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version in other projects wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia hypothesized alternative to a black hole not to be confused with gravatar or gravitar a diagram comparing the structure of a classical black hole with a gravastar in astrophysics a gravastar a blend word of gravitational vacuum star is an object hypothesized in a 2001 paper by pawel o mazur and emil mottola as an alternative to the black hole theory 1 it has the usual black hole metric outside of the horizon but de sitter metric inside a typical gravastar is as big as london but weighing ten solar masses on the horizon there is an ultra thin incredibly tight shell of entirely new unique exotic matter this solution to the einstein equations is stable and has no singularities 2 instead a gravastar is filled either with dark energy or with vacuum energy but also vacuum only the inside one is 10 44 times denser than the outside description edit in the original formulation by mazur and mottola 3 a gravastar is composed of three regions differentiated by the relationship between the pressure p and energy density ρ the central region consists of false vacuum or dark energy and in this region p ρ surrounding it is a thin shell of perfect fluid where p ρ on the exterior is true vacuum where p ρ 0 gravastar anatomy edit the interior of a gravastar behaves like dark energy and prevents collapse to a singularity the inner region has thermodynamically no entropy and may be thought of as a gravitational bose einstein condensate the outer thin shell stops an event horizon from forming which would otherwise cause light and energy to become infinitely concentrated severe red shifting of photons as they climb out of the gravity well would make the thin shell also seem very cold it is the coldest object theoretically possible at only a billionth of a degree above absolute zero in addition to the original thin shell formulation gravastars with continuous pressure have been proposed these objects must contain anisotropic stress 4 externally a gravastar appears similar to a black hole it is visible by the high energy radiation it emits while consuming matter and by the hawking radiation it creates citation needed astronomers search the sky for x rays emitted by infalling matter to detect black holes a gravastar would produce an identical signature it is also possible if the thin shell is transparent to radiation that gravastars may be distinguished from ordinary black holes by different gravitational lensing properties as the paths of massless particles may pass through it 5 discovery edit mazur and mottola suggest that the violent creation of a gravastar might be an explanation for the origin of our universe and many other universes because all the matter from a collapsing star would implode through the central hole and explode into a new dimension and expand forever which would be consistent with the current theories regarding the big bang 6 this new dimension exerts an outward pressure on the bose einstein condensate layer and prevents it from collapsing further gravastars also could provide a mechanism for describing how dark energy accelerates the expansion of the universe one possible hypothesis uses hawking radiation as a means to exchange energy between the parent universe and the child universe and so cause the rate of expansion to accelerate but this area is under much speculation citation needed gravastar formation may provide an alternative explanation for sudden and intense gamma ray bursts throughout space citation needed ligo s observations of gravitational waves from colliding objects have been found to be either inconsistent with the gravastar concept 7 8 9 or to be indistinguishable from ordinary black holes a plausible scenario as from the outside at least a gravastar is completely indistinguishable from a black hole 10 11 comparison with black holes edit by taking quantum physics into account the gravastar hypothesis attempts to resolve contradictions caused by conventional black hole theories 12 event horizons edit in a gravastar the event horizon is not present the layer of positive pressure fluid would lie just outside the radius where an event horizon would be prevented from complete collapse by the inner false vacuum 2 dynamic stability of gravastars edit in 2007 theoretical work indicated that under certain conditions gravastars as well as other alternative black hole models are not stable when they rotate 13 theoretical work has also shown that certain rotating gravastars are stable assuming certain angular velocities shell thicknesses and compactnesses it is also possible that some gravastars which are mathematically unstable may be physically stable over cosmological timescales 14 theoretical support for the feasibility of gravastars does not exclude the existence of black holes as shown in other theoretical studies 15 see also edit acoustic metric acoustic hawking radiation from