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A massive, spacetime-warping cluster of\u00a0galaxies\u00a0is the setting of today\u2019s NASA\/ESA Hubble Space Telescope\u00a0Picture of the Week. The galaxy cluster in question is Abell 209, which is located 2.8 billion light-years away in the constellation\u00a0Cetus\u00a0(The Whale).<\/p>\n
This Hubble image of Abell 209 shows more than a hundred galaxies, but there\u2019s more to this cluster than even Hubble\u2019s discerning eye can see. Abell 209\u2019s galaxies are separated by millions of light-years, and the seemingly empty space between the galaxies is actually filled with hot, diffuse gas that can be spotted only at X-ray wavelengths. An even more elusive occupant of this galaxy cluster is\u00a0dark matter: a form of matter that does not interact with light. The Universe is understood to be comprised of 5% normal matter, 25% dark matter, and 70% dark energy<\/p>\n
Hubble observations like the ones used to create this image can help astronomers answer fundamental questions about our Universe, including mysteries surrounding dark matter and\u00a0dark energy. These investigations leverage the immense mass of a galaxy cluster, which can bend the fabric of spacetime itself and create warped and magnified images of background galaxies and stars in a process called\u00a0gravitational lensing.<\/p>\n
While this image lacks the\u00a0dramatic rings\u00a0that gravitational lensing can sometimes create, Abell 209 still shows subtle signs of lensing at work, in the form of streaky, slightly curved galaxies within the cluster\u2019s golden glow. By measuring the distortion of these galaxies, astronomers can map the distribution of mass within the cluster, illuminating the underlying cloud of dark matter. This information, which Hubble\u2019s fine resolution and sensitive instruments help to provide, is critical for testing theories of how our Universe has evolved.<\/p>\n
[Image Description:<\/i>\u00a0A cluster of distant, mainly elliptical galaxies. They appear as brightly shining points radiating golden light that each take the shape of a smooth, featureless oval. They crowd around one that is extremely large and bright. A few spiral galaxies of comparable size appear too, bluer in colour and with unique shapes. Of the other, more small and distant galaxies covering the scene, a few are warped into long lines.]<\/p>\n<\/p><\/div>\n<\/p><\/div>\n