{"id":498428,"date":"2026-05-23T03:07:19","date_gmt":"2026-05-23T03:07:19","guid":{"rendered":"https:\/\/www.europesays.com\/ie\/498428\/"},"modified":"2026-05-23T03:07:19","modified_gmt":"2026-05-23T03:07:19","slug":"what-will-happen-if-the-milky-way-and-andromeda-galaxies-collide","status":"publish","type":"post","link":"https:\/\/www.europesays.com\/ie\/498428\/","title":{"rendered":"What will happen if the Milky Way and Andromeda galaxies collide?"},"content":{"rendered":"

When it comes to the Milky Way and Andromeda galaxies, there\u2019s a whole \u201cwill they or won\u2019t they\u201d thing going on. In 2012 scientists published their results<\/a> of Hubble Space Telescope observations examining the motion of Andromeda, the closest large spiral galaxy to our own. They found that, within the observational uncertainties at the time, Andromeda was essentially heading straight for us and would collide with our galaxy<\/a> in approximately four billion years.<\/p>\n

Subsequent studies have cast doubt on this supposedly inevitable smashup. Some showed a clean miss, and others showed a collision after much more time. The latest research, which includes the trajectory-tweaking gravitational effects of several satellite galaxies, indicates the odds of a collision are 50\u201350<\/a>\u2014a coin toss.<\/p>\n

In a purely pragmatic sense, you shouldn\u2019t lose sleep over an impending collision with Andromeda because this new study suggests it won\u2019t happen (if at all) for another eight billion years or so. But assuming it does occur all those eons in the future, would residents of either galaxy have anything to worry about? This depends, of course, on how exactly such a galactic train wreck unfolds.<\/p>\n

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A Milky Way\u2013Andromeda collision would see these two titans crashing together at roughly a million kilometers per hour. That\u2019s incredibly fast on human scales but much less so on a cosmic one. The Milky Way and Andromeda each boast a flattened stellar disk well more than 100,000 light-years, or a quintillion kilometers, across, so a million-kilometer-per-hour collision can take hundreds of millions of years to unfold. And even then, the aftermath will still resonate within the newly merged galaxy for billions of years to come.<\/p>\n

Andromeda has a mass that is 1.5 trillion times that of the sun, and our Milky Way\u2019s mass is about 800 billion times that of our home star<\/a>. That is a lot of mass, which means the gravitational attraction between the two galaxies is huge. But importantly, both galaxies are quite large, which means the gravitational effects are more than just a simple attraction.<\/p>\n

Let\u2019s imagine a point at which the approaching two galaxies, edge to edge, are separated by 120,000 light-years\u2014the approximate diameter of the Milky Way\u2019s disk. That would be the distance between the two closest edges of each disk. But the far side of the Milky Way\u2019s disk would be twice that distance from Andromeda, well more than 200,000 light-years. Gravity weakens with the square of the distance between the two, so a star that was on the far side of the Milky Way from the edge-on collision point would feel a much less powerful gravitational attraction than a star on the near side would. This change in gravity with distance is called the tidal force.<\/p>\n

The star on the near side would be pulled toward Andromeda much harder than one at the center of the Milky Way, which would itself be pulled harder than the star on the far side. This would have the effect of stretching the Milky Way. As the two galaxies converged, each would pull the other apart like taffy, creating long tendrils of stars, gas and dust called tidal tails<\/a>.<\/p>\n

All this, you might think, would be a prelude to the main event of the two galaxies\u2019 respective disks slamming together, which surely would involve a terrifying amount of damage, like a head-on collision between two 16-wheeler freight trucks. But galaxies aren\u2019t like trucks; they aren\u2019t solid bodies at all! Because of this, they can pass right through each other like ghosts in the night, their mutual gravity gradually drawing them back together in a series of collisions<\/a> that can result in the two galaxies merging into one. And even in scenarios where two such galaxies avoid a direct collision, they can still swing around each other in a complex gravitational dance, slinging out curving tidal tails that, despite their cosmic violence, are astonishingly lovely<\/a>. These gentler, more glancing interactions often result in a merger, too.<\/p>\n

