Sunday, September 07, 2008

M87 and it's gorgous jet

The giant elliptical galaxy Messier 87 (M87, NGC 4486), also called Virgo A, is one of the most remarkable objects in the sky.

Gorgeous detail of the Jet of M87 can be seen in this HST image which was processed by R. Mark Elowitz. The giant jet was discovered by H.D. Curtis of the Lick Observatory in 1918. This phenomenon extends thousands of light years (sources give 5,000, but maybe it is more as they are often based on too small distances of this galaxy; the present author would estimate 7-8,000 might be more likely). The jet is consisted of ejected gaseous material from the core of the galaxy. Polarimetric exposures of this jet have shown that its light is strongly polarized in a way which is typical for synchrotron radiation. It exhibits a continuous spectrum, and appears blue in (short exposure) color photos (as the one in J.D. Wray's Color Atlas of Galaxies). It is in violent turbulence; observations have shown apparent superluminal motion of gas clouds in this object - probably an illusion caused by the fact that the jet is pointing towards us.

While our Milky Way has the modest number of roughly 150 to 200 globulars, M87 possesses a remarkable system of several thousands of these objects: Moderate estimates such as the 1976 work quoted by Burnham give numbers of at least 4,000, while more modern values go up to 15,000, e.g. 13,000 in W.E. Harris' Globular Cluster Systems list), surrounding this giant galaxy in a conspicuous halo.

The telescopes at are able to image M87's fabulous jet as seen here in monochrome then in color images.

1 comment:

Dil said...

I think the jet is a particularly good example in the philosophy of science of the interplay between "as if" theories and observational data.

Without the "as if" theory, the explanations for supraluminal motion are just begging the question!