KIC 8462852 Faded Throughout the Kepler Mission

Over the four years that the Kepler telescope monitored this mysterious star, its light levels dropped by a total of about 3 percent--but not all at a constant rate. (For reference, the huge dip at the 800 mark is one of the huge dips that originally tipped off scientists that this was a freakin' weird star. "It was off the charts," says Montet.)

Over the four years that the Kepler telescope monitored this mysterious star, its light levels dropped by a total of about 3 percent–but not all at a constant rate. (For reference, the huge dip at the 800 mark is one of the huge dips that originally tipped off scientists that this was a freakin’ weird star. “It was off the charts,” says Montet.)

Benjamin T. Montet, Joshua D. Simon
KIC 8462852 is a superficially ordinary main sequence F star for which Kepler detected an unusual series of brief dimming events. We obtain accurate relative photometry of KIC 8462852 from the Kepler full frame images, finding that the brightness of KIC 8462852 monotonically decreased over the four years it was observed by Kepler. Over the first ~1000 days, KIC 8462852 faded approximately linearly at a rate of 0.341 +/- 0.041 percent per year, for a total decline of 0.9%. KIC 8462852 then dimmed much more rapidly in the next ~200 days, with its flux dropping by more than 2%. For the final ~200 days of Kepler photometry the magnitude remained approximately constant, although the data are also consistent with the decline rate measured for the first 2.7 yr. Of a sample of 193 nearby comparison stars and 355 stars with similar stellar parameters, 0.6% change brightness at a rate as fast as 0.341 +/- 0.041 percent per year, and none exhibit either the rapid decline by >2% or the cumulative fading by 3% of KIC 8462852. We examine whether the rapid decline could be caused by a cloud of transiting circumstellar material, finding while such a cloud could evade detection in sub-mm observations, the transit ingress and duration cannot be explained by a simple cloud model. Moreover, this model cannot account for the observed longer-term dimming. No known or proposed stellar phenomena can fully explain all aspects of the observed light curve.



SETI at Planck Energy: When Particle Physicists Become Cosmic Engineers

Brian C. Lacki
What is the meaning of the Fermi Paradox — are we alone or is starfaring rare? Can general relativity be united with quantum mechanics? The searches for answers to these questions could intersect. It is known that an accelerator capable of energizing particles to the Planck scale requires cosmic proportions. The energy required to run a Planck accelerator is also cosmic, of order 100 M_sun c^2 for a hadron collider, because the natural cross section for Planck physics is so tiny. If aliens are interested in fundamental physics, they could resort to cosmic engineering for their experiments. These colliders are detectable through the vast amount of “pollution” they produce, motivating a YeV SETI program. I investigate what kinds of radiation they would emit in a fireball scenario, and the feasibility of detecting YeV radiation at Earth, particularly YeV neutrinos. Although current limits on YeV neutrinos are weak, Kardashev 3 YeV neutrino sources appear to be at least 30–100 Mpc apart on average, if they are long-lived and emit isotropically. I consider the feasibility of much larger YeV neutrino detectors, including an acoustic detection experiment that spans all of Earth’s oceans, and instrumenting the entire Kuiper Belt. Any detection of YeV neutrinos implies an extraordinary phenomenon at work, whether artificial and natural. Searches for YeV neutrinos from any source are naturally commensal, so a YeV neutrino SETI program has value beyond SETI itself, particularly in limiting topological defects. I note that the Universe is very faint in all kinds of nonthermal radiation, indicating that cosmic engineering is extremely rare.

How SETI@Home Screens ET Candidates

SETI@Home volunteers have found 4.2 billion signals of interest since the project began in 1999. What happens to them?

SETI@Home is a distributed computing initiative that analyses radio signals for signs of extra terrestrial intelligence. It relies on volunteers who use their own computers to download and crunch data from the Arecibo Radio telescope in Puerto Rico using bespoke software available from the SETI@Home website.

The project’s central challenge is to spot a real ET signal against a background of noise and interference. The software searches for five different types of patterns that are unlikely to be produced by noise, things like three power spikes in a row and pulses that could represent digital signals.

Using these criteria, SETI@Home volunteers have identified some 4.2 billion signals of potential interest. That’s a significant number. But even though these signals have all been screened by the SETI@Home software, most, if not all, of them are likely to be the result of noise or interference.

So today, Eric Korpela at UC Berkeley and a few buddies outline how they analyse these candidates. One important task is to identify common sources of interference that produce intelligent-like signals. “By far, the most common source of interference in the SETI@home data set is radar stations on the island of Puerto Rico,” say Korpela and co.

Most of these and other types of interference can be identified and removed automatically. However the team is hoping to crowdsource the analysis of the signals that slip through using software that trains volunteers to inspect signals visually and identify those that are the result of interference.

One important criteria for ET signals is that they must be persistent in time and frequency. In other words, an interesting signal must be observable in the same area of sky at a later date. To monitor this, Korpela and co and have designed a program called the Near-Time Persistency Checker or NTPCkr that creates a kind of heat map of interesting signals in the sky.

When an interesting candidate turns up, a certain area of sky becomes ‘hot’. If the signal continues, that area of sky remains hot, otherwise it cools down over time. Anything that remains hot over a decent period of time is worth looking at in more detail.

So what has SETI@Home found? Nothing really. The most significant candidate is a sourse called Radio source SHGb02+14a which the team revealed in 2004. But even this is an unconvincing candidate. In the area of sky in which it was found, there are no stars within 1000 light years of Earth and most commentators think the signal is probably due to random variation.

Nevertheless, the search continues.

Ref: Candidate Identification and Interference Removal in SETI@home