We modeled the evolution of the Milky Way Galaxy to trace the distribution in space and time of four prerequisites for complex life: the presence of a host star, enough heavy elements to form terrestrial planets, sufficient time for biological evolution, and an environment free of life-extinguishing supernovae. We identified the Galactic habitable zone (GHZ) as an annular region between 7 and 9 kiloparsecs from the Galactic center that widens with time and is composed of stars that formed between 8 and 4 billion years ago. This GHZ yields an age distribution for the complex life that may inhabit our Galaxy. We found that 75% of the stars in the GHZ are older than the Sun.

https://science.sciencemag.org/content/sci/303/5654/59.full.pdf

The galactic habitable zone and the age distribution of complex life in the Milky Way.

An analysis of the data of Raup and Sepkoski (1984) is reported which suggests that the dominant cyclicity in major marine extinctions during at least the past 250 Myr is 30 + or - 1 Myr, with the standard deviation of an individual episode being + or - 9 Myr. This terrestrial cycle is found to be strongly correlated with the time needed for the solar system to oscillate vertically about the galactic plane. It is argued that galactic triggering or forcing of terrestrial biological crises may arise as a result of collisions or close encounters of the solar system with clouds of gas and dust, which would gravitationally perturb the solar system's family of comets and thereby increase the flux of comets and meteorites near the earth, leading to large-body impacts. A dominant cyclicity of 31 + or - 1 Myr is found for the observed age distribution of impact craters on earth, the phase of this cycle agreeing with the shown by the major biological crises.

/pdf/terrestrial-mass-extinctions-cometary-impacts-and-the-sun-s-4rgqwwj0z3.pdf

Terrestrial mass extinctions, cometary impacts and the Sun's motion perpendicular to the galactic plane

The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way

In recent years, wide-field sky surveys providing deep multi-band imaging have presented a new path for indirectly characterizing the progenitor populations of core-collapse supernovae (SN): systematic light curve studies. We assemble a set of 76 grizy-band Type IIP SN light curves from Pan-STARRS1, obtained over a constant survey program of 4 years and classified using both spectroscopy and machine learning-based photometric techniques. We develop and apply a new Bayesian model for the full multi-band evolution of each light curve in the sample. We find no evidence of a sub-population of fast-declining explosions (historically referred to as "Type IIL" SNe). However, we identify a highly significant relation between the plateau phase decay rate and peak luminosity among our SNe IIP. These results argue in favor of a single parameter, likely determined by initial stellar mass, predominantly controlling the explosions of red supergiants. This relation could also be applied for supernova cosmology, offering a standardizable candle good to an intrinsic scatter of 0.2 mag. We compare each light curve to physical models from hydrodynamic simulations to estimate progenitor initial masses and other properties of the Pan-STARRS1 Type IIP SN sample. We show that correction of systematic discrepancies between modeled and observed SN IIP light curve properties and an expanded grid of progenitor properties, are needed to enable robust progenitor inferences from multi-band light curve samples of this kind. This work will serve as a pathfinder for photometric studies of core-collapse SNe to be conducted through future wide field transient searches.

/pdf/towards-characterization-of-the-type-iip-supernova-14kaior7ex.pdf

Towards Characterization of the Type IIP Supernova Progenitor Population: a Statistical Sample of Light Curves from Pan-STARRS1

In recent years, wide-field sky surveys providing deep multiband imaging have presented a new path for indirectly characterizing the progenitor populations of core-collapse supernovae (SNe): systematic light-curve studies. We assemble a set of 76 grizy-band Type IIP SN light curves from Pan-STARRS1, obtained over a constant survey program of 4 yr and classified using both spectroscopy and machine-learning-based photometric techniques. We develop and apply a new Bayesian model for the full multiband evolution of each light curve in the sample. We find no evidence of a subpopulation of fast-declining explosions (historically referred to as Type IIL SNe). However, we identify a highly significant relation between the plateau phase decay rate and peak luminosity among our SNe IIP. These results argue in favor of a single parameter, likely determined by initial stellar mass, predominantly controlling the explosions of red supergiants. This relation could also be applied for SN cosmology, offering a standardizable candle good to an intrinsic scatter of 0.2 mag. We compare each light curve to physical models from hydrodynamic simulations to estimate progenitor initial masses and other properties of the Pan-STARRS1 Type IIP SN sample. We show that correction of systematic discrepancies between modeled and observed SN IIP light-curve properties and an expanded grid of progenitor properties are needed to enable robust progenitor inferences from multiband light-curve samples of this kind. This work will serve as a pathfinder for photometric studies of core-collapse SNe to be conducted through future wide-field transient searches.

/pdf/toward-characterization-of-the-type-iip-supernova-progenitor-4rc0x4vsrt.pdf

Toward Characterization Of The Type IIP Supernova Progenitor Population: A Statistical Sample Of Light Curves From Pan-STARRS1

MCCREA1,2 has proposed that the encounter of the Solar System with a dense cloud of interstellar material during its passage through a spiral arm of the Galaxy may produce such climatic catastrophes on Earth as the ice epochs. His thesis, an extension of several earlier investigations3,4,5, is based on the expected effect on the solar constant of an increased accretion rate. Unfortunately, the cloud density necessary to produce the required variation is 105 to 107 cm−3, and although clouds with such extreme densities are thought to exist6, Begelman and Rees7 point out that they are so compact and unusual as to reduce the likelihood of the Sun ever encountering one. (Dennison and Mansfield's suggestion8 that there is no evidence for the existence of a nearby super-dense cloud which could have caused the most recent ice epoch has been answered by McCrea9.) Begelman and Rees7 in fact showed that a much more modest cloud density (≃102 to 103 cm−3) would prevent the solar wind from reaching the Earth, with resulting modification of the near-Earth environment; however, the climate consequences of such a modification are not well understood. We present here an alternative hypothesis which still retains McCrea's association with the passage of the Solar System through a spiral arm, but which relates the initiation of an ice epoch, plus biological catastrophes, to an encounter of the Solar System with a nearby supernova outburst rather than a super-dense interstellar cloud.

Frequency of nearby supernovae and climatic and biological catastrophes

One of the Ugaritic texts of the Second Millennium BC describes a total eclipse of the Sun. The date is established as 1375 BC, May 3.

F. R. Stephenson

Papers

Frequency of nearby supernovae and climatic and biological catastrophes

The earliest known record of a solar eclipse.

The Earliest Known Record of a Solar Eclipse