Too Many Parsecs: Playing with NGC 1569

Sunday, June 17, 2012

Playing with NGC 1569

The nearby dwarf galaxy NGC 1569, about 11 million light years from us, is a hotbed of vigorous star birth activity which blows huge bubbles and super-bubbles that riddle the main body of the galaxy. The galaxy's vigorous "star factories" are also manufacturing brilliant blue star clusters. This galaxy had a sudden and relatively recent onset of star birth 25 million years ago, which subsided about the time the very earliest human ancestors appeared on Earth.

The image of NGC 1569 published on February 2004 on the ESA Hubble website. Credit: European Space Agency, NASA & Peter Anders (Göttingen University Galaxy Evolution Group, Germany)

In this image, taken with the NASA/ESA Hubble Space Telescope and published in 2004, the bubble structure is sculpted by the galactic super-winds and outflows caused by a colossal input of energy from collective supernova explosions that are linked with a massive episode of star birth.

The bubble-like structures seen in this image are made of hydrogen gas that glows when hit by the fierce winds and radiation from hot young stars and is racked by supernovae shocks. The first supernovae blew up when the most massive stars reached the end of their lifetimes roughly 20-25 million years ago. The environment in NGC 1569 is still turbulent and the supernovae may not only deliver the gaseous raw material needed for the formation of further stars and star clusters, but also actually trigger their birth in the tortured swirls of gas.

So much for the galaxy. As regards, however, the image of the galaxy, we can add something else. Unconsciously we are accustomed to consider astronomical images as a fact. Actually, the raw data made available by various observatories, including Hubble, are FITS files, which can be processed in very different ways.

Using a free image processing software, FITS Liberator 3, and a combination of filters and sliders available in it, we can obtain very different images of the same astronomical object, in this case NGC 1569. The first three images below are my experiments, based on the greyscale FITS files at 336, 555, 656, and 814 nm, made available on the ESA Hubble Space Telescope website. The last two images are similar tests made by other users.

FITS image processing is mainly aimed to highlight the faintest details without losing the more brilliant ones. Having said that, between the original FITS files and the final astronomical image there is a huge space of freedom, in which many parameters – hue, saturation, brightness, contrast, etc. – can be manipulated, based upon the personal aesthetic sense. This freedom influences the same concept of reality, I imagine. Is there a "true" image of NGC 1569?