Last week (Friday. Feb. 14th), the Breakthrough Listen Initiative released about 2 petabytes of optical and radio data that they have accumulated over the past four years. This is the second data release by the non-profit effort (as part of Breakthrough Initiatives) and the public is once again invited to search through the data for possible signs of extraterrestrial communications.

The announcement was made at a media briefing in Seattle, where the annual meeting of the American Association for the Advancement of Science (AAAS) was taking place. During the event, Andrew Siemion – the director of UC Berkeley’s SETI Research Center and Breakthrough Listen’s principal investigator – presented the latest data obtained by the initiative.

This constitutes the largest release of SETI data, the previous having been the petabyte that Breakthrough Listen released last June. As Matt Lebofsky – Breakthrough Listen’s lead system administrator – said in a Berkeley News release:

“Since Breakthrough Listen’s initial data release last year, we have doubled what is available to the public. It is our hope that these data sets will reveal something new and interesting, be it other intelligent life in the universe or an as-yet-undiscovered natural astronomical phenomenon.”

Breakthrough Listen, based at UC Berkeley, collects petabytes of data from the Green Bank Telescope in West Virginia (right) and the Parkes radio telescope in Australia (left). Credit: Breakthrough Listen

To date, Breakthrough Listen is the most extensive and ambitious SETI program ever conducted, which aims to find evidence of intelligent life through the study of cosmic radio waves. Once complete, it will have examined 1 million of the closest stars in the galactic pane and at the center of our galaxy, as well as the 100 closest galaxies beyond.

The survey relies on the Parkes Radio Telescope in New South Wales, Australia, the Green Bank Telescope in West Virginia, and the Automated Planet Finder (APF) at the Lick Observatory near San Jose, California. The location of these telescopes makes them ideal for surveying the entire disk of the Milky Way Galaxy and the region surrounding the supermassive black hole (SMBH) at the center of our galaxy – known as Sagittarius A*.

In this case, the survey data included signals that were between 1 and 12 gigahertz (GHz) on the radio spectrum from the plane of the Milky Way, the central region of our galaxy, and the interstellar comet 2I/Borisov.

Earth Transit Zone Survey

In particular, Siemion highlighted a small subset of the data known as that examined 20 stars of the nearest stars that are aligned with the plane of Earth’s orbit. For advanced civilizations living in any of these star systems, planet Earth could be detected when it passes in front of our Sun (aka. transits) relative to them.

The Parkes radio telescope, one of the telescopes comprising CSIRO’s Australia Telescope National Facility. Credit: CSIRO

This method of exoplanet detection, known as Transit Photometry, is the most effective way to confirm the existence of planets around other stars and was the method used by the Kepler Space Telescope – and currently by the Transitting Exoplanet Survey Satellite (TESS). Hence why this subset was given the name, “Earth Transit Zone Survey.”

Conducted using the Green Bank Telescope, this survey scanned these 20 stars in the 4 to 8 gigahertz range, or what is known as the C-band. Led by Sofia Sheikh (a former undergrad at UC Berkeley and now a graduate student at Pennsylvania State University), the GBT examined each star for 5 minutes, pointed away for another 5, and then repeated this same process twice more.

Each time, Sheikh and her team excluded any signal that didn’t disappear when the telescope was pointed away from the star being examined. Over time, they managed to reduce an initial data set of 1 million radio spikes down to a few hundred, while also eliminating signals from Earth-based interference. This left only four signals, which were attributed to passing satellites in orbit. As Sheikh explained:

“This is a unique geometry. It is how we discovered other exoplanets, so it kind of makes sense to extrapolate and say that that might be how other intelligent species find planets, as well. This region has been talked about before, but there has never been a targeted search of that region of the sky... “My search was sensitive enough to see a transmitter basically the same as the strongest transmitters we have on Earth, because I looked at nearby targets on purpose. So, we know that there isn’t anything as strong as our Arecibo telescope beaming something at us. Even though this is a very small project, we are starting to get at new frequencies and new areas of the sky.”

The Robert C. Byrd Green Bank Telescope (GBT) in West Virginia (NRAO/AUI)

The paper that describes their findings was recently submitted to The Astrophysical Journal. As they state in this study, Sheikh and her colleagues found no evidence of technological activity around these stars (aka. technosignatures). However, this latest analysis – along with other studies performed by the Breakthrough Listen group – is gradually placing constraints on the possible locations and ranges of radio transmissions.

