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A physicist investigating black holes has discovered that, in an increasing universe, Einstein’s equations require that the speed of the universe’s growth on the occasion horizon of each black gap should be a continuing, the identical for all black holes. In flip which means that the one power on the occasion horizon is darkish power, the so-called cosmological fixed. The examine is printed on the arXiv preprint server.
“In any other case,” mentioned Nikodem PopÅ‚awski, a Distinguished Lecturer on the College of New Haven, “the strain of matter and curvature of spacetime must be infinite at a horizon, however that’s unphysical.”
Black holes are an interesting matter as a result of they’re concerning the easiest issues within the universe: their solely properties are mass, electrical cost and angular momentum (spin). But their simplicity provides rise to a fantastical property—they’ve an occasion horizon at a vital distance from the black gap, a nonphysical floor round it, spherical within the easiest circumstances. Something nearer to the black gap, that’s, contained in the occasion horizon, can by no means escape the black gap.
Black holes have been predicted in 1916 by Karl Schwarzschild whereas serving as a German soldier on the Russian entrance, whereas he was affected by the painful autoimmune pores and skin illness pemphigus.
Utilizing Einstein’s equations of normal relativity, he assumed a large, nonrotating, completely spherical object in an in any other case empty and unchanging universe and found the occasion horizon. The radius of the occasion horizon is proportional to a black gap’s mass. Contained in the horizon, not even gentle, the quickest object within the universe, can escape the outlet.
Schwarzschild additionally discovered an obvious singularity on the black gap’s middle, a spot of infinite density the place Einstein’s legal guidelines of gravity apparently breakdown.
Astronomers have since discovered that almost all galaxies seem to have a supermassive black gap at their middle; for the Milky Approach it’s Sagittarius A*, with a mass over 4 million instances that of the solar. A black gap was straight imaged solely in 2019, a black spot with a halo of sunshine round it, situated within the middle of the galaxy Messier 87, 55 million light-years from Earth.
Going past Schwarzschild, PopÅ‚awski assumed a large, centrally symmetric object in an increasing universe. On this case, the answer to Einstein’s equations for the construction of spacetime across the mass was first obtained in 1933 by the British mathematician and cosmologist George McVittie.
McVittie discovered that close to the mass, spacetime is like that of Schwarzschild’s, with an occasion horizon, however removed from the mass the universe is increasing like our universe is at the moment. The Hubble parameter, additionally known as the Hubble fixed, specifies the speed of growth of the universe.
PopÅ‚awski used McVittie’s resolution to search out that the speed of the growth of house on the occasion horizon should be a continuing, associated solely to the cosmological fixed (which could be interpreted because the power density of the vacuum of spacetime). At this time we all know this because the density of darkish power. That’s, the one power on the horizon is darkish power. The consequence, he mentioned, is that completely different components of the universe develop at completely different charges.
In reality, one thing related has been discovered with the so-called “Hubble pressure,” a statistically vital discrepancy between two completely different measured values of the Hubble parameter, relying on whether or not “late universe” measurements are used or “early universe” strategies primarily based on measurements of the cosmic microwave background. In his work, PopÅ‚awski mentioned this discrepancy “is a pure consequence of an accurate evaluation of the spacetime of a black gap in an increasing universe inside Einstein’s normal concept of relativity.”
Moreover, his equations present {that a} consequence of the universe increasing at completely different charges is that the cosmological fixed—and therefore the worth of darkish power—should be optimistic. In any other case, with out that fixed, PopÅ‚awski mentioned, “a closed universe can be oscillatory and couldn’t create cosmic voids.”
“It’s the easiest rationalization of the noticed present acceleration of the universe.”
For a star, say, the universe can be increasing at its floor boundary, however the physique doesn’t develop as a result of it’s gravitationally and electromagnetically certain.
An occasion horizon, although, is a mathematically-abstract factor, not something made from matter or power however made merely of factors of house, so a continuing growth fee of house there isn’t a surprise. The occasion horizon itself (and thus a black gap) shouldn’t be increasing; factors of house exterior the horizon are shifting away from it.
Actual black holes rotate, but when the rotation is usually sluggish, PopÅ‚awski’s conclusions ought to apply to them as nicely to a superb approximation. However measuring the Hubble parameter at an occasion horizon is presently inconceivable, except new strategies are developed.
An observer on the occasion horizon may in precept measure the Hubble parameter there however can be endlessly unable to speak his worth to the remainder of the universe as he’s falling previous the occasion horizon, and no data can presumably be despatched again throughout it.
This ties in, Popławski mentioned, with a speculation he printed in 2010: that each black gap is definitely a wormhole (an Einstein-Rosen bridge) to a brand new universe on the opposite facet of its occasion horizon.
“The occasion horizon is a doorway from one universe to a different,” he mentioned. “This doorway doesn’t develop with the growth of the universe … If this happens for the occasion horizon of the black gap forming a universe, it must also work for the occasion horizons of different black holes in that universe.”
Extra data:
Nikodem Popławski, Black holes within the increasing Universe, arXiv (2024). DOI: 10.48550/arxiv.2405.16673
Journal data:
arXiv
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