sonic black holes black star semiclassical gravity dark energy star shell collapsar references edit mazur pawel o mottola emil 2023 02 15 gravitational condensate stars an alternative to black holes universe 9 2 88 arxiv gr qc 0109035 bibcode 2023univ 9 88m doi 10 3390 universe9020088 1 2 los alamos researcher says black holes aren t holes at all los alamos national laboratory archived from the original on 13 december 2006 retrieved 10 april 2014 mazur mottola 2024 p 88 cattoen celine faber tristan visser matt 21 october 2005 gravastars must have anisotropic pressures classical and quantum gravity 22 20 4189 4202 arxiv gr qc 0505137 bibcode 2005cqgra 22 4189c doi 10 1088 0264 9381 22 20 002 issn 0264 9381 s2cid 10023130 sakai nobuyuki saida hiromi tamaki takashi 17 november 2014 gravastar shadows physical review d 90 10 104013 arxiv 1408 6929 bibcode 2014phrvd 90j4013s doi 10 1103 physrevd 90 104013 issn 1550 7998 s2cid 119102542 chown marcus 7 june 2006 is space time a superfluid new scientist archived from the original on 2016 04 12 retrieved 2017 11 04 it s the big bang says mazur effectively we are inside a gravastar alternative url bibliotecapleyades net chirenti cecilia rezzolla luciano 11 october 2016 did gw150914 produce a rotating gravastar physical review d 94 8 084016 arxiv 1602 08759 bibcode 2016phrvd 94h4016c doi 10 1103 physrevd 94 084016 issn 2470 0010 s2cid 16097346 we conclude it is not possible to model the measured ringdown of gw150914 as due to a rotating gravastar did ligo detect black holes or gravastars sciencedaily october 19 2016 retrieved 2017 11 04 ligo s black hole detection survives the gravastar test extreme tech 2016 10 26 retrieved 2017 11 04 was gravitational wave signal from a gravastar not black holes new scientist 2016 05 04 retrieved 2017 11 04 our signal is consistent with both the formation of a black hole and a horizonless object we just can t tell cardoso vitor franzin edgardo pani paolo 27 april 2016 is the gravitational wave ringdown a probe of the event horizon physical review letters 116 17 171101 arxiv 1602 07309 bibcode 2016phrvl 116q1101c doi 10 1103 physrevlett 116 171101 issn 0031 9007 pmid 27176511 s2cid 206273829 stenger richard 22 january 2002 is black hole theory full of hot air cnn com retrieved 10 april 2014 cardoso vitor pani paolo cadoni mariano cavaglià marco 26 june 2008 ergoregion instability of ultracompact astrophysical objects physical review d 77 12 124044 arxiv 0709 0532 bibcode 2008phrvd 77l4044c doi 10 1103 physrevd 77 124044 issn 1550 7998 s2cid 119119838 chirenti cecilia b m h rezzolla luciano 8 october 2008 ergoregion instability in rotating gravastars pdf physical review d 78 8 084011 arxiv 0808 4080 bibcode 2008phrvd 78h4011c doi 10 1103 physrevd 78 084011 hdl 11858 00 001m 0000 0013 136e d issn 1550 7998 s2cid 34564980 archived from the original pdf on 4 march 2016 retrieved 10 april 2014 rocha p miguelote a y chan r da silva m f santos n o wang anzhong 23 june 2008 bounded excursion stable gravastars and black holes journal of cosmology and astroparticle physics 2008 6 25 arxiv 0803 4200 bibcode 2008jcap 06 025r doi 10 1088 1475 7516 2008 06 025 issn 1475 7516 s2cid 118669175 further reading edit camenzind max 2007 compact objects in astrophysics white dwarfs neutron stars and black holes astronomy and astrophysics library berlin new york springer pp 442 445 isbn 978 3 540 49912 1 ball philip 31 march 2005 black holes do not exist nature doi 10 1038 news050328 8 issn 0028 0836 mazur pawel o mottola emil 7 february 2024 gravitational condensate stars an alternative to black holes universe 9 2 88 arxiv gr qc 0109035 bibcode 2023univ 9 88m doi 10 3390 universe9020088 issn 2218 1997 the original paper by mazur and mottola visser matt wiltshire david l 2004 stable gravastars an alternative to black holes pdf classical and quantum gravity 21 4 1135 1151 arxiv gr qc 0310107 bibcode 2004cqgra 21 1135v doi 10 1088 0264 9381 21 4 027 issn 0264 9381 retrieved 2004 10 02 rezzolla luciano zanotti olindo 2018 relativistic hydrodynamics oxford oxford university press pp 599 603 isbn 978 0 19 852890 6 external links edit papers about gravastars on gr qc black hole s evil twin gravastars explained on youtube by kurzgesagt v t e black holes outline types btz black hole schwarzschild rotating charged virtual kugelblitz supermassive primordial direct collapse rogue malament hogarth spacetime size micro extremal electron stellar microquasar intermediate mass supermassive active galactic nucleus quasar lqg blazar bl lac fsrq formation stellar evolution gravitational collapse neutron star related links tolman oppenheimer volkoff limit oppenheimer snyder model white dwarf related links supernova micronova hypernova related links gamma ray burst binary black hole quark star supermassive star quasi star supermassive dark star x ray binary low mass high mass properties astrophysical jet gravitational singularity ring singularity bkl singularity shock singularity theorems