Home Popular Ask Ethan #111: Are galaxies dying?

Ask Ethan #111: Are galaxies dying?

by admin

Even the cosmic home of our solar system will someday disappear. But how exactly?

If you don’t say goodbye to your loved ones, and if you don’t move to a completely new place, you can only expect a long and gradual wear and tear, leading to eventual disappearance.
Jean Dubuffet

There were so many questions and suggestions for our occasional column this week, and I even had to ask for help in making a decision. And as a result, it was decided to answer John Little’s question asking us to go into the distant future :

Do galaxies die? If so, what does it look like?

Let’s start by examining our home, the Milky Way, and its neighbors.
Ask Ethan #111: Are galaxies dying?
It is generally accepted that the local group of galaxies (us and our cosmic neighbors) consists of us, Andromeda (our big sister), and a bunch of unknowns. It’s time to get to know them. In particular :
Ask Ethan #111: Are galaxies dying?
No. 3: the Triangle galaxy. Its mass is about 5% of the Milky Way, and it is the third largest galaxy in our local group. It has a spiral structure, has its own satellites, and may itself be a satellite of Andromeda.
Ask Ethan #111: Are galaxies dying?
No. 4: the Large Magellanic Cloud. Its mass is less than 1% of the Milky Way, but it is the fourth largest. It is very close to the Milky Way, no more than 200, 000 light years away, and it has explosive star formation activity. The gravitational tidal forces of our galaxy cause the gas to shrink and give birth to the newest, hottest and largest stars in the universe.
Ask Ethan #111: Are galaxies dying?
Ask Ethan #111: Are galaxies dying?
Ask Ethan #111: Are galaxies dying?
#5-7: the Small Magellanic Cloud, NGC 3190, and NGC 6822. Their masses are between 0.1% and 0.6% of the Milky Way, it is not clear who is larger, but these galaxies are also quite large – each has a billion solar masses of matter.
Nos. 8 and 9: The elliptical galaxies M32 and M110. They may be "only" satellites of Andromeda, but they each contain a billion stars, and may be more massive than #5, #6, and #7 mentioned.
And besides them, there are at least 45 other known, smaller galaxies that make up our local group. Despite their enormous numbers, masses, and sizes, none of them will remain as they are today in a few billion years.
Ask Ethan #111: Are galaxies dying?
Over time, galaxies interact through gravity. This not only pulls them together through gravity, but also affects them through tidal forces. To us, tides are what the moon creates by attracting the Earth’s oceans, resulting in a bulge, which is what gives the tidal effect when part of the planet passes through it.
But from a galactic perspective, the tides are not as pronounced. A part of a small galaxy close to a large galaxy will be attracted with more force, and a distant part of it will be attracted with less force. As a result, the small galaxies are stretched and eventually break apart through their interaction with the larger ones.
Ask Ethan #111: Are galaxies dying?
The small galaxies that make up the local group, including both Magellanic clouds and all the dwarf elliptical galaxies, will be ripped apart just like that, and their matter will be incorporated into the larger galaxies with which they will merge.
So what, you say. It’s not really death, because big galaxies like the Milky Way can survive anything. But we can’t stay like this forever either. In 4 billion years, the gravitational pull of the Milky Way and Andromeda will pull us into a joint gravitational dance leading to a merger. Although the process will take billions of years, the spiral structure of both galaxies will be destroyed, and the result will be one giant elliptical galaxy at the center of our group: the Milkdromeda.
As a result, the other galaxies of our local group will also be sucked in, and one giant galaxy will remain, consisting of all the absorbed ones. Such a process will sooner or later occur in all connected groups and clusters of galaxies throughout the Universe, and the dark energy will drag the groups and clusters further away from each other.
But it’s not death either, because the galaxy will still remain. But the galaxy is made up of stars, dust, and gas, and the amount of it all of course.
Ask Ethan #111: Are galaxies dying?
Although the mergers will take tens of billions of years, and dark energy will drive them apart across the universe by distances leading to invisibility and inaccessibility, on time scales measured in hundreds of billions of years, the stars will continue to live. The longest-living stars of today will burn their fuel for more than ten trillion years, and new stars will be born from the gas, dust, and stellar debris that fill the galaxies-though in fewer and fewer numbers.
Ask Ethan #111: Are galaxies dying?
And when the last stars burn out, their remnants, the white dwarfs and neutron stars, will continue to shine for hundreds of trillions or even quadrillions of years until they go dark. And when this inevitably happens as well, there will be brown dwarfs, sub-stars that sometimes join together, start nuclear fusion and create stellar light for tens of trillions of years more.
Ask Ethan #111: Are galaxies dying?
And when the last star burns out, in tens of quadrillion years (10 16 ), there will still be mass left in the galaxy. And even that would not be considered true death.
Ask Ethan #111: Are galaxies dying?
But even in darkness the galaxy will not exist forever! All these masses will gravitationally interact with each other, and gravitational objects of different masses behave strangely :
– Repeated passages and close encounters lead to exchanges of velocities and momentum.
– Objects of lesser mass are ejected from the galaxy, while objects of greater mass sink toward the center and lose velocity in a process of "violent relaxation" [violent relaxation].
– Over a fairly long period of time, from 10 19 to 10 20 years, most of the mass will be ejected from the galaxy, and only a small percentage of the remaining mass will bond even more strongly.
Ask Ethan #111: Are galaxies dying?
At the very center of the remnants of the galaxy will be a supermassive black hole. And this object will be the last of the existing ones, first enlarging to its maximum possible size, eating everything it can reach. At the center of Milkdromeda, we will find an object hundreds of millions of times more massive than the Sun; larger groups and clusters of black holes will have masses in excess of tens of billions of solar masses or even more!
But they won’t live forever either.
Ask Ethan #111: Are galaxies dying?
Hawking’s radiation will cause these objects to disintegrate as well. It will take from 10 80 to 10 100 years, depending on their mass, but they will still disappear.
And no matter how you define the galaxy or its remains, they will all unequivocally die. And how and when exactly – the exact answer to that question is left up to you!

You may also like