When looking up at the starry sky, the sky full of stars will always make us fascinated by the vastness of the universe, but what you may not know is that the stars we can see with the naked eye on the earth actually account for only a very small part of the many stars in the Milky Way, according to scientists' calculations, the number of stars visible to the naked eye in the global night sky is only more than 7,000, and most of them are not more than 1,000 light years away from us.
Known observational data show that the Milky Way has 200 billion to 400 billion stars, with a body diameter of at least 100,000 light-years.
A typical example is the Voyager 1 probe, as the farthest deep space probe to Earth to date, Voyager 1 took more than 40 years to fly about 24.3 billion kilometers, which is only equivalent to about 0.00257 light years, and its current speed is about 17 kilometers per second, which means that at this speed, it would take about 18,000 years to cross 1 light year, and this does not take into account the deceleration of the sun's gravity.
Of course, we can not rule out the possibility that human technology will advance by leaps and bounds in the future, and perhaps we can be optimistic that in the not-too-distant future, human beings will be able to develop spacecraft that use controlled nuclear fusion and even antimatter as an energy source, and then travel through space at speeds very close to the speed of light.
However, we all know that 1 light-year is the distance of a year in a straight line at the speed of light (referring to the speed of light in a vacuum), which means that even if you can travel at the speed of light, it will take at least 100,000 to cross the main structure of the Milky Way......
For us humans, the Milky Way is too big, and it can even be said that it is desperately big for humans, but compared to those large-scale structures in the universe, the Milky Way is actually very small, how small? Let's put it this way, in the Laniakea Supercluster, to which the Milky Way belongs, it's just a grain of sand.
It is important to know that most galaxies in the universe do not exist alone, they will be gathered into clusters or groups of galaxies under the influence of gravity, in fact, the Milky Way and dozens of neighboring galaxies form the Local Group of Galaxies, which spans about 10 million light years.
(↑ Local Group of Galaxies)
On a larger scale, galaxy clusters or groups of galaxies are clustered into larger structures, known as superclusters, and before the discovery of the Laniakea Supercluster, the Virgo Supercluster was once considered the largest structure to which the Milky Way belongs, spanning about 110 million light-years and containing about 100 clusters and groups of galaxies.
The discovery of the Laniakea Supercluster dates back to the 70s of the last century, when scientists studied the "cosmic background radiation" and found that the "cosmic background radiation" observed in one specific direction has a shorter wavelength (blueshift) and a longer wavelength (redshift) in another specific direction.
After that, scientists combined the observation data of the Earth's motion in the solar system and the motion of the solar system in the Milky Way, and came to a surprising conclusion: relative to the "cosmic background radiation", the Milky Way is actually moving at a high speed, with a speed of about 600 kilometers per second.
This means that the Milky Way is attracted to a huge gravitational source, which scientists later called "The Great Attractor".
Because the direction of the "giant gravitational source" is obscured by the galactic disk of the Milky Way, the related research has not progressed for a long time, and it is not until the development of observation technology based on infrared, radio waves and other wavelength bands that scientists gradually unveil the mystery of the "giant gravitational source".
Observational data shows that the "giant gravitational source" is more powerful than previously thought, about 150 million to 250 million light-years away, and its gravitational pull is so strong that hundreds of millions of light-years of nearby galaxies are attracted to it, and the Milky Way is just one of them.
Why is the gravitational pull of the "giant gravitational source" so strong? Scientists have come up with a variety of explanations, including the belief that the "giant gravitational source" is likely to be the gravitational center of a giant structure, and that the relevant observational data has become more abundant over time, and this view was confirmed by the scientific community in 2014.
Yes, this giant structure is the Laniakea Supercluster, which, according to scientists' estimates, spans about 520 million light-years and contains 300 to 500 clusters and groups of galaxies, with at least 100,000 galaxies, and the Virgo Supercluster is only one of its three main components (the other two are the Serpent-Centauri Supercluster and the Peacock-Indian Supercluster).
It is important to note that 100,000 galaxies is only a conservative estimate, and due to the limitations of observation conditions, we cannot accurately detect all the galaxies in the Laniakea Supercluster, so scientists generally believe that the true number of galaxies in the Laniakea Supercluster is likely to be much larger than that.
(↑ The red dot in the diagram indicates the location of the Milky Way, it should be noted that according to the true scale, the Milky Way is not that big, but should be a small and invisible dot)
On the whole, the Laniakea Supercluster is shaped like a giant feather in space, with many filamentous structures on it, each of which is made up of a large number of galaxies, and the Milky Way is only one of them, and in this huge structure, it is as small as a grain of sand......
However, such a "small" galaxy is a desperately large existence, can human beings really swim in the universe in the future? This is a question worth pondering.