Relativistic stars are rushing through space at speeds close to the speed of light
A star fired from the Milky Way, though not relativistically. Credit: NASA, ESA, and G. Bacon (STScI).
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We have become accustomed to the fact that material particles can, under certain circumstances, move at a speed close to the speed of light. But as the famous astrophysicist, popularizer and dreamer Avi Loeb from Harvard University in the USA points out, some stars are also whistling through the universe at a speed close to the speed of light. They are relativistic ghosts.
How can this happen to a star? They are fired by “gravitational slingshots” that form when galaxies and their supermassive black holes merge. When it measures the forces of titanic gravity of merging supermassive black holes, it can detonate a star that was carelessly spinning nearby, at a truly relativistic speed. This probably doesn’t happen very often, but relativistic stars might not be an extreme rarity. In some cases, stars may be able to accelerate at relativistic speeds with a single supermassive black hole, so merging black holes is not always necessary. It is also not always necessary for the star to fly away. It can circulate relativistically around a supermassive black hole.
Avi Loeb. Credit: Harvard University.
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According to Loeb, it would be most exciting to be on a planet with such a star and fly through space with it. Relativistic objects, of course, including time dilation, manifest themselves on relativistic objects. For potential inhabitants of potential planets of relativistic stars, this would mean recognizing an unexpectedly large piece of the universe. Relativistic stars begin their flight at the center of the parent galaxy, then fly through the galaxy and galactic halls, and then into space, where Luck blows.
Experts speculate that relativistic stars orbit supermassive black holes in many galaxies. And they can probably collide sometimes. Loeb is convinced that in such a case, the collision will detonate a supernova that is many times larger than classical supernovae.
Vera C. Rubin Observatory, August 28, 2020. Credit: Rubin Obs / NSF / AURA
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There’s a catch – it has to happen at a supermassive black hole that weighs more than 100 million Suns. A smaller supermassive black hole would crush such stars to tines with tidal forces before they reached relativistic speed. Paradoxically, this effect is weaker in large supermassive black holes. This also means that our supermassive black hole in the Milky Way is out of the game. It weighs “only” like about 4 million suns.
According to Loeb, collisions of relativistic stars near supermassive black holes are the most energetic explosion in the universe, ie in terms of known phenomena. They can be up to a thousand times stronger than standard supernovae. Loeb relies on the fact that such extreme supernovae from a very distant universe could be caught, for example, by the telescope of the Legacy Survey of Space and Time (LSST) project, which should start operating at the Vera C. Rubin Observatory in Chile within a few years.
It wouldn’t be Loeb if he didn’t spice it up with alien civilizations. He speculates that potentially advanced galactic civilizations are certainly looking for a region of supermassive black holes for reasons similar to those that draw viewers, scientists, and astronauts to Cape Canaveral, Florida. And Loeb recommends that we look there for any activities that such civilizations could do there.
Video: PHYS 211 Blackholes Class #5 : Avi Loeb “Black Hole Astrophysics”
Literature
Scientific American 1. 5. 2021.
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