This colorful view of Milky Way was captured when the NASA/ESA Hubble Space Telescope pointed its Advanced Camera for Surveys (ACS) towards the constellation of Sagittarius.
This Hubble image shows part of the sky in the constellation of Sagittarius. Image credit: NASA / ESA / Hubble.
Red and blue stars are scattered across this frame, set against a background of thousands of more distant stars and galaxies.
Two features are particularly striking: the colors of the stars, and the dramatic crosses that burst from the centers of the brightest bodies.
While some of the colors in this frame have been enhanced and tweaked during the process of creating the image from the observational data, different stars do indeed glow in different colors.
Stars differ in color according to their surface temperature: very hot stars are blue or white, while cooler stars are redder.
They may be cooler because they are smaller, or because they are very old and have entered the red giant phase, when an old star expands and cools dramatically as its core collapses.
The crosses are nothing to do with the stars themselves. They are actually known as diffraction spikes, and are caused by the structure of Hubble itself.
Like all big modern telescopes, Hubble uses mirrors to capture light and form images.
Hubble’s secondary mirror is supported by struts, called telescope spiders, arranged in a cross formation, and they diffract the incoming light.
Diffraction is the slight bending of light as it passes near the edge of an object.
Every cross in this image is due to a single set of struts within Hubble itself.
The color image was made from separate exposures taken in the visible and near-infrared regions of the spectrum with Hubble’s ACS camera.
It is based on data obtained through three filters: a blue filter (F435W), a broad V-band filter (F606W) and a near-infrared filter (F814W).
The color results from assigning different hues to each monochromatic image associated with an individual filter.