But just because galaxies can pass through each other doesn\u2019t mean a collision will have no negative effects. Planetary systems caught up in a tidal tail could be ejected from their host galaxy entirely, for example, although this change of location would be relatively slow and mostly harmless. A bigger concern could be collisions between stars, which aren\u2019t as ghostly as galaxies. But the chances for this are astronomically low\u2014at least for our neighborhood in the Milky Way. A typical star is very roughly a million kilometers across. The distance between stars around the sun\u2019s location averages about four light-years, or approximately 40 trillion kilometers. So an average star in our vicinity is a forty-millionth the size of its separation from its nearest neighbor. That\u2019s a mighty small target and one very unlikely to hit.<\/p>\n

The likelihood of stellar collisions ramps up toward the centers of galaxies, where millions of stars can be packed in the same volume of space we enjoy out here in the galactic suburbs. And when stars collide, the typical result are messy celestial fireworks you wouldn\u2019t want erupting in your backyard. The eye-catching stellar system of V838 Monocerotis is an example of such an event<\/a>.<\/p>\n

And while stars are small, the sprawling clouds of gas and dust<\/a> from which they\u2019re born are not. These can be hundreds of light-years across, making collisions not only inevitable but common during a galactic merger, potentially sparking bursts of star formation. The intense radiance from dozens or even hundreds of massive newborn stars may be beautiful from afar<\/a> but can cause all sorts of trouble for \u201clocal\u201d observers.<\/p>\n

But the most worrisome aspect of any collision between the Milky Way and Andromeda is the supermassive black hole that lurks at the center of each. Located at the core of the Milky Way, the black hole Sagittarius A*<\/a> is about four million times the mass of the sun. And in the heart of Andromeda, also called Messier 31 (M31), the black hole M31* is more like 140 million<\/a> times our home star\u2019s mass. During a collision, gas clouds could be thrown down toward each galaxy\u2019s center and ultimately fall into decaying orbits around each awaiting black hole, forming huge disks there that would become extremely hot and potentially extremely bright. If so, both galaxies could become \u201c active,\u201d<\/a> blasting out tremendously hazardous high-energy radiation that would make the emission from mere bursts of star formation seem like a mild sunburn.<\/p>\n

Even worse, a few billion years after the collision, the two monster black holes could themselves merge. If the black holes were to do so, they\u2019d send out a blast of gravitational waves<\/a> so energetic that they could be about as powerful as all the stars in the visible universe combined. Because this energy wouldn\u2019t manifest as electromagnetic radiation but rather the wobbling of spacetime itself, it\u2019s hard to gauge what, if any, effects the unification of two gargantuan black holes would have on surrounding stars and planets. Out of caution, though, I\u2019d advise against watching from the front row.<\/p>\n

The \u201cgood\u201d news is that the sun and Earth will be long gone by then<\/a>: by eight billion years from now, our star will have swollen into a red giant, cooked our planet and then shrunk to a brilliant but tiny white dwarf. We\u2019ll miss all the fireworks.<\/p>\n

In a sense, that\u2019s too bad because seeing a galactic collision from the inside would be an astronomer\u2019s dream! But eight billion years or so is a long time to wait. For now, we\u2019ll have to be happy with watching other, more distant galaxies and using them to better understand what will happen to our own in the coming eons, when it will get to know its nearest spiral neighbor a whole lot better.<\/p>\n","protected":false},"excerpt":{"rendered":"When it comes to the Milky Way and Andromeda galaxies, there\u2019s a whole \u201cwill they or won\u2019t they\u201d…\n","protected":false},"author":2,"featured_media":498429,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","_share_on_mastodon":"0"},"categories":[270],"tags":[13440,216782,18,189413,19,17,216783,133,451,7449],"class_list":["post-498428","post","type-post","status-publish","format-standard","has-post-thumbnail","category-space","tag-andromeda","tag-collision-point","tag-eire","tag-gravitational-effects","tag-ie","tag-ireland","tag-satellite-galaxies","tag-science","tag-space","tag-spiral-galaxy"],"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@ie\/116621688677868219","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts\/498428","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/comments?post=498428"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts\/498428\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/media\/498429"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/media?parent=498428"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/categories?post=498428"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/tags?post=498428"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}