“Worlds in Collision” –Dangers of Milky Way’s ‘Reawakened’ Supermassive Black Hole

 blobs of gas roughly the mass of Jupiter at Milky Way's Black Hole


“Beautiful as it is, our Universe is constantly evolving, often through violent events like the Milky Way’s forthcoming collision with the Large Magellanic Cloud,” said Carlos Frenk, Director of the Institute for Computational Cosmology at the University of Durham. “Barring any disasters, like a major disturbance to the Solar System, our descendants, if any, are in for a treat: a spectacular display of cosmic fireworks as the newly awakened supermassive black hole at the center of our galaxy, Sagittarius A*, reacts by emitting jets of extremely bright energetic radiation.”

Looking backward into the Milky Way’s ancient past, astronomers at the Harvard-Smithsonian Center For Astrophysics concluded that six to ten billion years ago the Milky Way merged in a head-on collision with a massive dwarf galaxy containing about one-to-ten billion solar masses in size, and that this collision could produce the character changes in stellar population currently observed in the Milky Way’s stellar halo.

CfA astronomer Federico Marinacci and his colleagues analyzed computer cosmological simulations and the galaxy interactions in them. In particular they analyzed the history of galaxy halos as they evolved following a merger event.

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Looking to the future The Galaxy posted that: “The destruction of the Large Magellanic Cloud, as it is devoured by the Milky Way, will wreak havoc with our galaxy, waking up the black hole that lives at its center and turning our galaxy into an ‘active galactic nucleus’ or quasar,” quoting astrophysicist Marius Cautun, with Durham University’s Institute for Computational Cosmology about new research predicting our galaxy’s collision two billion years from now with the Large Magellanic Cloud.

The CfA image at the top of the page shows blobs of gas roughly the mass of Jupiter that could form near the supermassive black hole at the center of the Milky Way and shoot into intergalactic space.

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“This phenomenon will generate powerful jets of high energy radiation emanating from just outside the black hole,” Cautun added. “There is a small chance that we might not escape unscathed from the collision between the two galaxies which could knock us out of the Milky Way and into interstellar space.”

The collision could occur much earlier than the predicted impact between the Milky Way and another neighboring galaxy, Andromeda, which scientists say will hit our galaxy in eight billion years.


Milky Way Galactic Center


The catastrophic coming together with the Large Magellanic Cloud could wake up the Milky Way’s dormant black hole, which would begin devouring surrounding gas and increase in size by up to ten times. As it feeds, the now-active black hole would throw out high-energy radiation and while these cosmic fireworks are unlikely to affect life on Earth, the scientists say there is a small chance that the initial collision could send our Solar System hurtling into space.

Galaxies like our own Milky Way are surrounded by a group of smaller satellite galaxies that orbit around them, in a similar way to how bees move around a hive. Typically, these satellite galaxies have a quiet life and orbit around their hosts for many billions of years. However, from time to time, they sink to the center, collide and are devoured by their host galaxy.

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The Large Magellanic Cloud is the brightest satellite galaxy of the Milky Way and only entered our neighborhood about 1.5 billion years ago. It sits about 163,000 light years from the Milky Way. Until recently astronomers thought that it would either orbit the Milky Way for many billions of years, or, since it moves so fast, escape from our galaxy’s gravitational pull.

However, recent measurements indicate that the Large Magellanic Cloud has nearly twice as much dark matter than previously thought. The researchers say that since it has a larger than expected mass, the Large Magellanic Cloud is rapidly losing energy and is doomed to collide with our galaxy.

The research team, led by scientists at Durham University’s Institute for Computational Cosmology working with the University of Helsinki, in Finland, used the EAGLE galaxy formation supercomputer simulation to predict the collision.

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“We think that up to now our galaxy has had only a few mergers with very low mass galaxies,” said Alis Deason, also with the Institute for Computational Cosmology. “This represents very slim pickings when compared to nearby galaxies of the same size as the Milky Way. For example, our nearest neighbor, the Andromeda galaxy, devoured galaxies weighing nearly 30 times more than those consumed by the Milky Way. Therefore, the collision with the Large Magellanic Cloud is long overdue and it is needed to make our galaxy typical.”

Flashing back to the new Harvard-Smithsonian Center For Astrophysics research: Our Milky Way galaxy has probably collided or otherwise interacted with other galaxies during its lifetime; such interactions are common cosmic occurrences. Astronomers can deduce the history of mass accretion onto the Milky Way from a study of debris in the halo of the galaxy left as the tidal residue of such episodes.

The approach has worked particularly well for studies of the most recent events like the infall of the Sagittarius dwarf galaxy a few billion years ago that left tidal streamers of stars visible in galaxy maps. The damaging effects these encounters can cause to the Milky Way have, however, not been as well studied, and events even further in the past are even less obvious as they become blurred by the galaxy’s natural motions and evolution.

Some episodes in the Milky Way’s history, however, were so cataclysmic that they are difficult to hide. Scientists have known for some time that the Milky Way’s halo of stars drastically changes in character with distance from the galactic center as revealed by the composition of the stars, the stellar motions, and the stellar density.

The Daily Galaxy via Harvard-Smithsonian Center For Astrophysics and University of Durham


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