event horizon photon sphere innermost stable circular orbit ergosphere penrose process blandford znajek process accretion disk corona wind hawking radiation gravitational lens microlens cauchy horizon mass inflation bondi accretion m sigma relation quasi periodic oscillation thermodynamics bekenstein bound bousso s holographic bound immirzi parameter schwarzschild radius spaghettification issues information paradox complementarity soft hair cosmic censorship er epr final parsec problem firewall physics holographic principle no hair theorem metrics schwarzschild derivation kerr reissner nordström kerr newman hayward alternatives nonsingular black hole models black star dark star dark energy star gravastar magnetospheric eternally collapsing object planck star q star fuzzball geon analogs optical black hole sonic black hole lists black holes most massive nearest quasars microquasars related outline of black holes black hole initiative black hole starship black holes in fiction big bang big bounce compact star exotic star quark star preon star gravitational waves gamma ray burst progenitors gravity well hypercompact stellar system membrane paradigm naked singularity population iii star supermassive star quasi star supermassive dark star rossi x ray timing explorer superluminal motion timeline of black hole physics white hole wormhole tidal disruption event notable 1es 1927 654 3c 273 a0620 00 at2018hyz centaurus a cygnus x 1 gaia bh1 hercules a markarian 501 ms 0735 6 7421 neve 1 oj 287 phoenix cluster pks 1302 102 pso j030947 49 271757 31 q0906 6930 sagittarius a sdss j0849 1114 swift j1644 57 ton 618 ulas j1342 0928 xte j1118 480 xte j1650 500 category commons v t e stars list formation accretion molecular cloud bok globule young stellar object protostar pre main sequence herbig ae be t tauri herbig haro object hayashi track henyey track evolution main sequence red giant branch horizontal branch red clump asymptotic giant branch post agb super agb blue loop planetary nebula protoplanetary wolf rayet nebula pg1159 dredge up oh ir instability strip luminous blue variable stellar population supernova superluminous hypernova classification early late main sequence o b a f g k m subdwarf o b wr ob subgiant hertzsprung gap giant blue red yellow bright giant supergiant blue red yellow hypergiant yellow carbon s cn ch white dwarf chemically peculiar am ap bp cemp hgmn he weak barium lambda boötis lead technetium be shell b e helium extreme blue straggler remnants compact star white dwarf helium planet neutron radio quiet pulsar binary x ray magnetar black hole stellar black hole supermassive black hole x ray binary burster sgr hypothetical blue dwarf black dwarf exotic boson electroweak strange preon planck dark dark energy quark q black quasi star gravastar thorne żytkow object iron blitzar white hole nucleosynthesis deuterium burning lithium burning proton proton chain cno cycle helium flash triple alpha process alpha process c burning ne burning o burning si burning s process r process p process nova symbiotic remnant luminous red nova recurrent micronova supernova structure core convection zone microturbulence oscillations radiation zone atmosphere photosphere starspot chromosphere stellar corona alfvén surface stellar wind bubble bipolar outflow accretion disk protoplanetary disk proplyd asteroseismology helioseismology circumstellar dust cosmic dust circumstellar envelope eddington luminosity kelvin helmholtz mechanism properties designation dynamics effective temperature luminosity kinematics magnetic field absolute magnitude mass loss metallicity rotation gravity darkening starlight variable photometric system color index hertzsprung russell diagram color color diagram strömgren sphere kraft break star systems binary contact common envelope eclipsing symbiotic multiple cluster open globular super planetary system earth centric observations sun solar eclipse solar radio emission solar system sunlight pole star circumpolar constellation asterism magnitude apparent extinction photographic radial velocity proper motion parallax photometric standard lists proper names arabic chinese extremes most massive highest temperature lowest temperature largest volume smallest volume brightest historical brightest most luminous nearest bright most distant with resolved images with multiple exoplanets brown dwarfs red dwarfs white dwarfs milky way novae supernovae candidates remnants planetary nebulae timeline of stellar astronomy related substellar object brown dwarf desert sub planet galactic year galaxy guest gravity intergalactic neutron star merger planet hosting stars stellar collision stellar engulfment tidal disruption event category stars portal commons portals astronomy outer space retrieved from https en wikipedia org w index php title gravastar oldid 1375131455 categories stellar black holes black holes quantum gravity star types hypothetical stars fringe physics hidden 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