[HN Gopher] Growing Inventory of Black Holes Offers a Radical Pr...
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Growing Inventory of Black Holes Offers a Radical Probe of the
Cosmos
Author : theafh
Score : 37 points
Date : 2021-02-17 15:29 UTC (5 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| eutropia wrote:
| Can someone offer some insight as to what gravitational wave
| physicists hope to find that would be in the realm of "new
| physics"?
|
| So far the most radical thing about this catalogue of BHMs seems
| to be another orthogonal measurement axis for the universe -- but
| otherwise seems to be aimed at confirming existing models, right?
| imglorp wrote:
| Max Tegmark made a nice comment on the Lex Fridman podcast
| recently. This advancement tells us things about the messenger
| (gravitational waves) as well as the message (big objects
| interacting). So it's a twofer, at least.
| marcosdumay wrote:
| "Confirming existing models" and "searching for new physics"
| are the same activity. You don't know what will be confirmed
| beforehand.
|
| Trying the existing models predictions with a completely new
| measurement apparatus is the most promising way to look for new
| physics.
| NikolaeVarius wrote:
| I mean confirming stellar mass black hole merge events was "new
| physics" only 5 or so years ago. Finding larger and more
| massive supermassive black hole mergers is still disputed if
| they even exist or not.
|
| Black holes are still mostly math on a computer and indirect
| observations of its properties. The actual singularity physics
| still /shrug
|
| not an expert, but try and keep up with space and astronomy
| science articles
| raattgift wrote:
| > only 5 years ago
|
| You are conflating new physics with new experiments testing
| the limits of established physics.
|
| New physics is the requirement for explanations of
| observations which cannot accord with or be derived from
| existing _fundamental_ theory. In the case of merger chirps
| detected at LIGO, Virgo, and other detectors, that 's General
| Relativity. New physics would be chirps that [a] are
| traceable to a compact-object merger event through other
| observations (direct emissions of various types of radiation,
| and their echoes) but [b] have a chirp waveform that
| contradicts "balding" (deformations of the event horizons
| raised by each pair-member on the other should disappear in
| on the order of horizon light-crossing time) or flavours of
| equivalence principle (e.g., the universality of free fall
| shapes the chirp).
|
| Nobody working in high energy astrophysics seriously doubts
| the existence of astrophysical black holes, nor that they are
| extremely well-modelled by small perturbations of a handful
| of simple metrics (General Relativity being a metric theory
| of gravitation). There are plenty of arguments about the
| details of the perturbations and about whether General
| Relativity itself can be derived from some more fundamental
| theory, but those arguments are confronted with quite a bit
| of observational data that completely support General
| Relativity and offer no support for practically any proposal
| which reduces to (or produces) General Relativity in the
| centres of active galaxies.
|
| Furthermore, there is plenty of evidence for the mergers of
| galaxies, and nothing (in General Relativity) forbidding the
| merger of such galaxies' central black holes. Nobody should
| seriously dispute the merger of supermassive black holes,
| even if the "final parsec" mechanisms that allow for quicker
| mergers (i.e., billions of years -- less than the age of the
| universe, in particular -- rather than trillions of years)
| are not yet strongly understood.
|
| > The actual singularity physics
|
| are unobserved. Searches for primordial BH evaporation
| remnants and naked singularities will continue -- you
| automatically get the latter searches in chirp analysis and
| multimessenger matching -- and you'd have evidence for new
| physics if there is any evidence for such things, because
| they are not allowed by General Relativity.
|
| Astrophysically, black holes are characterized by the
| properties of their event horizons, not the properties of
| their singularities (even theoretically it's the exterior
| metric that counts; nobody, especially not Kerr himself,
| thinks the interior BH metric is generally a good physical
| description). As long as it stays enshrouded by a horizon
| (thus protecting the exterior metric tensor and some energy
| conditions), the matter that has fallen in can be in any sort
| of arrangement inside the horizon, including but far from
| limited to a classical singularity. Post Ken Wilson
| (renormalization and effective field theory), we should be
| agnostic about such things.
|
| > indirect observations of [black hole] properties
|
| The chirp mass is a physical property of the black hole pair
| that is directly measured by gravitational wave detectors,
| comparable to how the reduced mass is a directly measurable
| attribute of pairs of non-relativistic celestial objects (and
| cf. linearized gravity). Chirp masses are verifiable by
| studying the orbits of stars and molecular clouds around or
| past the merging pair.
| ncmncm wrote:
| I wonder when will be the first merger notably affected by tidal
| influence from a third body; or if that has already happened.
| aszantu wrote:
| how do they distinguish between different black holes? isn't it
| "just Waves"?
| definataly wrote:
| They use trilateration to know where it came from. Since there
| are 3 observatories (Hanford, Livingston and Virgo) the waves
| will arrive at slightly different amplitudes / times / angles
| ... which allows you to estimate where in the sky it came from.
|
| The waves also have different shapes (frequency, amplitude,
| shape) which tells us about the nature of the merger.
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