Giant galaxies put the size of the Milky Way in perspective
– News of May 28, 2019 –
In comparison to the dwarf galaxies that surround us, the Milky Way and Andromeda may seem immense. Their diameter is indeed spread over hundreds of thousands of light-years. But if you search the whole observable universe, you can find even more impressive galaxies, for example IC 1101 which is one of the largest galaxies we know so far. It is located more than a billion light-years away from us. Measuring distances and lengths is therefore a delicate work. We estimate that it is spread over 4 to 6 million light-years and includes more than a hundred thousand billion stars. In comparison, the Milky Way is a dwarf galaxy.
3C348 is another gigantic galaxy. It is also more than a million light-years in diameter. Observed on radio waves, we can see two huge jets. Each of them is about ten times larger than the Milky Way. We are not sure of the mechanisms that allow such a debauchery of energy, but we think that this galaxy shelters a monstrous black hole, a thousand times more massive than Sagittarius A *.
These two galaxies are elliptical galaxies. Unlike the Milky Way or Andromeda, they have no structure with arms. They look more like big blur spots whose center is a little denser. The Milky Way is one of the very large barred spiral galaxies, but not the largest. The largest galaxy of this type is Malin 1. Despite its size of more than a million light-years, it was only discovered in the 1980s because it is very diffuse. Other galaxies will probably be discovered as the resolution of our telescopes increases.
Image by NASA, ESA, and The Hubble Heritage Team (STScI/AURA) [Public domain]