Galaxies beyond the Milky Way: What are they like?

Hyperaxion January 30, 2020 2:10 am

Here are some interesting facts about galaxies beyond our own.

We know that there are billions of galaxies across the Universe. But what are they like? Galaxies can have several shapes, including the spiral, like our Milky Way. Spiral galaxies are flat, have arms and a shiny core. It is in the arms that the vast majority of stars, like our Sun, are born and live. It is also in them that the gas and dust will form other stars.

Blue galaxies

Andromeda Galaxy
Andromeda Galaxy has a spiral shape and is 2.54 million light years away from Planet Earth. (Source: NASA/JPL/California Institute of Technology).

When we see a bluish galaxy, we know its stars are young and that there is still gas and dust to form more stars. But if there is a lot of dust, the light of the newly born stars is dimmed and the galaxy becomes more red. It is not enough to observe the visible light to understand what is really happening there; we also need to capture light in colors that our eyes cannot see, such as infrared, ultraviolet, radio waves and X-rays.

Elliptical galaxies tend to be orange

Centaurus A Galaxy
Centaurus A, also known as NGC 5128, is a very strange elliptical galaxy, full of unusual features. (Source: NASA/JPL-Caltech/J. Keene).

The largest galaxies we know are elliptical, homogeneous and must have arisen from the junction of massive galaxies, such as two or more spirals, or by cannibalism in clusters of galaxies. They have a slightly orange color. This is because the “fuel” (gas and dust) of these galaxies was all consumed during mergers, and many stars are formed at once.

What does the color mean?

The way we interpret colors in astronomy is a bit different from the way we do it day-to-day. Blue means warmer, while red means colder. The biggest and hottest stars have a short life span and are bluish, while the smaller and cooler stars live longer and are reddish. And since in the elliptical galaxies the fuel ran out, we only see the orange color due to the low mass stars (like the Sun or even smaller ones) that survive much longer.

Black holes

M87 Black Hole
The Event Horizon telescope took the first image of a supermassive black hole and its shadow. The image reveals the central black hole of Messier 87, a huge galaxy in the Virgo cluster. (Source: Event Horizon Telescope – CC BY).

Within these different shapes, these galaxies hide supermassive black holes. These objects can have up to billions of times the mass of the Sun. In some cases, they are active and can eject material from their neighborhoods at high speeds into the intergalactic medium. This is the case with M87, an elliptical galaxy. In the middle of it, we managed, for the first time, to make an image of a black hole.

30 years since the launch of the Hubble Space Telescope

Hubble Space Telescope at the moment of release. (Source: NASA/IMAX).

Edwin Hubble (1889-1953) was the first to propose a classification scheme for galaxies and, after noting that they are moving away from each other, he was the first to claim that the universe is expanding. NASA named the Hubble Space Telescope after him. On April 24, it will be 30 years since the launch of the Hubble Space Telescope: 30 years unraveling the universe and providing us with breathtaking images!

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