Dark Energy: Standard Candles Reliable

by | Jul 5, 2010 | | 12 Comments

Getting a handle on dark energy is one of the great goals of modern physics. But understanding what it is that seems to be accelerating the expansion of the universe depends upon the accuracy of our measurements. We can study this acceleration by looking at the behavior of Type Ia supernovae, which can be used as 'standard candles' -- the distance to a galaxy can be measured because the visual magnitude of this type of supernova depends on its distance. But how reliable are our standard candles? New work confirms the usefulness of these stellar events while explaining why some supernovae can look different from others. A Type Ia supernova occurs when a white dwarf gathers material from a nearby companion star and approaches the Chandrasekhar limit (about 1.38 solar masses), at which point the pressure and density have grown beyond the point that the star can support its own weight. Various processes have been invoked to explain the details, but while these supernovae seem alike, some...

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Early Multicellular Life and Its Implications

by | Jul 2, 2010 | | 13 Comments

We often speak in these pages about extinction events, and cite such examples as the Cretaceous-Tertiary event some 65.5 million years ago, when the mass extinction of dinosaurs and numerous animal and plant species occurred. Whether caused by an incoming asteroid or comet or through a series of catastrophes including volcanic eruptions (the Deccan traps), the K-T event is the classic reminder of the perils that confront life. But perhaps the largest extinction event of all was the so-called 'oxygen catastrophe,' an environmental change that caused oxygen to become widely available in the atmosphere and shallow ocean water. The oxygen catastrophe occurred around 2.4 billion years ago and doomed the bulk of Earth's anaerobic inhabitants. Astrobiologists are fascinated with how life adapts to changing environments, so we'd like to learn much more about how these events proceeded. Now comes news of fossils in black shale formations in Africa that are apparently 200 million years older...

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Costs of an Interstellar Probe

by | Jul 1, 2010 | | 19 Comments

When does it make sense to build a starship? Back in the late 1960s, Freeman Dyson went to work on the question of how much an interstellar probe might cost. Extrapolating from nuclear pulse propulsion and the state of the art in spacecraft design as then understood, Dyson arrived at an estimate of $100 billion to build the craft, which translates into roughly $650 billion today. Though stark, that figure is by no means as eye-popping as one of the estimates drawn up by the original Project Daedalus team: $100 trillion in 1978 dollars. These figures numb the senses, and you may recall the recent work by Ralph McNutt (Johns Hopkins Applied Physics Laboratory) and team, which pegged the cost of a series of human expeditions into the outer Solar System at $4 trillion. It's helpful to remember, though, that calculating when a project becomes fiscally feasible can be a useful undertaking in itself. Richard Obousy goes to work on these matters in a recent post in the Project Icarus blog,...

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Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

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