Wednesday, February 1, 2023

# How fast do galaxies move?

I understand that the question refers to the motion of galaxies with respect to the rest of the universe, for example, not to the rotation of a galaxy around its axis. The first thing I wanted to make clear is that the same motion cannot be quantified for all galaxies. It can be said that each galaxy moves in its own way. And the same happens with the rest of the things that make up the universe, everything moves in it.

A galaxy’s speed depends on several factors: its age, where it is located and what is around it. The total speed depends on how it is pulled into the universe by the speed of the expansion of space (the Hubble flow), since we already know that the universe has expanded since the Big Bang, causing mass between objects. The location of increases with time. This is the factor that dominates in the most distant, most primitive universe. This most distant universe is much busier than the present universe, and the galaxies in that universe are the ones that move the fastest, much faster than the present universe.

As I was saying, not all galaxies move at the same speed, but to give you an idea, the ones around our Milky Way move, more or less, in the range of 100 to 2,000 kilometers per second; Those that are a little further away can move at about 5,000 kilometers per second and the most distant can move at more than 10,000 kilometers per second.

For example, the galaxy in which a supermassive black hole was first detected, called Messier 87, moves at about 1,600 kilometers per second and our Milky Way, travels at 600 kilometers per second. does. Those are huge numbers because we’re talking about kilometers per second. In the case of the Milky Way, its speed is roughly the same as traveling from Madrid to Cádiz in a jiffy.

To this motion of the pull due to the expansion of space in the universe, we must add the motion that deviates from distance due to cosmic expansion, which is known as the peculiar motion (specific velocity in English). In this case we are talking about the local motion/velocity of the galaxies within our neighborhood. For example, it depends on whether the galaxy is in a cluster, which is a cluster of about fifty galaxies, or a cluster, which is a cluster of hundreds of galaxies together.

The Milky Way moves at 600 kilometers per second towards a large concentration of matter called the Great Attractor, which is between Virgo and Leo. And this is due to the gravity exerted on it by this Great Attractor.

If, in addition to being in the universe and affected by its expansion, being in a larger or smaller neighborhood, it also produces a kind of dance between them, coming near and going away from them, Which also affects their effect. total speed. This is what happens, for example, to the Milky Way (or more generally to galaxies in the process of interaction-fusion) with Andromeda. And this can also lead to a change in speed. While these changes are usually relatively small, they are significant if we compare them to the rate of expansion of space in the universe and the peculiar motion caused by the environment.

You may be surprised that the speed of the Milky Way is about 600 kilometers per hour, the speed of Andromeda is the same, but negative. And that’s because you also have to consider the direction of motion. One very important thing is the reference system, which tells us whether the velocity is positive or negative. In everyday life it is handy to have a common fixed point of reference, and this is why we don’t use negative velocities. The sign of motion tells us where it’s moving (if it’s moving toward or away from something), because we can’t go back in time or move into a negative space that doesn’t exist. But the sign is important when we measure the motion of galaxies, because of the reference frame we use.

For a long time it was difficult to measure the motion of objects in the universe because of the difficulty in finding common reference systems for when everything is moving. But in the 1960s a ubiquitous fossil radiation from the Big Bang was discovered, the microwave background radiation that appeared very soon after the Big Bang, expanding with the universe and we find it everywhere. No matter where we focus the telescope, there is background microwave radiation. And this radiation that fills everything can be considered as the most fixed point that we can find, it also moves, but it is the most stable thing in the universe and all the motion I mentioned in my answer That radiation is in the context of the cosmic background.

sarah cazzoli is Doctor in Astrophysics, Researcher at the Astrophysics Institute of Andalusia (CSIC)

Question submitted by Cesar Mesa

Coordination and Writing: Victoria Bull

we answer is a weekly scientific consultation sponsored by Dr Foundation Anthony Steve and programs L’Oréal-UNESCO ‘For Women in Science’, which answers readers’ questions about science and technology. He is a scientist and technologist, a member of AMIT (Association of Women Researchers and Technologists), which answers those questions. send your questions to nosotrasrespondemos@gmail.com Or #werspond via Twitter.

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