The Milky Way has only 4 billion years to live, but our Sun will survive
This is not science fiction but a scientific prediction: in four billion years, our galaxy will collide with our neighboring great spiral, Andromeda.
In four billion years, our galaxy will collide with our neighboring reat spiral, Andromeda.
In four billion years, our galaxy, the Milky Way, will collide with our neighboring great spiral, Andromeda.
The galaxies as we know them will not survive it.
Our solar system will outlive our galaxy. When the merger occurs, the sun will not yet be a giant red ball, but it will have grown large enough to fry the Earth's surface. The life forms that will still live there will have the right to a particularly remarkable cosmic spectacle.
Today, Andromeda is about 2.5 million light years from the Milky Way. Attracted by gravity, the two galaxies crash into it at a speed of 402,000 km/h. Even at such a speed, it will take 4 billion years for them to meet. They will collide head-on before crossing each other, leaving behind trails of gas and stars. They will continue to move closer and further apart again for millions of years, mixing the stars and redrawing the constellations as they pass. Finally, after about a billion years, the two galaxies will merge.
At that time, the solar system will have a new cosmic home: a giant oval galaxy, formed by the collision and then the merger of the Milky Way and Andromeda.
This is not science fiction; it is a true scientific prediction. Halley predicted the return of the eponymous comet, and modern astronomers, the end of the Milky Way. This gift of foresight is really just a mathematical understanding of the physical laws that govern the motion of celestial bodies.
"With the help of Newton's laws of gravitation alone, we astronomers can predict with certainty that in a few billion years our galaxy, the Milky Way, will merge with our neighboring galaxy, Andromeda," says the COSMOS presenter, Neil DeGrasse Tyson. “The stars are so far apart, relative to their size, that very few, if any, of them will collide. Potential life forms on the stars of this very distant future should not be in danger, but will have the chance to witness an incredible light show of several billion years. »
?BUT HOW DO WE KNOW IT WILL HAPPEN
It all goes back to the beginning of the 20th century with the astronomer Vesto Slipher, when he measured the radial velocity of Andromeda, or, in other words, the speed at which the galaxy is approaching or moving away from Earth. . To do this, Slipher looked for evidence of expansion or compression of light from Andromeda reaching Earth. Light emitted by receding objects is slightly stretched, creating a redshift. Conversely, light emitted by approaching objects is compressed, creating a blue shift.
The result was surprising to say the least. "It can be concluded that the Andromeda Nebula is approaching the solar system at a speed of about 300 kilometers per second," Slipher wrote in the Lowell Observatory Bulletin in 1913 (Andromeda was still called a nebula at the time, because astronomers had not realized that it was not part of the Milky Way; Slipher's calculations strongly suggested that this assumption should be reconsidered).
An artist's impression of the future Earth, whose oceans will have evaporated due to the increasing heat of the Sun, exiled at the end of the new merged galaxy that astronomers nickname "Milkomeda".
Andromeda was approaching us; that at least was clear. On the other hand, that its arrival would sound the end of the Milky Way was not defined. For decades, scientists had no way of knowing whether Andromeda and the Milky Way would collide head-on, or whether they would glide past each other like starships in the cosmic night.
It turns out that it is relatively simple to measure the speed of distant objects approaching or receding from us; but it is much more difficult to measure their lateral movement (what scientists call “proper movement”). The more distant the object, the more difficult it is to measure its lateral movement because this does not produce any stretched or compressed wavelengths observable by astronomers. The latter will rather start from detailed observations of the position of an object in relation to the stars in the background; a tiny, very subtle shift that, without the aid of high-performance telescopes, can take centuries to observe.
In 2007, astrophysicist Avi Loeb of Harvard University decided to look again at the question of the imminent arrival of Andromeda. “Most theorists want to replicate systems from our past that are observable today; they are reluctant to make predictions that will only be tested billions of years from now,” comments Loeb. “I did not understand this logic. I am just as curious about the future as I am about the past. »
Accompanied by TJ Cox, then a post-doctoral student, Loeb simulated the collision and merger of Andromeda and the Milky Way using estimates of Andromeda's proper motion. The results showed a fair chance of a head-on collision between the two galaxies, with the good possibility that the solar system would be propelled towards the end of the new elliptical galaxy, dubbed "Milkomeda" by Loeb.
Today ; in 2 billion years; in 3.75 billion years; in 3.85 billion years; in 3.9 billion years; in 4 billion years; in 5.1 billion years; in 7 billion years, when the galaxies will have created a gigantic elliptical galaxy.
In 2012, a team of astronomers based at the Space Telescope Science Institute recalculated the collision, this time using direct measurements of Andromeda's proper motion. After all these years, the team was able to recover these measurements thanks to the Hubble Space Telescope and have an observation mission gathering years of data, including the first images captured in 2002.
"We compared images taken at different times by the Hubble Space Telescope, and we measured the displacement of the stars in Andromeda relative to the blurry galaxies in the distant background," says Sangmo astronomer Tony Sohn. “It gives us an idea of the speed of Andromeda stars in the sky. »
The team concluded that Andromeda's proper motion was small, and that a head-on collision was pretty much inevitable. It may seem catastrophic, but the merging of two galaxies is not an unusual phenomenon. The Hubble Space Telescope captured splendid images of distant mergers and collisions, and astronomer Halton Arp included a number of galactic interactions in his "Atlas of Peculiar Galaxies" published in 1966. They are all very beautiful.
The good news, as Tyson says, is that stars are so far apart that even if galaxies collide, the probability of multiple stars colliding is still low. The Sun and its planets will likely be able to survive Milkomeda's birth, even though Earth will have lost its place in the Milky Way. We will no longer live in a spiral galaxy. Milkomeda will have an elliptical shape, and will definitely sport a red color, as can be seen towards the end of the 2012 animation made by the team, as well as in the animation above.
What is beyond doubt is that this merger will be spectacular. And there is a good chance that the small Triangle galaxy, located nearby, will be sucked into the event. For my part, I regret not being able to attend this great spectacle of cosmic lights. It only remains for me to admire the series of illustrations below.
Source : websites