But later, people found in the observation of the night sky that some dim and invisible stars would suddenly light up, and then the luminosity would gradually weaken in the next few weeks or even a month until they disappeared. Only then do we know that stars have a life cycle and will die.
So today's question is: since stars will die, will galaxies made up of stars die in a long time? What will it look like in the end?
To answer this question, let's take a look at our group this week. When we usually talk about this group of galaxies, we will only mention the two giant galaxies, the Milky Way and Andromeda, and generally ignore some dwarf galaxies around us. Now let's look at these nobody:
Triangle galaxy is about 5% of the mass of the Milky Way, and it is the third largest galaxy in this galaxy group after the Milky Way. This galaxy has a spiral structure, which is probably the satellite galaxies of Andromeda.
Large magellanic cloud. The mass of this galaxy is dwarfed by that of our Milky Way, which is only 1%, but it is already the fourth largest galaxy in this galaxy group. Because it is very close to the Milky Way at present, only less than 200,000 light years away, the huge gravity of the Milky Way has had a great influence on this galaxy.
Under the tidal gravity of the Milky Way, the gas in the large magellanic cloud has begun to collapse and chaos, and the newest, hottest and largest stars in the universe have begun to emerge. This process is a period of star explosion in a galaxy, which we call a starburst galaxy.
This explains why the most massive star in our universe is located in the Tarantula Nebula in the large magellanic cloud.
Small magellanic cloud, NGC 3 190 and NGC 6822 in the above picture. At present, we are not sure which galaxy is bigger, but their mass is between 0. 1% and 0.6% of the mass of the Milky Way. Although these three galaxies are small, each contains more than 1 100 million times the mass of the sun, so they are also very important sources of material in this galaxy group.
Above, around M3 1 (Andromeda galaxy) are elliptical galaxies M32 and M 1 10. They are just satellite galaxies of Andromeda galaxy, with a very small mass, but they also contain more than 654.38 billion stars, and the mass of this galaxy may even be greater than the three galaxies mentioned above.
In addition to the above-mentioned galaxies, there are at least 45 known smaller galaxies in the local galaxy group, which together with the above-mentioned galaxies constitute our local galaxy group.
No matter how many galaxies there are and what their mass and size are, in the next few billion years, all these galaxies will experience a very important event, and they will not exist as they do today.
All the galaxies in this galaxy group are integral structures bound by gravity. No matter how the universe expands, they don't want to be far away from each other. On the contrary, these galaxies are close to each other under the action of gravity. In addition to the pull of gravity, if two galaxies are close to each other, they will also produce a very large tidal force.
Speaking of tidal force, we usually think that the tidal attraction of the moon to the earth causes the ocean to bulge in one direction, and this happens when the earth rotates to the bulge position? The climax occurs when the earth rotates through a trough? Low tide? .
But judging from the size of the galaxy, tidal force's influence is stronger. When one side of a small galaxy is close to a large galaxy, this side will be more attractive than the other. As a result, small galaxies are stretched and deformed and eventually torn apart by large galaxies.
These small galaxies, the Magellanic Cloud and all dwarf galaxies were eventually torn apart and swallowed up by large galaxies.
But this is not really death, because large galaxies will still exist for some time. However, our Milky Way galaxy and Andromeda galaxy will not remain the same forever, because now these two galaxies have danced with each other in space under the action of gravity, and they will merge in the next 4 billion years or so. This merger will last for billions of years, but in the end, the current spiral structure of both galaxies will be destroyed, and eventually a huge elliptical galaxy will be formed.
No matter how many galaxies existed before this local group of galaxies, they will be pulled together by gravity to form a single galaxy, which is composed of all the substances in the current local group of galaxies. Not only our local galaxy clusters, but all the galaxy clusters and galaxy clusters bound by gravity have the same fate as us in the universe, but those structures that are not bound by gravity will be far away from each other under the action of dark energy. In other words, there will be fewer and fewer galaxies in the future universe.
But this is not the real death of galaxies in the universe, because there are still galaxies. But galaxies are made up of stars, gas and dust, and the amount of these substances is limited.
In the universe, the merger of galaxies may take tens of billions of years to complete. At this time, dark energy will also expand these merged galaxies to a very long distance and accelerate to a very high speed, making all galaxies invisible and unreachable. At that time, we could only see the stars of our own galaxy on the earth, and only one galaxy in the universe, our own galaxy.
Although other galaxies are invisible, stars always exist for a long time. Because the longest-lived red dwarf in the universe needs at least 654.38 million+years to burn its own fuel, new stars will be born in each galaxy, but with the decrease of gas clouds, the rate of star formation will be lower and lower until it is impossible to form stars.
Even if the last star in the universe burns out its fuel, there will still be star residues (white dwarfs and neutron stars) in the universe, which will last for hundreds of trillions of years before disappearing. When these stars disappear, there are still some failed stars in the universe: brown dwarfs, which occasionally merge to rekindle nuclear fusion and will continue to shine for trillions of years.
However, when the last star burns out in the next 10 16 years, the mass of the galaxy will still exist. In a sense, this is not? Real death? .
But the galaxy itself will not last forever! We know that objects of all masses in a galaxy will interact under the action of gravity, but the following things will happen when substances of different masses interact:
When two mass substances are in close contact, the exchange of speed and momentum will occur.
In this process, low-mass objects will gain extra speed and be? Kick? If you leave the galaxy, high-quality objects will lose speed and sink into the center of the galaxy.
After a long enough time scale (about 10 19 to 10 20 years), most of the mass of the Milky Way will be thrown out, and only a small part of the remaining mass will be more tightly bound together.
There is basically a supermassive black hole in the center of a galaxy, and this black hole will become very huge because of inhaling too much matter, which may create a supermassive black hole unique in the universe since its birth.
However, even black holes will not last forever.
Due to Hawking radiation, black holes will slowly lose mass. It may take 10 80 to 10 100 years, depending on the mass of supermassive black holes.
So no matter how we define a galaxy or its remnants, they will die out.