dimming could theoretically be caused by shifts in an alien megastructure surrounding the star – perhaps a giant energy-generating Dyson sphere built by an advanced civilization.

Later studies reported that the star, which is located 1,500 light-years from Earth in the constellation Cygnus, had undergone other long-term dips in brightness.

Is it aliens? Wright says the idea is “not completely ruled out, yet” but “very unlikely.” In their latest study, Wright and Sigurdsson say stellar observations from the European Space Agency’s Gaia satellite could definitively rule out the alien hypothesis or keep it alive.

Many other explanations have been proposed for the observations of Boyajian’s Star, including variability in the star, or swarms of comets passing in front of it. But Wright and Sigurdsson favor a scenario in which small-scale density variations crop up in the interstellar medium between us and the star.

Those types of variations – for example, short-lived patches of gas and dust, or small molecular clouds – would have to be rare. “But it turns out rare dense patches are a thing!” Wright says.

Future observations, either of repeated dimming patterns at Boyajian’s Star or of similar dimming by other stars, would lend additional support to this hypothesis. The comet swarm hypothesis is also still in the running, plausibility-wise.

For what it’s worth, there’s talk about even more dramatic patterns of irregular dimming that have been observed in a star called EPIC 204278916.

The observations from Kepler’s K2 mission were reported in a paper published last month in the Monthly Notices of the Royal Astronomical Society. The study could bring additional perspective to the debate over Boyajian’s Star.

To get the rundown on the full range of hypotheses for Boyajian’s Star, including black holes, check out the research paper as well as the AAS Nova update and Wright’s analysis on his AstroWright blog.

Quelle: GeekWire

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Update: 4.09.2016

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Our galaxy's most-mysterious star is even stranger than astronomers thought

This artist's conception shows a star behind a shattered comet. One of the theories for KIC 8462852's unusual dimming is the presence of debris from a collision or breakup of a planet or comet in the star's system, creating a short-term cloud that blocks some starlight.
Credit: Image is courtesy of NASA/JPL-Caltech
 
 

A star known by the unassuming name of KIC 8462852 in the constellation Cygnus has been raising eyebrows both in and outside of the scientific community for the past year. In 2015 a team of astronomers announced that the star underwent a series of very brief, non-periodic dimming events while it was being monitored by NASA's Kepler space telescope, and no one could quite figure out what caused them. A new study from Carnegie's Josh Simon and Caltech's Ben Montet has deepened the mystery.

Simon and Montet's findings have been accepted for publication by The Astrophysical Journal.

The researchers analyzed further Kepler observations of the puzzling star and showed that in addition to its rapid unexplained brightness changes, the star also faded slowly and steadily during the four years it was watched by Kepler.

Speculation to explain KIC 8462852's dips in brightness has ranged from an unusually large group of comets orbiting the star to an alien megastructure. In general, stars can appear to dim because a solid object like a planet or a cloud of dust and gas passes between it and the observer, eclipsing and effectively dimming its brightness for a time. But the erratic pattern of abrupt fading and re-brightening in KIC 8462852 is unlike that seen for any other star.

Spurred by a controversial claim that the star's brightness gradually decreased by 14 percent from 1890 to 1989, Montet and Simon decided to investigate its behavior in a series of Kepler calibration images that had not previously been used for scientific measurements.

"We thought that these data could confirm or refute the star's long-term fading, and hopefully clarify what was causing the extraordinary dimming events observed in KIC 8462852," explained Simon.

Simon and Montet found that, over the first three years of the Kepler mission, KIC 8462852 dimmed by almost 1 percent. Its brightness then dropped by an extraordinary 2 percent over just six months, remaining at about that level for the final six months of the mission.

The pair then compared this with more than 500 similar stars observed by Kepler and found thata small fraction of them showed fading similar to that seen in KIC 8462852 over the first three years of Kepler images. However, none exhibited such a dramatic dimming in just six months, or a total change in brightness of 3 percent.

"The steady brightness change in KIC 8462852 is pretty astounding," said Montet. "Our highly accurate measurements over four years demonstrate that the star really is getting fainter with time. It is unprecedented for this type of star to slowly fade for years, and we don't see anything else like it in the Kepler data."

"This star was already completely unique because of its sporadic dimming episodes. But now we see that it has other features that are just as strange, both slowly dimming for almost three years and then suddenly getting fainter much more rapidly," Simon added.

Astronomers were already running short of good ideas to account for the dips in KIC 8462852's brightness, and the new results will make that task even harder. Simon and Montet think that the best proposal so far for explaining the star's drastic six month dimming might be a collision or breakup of a planet or comet in the star's system, creating a short-term cloud of dust and debris that blocks some starlight. However, this wouldn't explain the longer-term dimming observed during the first three years of Kepler and suggested by measurements of the star dating back to the nineteenth century.

"It's a big challenge to come up with a good explanation for a star doing three different things that have never been seen before," Montet said. "But these observations will provide an important clue to solving the mystery of KIC 8462852."


Quelle: SD
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Update: 27.10.2016
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Dish to listen for ET around strange star

  • Green Bank TelescopeImage copyrightNRAO
Image captionThe Green Bank Telescope is located in a rural area of West Virginia

A $100m initiative to listen for signals from alien life is targeting a star with an unusual dimming pattern.

