- 4022 - BLACKHOLES - are they spacetime defects? Black holes might be defects in spacetime. Physicists have discovered a strange structure in space-time that to an outside observer would look exactly like a black hole, but upon closer inspection would be anything but: they could be defects in the very fabric of the universe.
------------- 4022 - BLACKHOLES - are they spacetime defects?
- Einstein's
general theory of relativity predicts the existence of black holes, formed when
giant stars collapse. But that same theory predicts that their centers are
singularities, which are points of infinite density.
-
- Since we know
that infinite densities cannot actually happen in the universe, we take this as
a sign that Einstein's theory is incomplete. But after nearly a century of
searching for extensions, we have not yet confirmed a better theory of gravity.
-
- But we do have
candidates, including string theory. In string theory all the particles of the
universe are actually microscopic vibrating loops of string. In order to
support the wide variety of particles and forces that we observe in the
universe, these strings can't just vibrate in our three spatial dimensions.
Instead, there have to be extra spatial dimensions that are curled up on
themselves into manifolds so small that they escape experimentation.
-
- That exotic
structure in spacetime gave a team of researchers the tools they needed to
identify a new class of object, something that they call a “topological
soliton”. In their analysis they found that these topological solitons are
stable defects in space-time itself. They require no matter or other forces to
exist. They are as natural to the fabric
of space-time as cracks in ice.
-
- The researchers
studied these solitons by examining the behavior of light that would pass near
them. Because they are objects of extreme space-time, they bend space and time
around them, which affects the path of light. To a distant observer, these solitons
would appear exactly as we predict black holes to appear. They would have
shadows and rings of light. Images derived from the Event Horizon Telescope and
detected gravitational wave signatures would all behave the same.
-
- It's only once
you got close would you realize that you are not looking at a black hole. One
of the key features of a black hole is its event horizon, an imaginary surface
that if you were to cross it you would find yourself unable to escape.
Topological solitons, since they are not singularities, do not feature event
horizons.
-
- These topological
solitons are incredibly hypothetical objects, based on our understanding of
string theory, which has not yet been proven to be a viable update to our
understanding of physics. However, these exotic objects serve as important test
studies. If the researchers can discover an important observational difference
between topological solitons and traditional black holes, this might pave the
way to finding a way to test string theory itself.
-
- Even stars
and blackholes start with a gas cloud.
All stars are born from the collapse of clouds of dust and gas. But
triggering star formation is a tricky process, because these gas clouds can
just hang out doing nothing for billions of years.
-
- When clouds of gas collide, several things
happen at once. The gas and dust tangle up on each other and immediately
trigger turbulent ripples that race throughout the newly merged clump.
Shockwaves can also form, which travel at their own speed through the chaos. In
all of the mess pockets of the cloud can destabilize. When they do, they pinch
off from the rest of the cloud and quickly collapse as the gravitational force
within them overwhelms any other form of support.
-
- When that happens, clusters of stars form.
Astronomers have long suspected this story to be true, but it but mysteries
remain as to the details of how a cloud of gas transforms into stars.
-
-They found that the largest
influence on star formation was not the properties of the gas clouds themselves
but on the background they find themselves in. If two gas clouds merge together
in an environment that has a relatively high density, then the gas clumps tend
to produce more compact merger remnants. This leads to fewer but more massive
stars.
-
- Conversely, if the gas clouds are relatively
isolated, they produce more numerous but less massive stars.
-
May
24, 2023 BLACKHOLES - are
they spacetime defects? 4022
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--------------------- --- Thursday, May 25, 2023
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