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 20, 2022 Webb Uncovers Dense Cosmic Knot in the Early Universe
October 18, 2022 IXPE Helps Unlock the Secrets of Famous Exploded Star Cassiopeia A
October 13, 2022 Chandra Finds Galaxy Cluster Collision on a "WHIM” (Abell 98)
September 28, 2022 Hubble Detects Protective Shield Defending a Pair of Dwarf Galaxies
September 5, 2022 Galactic Overlap (SDSS J115331 and LEDA 2073461)
August 29, 2022 Hubble Gazes into M74
August 22, 2022 A Marvel of Galactic Morphology (NGC 1156)
July 25, 2022 Follow the LEDA
July 12, 2022 Webb Delivers Deepest Image of Universe Yet
June 16, 2022 New Images Using Data From Retired Telescopes Reveal Hidden Features
June 7, 2022 Colossal Collisions Linked to Solar System Science: Abell 2146
April 19, 2022 Celebrating Hubble's 32nd Birthday with an Eclectic Galaxy Grouping
April 5, 2022 SOFIA Maps the First Magnetic Fields of a Galactic Bone in Their Entirety
April 4, 2022 Hubble Spies a Serpentine Spiral Galaxy (NGC 5921)
March 14, 2022 Eye of the Galaxy (NGC 1097)
March 9, 2022  Tilted Galaxy Turns Studies Topsy-Turvy
February 22, 2022 Hubble Looks at a ‘Space Triangle’ Spawned by a Galaxy Collision
February 7, 2022 A Cosmic Draw (Arp 282)
January 24, 2022 Strike! (NGC 7764A)
January 12, 2022 1,000-Light-Year-Wide Bubble Surrounding Earth Is Source of All Nearby, Young Stars
December 16, 2021 Our Milky Way May Be More Fluffy, Less Wiry