https://www.space.com/imageoftheday/image_of_day_080918.html

A
massive swarm of galaxies located 2.3 billion light years away shows signs of
merging, as seen by NASA's Chandra X-ray Observatory and Hubble Space Telescope.

The
large galaxy cluster, known as Abell 1689, has a smooth appearance in the X-ray
spectrum that stands in contrast to other merging systems such as the Bullet
Cluster. Chandra sees the X-rays emitted by the hundred-million-degree background
gas as purple, while Hubble's optical view shows galaxies colored yellow.

Long
arcs in Hubble's optical view represent gravitational lensing, where light from
distant sources bend around a massive object. Astronomers still need to figure
out the difference in mass estimates from the X-ray data and gravitational
lensing.

• Video
  - Hubble Service Mission 4 Countdown


• Video:
  Chandra: A Great Observatory


• Video
  Player: Star Cluster Close-Up

— NASA/CXC/MIT/STScI and SPACE.com Staff

Credit: NASA/CXC/MIT/STScI/E.-H
Peng et al