Galaxies

Our galaxy, the Milky Way, is typical: it has hundreds of billions of stars, enough gas and dust to make billions more stars, and at least ten times as much dark matter as all the stars and gas put together. And it’s all held together by gravity.

Like more than two-thirds of the known galaxies, the Milky Way has a spiral shape. At the center of the spiral, a lot of energy and, occasionally, vivid flares are being generated. Based on the immense gravity that would be required to explain the movement of stars and the energy expelled, the astronomers conclude that the center of the Milky Way is a supermassive black hole.

Other galaxies have elliptical shapes, and a few have unusual shapes like toothpicks or rings. The Hubble Ultra Deep Field (HUDF) shows this diversity. Hubble observed a tiny patch of sky (one-tenth the diameter of the moon) for one million seconds (11.6 days) and found approximately 10,000 galaxies, of all sizes, shapes, and colors. From the ground, we see very little in this spot, which is in the constellation Fornax.

Universe Galaxies-3 Deep Field

Hubble Ultra Deep Field galaxies:
Credit: NASA, ESA, S. Beckwith (STScI) and the HUDF Team

 

Formation

After the Big Bang, the Universe was composed of radiation and subatomic particles. What happened next is up for debate - did small particles slowly team up and gradually form stars, star clusters, and eventually galaxies? Or did the Universe first organize as immense clumps of matter that later subdivided into galaxies?

Collisions

The shapes of galaxies are influenced by their neighbors, and, often, galaxies collide. The Milky Way is itself on a collision course with our nearest neighbor, the Andromeda galaxy. Even though it is the same age as the Milky Way, Hubble observations reveal that the stars in Andromeda's halo are much younger than those in the Milky Way. From this and other evidence, astronomers infer that Andromeda has already smashed into at least one and maybe several other galaxies.

Recent Discoveries

Date Discovery
October 30, 2017 Spitzer Reveals Ancient Galaxies' Frenzied Starmaking
October 16, 2017 Abell's Richest Cluster - Abell 665
October 16, 2017 A Glimpse of the Future - NGC 2623
October 9, 2017 Size Can be Deceptive - ESO 553-46
September 28, 2017 Result of a Galactic Crash - NGC 4490
September 25, 2017 Mapping the Nearby Universe - ESO 376-16
September 20, 2017 Herschel's Chronicles of Galaxy Evolution
September 18, 2017 More Than Meets the Eye - NGC 6753
August 28, 2017 From Microwaves to Megamasers
August 21, 2017 A Double Discovery (NGC 178)
August 10, 2017 A Starburst Galaxy with the Prospect of Gravitational Waves (IC 10)
July 31, 2017 The Hockey Stick Galaxy (NGC 4656)
July 27, 2017 Galactic David and Goliath (NGC 1512 and NGC 1510)
July 3, 2017 Hidden Galaxy (IC 342)
June 21, 2017 Massive Dead Disk Galaxy that Challenges Theories of Galaxy Evolution
June 19, 2017 Surveying the Cosmos (ESO 486-21)
June 6, 2017 Hubble Captures Gallery of Ultra-Bright Galaxies
May 8, 2017 Close Encounter (IRAS 06076-2139)
May 2, 2017 Giant Waves Rolling Through the Perseus Galaxy Cluster
May 1, 2017 A Cosmic Conversation (NGC 5817)
April 20, 2017 A Close Galactic Pair (NGC 4302 and NGC 4298)
March 27, 2017 NuSTAR Probes Puzzling Merger
March 20, 2017 Defying Cosmic Convention
January 23, 2017 Starbirth with a Chance of Winds? (NGC 4861)