Giant Elliptical Galaxy M87 and its Jet

This image shows a number of galaxies in a very small part of the Virgo cluster, which spans a large area of the sky and features groups of galaxies such as Markarian’s Chain. Imaging the cluster is best done using the wide field view of a DSLR camera, but telescopic views of some of the galaxies can reveal plenty of detail.

As an elliptical galaxy – albeit a huge one – M87 is not a spectacular telescopic target. These objects usually take the form of amorphous blobs of light and display little structure, in contrast to the spiral arms and active H-II regions that make other galaxies so attractive. However I had a particular reason for targeting this object, as I explain below.

The next image adds labels for the major galaxies visible here. North is toward the 8 o’clock direction, as can be seen from the increasing declination labels.

M87’s fairly bland appearance belies its true dimensions. This galaxy is huge: as the dominant member of the Virgo Group it is about 54 million light years away and with about one trillion (10¹²) stars is much more massive than our Milky Way. It also has about 15,000 globular clusters compared with around 200 in our galaxy. But its most spectacular feature is invisible: it has been found to harbour a supermassive black hole at its centre, with a mass of around 4 billion suns (compare this with the black hole at the centre of the Milky Way with a mass of about 4 million suns). Although black holes do not emit any light, it is possible to image the region close to them and observe the distortion of spacetime caused by their presence. Such an image of the region around M87’s black hole was obtained by the Event Horizon Telescope and published in 2017.

The other spectacular feature of M87 is a huge jet of plasma, about 5,000 light years long, that is being ejected from the core at relativistic speeds (by which we mean speeds that are an appreciable fraction of the speed of light). The amount of energy in the jet is almost beyond belief, and it is believed to originate in the spinning accretion disk surrounding the giant black hole.

The jet is the reason I decided to target this rather bland galaxy, as I was curious to see whether my equipment could successfully image it. Theoretically it was possible as the jet is at least 10 arc-seconds long, but I was unsure whether the contrast with the bright core of the galaxy would cause problems.

However, the jet can just be made out in the image above, pointing toward the 11 o’clock direction. To show it more clearly, the image must be stretched differently – and not excessively. The result is shown in the image below. Note that, although the galaxy appears to be about the same size as in the main image above, it is zoomed by a factor of 3, the effect of the different contrast settings being to render the outer parts of the galaxy invisible in the image below.

As this exercise was simply to reveal the jet rather than produce a pretty colour picture I elected for a monochrome image and a modest exposure time.

Technical details:

Planewave CDK-14 corrected Dall-Kirkham reflector, FLI Proline P9000 cooled CCD camera and filter wheel with Astrodon filters. Total exposure time was 5.5 hours through the Luminosity (virtually clear) filter. Processed in PixInsight.