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
July 11, 2016 'Frankenstein' Galaxy Surprises Astronomers (UGC 1382)
July 11, 2016 A Lonely Birthplace  (MCG+07-33-027)
July 4, 2016 A Stubborn Dwarf Galaxy (LEDA 677373)
June 27, 2016   Bursting at the Seams (NGC 1569)
May 9, 2016 A Spiral Snowflake  (NGC 6814)
April 18, 2016 Elegance Conceals an Eventful Past (NGC 4111)
March 31, 2016 Journey to the Center of Our Galaxy
March 28, 2016 A Distinctly Disorganized Dwarf (UGC 4459)
March 10, 2016 Telescopes Combine to Push Frontier on Galaxy Clusters
March 3, 2016 New Cosmic Distance Record (GN-z11)
January 28, 2016 Monstrous Cloud Boomerangs Back to Our Galaxy
January 25, 2016 A Misbehaving Spiral (LO95 0313-192)
January 15, 2016 Most Luminous Galaxy is Ripping Itself Apart (W2246-0526)
January 7, 2016 NASA's Great Observatories Weigh Massive Young Galaxy Cluster
January 6, 2016 Spitzer, Hubble Find 'Twins' of Superstar Eta Carinae in Other Galaxies
January 5, 2016 Andromeda Galaxy Scanned with High-Energy X-ray Vision
January 4, 2016 Supermassive and Super-hungry (NGC 4845)