Dec 18, 2020 11:08 PM
(This post was last modified: Dec 18, 2020 11:31 PM by C C.)
The New History of the Milky Way
https://www.quantamagazine.org/the-new-h...-20201215/
EXCERPT: Taken together, these results have spun a new story about our galaxy’s turbulent past and its ever-evolving future. “Our picture of the Milky Way has changed so quickly,” said Michael Petersen, an astronomer at the University of Edinburgh. “The theme is that the Milky Way is not a static object. Things are changing rapidly everywhere.” (MORE - details)
NASA says a gargantuan supermassive black hole is somehow missing
https://www.zmescience.com/science/super...-90423432/
INTRO: Astronomers surveying the heart of the giant galaxy cluster Abell 2261 were expecting to find a hefty supermassive black hole, with an appetite for matter and energy that matched the enormous scale of its cosmic home. But although the supermassive black hole should have had a mass between 3 to 100 billion times that of the sun — very conspicuous to most observations — there was no object to be found. NASA scientists don’t know what to make of the missing black hole and its elusive nature may be yet another reminder that we still know very little about these mysterious objects.
Just like stars cluster around the core of a galaxy, so do galaxies group together, bound by the gravity of an extremely dense core. Most known galaxies, including the Milky Way, have a supermassive black hole at their core that keeps their stars together. Similarly, clusters of hundreds or thousands of galaxies have a core, with an even larger supermassive black hole bounding all those galaxies in place. The galaxy nearest this core is known as the brightest cluster galaxy (BCG) — this is where the cluster’s most important supermassive black hole should be found.
Abell 2261’s BCG is a staggering one million light-years across, making it about 10 times larger than the Milky Way. What’s more, it has a huge core 10,000 light-years across, the largest galactic core ever found. But, defying all expectations, a team of astronomers led by Kayhan Gultekin from the University of Michigan couldn’t find any supermassive black hole in the galaxy in the middle of Abell 2261, located about 2.7 billion light-years from Earth... (MORE - details)
RELATED: Physics at the tiniest scale could explain 'impossible' black holes
A new particle, the ultralight boson, could swirl around black holes, releasing detectable gravitational waves
https://www.space.com/new-particle-dark-...-candidate
EXCERPTS: A hypothetical particle known as the ultralight boson could be responsible for our universe's dark matter. While the ultralight boson isn’t directly observable, it might clump up around black holes, triggering an exotic mechanism that causes it to explode — in a massive burst of gravitational waves. Even better: these gravitational waves may be detectable with the next generation of detectors.
[...] Among the candidates is a hypothetical particle known as an axion. The axion was first proposed to existback in 1977, before we even knew that dark matter was a thing, and it has some properties that make it attractive and alluring as a dark matter candidate. For one, axions can be light — very light — which makes it easy for them to flood the universe. This is exactly what we expect dark matter to be like, as it is after all the most dominant form of matter in the cosmos. Second, the axion (and theoretical particles related to the axion, like the so-called "dark photons," which are like axions but they can carry a hypothetical fifth force of nature) doesn't really interact with radiation or normal matter, which is yet another criteria that would align with dark matter.
[...] The axions swirl around, stealing some energy from the black hole and that extra energy causes them to swirl around even faster, coming even closer to the black hole. That then pulls even more energy to the axions, causing them to swirl faster and faster. This process is called the "superradiant instability," but I prefer the term "black hole bomb."
[...] As of yet, there's no evidence in the gravitational wave background for these black hole bombs — and hence no evidence linking them to the dark matter behind them. But that non-detection helps us understand these models — if the axion was heavier than a certain mass (and we're right about how black hole bombs work), then they would've shown up in the background by now. The next generation of gravitational wave detectors will be even more sensitive, and we just might see our first black hole bomb. And, along with it, our first conclusive evidence of the identity of dark matter... (MORE - details)
https://www.quantamagazine.org/the-new-h...-20201215/
EXCERPT: Taken together, these results have spun a new story about our galaxy’s turbulent past and its ever-evolving future. “Our picture of the Milky Way has changed so quickly,” said Michael Petersen, an astronomer at the University of Edinburgh. “The theme is that the Milky Way is not a static object. Things are changing rapidly everywhere.” (MORE - details)
NASA says a gargantuan supermassive black hole is somehow missing
https://www.zmescience.com/science/super...-90423432/
INTRO: Astronomers surveying the heart of the giant galaxy cluster Abell 2261 were expecting to find a hefty supermassive black hole, with an appetite for matter and energy that matched the enormous scale of its cosmic home. But although the supermassive black hole should have had a mass between 3 to 100 billion times that of the sun — very conspicuous to most observations — there was no object to be found. NASA scientists don’t know what to make of the missing black hole and its elusive nature may be yet another reminder that we still know very little about these mysterious objects.
Just like stars cluster around the core of a galaxy, so do galaxies group together, bound by the gravity of an extremely dense core. Most known galaxies, including the Milky Way, have a supermassive black hole at their core that keeps their stars together. Similarly, clusters of hundreds or thousands of galaxies have a core, with an even larger supermassive black hole bounding all those galaxies in place. The galaxy nearest this core is known as the brightest cluster galaxy (BCG) — this is where the cluster’s most important supermassive black hole should be found.
Abell 2261’s BCG is a staggering one million light-years across, making it about 10 times larger than the Milky Way. What’s more, it has a huge core 10,000 light-years across, the largest galactic core ever found. But, defying all expectations, a team of astronomers led by Kayhan Gultekin from the University of Michigan couldn’t find any supermassive black hole in the galaxy in the middle of Abell 2261, located about 2.7 billion light-years from Earth... (MORE - details)
RELATED: Physics at the tiniest scale could explain 'impossible' black holes
A new particle, the ultralight boson, could swirl around black holes, releasing detectable gravitational waves
https://www.space.com/new-particle-dark-...-candidate
EXCERPTS: A hypothetical particle known as the ultralight boson could be responsible for our universe's dark matter. While the ultralight boson isn’t directly observable, it might clump up around black holes, triggering an exotic mechanism that causes it to explode — in a massive burst of gravitational waves. Even better: these gravitational waves may be detectable with the next generation of detectors.
[...] Among the candidates is a hypothetical particle known as an axion. The axion was first proposed to existback in 1977, before we even knew that dark matter was a thing, and it has some properties that make it attractive and alluring as a dark matter candidate. For one, axions can be light — very light — which makes it easy for them to flood the universe. This is exactly what we expect dark matter to be like, as it is after all the most dominant form of matter in the cosmos. Second, the axion (and theoretical particles related to the axion, like the so-called "dark photons," which are like axions but they can carry a hypothetical fifth force of nature) doesn't really interact with radiation or normal matter, which is yet another criteria that would align with dark matter.
[...] The axions swirl around, stealing some energy from the black hole and that extra energy causes them to swirl around even faster, coming even closer to the black hole. That then pulls even more energy to the axions, causing them to swirl faster and faster. This process is called the "superradiant instability," but I prefer the term "black hole bomb."
[...] As of yet, there's no evidence in the gravitational wave background for these black hole bombs — and hence no evidence linking them to the dark matter behind them. But that non-detection helps us understand these models — if the axion was heavier than a certain mass (and we're right about how black hole bombs work), then they would've shown up in the background by now. The next generation of gravitational wave detectors will be even more sensitive, and we just might see our first black hole bomb. And, along with it, our first conclusive evidence of the identity of dark matter... (MORE - details)