“We didn’t find any aliens, but we are setting very rigorous limits on the presence of a technologically capable species, with data for the first time in the part of the radio spectrum between 4 and 8 gigahertz,” said Siemion. “These results put another rung on the ladder for the next person who comes along and wants to improve on the experiment.”

Galactic Center

Breakthrough Listen also collected considerable data on the center of our galaxy because of the higher likelihood of finding an artificial signal from this dense region of stars. Around this region, roughly 10 million stars are estimated to exist within a volume of space measuring no wider than 2.35 light-year (1 parsec).

It is also possible that the center of our galaxy constitutes a focal point (or Schelling Point) where civilizations meet up or place beacons to communicate with other intelligent species. For a sufficiently-advanced civilization, a powerful intergalactic transmitter could be placed here that would be powered by Sagittarius A* itself.

View of the stars at the center of the Milky Way, captured using the Spitzer Space Telescope. Credit: Suzan Stolovy (SSC/Caltech), JPL-Caltech, NASA

If this method of letting other intelligent species know that they are not alone in our galaxy is uncommon as a practice, then the most likely place to find transmissions would be within the billions of stars in the Milky Way’s disk. Hence why Breakthrough Listen pursues the two-pronged approach of observing both the disk and the galactic center of the Milky Way. As Siemion puts it:

“The galactic center is the subject of a very specific and concerted campaign with all of our facilities because we are in unanimous agreement that that region is the most interesting part of the Milky Way galaxy. If an advanced civilization anywhere in the Milky Way wanted to put a beacon somewhere, getting back to the Schelling point idea, the galactic center would be a good place to do it. It is extraordinarily energetic, so one could imagine that if an advanced civilization wanted to harness a lot of energy, they might somehow use the supermassive black hole that is at the center of the Milky Way galaxy.”

Checking Borisov for Signs of Life

Last, but not least, Breakthrough Listen also shared their latest data concerning certain “interstellar visitors.” Back in 2017, when ‘Oumuamua was on its way out of our Solar System, Breakthrough Listen dedicated some observation time to scan this interstellar object for signs of artificial transmissions. And with the announcement of a second interstellar visitor last year, Breakthrough Listen once again jumped at the chance to scan it.

The latest object, 2I/Borisov, made its closest pass to the Sun back in December of 2019 and is now on its way out of the Solar System. Once again, Breakthrough Listen found no evidence of technosignatures from this object, which should come as no surprise. Whereas ‘Oumuamua’s true nature continues to be a mystery, 2I/Borisov exhibited all the behavior of a comet.

A Hubble image of comet 2I/Borisov speeding through our Solar System. Credit: NASA/ESA/D. Jewitt (UCLA)

Steve Croft, a research astronomer with the Berkeley SETI Research Center and Breakthrough Listen, related why examining these objects is important:

“If interstellar travel is possible, which we don’t know, and if other civilizations are out there, which we don’t know, and if they are motivated to build an interstellar probe, then some fraction greater than zero of the objects that are out there are artificial interstellar devices. Just as we do with our measurements of transmitters on extrasolar planets, we want to put a limit on what that number is.”

In addition to this second release of data, the National Radio Astronomy Observatory (NRAO) and the SETI Institute recently announced that they were entering into a new partnership. In accordance with this agreement, the two organizations will be collaborating to add SETI capabilities to radio telescopes operated by NRAO.

The first project will involve the National Science Foundation’s famed Karl G. Jansky Very Large Array (VLA) in New Mexico, where the SETI Institute will install a state-of-the-art digital backend interface that will allow astronomers unprecedented access to the rich data stream the array provides. This upgrade is expected to enable far more sweeping and detailed SETI surveys than any conducted by the VLA before.

The Very Large Array, a radio telescope array located in New Mexico. Credit: NRAO

And as Yuri Milner, the founder of Breakthrough Listen, said about his organization’s most recent data release:

“For the whole of human history, we had a limited amount of data to search for life beyond Earth. So, all we could do was speculate. Now, as we are getting a lot of data, we can do real science and, with making this data available to general public, so can anyone who wants to know the answer to this deep question.”

The troves of data being collected by Breakthrough Listen and its partner institutions, as well as the way it is being shared with the public, is a testament to the current age of astronomical research. On the one hand, you have collaborative efforts and data-sharing happening between public and private organizations. On the other, you have an unprecedented level of public engagement and crowdsourcing.

If there is life out there to be found, it is collaborative and cooperative efforts like these that will make finding it that much more likely! If you’re interested in taking part, check out Breakthrough Listen’s Open Data Archive.

Further Reading: Berkeley News, Breakthrough Initiatives, SETI Institute