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
September 16, 2019 Not So Dead After All (Messier 110)
July 29, 2019 Feeling Edgy (NGC 3432)
July 15, 2019 A Beautiful Whorl (NGC 2985)
July 8, 2019 Galactic Cherry Blossom (NGC 1156)
May 20, 2019 Come a Little Closer (Messier 90)
May 16, 2019 Creative Destruction as Galaxies Collide (NGC 4485)
May 8, 2019 New Clues About How Ancient Galaxies Lit up the Universe
May 6, 2019 Distant and Ancient (SPT-CL J0615-5746)
March 7, 2019 What Does the Milky Way Weigh?
March 5, 2019 Weighing Galactic Wind Provides Clues to Evolution of Galaxies
March 4, 2019 Colliding Galaxies (NGC 6052)
February 27, 2019 Why do Some Galactic Unions Lead to Doom?
January 31, 2019 Hubble Accidentally Discovers a New Galaxy in Cosmic Neighborhood
January 24, 2019 Plunging Galaxy Losing Its Gas (D100)
January 7, 2019 Triangulum Galaxy Shows Stunning Face (Messier 33)
January 7, 2019 Messier 105
December 17, 2018 Abell 2744
November 15, 2018 To Boldly Go into Colliding Galaxy Clusters (Abell 1033)
November 5, 2018 Feeling Blue (ESO 338-4)
October 22, 2018 A Galaxy with a Bright Heart (NGC 5033)
October 8, 2018 Rings Upon Rings (NGC 3351)
September 27, 2018 Making Head or Tail of a Galactic Landscape (Abell 2142)
June 4, 2018 Threads of Blue (IC 4870)