Astronomers have known this for a long time. Andromeda, the large neighboring galaxy, which is only 2.5 million light-years away, is approaching us so quickly (more than 100 kilometers per second, about 400 thousand kilometers per hour) that it will end up colliding with the Milky Way, the galaxy in which we live. However, despite this speed, the titanic encounter would not occur for approximately 4 billion years, which is a very long time on a human scale, and our species would likely not exist by then.
In fact, the collision between galaxies is a long process that implies that the two heroes perform, for several billion years, an endless “gravitational dance” during which they move closer and closer several times, as if united by an enormous elastic rubber. It expands and contracts. Their own pulses through space send them past and away from the other galaxy, but the gravitational force between them brings them back together irrevocably, again and again.
Only at the end of this cosmic dance does the real encounter occur, as the two galaxies finally merge, intersect, and their billions of stars mingle and give rise to a new, larger galaxy that is the sum of the two previous galaxies.
In our case, this final merger will begin in about 3.8 billion years, but it will not end until about 2 billion years later, which is about 5.8 billion years from now. At that time, Andromeda and the Milky Way will have merged forever into one new giant galaxy, which scientists have named “Lactomeda.” It is true that there is a long way to go, but the initial stages of the process, according to several recent studies, could have begun, as the vast halos of matter surrounding both galaxies appear to have touched.
This is what the collision would look like
Over the past few years, many simulations have been performed to visualize exactly what this process looks like, but nothing is better than seeing it with our own eyes. Now, a team of astronomers was able to capture, with the cameras of the 8-meter-diameter Gemini Southern Observatory telescope in Chile, an image of a distant collision. As they explain, It faithfully reflects what our future collision with Andromeda will be like.
This is NGC 7727, in the constellation Aquarius and about 90 million light-years from Earth. There, two giant spiral galaxies (such as Andromeda and the Milky Way) merge, and when they become a large, bloated mass with no spiral shapes or arms, they release giant waves of stars into the universe.
Astronomers believe the collision that created NGC 7727 began more than a billion years ago. They explained that within all the chaos and mayhem the image shows, there is a pair of supermassive black holes, one for each parent galaxy. They are the closest pair of supermassive black holes to Earth that have been observed so far.
In fact, one has the mass of 154 million suns and the other is smaller, with only 6.3 million solar masses. For reference, let’s remember that the central black hole in our Milky Way Galaxy, Sagittarius A*, has a mass of about four million solar masses.
Right now, the two black holes in NGC 7727 are about 1,600 light-years apart (that is, they’re very close together), which is why astronomers estimate that they will merge fairly soon, in “only” about 250 million years. The collision, which will send violent waves of gravitational waves into space, will create a larger black hole. If humankind still exists by then, a future version of LIGO, the largest gravitational-wave observatory today, will allow future astronomers to view and record the event.
The image shows that although the collision occurred a long time ago, the galaxy NGC 7727 is still affected by the collision. Enormous “swells” of stars sparkle with very young stars, born in stellar nurseries that are greatly energized by gravitational perturbations caused by the collision. In fact, 23 of the objects observed in this system are candidates for young globular clusters, dense spherical collections made up of thousands of stars. Astronomers say these “star clusters” often form in regions where star formation is higher than normal, and are particularly common in galaxies that are in complete interaction, as is the case with NGC 7727.
Scientists believe that what is observed in this new galaxy in the process of formation is a faithful reflection of what will also happen when the Milky Way collides with Andromeda. In fact, our galaxy has already begun its gravitational dance with its massive neighbor, and when the two come together, they will likely also unleash waves of new stars into the universe.
Many astronomers believe that at that time, the Sun and our solar system will be thrown into a different region than the one it occupies today. Due to the large separation between stars, galaxy mergers rarely involve direct collisions between them, which somehow ensures that in 3.8 billion years the Earth is not already destroyed by some other cause (e.g., the death of the Sun, most likely), it will be able To survive to see the beginning of the new era of Lactomida.
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