Astrophysicists says universe could be giant 3D donut + Mountains on neutron stars

C C Offline
Astrophysicists say our universe could actually be a giant 3D donut

INTRO: Imagine a Universe where you could point a spaceship in one direction and eventually return to where you started. If our Universe were a finite donut, then such movements would be possible and physicists could potentially measure its size.

"We could say: Now we know the size of the Universe," astrophysicist Thomas Buchert, of the University of Lyon, Astrophysical Research Center in France, told Live Science in an email.

Examining light from the very early Universe, Buchert and a team of astrophysicists have deduced that our cosmos may be multiply connected, meaning that space is closed in on itself in all three dimensions like a three-dimensional donut.

Such a Universe would be finite, and according to their results, our entire cosmos might only be about three to four times larger than the limits of the observable Universe, about 45 billion light-years away... (MORE)

RELATED: Shape of the universe (Wikipedia) ...... In space, do all roads lead to home? (Plus Maths Magazine)

Millimeter-tall 'mountains' on neutron stars

RELEASE: New models of neutron stars show that their tallest mountains may be only fractions of millimetres high, due to the huge gravity on the ultra-dense objects. The research is presented today at the National Astronomy Meeting 2021.

Neutron stars are some of the densest objects in the Universe: they weigh about as much as the Sun, yet measure only around 10km across, similar in size to a large city.

Because of their compactness, neutron stars have an enormous gravitational pull around a billion times stronger than the Earth. This squashes every feature on the surface to miniscule dimensions, and means that the stellar remnant is an almost perfect sphere.

Whilst they are billions of times smaller than on Earth, these deformations from a perfect sphere are nevertheless known as mountains. The team behind the work, led by PhD student Fabian Gittins at the University of Southampton, used computational modelling to build realistic neutron stars and subject them to a range of mathematical forces to identify how the mountains are created.

The team also studied the role of the ultra-dense nuclear matter in supporting the mountains, and found that the largest mountains produced were only a fraction of a millimetre tall, one hundred times smaller than previous estimates.

Fabian comments, “For the past two decades, there has been much interest in understanding how large these mountains can be before the crust of the neutron star breaks, and the mountain can no longer be supported.”

Past work has suggested that neutron stars can sustain deviations from a perfect sphere of up to a few parts in one million, implying the mountains could be as large as a few centimetres. These calculations assumed the neutron star was strained in such a way that the crust was close to breaking at every point. However the new models indicate that such conditions are not physically realistic.

Fabian adds: “These results show how neutron stars truly are remarkably spherical objects. Additionally, they suggest that observing gravitational waves from rotating neutron stars may be even more challenging than previously thought.”

Although they are single objects, due to their intense gravitation, spinning neutron stars with slight deformations should produce ripples in the fabric of spacetime known as gravitational waves. Gravitational waves from rotations of single neutron stars have yet to be observed, although future advances in extremely sensitive detectors such as advanced LIGO and Virgo may hold the key to probing these unique objects.
Magical Realist Offline
Something to contemplate during my next visit to Duncan Donuts.
C C Offline
Why The Universe Probably Isn’t Shaped Like A Donut

EXCERPT: . . . That’s precisely what the latest study is about that’s sparking the recent headlines: the revival of an 18-year-old idea in a slightly different incarnation. Much like the idea that the Universe could have the topology of a dodecahedron, the idea that the Universe has the topology of a donut does come along with implications for what we should observe, but these too are only implications in a statistical sense. Dependent on the size of the donut/torus, particularly if it’s only a little bit larger than the observable part of our Universe, its predictions are slightly more consistent with our observations than a flat, simply-connected Universe that requires this ~0.1% likelihood to have been spontaneously realized.

Because it accounts for the suppressed power on these large angular scales, the idea is definitely worth keeping an eye on. However, this violates the cardinal rule of a compelling new theoretical idea: you must not invoke one new parameter to better account for one unanticipated observation. In theoretical physics, we demand predictive power. If you’re going to add a new ingredient to your Universe, it had better:

• reproduce all the successes of the old theory,
• account for the observations the old theory could not,
• and make new, testable predictions that differ from the predictions of the old theory.

Add-ons that fold in one new parameter to account for one new observable are a dime-a-dozen, unfortunately, and that’s all this “new proposal” does.

The true problem with the Universe is that there’s only one to observe, or at least, only one that we’re capable of observing. We don’t have a large sample of Universes to compare between, and we don’t have a large set of data points available to us within our Universe. It’s like rolling five dice, together, once. Your odds of getting all sixes is small: about 1-in-7800. Yet if you rolled five dice at once and saw that it came up all sixes, you wouldn’t necessarily conclude that it was anything more than random chance. Sometimes, nature just doesn’t give you the most likely outcome.

It’s possible that the leftover photons from the Big Bang, reaching us today as a snapshot from 13.8 billion years ago, really are the result of expanding from a donut-shaped Universe, one that’s barely larger than the observational limits of what we perceive today. But the one piece of evidence we have to support that scenario isn’t particularly compelling, and cannot rule out the null hypothesis: that we live in a Universe indistinguishable from flat, simply connected, and without any fancy topological traits. Unless we find a way to extract more information from our Universe — and we’ve already pulled everything out of the cosmic microwave background that we can, to the limits of our observations — we may never be able to meaningfully discriminate between these two possibilities... (MORE - missing details)

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