On the abundance of extraterrestrial life after the Kepler mission

Amri Wandel
The data recently accumulated by the Kepler mission have demonstrated that small planets are quite common and that a significant fraction of all stars may have an Earth-like planet within their Habitable Zone.
These results are combined with a Drake-equation formalism to derive the space density of biotic planets as a function of the relatively modest uncertainty in the astronomical data and of the (yet unknown) probability for the evolution of biotic life…
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Read also: How Data From The Kepler Space Telescope Is Changing The Drake Equation

Astrophysicists Identify The “Habitable” Regions Of The Entire Universe

It’s not just stars and galaxies that have habitable zones. Some regions of universe are more life-friendly than others

Gamma ray bursts are among the most powerful events in the universe. And although the SGR 1806 -20 flare was relatively mild, it was an unwelcome reminder that life on this planet is constantly threatened by events of unimaginable power.

But here’s the thing: gamma ray bursts are much more common in some parts of the universe than others. That raises the curious prospect that some parts of the universe ae much more inhospitable to life than others. So where are these death zones and what kind of constraints do they place on the origin of life?

Today, Tsvi Piran at The Hebrew University in Jerusalem, Israel and Raul Jimenez at Harvard University in Cambridge say they’ve worked out where in the universe gamma ray bursts are most deadly. As a result, they are able to work out for the first time the universe’s habitable zones.

Gamma ray bursts are a significant mystery—nobody is quite sure how or where the most powerful ones occur. But astronomers know that a burst could do significant damage to the Earth if it happened nearby. The gamma rays would rapidly strip the planet of its ozone layer, leaving the creatures on the surface vulnerable to ultraviolet light and other kinds of high-energy radiation. Indeed, several studies have examined the very real possibility that gamma ray bursts may have brought life on Earth to the edge of extinction on several occasions in the past.

Exactly how often a given planet would be hit by gamma ray bursts obviously depends on its neighbourhood. So the starting point for the work of Prian and Jimenez is to determine how common these powerful events are. Continue reading Astrophysicists Identify The “Habitable” Regions Of The Entire Universe

Astrosociology: Interwiews about an infinite universe

visible universe

click to enlarge

Erik Høg

If the universe is infinite now it has always been infinite. This is the opinion of many astronomers today as can be concluded from the following series of interviews, but the opinions differ much more than I had expected.
Many astronomers do not have a clear opinion on this matter. Others have a clear opinion, but very different from the majority. Detailed arguments by two experts on general relativity are also included.
Observations show that the universe is flat, i.e. the curvature is zero within the small uncertainty of measurements.
This implies an infinite universe, though most probably we will never know that for certain. For comparison with the recent interviews, opinions during the past 2300 years since Aristotle about the universe being finite or infinite have been collected from literature, and it appears that the scientists often had quite definite opinions…

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The Ĝ Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies

I.  Background and Justification

J. T. Wright, B. Mullan, S. Sigurðsson, M. S. Povich

We motivate the Ĝ infrared search for extraterrestrial civilizations with large energy supplies.
We discuss some philosophical difficulties of SETI, and how communication SETI circumvents them.
We review “Dysonian SETI”, the search for artifacts of alien civilizations, and find that it is highly complementary to traditional communication SETI; the two together might succeed where either one, alone, has not.
We discuss the argument of Hart (1975) that spacefaring life in the Milky Way should be either galaxy-spanning or non-existent, and examine a portion of his argument that we dub the “monocultural fallacy”.
We discuss some rebuttals to Hart that invoke sustainability and predict long Galaxy colonization timescales.
We find that the maximum Galaxy colonization timescale is actually much shorter than previous work has found (109 yr), and that many “sustainability” counter-arguments to Hart’s thesis suffer from the monocultural fallacy.
We extend Hart’s argument to alien energy supplies, and argue that detectably large energy supplies can plausibly be expected to exist because life has potential for exponential growth until checked by resource or other limitations, and intelligence implies the ability to overcome such limitations.
As such, if Hart’s thesis is correct then searches for large alien civilizations in other galaxies may be fruitful; if it is incorrect, then searches for civilizations within the Milky Way are more likely to succeed than Hart argued. We review some past Dysonian SETI efforts, and discuss the promise of new mid-infrared surveys, such as that of WISE…
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IRIS: Observing a Gigantic Solar Eruption

A coronal mass ejection burst off the side of the sun on May 9, 2014. The giant sheet of solar material erupting was the first CME seen by NASA’s Interface Region Imaging Spectrograph, or IRIS. The field of view seen here is about five Earth’s wide and about seven and a half Earth’s tall.

