The massive galaxy cluster MACS J0717
This composite image shows the massive galaxy cluster MACS J0717.5+3745 (MACS J0717, for short), where four separate galaxy clusters have been involved in a collision, the first time such a phenomenon has been documented. Hot gas is shown in an image from the Chandra X-ray Observatory, and galaxies are shown in an optical image from the Hubble Space Telescope. The hot gas is color-coded to show temperature, where the coolest gas is reddish purple, the hottest gas is blue, and the temperatures in between are purple. MACS J0717 is located about 5.4 billion light-years from Earth. It is one of the most complex galaxy clusters ever seen.
The repeated collisions in MACS J0717 are caused by a 13-million-light-year-long stream of galaxies, gas, and dark matter, known as a filament, pouring into a region already full of matter. A collision between the gas in two or more clusters causes the hot gas to slow down. However, the massive and compact galaxies do not slow down as much as the gas does, and so move ahead of it. Therefore, the speed and direction of each cluster's motion, perpendicular to the line of sight, can be estimated by studying the offset between the average position of the galaxies and the peak in the hot gas
© Stocktrek Images
The Northern Lights Are Captured Over HMS Ocean
Whilst conducting Cold Weather Amphibious Warfare Training within the beautiful Fjords of Northern Norway, 150 miles north of the Arctic Circle, HMS Ocean's embarked photographer was able to capture this stunning image of the Northern Lights shimmering above the Helicopter Carrier's Flight Deck.
HMS Ocean is the Royal Navy's largest warship and was operating in the region in December 2009 as part of the UK's Amphibious Task Group, conducting Exercise Cold Response; a multinational exercise conducted alongside the Norwegian Armed Forces
© Crown Copyright
Glow-in-the-dark blue waves caused by the phenomenon known as harmful algal bloom or red
Glow-in-the-dark blue waves caused by the phenomenon known as harmful algal bloom or "red tide", are seen at night near Sam Mun Tsai beach in Hong Kong January 22, 2015. Algal blooms occur when there is a sharp growth in algae population in a water system, and are considered harmful when resulting in negative impacts on other organisms. Picture taken using long exposure. REUTERS/Tyrone Siu (CHINA - Tags: SOCIETY ENVIRONMENT TPX IMAGES OF THE DAY)