Masers in stellar nurseries

Masers in Stellar Nurseries
A false-color infrared image of a young star showing outflowing jets as green beams of shocked gas (actually two of the stars in this image have jets). A new study using the SMA has found that bright methanol masers, often seen in such star-forming regions and long thought to indicate only the youngest such stars, are also found around more mature stars. Credit: NASA-Spitzer Space Telescope
(Phys.org)—Astronomers have come to realize that the process of star formation, once thought to consist essentially of just the simple coalescence of material by gravity, occurs in a complex series of stages. As the gas and dust in giant molecular clouds comes together into stars, dramatic outflowing jets of material develop around each, as do circumstellar disks (possibly pre-planetary in nature). Other features are present as well: Astronomers in the 1960s were amazed to discover that these star-forming regions sometimes produce natural masers (masers are the bright, radio wavelength analogs of lasers). Clouds of water vapor or methanol vapor in regions of active star formation generate some of the most spectacular masers.

Although associated with the complex activity of star formation, the role of masers in the building of a is thought to be minor (although it is not understood). However masers, because they are so bright, provide valuable diagnostic probes of the regions where star formation is underway. Exactly what they reveal is less clear, but many astronomers have thought that methanol masers can signal the very earliest stages of star formation, perhaps less than about ten thousand years old. One of the key questions masers can possibly help resolve is how stars more massive than the Sun form. Understanding the birth of such is essential not only in its own right, but also because these stars end up as which enrich the cosmos with elements essential to life. The birth of massive stars is, however, notoriously tricky to understand because their larger masses prompt the young star to mature very quickly, in less than about one hundred thousand years and much faster than lower-mass stars. As a result, many growth stages are blurred together. Masers are thought to offer a way to probe these earliest times of star formation.

SAO astronomers Claudia Cyganowski and Qizhou Zhang, with five colleagues, used the Submillmeter Array (SMA) to study regions of massive star formation identified in infrared images as having outflows typical of massive young stars. The SMA was able to identify all of the protostellar cores from their millimeter dust emission. They found one such protocluster of young stars that also contained a variety of types of methanol masers, enabling a comparative study of masers and star- formation activity. Writing in the latest issue of the Astrophysical Journal Letters, the scientists report finding that, contrary to the conventional wisdom, methanol masers thought to be associated with very young stages of are found occurring with more evolved embryos. The new results show for the first time that the mechanisms at work to make these methanol masers, shocks for example, are found in a much wider range of situations than previously suspected. The new results are not atypical of progress in astronomy.


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Dec 25, 2012
According to Wikipedia, most astrophysical masers seem associated with newborn stars, and supernovae remnants, interacting with dense molecular clouds. Inexpertly, a masing cloud could be compared, to an irregularly shaped scree of dominoes on top of a table, which have been set up ("pumped" into an excited state), so that a single finger flick ("trigger" photon) could knock numerous dominoes down (maser). Seemingly clearly, longer path-lengths of set-up dominoes ("pumped" molecules) could harbor more dominoes able to fall down in that direction (mase). But, if radiation stimulates the de-excitation of molecules ("knocks dominoes down"), what excites them ("sets dominoes up")? Perhaps molecules are kinetically collisionally excited, and radiatively de-excited? The common denominator, between newborn stars, and supernovae remnants, could be winds & ejecta, that collisionally shock molecular cloud material?

http://en.wikiped..._regions

Dec 25, 2012
On second thought...

according to "Advanced Astrophysics" by Neb Duric, maser emissions derive from rotational & vibrational modes of molecules, in dense cold molecular clouds, having long lifetimes (10s Myrs). And, according to the History Channel documentary "The Universe -- how the solar system was made", dense molecular clouds are so cold, that molecules move little, and essentially sit suspended in space. Such static motionlessness could account, for the velocity coherence of maser-emitting clouds (no relative Doppler shifts, because no relative motion). Moreover, maser emissions vary quickly, over days to years. Masing clouds "flash" pulses of emission, before burning out. Perhaps molecular clouds naturally collisionally excite rotational & vibrational modes, and then sit in space, for Myrs, waiting to be "triggered"? Perhaps synchrotron radio emissions, from new stars, then stimulate cloud de-excitations?

http://www.naic.e...sPR.html

Dec 26, 2012
on third thought...

When molecules of OH form, by the collisional encounter of an H with an O, must the molecule form, with an initial rotation, in order to offset the angular momentum, of the photon emitted, by the bonding? If so, then newly formed molecules would all be "born" spinning. Then, if molecules formed before thermal processes could equipartition their energies, then a young cloud, full of freshly-formed molecules, would be generated, into the population-inverted state.

Dec 26, 2012
Maser photons, with wavelengths of order 10cm, have energies of order 10^(-5) eV, equivalent to about 0.1K. So, even in cold molecular space gas, at ~100K, the rotational excitation states are nearly energy degenerate. So, there Boltzmann factors are nearly unity, e^(-E/kT) ~ 1. And so, if there are N such states, then each such state will harbor ~1/N of all molecules.

Perhaps all of the higher excited states have short lifetimes, quickly spontaneously decaying into the first excited state? If so, then collisions would thermalize the population, exciting ~1/N of all molecules into each state. But, then, all of the higher excited states would swiftly spontaneously decay down into the 1st excited state, which is metastable, persisting for ~10Myr. That would "telescope" all excited states into the 1st excited state; for every 1 molecule in the ground state, ~N would wind up in the first excited state. Such a process would generate an ~N:1 population inversion. N>>1 since NE~kT.

Dec 26, 2012
"masers are the bright, radio wavelength analogs of lasers"

That's astrophysical code for electric currents that are powering the stars, just as the Sun has. These "masers" have a higher current density, so instead of the dark mode plasma that energizes the Sun, the "masers" are excited to glow mode discharge and the star is, of course, arc mode discharge.

Dec 27, 2012
"masers are the bright, radio wavelength analogs of lasers"

That's astrophysical code for electric currents that are powering the stars, just as the Sun has. These "masers" have a higher current density, so instead of the dark mode plasma that energizes the Sun, the "masers" are excited to glow mode discharge and the star is, of course, arc mode discharge.


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