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The Megamaser Cosmology Project Measures the Age of the Universe

Post by bystander » Sun Jun 21, 2020 4:30 pm

The Megamaser Cosmology Project Measures the Age of the Universe
SAO Weekly Science Update | 2020 Jun 19
A maser, like a laser, is a source of bright, monochromatic electromagnetic radiation, with the difference being that maser radiation is not optical light but rather longer wavelength microwave radiation. Dense molecular clouds in interstellar space sometimes produce natural masers when specific molecules (water and OH are two examples) or atoms are stimulated by the local conditions to emit very narrow-line radiation.

Such astronomical masers were first identified in space over fifty years ago, and have since been found in many locations in our Milky Way as well as in other galaxies, with the most spectacular examples found in regions of active star formation. In some cases the energy emitted in a single maser line exceeds the emission from the Sun over its entire visible spectrum making masers valuable diagnostic probes of their local conditions. These "megamasers" can be found in the nuclear regions of galaxies with active supermassive black holes and their brightness makes them potentially useful tools for cosmological studies. ...

The Megamaser Cosmology Project is a multi-year campaign to find, monitor, and map systems with the goal of constraining Ho to a precision of several percent with precise geometric distance measurements to water megamaser galaxies whose known recession velocities were also remeasured precisely. CfA astronomers Dom Pesce and Mark Reid are lead members of the team, which has just published its improved value for Ho of 73.9 +-3.0 (in usual units) corresponding to an age of the universe (with some assumptions) of 12.9 +-0.5 billion years. The team used their analyses of megamasers in six galaxies for this result. For comparison, other projects using measurements from galaxies have reported a consistent value, about 74.0, however the CMBR results from the Planck satellite give a value of value for Ho of about 67.4 and a corresponding age that is significantly older: 14.2 billion years. The team notes that their future megamaser observations will improve on this precision and help astronomers address this critical discrepancy.

The Megamaser Cosmology Project. XIII. Combined Hubble Constant Constraints ~ D. W. Pesce et al
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Inferring Temperature Structure of Circumstellar Disks

Post by bystander » Sat Jun 27, 2020 4:24 pm

Inferring the Temperature Structure of Circumstellar Disks from Polarized Emission
SAO Weekly Science Update | 2020 Jun 26
Image
An ALMA submiilimeter image of the dusty circumstellar disc around a young
star. Astronomers are using ALMA polarization maps of the radiation from discs
similar to this one to infer the presence of a temperature gradient, and infer
possible accretion onto the disc. © Lee, Chin-Fei et al., 2017 SciAdv

Polarized light is a familiar phenomenon because the scattering or reflection of light results in one of its two components being preferentially absorbed. The majority of sunlight on Earth, for example, is preferentially polarized due to scattering in the atmosphere (this helps make polarized sunglasses effective). Electromagnetic radiation from astrophysical sources can also be polarized, typically because of scattering from elongated dust grains that are aligned with each other by the local magnetic fields. These fields are thought to play a major, perhaps even a dominant role in controlling the shapes and motions of interstellar gas clouds and are extremely difficult to measure directly. Observations of polarization by dust grains offer a unique way to probe the magnetic fields.

The polarized emission from aligned grains in discs around young stellar objects is of particular interest to astronomers studying how planets develop and evolve in these discs. The polarized emission can reveal not only the details of the magnetic fields present but also (depending on the grain shapes and properties) other structural features of the disk environment, for example the presence of anisotropic stellar radiation. ...

Probing the Temperature Structure of Optically Thick Disks
Using Polarized Emission of Aligned Grains
~ Zhe-Yu Daniel Lin et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor