The existence of other galaxies was confirmed surprisingly late by humans. It was only 100 years ago, when Edwin Hubble discovered a type of star called Cepheids in the constellation Andromeda and used it to measure the distance of the galaxy.
Since then, astronomical equipment and techniques have advanced, and more and more data has been collected on Andromeda and many of the estimated 2 trillion galaxies in the observable universe. As luck would have it (or, more accurately, distance, since Andromeda is one of our closest neighbors), we soon found evidence that the first galaxy we discovered beyond our own was likely on a collision course with the Milky Way.
“Traveling at 250,000 miles per hour, the neighboring giant spiral is expected to collide head-on with our galaxy in about 4 billion years,” NASA explains. “Subsequent collisions over 2 billion years will create a combined elliptical galaxy, full of stars scattered in new orbits. It looks as though the Earth, Sun, and planets of our solar system will survive the collision but assume new coordinates in the cosmos.”
But Andromeda and our own galaxy are being continuously monitored, and the better the information we get, the better we can get a picture of when this collision will occur – if it will occur at all.
In a new, not yet peer-reviewed study, a team examined the latest and most precise observations from the Gaia and Hubble space telescopes, as well as recent estimates of the mass of galaxies within the Local Group.
The team attempted to identify areas of uncertainty in the evolution of the Local Group of Galaxies and predict its evolution over the next ten billion years.
“In order to predict future mergers, knowledge of the current coordinates, velocities and masses of the systems involved in the interaction is required,” the team explained in its article. “In addition to the gravitational force between galaxies, dynamic friction is the dominant process in the run-up to galactic mergers. It describes a transfer of kinetic energy of the orbit into the internal energy of the objects involved and consequently leads to the decay of the galactic orbits.”
Although these forces all play a role in the final stages of a merger, it is gravity that plays the biggest role in whether galaxies collide. The team looked for areas of uncertainty that could affect the evolution of the group and found that uncertainties surrounding Andromeda (M31) and Messier 33 significantly affect the probability of a merger between Andromeda and the Milky Way.
“While the inclusion of M33 increases the likelihood of a merger, the orbit of the Large Magellanic Cloud is perpendicular to the orbit of the Milky Way and Andromeda galaxies, making their merger less likely,” the team explained. “In the overall system, we find that uncertainties in the present positions, motions and masses of all galaxies leave room for drastically different outcomes, and there is a nearly 50 percent probability that there will be no merger of the Milky Way and Andromeda galaxies in the next 10 billion years.”
The team is naturally cautious about their findings, saying that more observations are needed to determine whether Andromeda will collide with our galaxy. But “as it stands, claims of our galaxy’s impending doom appear greatly exaggerated.”
The study was published on the preprint server arXiv.
