The Triangulum Galaxy, otherwise known as Messier 33, lies almost 3 million light-years from Earth, and is a near neighbor of the Andromeda Galaxy. The galaxy is imaged here by the Nicholas U. Mayall 4-meter Telescope, located at Kitt Peak National Observatory (KPNO), a Program of NSF’s NOIRLab. The Triangulum Galaxy is the third-largest member of the Local Group, a cluster of galaxies that includes our Milky Way and its closest neighbors. The Andromeda Galaxy is the largest member. The Triangulum Galaxy and Andromeda Galaxy have history together, but astronomers are still investigating the details. Their close proximity has caused some researchers to suggest that Triangulum is a satellite of the Andromeda Galaxy, not unlike the way the Moon is a satellite of the Earth — just on a much, much bigger scale. Alternatively, some researchers propose that these two galaxies may be independent and have simply brushed past each other, as evidenced by streams of stars and neutral hydrogen gas linking the two galaxies. However they have interacted, it’s probable that they will dramatically collide in 2.5 billion years, resulting in their consolidation and eventual evolution into a lenticular galaxy.

Scientists have used Chandra to make a detailed study of an enormous cloud of hot gas enveloping two large, colliding galaxies in the system known as NGC 6240. This unusually large reservoir of gas contains as much mass as 10 billion Suns, spans about 300,000 light years, radiates at a temperature of more than 7 million degrees, and glows in X-rays (purple). The Chandra data have been combined with optical data from the Hubble, which show long tidal tails from the merging galaxies, extending to the right a

This is the first image of a celestial object taken with the newly repaired Advanced Camera for Surveys (ACS). The camera was restored to operation during the STS-125 Servicing Mission to upgrade the NASA/ESA Hubble Space Telescope. The barred spiral galaxy NGC 6217 was photographed on 13 June and 8 July 2009, as part of the initial testing and calibration of Hubble’s ACS. The galaxy lies up to 90 million light-years away in the north circumpolar constellation Ursa Major.

This Hubble Picture of the Week — taken using the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS) — shows Arp 107, a celestial object that comprises a pair of galaxies in the midst of a collision. The larger galaxy (on the left of this image) is an extremely energetic galaxy of a type known as a Seyfert galaxy, which house active galactic nuclei at their cores. Seyfert galaxies are notable because, despite the immense brightness of the active core, radiation from the entire galaxy

Not all galaxies are neatly shaped, as this new NASA/ESA Hubble Space Telescope image of NGC 6240 clearly demonstrates. Hubble previously released an image of this galaxy back in 2008, but the knotted region, shown here in a pinky-red hue at the centre of the galaxies, was only revealed in these observations from Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys. NGC 6240 lies 400 million light-years away in the constellation of Ophiuchus (The Serpent Holder). This galaxy has an elongated shape