Not an Alien Megastructure, a Cloud of Dust on a 700-Day Orbit

The mystery of KIC 8462852 (aka. Boyajian’s Star or Tabby’s Star) continues to excite and intrigue! Ever since it was first seen to be undergoing strange and sudden dips in brightness (back in October of 2015) astronomers have been speculating as to what could be causing this. Since that time, various explanations have been offered, including large asteroids, a large planet, a debris disc or even an alien megastructure.

Many studies have been produced that have sought to assign some other natural explanation to the star’s behavior. The latest comes from an international team of scientists – which included Tabetha Boyajian, the lead author on the original 2016 paper. According to this latest study, which was recently published in The Astrophysical Journal, the star’s long-term dimming patterns are likely the result of an uneven dust cloud moving around the star.

The study, titled “Extinction and the Dimming of KIC 8462852“, was led by Huan Y. A. Meng of the Steward Observatory at the University of Arizona. The team also included members from the Astrolab IRIS in Belgium, the Johns Hopkins University Applied Physics Laboratory (JHUAPL), the University of Cambridge, Iowa State University, Pennsylvania State University, Louisiana State University, and the University of Leuven, Belgium.

Artist’s impression of an orbiting swarm of dusty comet fragments around Tabby’s Star. Credit: NASA/JPL-Caltech

For the sake of their study, the team consulted data that was obtained by NASA’s Spitzer Space Telescope and the Swift Gamma-Ray Burst mission between January and December of 2016. Whereas Spitzer conducted observations in the infrared band, Swift gathered data in the ultraviolet band. This was then compared to visible light gathered during the same period by AstroLAB IRIS’s 68-cm (27-inch) reflecting telescope.

What they found was that KIC 8462852 experienced less dimming in the infrared band than in the ultraviolet. This, they concluded, was a strong indication that material transiting in front of the star was likely no larger than a few micrometers (about one ten-thousands of an inch) in diameter, since anything larger would cause the light to dim equally across all wavelengths.

This finding contradicts many theories that have been ventured since the mysterious dimming of Tabby’s Star was first noticed. As Dr. Meng indicated in a recent NASA press statement:

“This pretty much rules out the alien megastructure theory, as that could not explain the wavelength-dependent dimming. We suspect, instead, there is a cloud of dust orbiting the star with a roughly 700-day orbital period.”

Artist’s concept of KIC 8462852, which has experienced unusual changes in luminosity over the past few years. Credit: NASA, JPL-Caltech

Based on the strong dip in the ultraviolet band, the research team also concluded that the particles must be larger than interstellar dust. Otherwise, the pressure caused by KIC 8462852’s solar wind would drive these particles out into space over time. A circumstellar disk of dust particles would not only be able to remain in orbit, it would also explain the uneven changes in the star’s brightness.

So far, this is the best explanation for the mysterious long-term behavior of Tabby’s Star. As with previous observations, much of the credit for this latest study goes to amateur astronomers who assisted in the observations. It was participants in the Planet Hunters project, which provides open to access Kepler mission data, that first noticed that light coming from KIC  8462852 was experiencing strange dips.

In addition, it was the work of amateur astronomers – who provided the necessary technical and software support to AstroLAB – allowed for this study to take place. After the Astrolab group posted the data they had obtained on Tabby’s star in a public astronomy archive, George Rieke (one of the co-authors on this latest study) contacted them and proposed combining their results.

The AstroLAB group consists of Franky Dubois, who operated the telescope during the Tabby’s Star observations, Ludwig Logie, who helps with technical issues on the telescope, and Steve Rau, who processes observations of star brightness, is a trainer at a Belgian railway company. Together, they began monitoring Tabby’s Star after they read Dr. Boyajian 2016 study.

Ever since it was first announced in 2015, there has been speculation as to what could account for the dimming of KIC 8462852. Credit: SentientDevelopments.com

Naturally, more observations and research is needed to confirm this latest study. While it does fit the long-term observations, there is still the matter of shorter-term dimming events. These include the three-day spurts that were noticed in 2017, as well as the major 20-percent dips that were observed during Kepler’s primary mission. The theory that these could have been the result of a swarm of comets is also still a possible explanation.

This theory, which was based on data collected by the Wide-field Infrared Survey Explorer (WISE) mission, could explain both the short period dips and the longer-term dips. Whereas the comets passing in front of the star could explain the former, dust produced by the sublimation of material from the comets as they draw nearer the star (or through collisions) could explain the latter. As Vanaverbeke said:

“Tabby’s Star could have something like a solar activity cycle. This is something that needs further investigation and will continue to interest scientists for many years to come.”

So for those hoping that Tabby’s Star was the first indication of an alien megastructure, there’s still hope (albeit a faint one)! As Professor Loeb of the Harvard Smithsonian Center for Astrophysics (CfA) told Universe Today recently (with regards to a new study he co-authored), there’s always the possibility that dimming patterns are due to massive structures – like a magnetic shield – passing in front of a host star:

“The imprint of a shield built by another civilization could involve the changes it induces in the brightness of the host star due to occultation (similar behavior to Tabby’s star)  if the structure is big enough,” he said. “The situation could be similar to Dyson’s spheres, but instead of harvesting the energy of the star the purpose of the infrastructure is to protect a technological civilization on a planet from the flares of its host star.”