IRIS must commit to pointing at certain areas of the sun at least a day in advance, so catching a CME in the act involves some educated guesses and a little bit of luck.


Massive Black Hole Duo: Possible Sighting by NASA’s WISE


Two black holes are entwined in a gravitational tango in this artist’s conception. Supermassive black holes at the hearts of galaxies are thought to form through the merging of smaller, yet still massive black holes, such as the ones depicted here. Image credit: NASA

Astronomers have spotted what appear to be two supermassive black holes at the heart of a remote galaxy, circling each other like dance partners. The incredibly rare sighting was made with the help of NASA’s Wide-field Infrared Survey Explorer, or WISE.

Follow-up observations with the Australian Telescope Compact Array near Narrabri, Australia, and the Gemini South telescope in Chile, revealed unusual features in the galaxy, including a lumpy jet thought to be the result of one black hole causing the jet of the other to sway.

“We think the jet of one black hole is being wiggled by the other, like a dance with ribbons,” said Chao-Wei Tsai of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., who is lead author of a paper on the findings appearing in the Dec. 10 issue of Astrophysical Journal. “If so, it is likely the two black holes are fairly close and gravitationally entwined.”

The findings could teach astronomers more about how supermassive black holes grow by merging with each other.

The WISE satellite scanned the entire sky twice in infrared wavelengths before being put into hibernation in 2011. NASA recently gave the spacecraft a second lease on life, waking it up to search for asteroids, in a project called NEOWISE.

The new study took advantage of previously released all-sky WISE data. Astronomers sifted through images of millions of actively feeding supermassive black holes spread throughout our sky before an oddball, also known as WISE J233237.05-505643.5, jumped out.

“At first we thought this galaxy’s unusual properties seen by WISE might mean it was forming new stars at a furious rate,” said Peter Eisenhardt, WISE project manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and a co-author of the study. “But on closer inspection, it looks more like the death spiral of merging giant black holes.”

Almost every large galaxy is thought to harbor a supermassive black hole filled with the equivalent in mass of up to billions of suns. How did the black holes grow so large? One way is by swallowing ambient materials. Another way is through galactic cannibalism. When galaxies collide, their massive black holes sink to the center of the new structure, becoming locked in a gravitational tango. Eventually, they merge into one even-more-massive black hole.

The dance of these black hole duos starts out slowly, with the objects circling each other at a distance of about a few thousand light-years. So far, only a few handfuls of supermassive black holes have been conclusively identified in this early phase of merging. As the black holes continue to spiral in toward each other, they get closer, separated by just a few light-years.

It is these close-knit black holes, also called black hole binaries, that have been the hardest to find. The objects are usually too small to be resolved even by powerful telescopes. Only a few strong candidates have been identified to date, all relatively nearby. The new WISE J233237.05-505643.5 is a new candidate, and located much farther away, at 3.8 billion light-years from Earth.

Radio images with the Australian Telescope Compact Array were key to identifying the dual nature of WISE J233237.05-505643.5. Supermassive black holes at the cores of galaxies typically shoot out pencil-straight jets, but, in this case, the jet showed a zigzag pattern. According to the scientists, a second massive black hole could, in essence, be pushing its weight around to change the shape of the other black hole’s jet.

Visible-light spectral data from the Gemini South telescope in Chile showed similar signs of abnormalities, thought to be the result of one black hole causing disk material surrounding the other black hole to clump. Together, these and other signs point to what is probably a fairly close-knit set of circling black holes, though the scientists can’t say for sure how much distance separates them.

“We note some caution in interpreting this mysterious system,” said Daniel Stern of JPL, a co-author of the study. “There are several extremely unusual properties to this system, from the multiple radio jets to the Gemini data, which indicate a highly perturbed disk of accreting material around the black hole, or holes. Two merging black holes, which should be a common event in the universe, would appear to be simplest explanation to explain all the current observations.”

The final stage of merging black holes is predicted to send gravitational waves rippling through space and time. Researchers are actively searching for these waves using arrays of dead stars called pulsars in hopes of learning more about the veiled black hole dancers (see ).

The technical paper is online at