Astronomers: If there are artificial Dyson spheres out there, we can detect them

In a preprint science paper published on October 26, 2021, astronomers review the impact a Dyson sphere might have on its central star and conclude that modern astronomical instruments should be able to identify these changes. From the abstract:

The search for signs of extraterrestrial technology, or technosignatures, includes the search for objects which collect starlight for some technological use, such as those composing a Dyson sphere. These searches typically account for a star’s light and some blackbody temperature for the surrounding structure. However, such a structure inevitably returns some light back to the surface of its star, either from direct reflection or thermal re-emission. In this work, we explore how this feedback may affect the structure and evolution of stars, and when such feedback may affect observations. We find that in general this returned light can cause stars to expand and cool. Our MESA models show that this energy is only transported toward a star’s core effectively by convection, so low mass stars are strongly affected, while higher mass stars with radiative exteriors are not. Ultimately, the effect only has significant observational consequences for spheres with very high temperatures (much higher than the often assumed ~300 K) and/or high specular reflectivity. Lastly, we produce color-magnitude diagrams of combined star-Dyson sphere systems for a wide array of possible configurations.

A plain-language description of the paper can be found here, which summarizes this work as follows:

This study shows that Dyson spheres can result in measurable changes to stellar properties. Megastructures have long been confined to science fiction, imagination and certain video games. However, if there are indeed Dyson spheres out there waiting to be found, we could soon be in a position to find them.

2,000 nearby stars found that see the Earth cross in front of the Sun

Astronomers have identified 2,134 nearby stars that at some point in the past, present, or future are properly positioned along the solar system’s ecliptic so that the Earth can be seen transiting in front of the Sun.

From their paper’s abstract:

[W]e report that 1,715 stars within 100 parsecs from the Sun are in the right position to have spotted life on a transiting Earth since early human civilization (about 5,000 years ago), with an additional 319 stars entering this special vantage point in the next 5,000 years. Among these stars are seven known exoplanet hosts, including Ross-128, which saw Earth transit the Sun in the past, and Teegarden’s Star and Trappist-1, which will start to see it in 29 and 1,642 years, respectively. We found that human-made radio waves have already swept over 75 of the closest stars on our list. [emphasis mine]

I like the detail highlighted. Of the stars that could definitely identify the Earth by transits, 75 are also now close enough to have also heard our radio broadcasts. Should any of those stars also have a sufficiently advanced alien civilization, they could know of our existence. These same stars in turn make for very good targets of study for us to see if there is alien life there.

Astronomers look at one patch of sky and see no signs of alien life

Worlds without end: Using an Australian radio telescope array focused in the FM frequencies, astronomers did a seventeen hour sweep of one small of sky and found no evidence of alien transmissions.

“We observed the sky around the constellation of Vela for 17 hours, looking more than 100 times broader and deeper than ever before. With this dataset, we found no technosignatures—no sign of intelligent life.”

Professor Tingay said even though this was the broadest search yet, he was not shocked by the result. “As Douglas Adams noted in The Hitchhikers Guide to the Galaxy, ‘space is big, really big’. … And even though this was a really big study, the amount of space we looked at was the equivalent of trying to find something in the Earth’s oceans but only searching a volume of water equivalent to a large backyard swimming pool.

The radio array used in this search is only a small precursor to a much larger array, dubbed the Square Kilometer Array (SKA), which is under construction and many times more sensitive.

More data says no alien civilization at KIC 8462852

New observations of the star KIC 8462852 to see if an alien civilization had produced laser signals has produced a null result, reinforcing the conclusion that the erratic dimming of the star is not caused by alien megastructures.

On six nights between October 29 and November 28, 2015, scientists searched for pulses as short as a billionth of a second at the Boquete Optical SETI Observatory in Panama, using a 0.5 m Newtonian telescope. The observatory’s relatively small telescope uses a unique detection method having enhanced sensitivity to pulsed signals. If any hypothetical extraterrestrials had beamed intentional laser pulses in the visible spectrum toward Earth, the Boquete observatory could have detected them so long as they exceeded the observatory’s minimum detectable limit.