The Breakthrough Initiative, backed by Prof Stephen Hawking and Facebook's Mark Zuckerberg, will train a US radio telescope on a target called Tabby's Star.

Tabby's Star has been a subject of attention and controversy over its irregular dimming pattern.

Some scientists have been puzzled by large dips in the star's brightness.

Hawking backs new search for aliens

One of the most favoured explanations for this behaviour is that a swarm of comet fragments is periodically blocking light from the star, which also known by its official designation - KIC 8462852.

One very remote and speculative idea - yet one that has attracted much attention in the media - is that the pattern is caused by some kind of artificial structure, or a collection of structures, around the star.

The co-director of the Breakthrough Listen programme, Dr Andrew Siemion, said he was sceptical of explanations that involved intelligent life.

He added: "The Breakthrough Listen programme has the most powerful SETI equipment on the planet, and access to the largest telescopes on the planet.

"We can look at it with greater sensitivity and for a wider range of signal types than any other experiment in the world."

The team plans to use the 100m Green Bank Telescope in West Virginia, US, to observe the star, which is named after the leader of the team that discovered it - Tabetha Boyajian, assistant professor at Louisiana State University.

Breakthrough Initiative press briefingImage copyrightGETTY IMAGES
Image captionThe $100m (£82m) initiative was launched at the Royal Society in London in 2015

Previous searches, using the Hubble Space Telescope and the Keck Observatory, have failed to find any unusual signals around the star.

But Dr Siemion explained: "The Green Bank Telescope is the largest fully steerable radio telescope on the planet, and it's the largest, most sensitive telescope that's capable of looking at Tabby's star given its position in the sky."

The unusual behaviour around Tabby's star was first reported in September 2015 by Dr Boyajian, who was then a postdoctoral student at Yale University. The findings were published in the Monthly Notices of the Royal Astronomical Society.

The team was actually looking for evidence of planets orbiting stars other than our own.

While most such dimming by transiting planets is brief, regular and blocks just 1 or 2% of the light of the star, Tabby's star dims for days at a time, by as much as 22%, and at irregular intervals.

Speculation that the phenomenon could be caused by a "megastructure" built by an intelligent civilisation, has been dismissed by most scientists. But it has propelled the stellar object to prominence in the popular media.

"I don't think it's very likely - a one in a billion chance or something like that - but nevertheless, we're going to check it out," said Dan Werthimer, chief scientist at Berkeley SETI, based at the University of California, Berkeley.

Yet Tabby's Star remains a fascinating conundrum for astronomers. Some observations show that the dips in brightness are more irregular than a comet swarm would produce. And another study suggested that it had been dimming at a steady rate for the past century. 

The Breakthrough Listen initiative was launched in 2015 at an event in London. It is backed by Prof Hawking, Mr Zuckerberg and Russian entrepreneur Yuri Milner - who also supports the Breakthrough Prizes for science and maths.

Quelle: BBC

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Kepler's 'Alien Megastructure' Star to Spill SETI Secrets?

The Breakthrough Listen SETI project will aim one of the worlds most powerful radio telescopes at Tabby's Star for three nights in the hope of detecting an alien civilization.

 

nrao-telescope

 

The star KIC 8462852 — informally known as Tabby's Star — has been the focus of the worlds' attention for months now, and for good reason. Its strange behavior could be a sign that there's a super-advanced alien civilization carrying out the mother of all engineering projects in orbit. But the mysterious dips in observed light from the star could alternatively just be a huge swarm of comets or some other as-yet-to-be-understood stellar phenomenon.

Although astronomers are generally skeptical that there really is an extraterrestrial civilization constructing a starlight-blocking megastructure only 1,480 light-years from Earth, the Breakthrough Listen SETI (Search for Extraterrestrial Intelligence) project is committing radio telescope time of one of the most powerful observatories on the planet to at least test the intelligent alien hypothesis. 

The project is a part of the $100 million Breakthrough Prize Foundation that's funded by Russian entrepreneur Yuri Milner and backed by British theoretical physicist Stephen Hawking and Facebook founder Mark Zuckerberg.

Starting Wednesday (Oct. 26), a team of astronomers will use the renowned 100-meter Green Bank Telescope (pictured above) that is located deep in a radio-silent corner of West Virginia to study Tabby's Star. For eight hours per night for three nights over the next two months, a special instrument attached to the huge radio telescope will be used to carry out an unprecedented observation campaign of the star.

"The Breakthrough Listen program has the most powerful SETI equipment on the planet, and access to the largest telescopes on the planet," said Andrew Siemion, director of the Berkeley SETI Research Center and co-director of Breakthrough Listen, in a statement. "We can look at it with greater sensitivity and for a wider range of signal types than any other experiment in the world."

Although other projects have tried to eavesdrop on the star before, SETI campaigns have typically been limited by the number of radio frequencies that can be recorded simultaneously and the amount of time committed to just one star in the sky. This new instrument is able to record a huge amount of data across a range of frequencies at the same time, potentially allowing us to detect the radio transmissions from any transmitting intelligent aliens at Tabby's Star.

