Oort Cloud's close stellar encounters + If black hole at MW's center is dark matter?

C C Offline
The Oort Cloud and Close Stellar Encounters

EXCERPTS: If we assume that the Oort Cloud, that enveloping shroud of comets that surrounds our Solar System and extends to 100,000 AU or beyond, is a common feature of stellar systems, then it’s conceivable that objects are interchanged between the Sun and Alpha Centauri where the two clouds approach each other. That makes for the ‘slow boat to Centauri’ concept I’ve written about before, where travel between the stars essentially mines resources along the way in migrations lasting thousands of years. The resulting society would not be planet-oriented.

[...] Bear in mind that at the Sun’s birth, numerous other stars would have been nearby, from which objects in their circumstellar disks could have been exchanged, along with free-floating debris in the parent star cluster and other interstellar objects. Indeed, a high percentage of the Oort Cloud’s material could have come from such sources, as the paper notes: “About half the inner Oort cloud, between 100 and 104 au, and a quarter of the material in the outer Oort cloud ≳ 104 au could be non-native to the Solar system but was captured from free-floating debris in the cluster or from the circumstellar disk of other stars in the birth cluster.”

[...] The transport of material from one star to another is seen in the simulations to be “rather symmetric.” While the Solar System is what the authors call “a copious polluter of interstellar space,” so too is it receiving material from other systems. The authors argue that stars in the Sun’s birth cluster would have experienced numerous encounters with other stars, and that the Solar System shows evidence of both single strong encounters and a series of relatively weak encounters, based on the orbital parameters of Sedna and the complexity of the orbits found in the scattered Kuiper Belt beyond 45 AU.

[...] The paper is Zwart et al., “Oort cloud Ecology II: The chronology of the formation of the Oort cloud,” accepted at Astronomy & Astrophysics. (MORE - missing details)

What if the black hole at the center of the Milky Way is actually a mass of dark matter?

RELEASE: A team of researchers at the International Center for Relativistic Astrophysics has found evidence that suggests Sagittarius A* is not a massive black hole but is instead a mass of dark matter. In their paper published in the journal Monthly Notices of the Royal Astronomical Society: Letters, the group describes the evidence they found and how it has stood up to testing.

For several years the scientific community has agreed that there is a mass at the center of the Milky Way galaxy and that the mass is a supermassive black hole—it has been named Sagittarius A*. Its presence has never been verified directly, however, instead it has been inferred by noting the behavior of bodies around it. In this new effort, the researchers suggest that another type of mass could produce the same reactions by other bodies and in fact could help explain some anomalies that have been seen.

Back in 2014, astrophysicists were confronted with a problem they could not explain—a gas cloud that had been named G2 moved to a position close enough to Sagittarius A* that it should have been destroyed and pulled in by the black hole. Instead, the gas cloud continued on its way, unharmed.

The researchers in this new effort suggest the reason G2 was able to survive its journey past Sagittarius A*, was because Sagittarius A* is not a black hole—it is a mass of dark matter. To come to this conclusion, they created a simulation of the Milky Way, where Sagittarius A* was replaced by a mass of dark matter and then let it run. In so doing, they found the Milky Way could run pretty much the same way it would if there were a black hole at its center—nearby S-stars would behave the same, for example, as would the rotational curve of the Milky Way's outer halo. The researchers went even further, suggesting that such a mass would be composed of darkinos, which would belong to the same group as fermions. If they were to clump together, the simulation showed, they would have characteristics very similar to a black hole—the exceptions being its most extreme features.
Syne Offline
Any article about science that begins with "what if" is typically just speculative garbage.

An analysis published on July 21, 2014, based on observations by the ESO's Very Large Telescope in Chile, concluded alternatively that the cloud, rather than being isolated, might be a dense clump within a continuous but thinner stream of matter, and would act as a constant breeze on the disk of matter orbiting the black hole, rather than sudden gusts that would have caused high brightness as they hit, as originally expected. Supporting this hypothesis, G1, a cloud that passed near the black hole 13 years ago, had an orbit almost identical to G2, consistent with both clouds, and a gas tail thought to be trailing G2, all being denser clumps within a large single gas stream.
- https://en.wikipedia.org/wiki/Sagittariu...ion_course

Here, they're ignoring this parsimonious explanation of observations to postulate something we've yet to determine actually exists.
stryder Offline
@ The middle of the Milyway

I always considered the centre to be multiple lagrangian points (along with scalar version of points between points) from the collective mass in the milky way. If that was the case, the strength of the gravitation of the center would slowly dissipate over time as the galaxy expands out. I'd even question how such multipoints would effect the overall galactic topology (Would it flatten disc like? etc)

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