KIC 8462852 has puzzled astronomers because it shows irregular dimming unlike anything seen for another star. The anomalous light curve was measured using NASA’s Kepler telescope, as part of its search for exoplanets. However, even though a planet the size of Jupiter would cause dimming of approximately 1%, the dimming observed for KIC 8462852 was far greater – up to 22%. Just as strange, the dimming didn’t follow the regular pattern of a planet orbiting a star, but instead was unpredictable. The best explanation to date is that the dimming may have been caused by cometary fragments in a highly elliptical orbit around KIC 8462852, intercepting starlight at the same time the Kepler mission was observing it.

Astronomers find no evidence of nearby alien civilizations

New observations of the best candidate galaxies now suggests that very advanced civilizations are very rare or don’t exist in the local universe.

They looked at several hundred nearby galaxies that emitted a high amount of mid-infrared radiation, which could possibly be produced as the waste heat from civilizations using energy on galactic scales.

Professor Michael Garrett (ASTRON & University of Leiden) has used radio measurements of the very best candidate galaxies and discovered that the vast majority of these systems present emission that is best explained by natural astrophysical processes. In particular, the galaxies as a sample, follow a well-known global relation that holds for almost all galaxies – the so-called “Mid-Infrared Radio correlation”. The presence of radio emission at the levels expected from the correlation, suggests that the mid-IR emission is not heat from alien factories but more likely emission from dust – for example, dust generated and heated by regions of massive star formation.
As Professor Garrett explains: “the original research at Penn State has already told us that such systems are very rare but the new analysis suggests that this is probably an understatement, and that advanced Kardashev Type III civilisations basically don’t exist in the local Universe. In my view, it means we can all sleep safely in our beds tonight – an alien invasion doesn’t seem at all likely!”.

Joking aside, Professor Garrett is still looking at a few candidate galaxies that lie off of the astrophysical correlation: “Some of these systems definitely demand further investigation but those already studied in detail turn out to have a natural astrophysical explanation too. It’s very likely that the remaining systems also fall into this category but of course it’s worth checking just in case!”

Obviously, the uncertainty of these results is quite high. Nonetheless, the results indicate that either humanity really is the only intelligent species in this part of the universe, or advanced civilizations are far more efficient in their use of energy than is reasonable to assume.

Organic material from Mars?

The uncertainty of science: Scientists theorize that the carbon material found in a 2011 meteorite could be Martian biological material.

Ejected from Mars after an asteroid crashed on its surface, the meteorite, named Tissint, fell on the Moroccan desert on July 18, 2011, in view of several eyewitnesses. Upon examination, the alien rock was found to have small fissures that were filled with carbon-containing matter. Several research teams have already shown that this component is organic in nature. But they are still debating where the carbon came from.

Chemical, microscopic and isotope analysis of the carbon material led the researchers to several possible explanations of its origin. They established characteristics that unequivocally excluded a terrestrial origin, and showed that the carbon content were deposited in the Tissint’s fissures before it left Mars.

One scientist’s modeling of the early universe suggests to him that intelligent life could have evolved as early as 15 million years after the Big Bang.

Theories! One scientist’s modeling of the early universe suggests to him that intelligent life could have evolved as early as 15 million years after the Big Bang.

This is fun stuff, but entirely theoretical and not to be taken very seriously. We know with certainty as much about the early universe as a mouse understands Shakespeare. To predict accurately the nature or even existence of life at that time is stretching our knowledge considerably.

A targeted SETI observation of Gliese 581, the nearest star with exoplanets in the habitable zone, has found no evidence of alien communications.

Radio silence: A targeted SETI observation of Gliese 581, the nearest star with exoplanets in the habitable zone, has found no evidence of alien communications.

This was a proof of concept experiment, and though they detected nothing, they also did not rule out the possibility of alien life, as their radio telescope wasn’t sensitive enough to do so. You can download the actual paper here.