Researchers find evidence of periodic disk instability in massive Galactic Core

(ORDO NEWS) — An international research team led by Willem Adrianus Baan of the Chinese Academy of Sciences (CAS) Star Formation and Evolution Study Group has found evidence of periodic disc instability in the H2O megagalaxy NGC 4258.

NGC 4258, also named Messier 106, is a nearby galaxy that has a prominent H2 emission. This radiation originates in a rapidly rotating disk surrounding an active galactic nucleus, but the physical conditions that provoke these emissions remain unclear.

The researchers conducted space-based very long baseline interferometry (SVLBI) experiments using the Russian observatory RadioAstron in an extended Earth orbit, as well as large ground-based telescopes at Green Bank (USA) and Effelsberg (Germany).

They observed that a series of equally spaced clouds within the gaseous disk surrounding the core of NGC 4258 is responsible for H2.

These SVLBI experiments were carried out with an Earth-to-space baseline up to 19.5 Earth diameters and a high observational angular resolution of 11 micro-arcseconds (3 x 10-9 degrees).

The observed molecular emission regions were found to rotate within a thin disk at a distance of only 0.126 parsecs (0.38 light years) from the core of the black hole galaxy.

The megamaser radiation (radiation that can originate in molecular clouds, comets, planetary atmospheres, stellar atmospheres, or various other conditions of interstellar space) H2O generated in these regions results from the maser amplification of excited/pumped water molecules when numerous clouds drift in front of radio continuum in the core of NGC 4258.

The formation of these emission regions, their regular velocity separation, and time-dependent emission are apparently consistent with the appearance of a periodic magneto-rotational instability.

This type of instability is due to differential rotation in the disk and has long been thought to govern radial momentum transfer and viscosity in the accretion disk.

These SVLBI observations provide the first detailed view of the thin Keplerian accretion disk around an active galactic nucleus.

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