"The Green Bank Telescope is the largest fully steerable radio telescope on the planet, and it's the largest, most sensitive telescope that's capable of looking at Tabby's star given its position in the sky," said Siemion. "We've deployed a fantastic new SETI instrument that connects to that telescope, that can look at many gigahertz of bandwidth simultaneously and many, many billions of different radio channels all at the same time so we can explore the radio spectrum very, very quickly."

It's estimated that up to one petabyte of data may be collected over the observing run — that's enough data to fill a thousand computer hard drives (assuming each can store one terabyte). The researchers say that it could be over a month before we know whether or not a signal was detected because it will take a long time to process all the observations.

With Siemion, Tabetha Boyajian, from Louisiana State University, and visiting UC Berkeley astronomer Jason Wright will be heading the study. Boyajian was the first to report on KIC 8462852's peculiar light-curve in September 2015, which was initially flagged by citizen scientists participating in the Planet Hunters project. Tabby's Star is so-named in honor of Boyajian.

The project asks for the help of the public to look at candidate exoplanet transits from NASA's Kepler Space Telescope. Kepler has confirmed hundreds of worlds orbiting other stars by detecting the dip in brightness of a star (described by the star's "light-curve") by an exoplanet passing in front — an event known as a "transit." And the transit signal produced by Tabby's star was as dramatic as it was bizarre.

Typically, an exoplanet signal might dim a star's light by around 2%. But several of the irregular transits of Tabby's Star caused the starlight to drop by up to 22%. This means that something very big must be passing in front. What's more, it seems the star's brightness has been dimming for hundreds of years according to historical astronomical records, only adding to the intrigue. Although several ideas have been put forward to explain the signal, the key one being the possibility of a huge cloud of comets drifting in front of the star, all have fallen short of fully explaining the Kepler observation.

After the weirdness of Tabby's Star was known, Jason Wright discussed the possibility of Tabby's Star's dimming not being caused by natural phenomena; could the dimming be caused by an advanced alien intelligence creating a "megastructure" around the star? Could this be the first observational evidence of a huge solar array (like a Dyson Sphere) being built?

For now, this is pure speculation, but Breakthrough Listen hopes to investigate further. If this hypothetical alien civilization is transmitting powerful radio signals into space, perhaps we'll detect it. Though it is highly unlikely an artificial radio signal will be detected, the mere chance Tabby's Star might spill its secrets in the form of transmissions from an advanced alien race is enough for us to at least try.

WATCH VIDEO: We're Not Saying The Kepler Discovery Is Aliens, But...

Quelle: Seeker
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Update: 10.01.2017
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Alien megastructure’ signal may be due to star eating a planet

 

Asteroids around a star

NASA/JPL-Caltech/T. Pyle

 

Orbiting debris could be making Tabby’s star blink

When you are a messy eater, it can take a long time to clean up after a meal. The slow dimming of Tabby’s star and the sudden dips in its light may be caused by an orbiting cloud of debris left over from when it partially gobbled a planet.

The star KIC 8462852 rose to prominence in 2015, when a team of astronomers led by Yale’s Tabetha Boyajian (after whom the star is nicknamed) observed a series of abrupt dips in its brightness, in which it dimmed by up to 22 per cent before going back to normal.

There are many ideas about what causes the star’s sporadic blinking, from internal stellar dynamics to swarms of orbiting comets to an enormous alien megastructure.

Things got more complicated in January 2016, when a review of old photographic plates revealed that Tabby’s star dimmed by 14 per cent between 1890 and 1989. It faded by another 3 per cent over the four years it was observed by the Kepler space observatory.

Now Brian Metzger at Columbia University in New York and his colleagues have a theory that could explain both the brief dips in light and the gradual dimming. The group thinks Tabby’s star is just returning to its natural state – after a large, messy meal.

Planetary crumbs

If Tabby’s star devoured a planet in the past, the planet’s energy would have made the star temporarily brighten, then gradually dim to its original state. The bigger the planet was, the longer the star would take to dim. Depending on the size of the planet, this event could have happened anywhere between 200 and 10,000 years ago.

As the planet fell into its star, it could have been ripped apart or had its moons stripped away, leaving clouds of debris orbiting the star in eccentric orbits. Every time the debris passes between us and the star, it would block some light, making the star seem to blink.

If this is true, these sorts of collisions might be much more common than we expected. “We estimated that if Tabby’s star were representative, something like 10 Jupiters would have to fall into a typical star over its lifetime, or maybe even more,” says Metzger – and that number grows into the thousands if the objects are smaller.

Next time we see the light from Tabby’s star dip, Metzger hopes that astronomers will be able to see signatures of planetary debris passing close to the star. “These transits only last a few days, so when we see one, we have to alert all the telescopes and basically point every telescope we have at Tabby’s star,” he says.

A collision of star and planet explains the behaviour of Tabby’s star well, says Jason Wright at Penn State University in University Park. “This paper puts a merger scenario on the table in a credible way,” he says. “I think this moves it into the top tier of explanations.”

Quelle: NewScientist

 


 

 

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