While the Kepler mission is no longer in a position to observe Tabby’s Star (now that it is conducting its K2 mission), next-generation telescopes are expected to pick up where it left off. These include NASA’s James Webb Space Telescope, the Wide Field Infrared Survey Telescope (WFIRST), and ground-based observatories like the Extremely Large Telescope (VLT) array.

Further Reading: NASA, The Astrophysical Journal

Foom! ‘Superflares’ Erupt From Tiny Red Dwarf Star, Surprising Scientists

Don’t get too close to this little star! In April, a red dwarf star sent out a series of explosions that peaked at 10,000 times as powerful as the largest solar flare ever recorded.

The tiny star packs a powerful punch because its spin is so quick: it rotates in less than a day, or 30 times faster than the Sun does. Astronomers believe that in the distant past, when the Sun was young, it also was a fast turner — and could have produced “superflares”, as NASA terms the explosions, of its own.

“We used to think major flaring episodes from red dwarfs lasted no more than a day, but Swift detected at least seven powerful eruptions over a period of about two weeks,” stated Stephen Drake, an astrophysicist at NASA’s Goddard Space Flight Center in Maryland. “This was a very complex event.”

The surprising activity came from a red dwarf star in a binary system that together is known as DG Canum Venaticorum (DG CVn). Located just 60 light-years away, the two red dwarfs are each about one-third the size and mass of the Sun. Astronomers can’t say for sure which one sent out the eruption because the stars were so close to each other, at about three times the distance of Earth’s average distance to the sun.

The first flare (which sent out a burst of X-rays) caused an alert in NASA’s Swift Space Telescope’s burst alert telescope on April 23. It’s believed to be caused by the same process that creates flares on our Sun — magnetic field lines twisting and then releasing a burst of energy that sends out radiation.

Three hours later came another flare — scientists have seen similar events on the Sun after one active region sets off flares in another — and then came “successively weaker blasts” in the next 11 days, NASA said. Normal X-ray emissions stabilized about 20 days after the first flare. Swift is now monitoring this star for further activity.

Drake presented his results at the August meeting of the American Astronomical Society’s high energy astrophysics division, which was highlighted in a recent release from NASA.

Source: NASA

GRB Lights Up Ancient Hidden Galaxy

Once upon a time, more than 12.7 billion years ago, a star was poised on the edge of extinction. It made its home in a galaxy too small, too faint and too far away to even be spotted by the Hubble Space Telescope. Not that it would matter, because this star was going to end its life before the Earth formed. As it blew itself apart, it expelled its materials in twin jets which ripped through space at close to the speed of light – yet the light of its death throes outshone its parent galaxy by a million times.

“This star lived at a very interesting time, the so-called dark ages just a billion years after the Big Bang,” says lead author Ryan Chornock of the Harvard-Smithsonian Center for Astrophysics (CfA).

“In a sense, we’re forensic scientists investigating the death of a star and the life of a galaxy in the earliest phases of cosmic time,” he adds.

When this unsung star expired, it created one of the scariest things in astronomy… a gamma-ray burst (GRB). However, it wasn’t just a normal, garden variety GRB – it was long one, lasting more than four minutes. After century upon century of travel, the light reached our little corner of the Universe and was detected by NASA’s Swift spacecraft on June 6th. Chornock and his team quickly organized follow-up observations by the MMT Telescope in Arizona and the Gemini North telescope in Hawaii.

“We were able to get right on target in a matter of hours,” Chornock says. “That speed was crucial in detecting and studying the afterglow.”

Time to kick back and have a smoke? In a sense. The “afterglow” of a GRB happens when the jets impact the surrounding gas in an almost tsunami-like effect. As it sweeps up the material, it begins to heat and glow. As this light traverses the parent galaxy, it impacts clouds of interstellar gas, illuminating their spectra. Through these chemical signatures, astronomers are able to ascertain what gases the distant galaxy may have contained. As we know, all chemical elements heavier than hydrogen, helium, and lithium are the product of stars. Researchers refer to this as “metal content” and it takes a certain amount of time to accumulate. In the scheme of creation, the elements necessary for life – carbon and oxygen – didn’t exist. What Chornock and his team discovered was the GRB galaxy was host to only about a tenth of the “metals” in our solar system. What does that mean? In the eyes of the astronomers, rocky planets might have been able to form in that far away galaxy, but chances are good that life could not.

“At the time this star died, the universe was still getting ready for life. It didn’t have life yet, but was building the required elements,” says Chornock.

At a redshift of 5.9, or a distance of 12.7 billion light-years, GRB 130606A is one of the most distant gamma-ray bursts ever found.

“In the future we will be able to find and exploit even more distant GRBs with the planned Giant Magellan Telescope,” says Edo Berger of the CfA, a co-author on the publication.

Original Story Source: Harvard Smithsonian Center for Astrophysics News Release.