“Worlds in Collision” – Reawakening Milky Way’s 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.”

Head-On Collision 6-10 Billion Years Ago

Looking back into the Milky Way’s ancient past, astronomers at the Harvard-Smithsonian Center For Astrophysics produced a study concluding 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. The study also concluded that this collision could produce the chemical diversity currently observed in the Milky Way’s stellar halo

Lead author Azadeh Fattahi along with 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.

Future Collisions Will Reawaken Sagittarius A*

Fast forward to the ‘collision future’ for our galaxy: “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.

Shooting Spitballs the Size of Jupiter Towards Earth

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. After a black hole devours a star, it shoots out planet-size “spitballs” at speeds of about 20 million mph (32 million km/h), and would take roughly a million years to reach Earth’s neighborhood. “Other galaxies, like Andromeda, are shooting these ‘spitballs’ at us all the time,” says James Guillochon, an astrophysicist at the CfA.

“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 just over four billion years.

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.

2019 –75-fold Increase in Brightness

In 2019, in an event unrelated to the future collision with the Large Magellanic Cloud, UCLA astrophysicist Tuan Do, Deputy Director of the Galactic Center Group, reported that in the space of two hours, the brightness of black hole the heart of our galaxy usually a passive flickering object about twenty-five thousand light years from Earth,  increased 75-fold – the brightest it has been since scientists first started studying it more than 20 years ago.

Sagittarius A* Milky Way Galaxy’s Black Hole –“Suddenly Flashing 75-Times Brighter”

Do was watching the Keck telescope in Hawaii as it was pointed at the center of the Milky Way on the evening of May 12. He reports that he was baffled by an unusually bright spot on the readings at first, thinking it was the nearby star S0–2, when he was aware as it became brighter that it was the enigmatic supermassive monster , which is four million times the mass of our sun.

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.

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.

Doomed to Collide with the Milky Way

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.

“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: 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.

“The Invisible Galaxy” –100 Million Black Holes Lurking in the Milky Way

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.

Jackie Faherty, astrophysicist, Senior Scientist with AMNH via Harvard-Smithsonian Center For Astrophysics and University of Durham.



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