Milky Way and Andromeda: The Galactic Collision That May (or May Not) Happen

Seen to the naked eye as a hazy patch in the night sky, The Andromeda galaxy has been mentioned by astronomers since 964 ADWhen it was included in the “Book of Fixed Stars” by Iranian Abdurrahman al-Sufi. But Edwin Hubble, the patron of today’s space telescope, had to prove definitively that this was a separate galaxy from the Milky Way of 100 years ago, using a 100-inch Hooker telescope.

Scientists who studied the giant celestial body as an autonomous structure realized that what is called M31 poses a threat to us. Since it has a negative radial velocity, It was (and is) moving towards the Milky Way at 110 km/hThis points to a collision within the next 5 billion years.

Now, a recently published paper by researchers at the University of Helsinki, Finland, suggests: “The probability of no merger is close to 50% “The study, hosted on the arXiv preprint repository and not yet peer-reviewed, was based on up-to-date, accurate observations from the Gaia and Hubble space telescopes, as well as more recent consensus theoretical calculations.”

Why do researchers rule out the Milky Way colliding with Andromeda?

To challenge such “galactic” calculations, the authors took advantage of a physics concept recently popularized in a TV series: the three-body problem, which in the current study involves four objects. The solution is simple when the problem involves only two objects gravitationally attracting each other (the Milky Way and Andromeda), but things get more complicated when a third object (the M33 Triangulum galaxy) is involved. Then there’s the Large Magellanic Cloud.

I can’t evaluate Interactions between Andromeda and the Milky Way in a single region of the universe consisting of about 100 galaxies, are mostly smaller, in what astronomers call the Local Group. The largest of these, the Triangulum, has “only” 40 billion stars, 40% of the 100 billion stars in the Milky Way, but only 4% of the 1 trillion stars in Andromeda.

Fraser Cain, editor of Universe Today, who provides some insight into the orbital mechanics of the “entanglement” between the two galaxies, reminds us that each of the galaxies in the Local Group has its own gravitational pull, which affects the paths of Andromeda and the Milky Way. And to complicate matters even further, there’s the Large Magellanic Cloud, which is larger than the Milky Way, less massive than M33, but still has a significant gravitational pull.

How was the 50% collision-free estimate calculated?

The study authors found that our larger neighbors in the Local Group, M33 and the Large Magellanic Cloud, “significantly and radically affect the orbit of the Milky Way-Andromeda.” While the probability of a merger with M33 increases in the equation, the inclusion of the Large Magellanic Cloud, whose orbit is perpendicular to the orbits of the two colliding galaxies, reduces the probability of a merger.

As with the three-body problem, the challenge is to reduce uncertainty. But when the problem involves converting the rotation speeds of the four galaxies involved, or the distance between them, into numbers, uncertainty takes over. Modeling the motion of fluid objects made up of billions of stars, gas, and dust is extremely difficult. Not to mention the effects of dark matter, something we don’t even know exists.

According to the study, the authors therefore chose to set aside concrete figures and instead set a “probability of close to 50% that there will be no merger.” In any case, there is still a lot of uncertainty in this estimate and many factors to consider: The combined effect of other galaxies in the Local Group.

Whatever the case, the possibility of a grandiose merger of two galaxies into the so-called Milkomeda remains a mystery that only time will tell, but when it happens (or doesn’t) neither we nor our Earth will be here to witness it.

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