Friday, December 8, 2017

Australian Aboriginal Myth Describes Variable Brightness Stars

Did you know that a few stars that are visible in the night sky vary in brightness over time, in time frames and magnitude of brightness variability that differ from star to star?

Modern astronomers do and ancient Egyptian astronomers did, but in Western European astronomy this wasn't discovered until a few years before the dawn of the 18th century CE, and many ordinary people today don't know this fact. But, Australian aborigines were well aware of it and embedded it in their mythology.
[N]ew research, recently published in The Australian Journal of Anthropology, reveals that Aboriginal oral traditions describe the variable nature of three red-giant stars: Betelgeuse, Aldebaran and Antares.
From here.

The myths not only embed the variable stars in the myths about the constellations that are home to them, but also recount the relative frequency with which their magnitude varies.

Thursday, December 7, 2017

More Data Narrows Primordial Black Hole Dark Matter Parameter Space

Black hole merger events detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) have revived dark matter models based on primordial black holes (PBH) or other massive compact halo objects (MACHO). This macroscopic dark matter paradigm can be distinguished from particle physics models through their gravitational lensing predictions: compact objects cause most lines of sight to be demagnified relative to the mean, with a long tail of higher magnifications. We test the PBH model using the lack of lensing signatures on type Ia supernovae (SNe), modeling the effects of large scale structure, allowing for a non-gaussian model for the intrinsic SNe luminosity distribution and addressing potential systematic errors. Using current JLA (Union) SNe data, we derive bounds ΩPBH/ΩM<0.346(0.405) at 95% confidence, ruling out the hypothesis of MACHO/PBH comprising the totality of the dark matter at 5.01σ(4.28σ) significance. The finite size of SNe limits the validity of the results to MPBH≳0.01M⊙, fully covering the black hole mergers detected by LIGO and closing that previously open PBH mass range.
Miguel Zumalacarregui and Uros Seljak,"No LIGO MACHO: Primordial Black Holes, Dark Matter and Gravitational Lensing of Type Ia Supernovae"(December 7, 2017).

The limiting minimal size of PBH covered by the exclusion, 0.01M⊙, is equivalent to about ten times the mass of Jupiter (which implies an event horizon of the Primordial Black Hole with a radius of approximately 28 meters, which would fit comfortably within a baseball field).

This is notable, because it makes previous MACHO/PBH exclusions more robust, but the sweet spot for MACHO dark matter was already limited to PBH objects with a mass on the order of the Moon (many hundreds of times less than the mass of Jupiter), and a event horizon radius on the order of millimeters.

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Ad hominem attacks in the comment are completely unacceptable at this blog, and they will be made in original posts here only in very exceptional circumstances.

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If you have a criticism of something that someone else has said, you need to figure out how to say that without making it personal (and without making it a racial or ethnic slur or making your point in any otherwise offensive manner).

Northern Chinese Ancient DNA

There is population genetic continuity in Northern China near where the Han Dynasty originated, back to the early Bronze Age (ca. 2000 BCE) according to the ancient DNA that could be extracted from sixty individuals buried a cemetery from that time period.