Cosmological Expansion Rate – Hubble's Constant| Cosmological Expansion Rate – Hubble's Constant |
Observational Values 
s.a. cosmological expansion; issues and effects
[including global-local discrepancy, isotropy]; Cosmography;
friedmann equation.
* Hubble's constant: Defined
as H0:= R
·/R, from Hubble's Law; It is the most
important number in extragalactic astronomy.
* Status:
2000, The main source of uncertainty in its value (about 10%) comes
from distances to galaxies, determined mainly using Cepheid variables
in the case of nearby galaxies; 2015, Many object-based measurements
of H0 give 72-74 km/s/Mpc
with typical errors of 2-3 km/s/Mpc, while cmb-based measurements give
67-68 km/s/Mpc with typical errors of 1-2- km/s/Mpc, so accuracy rather
than precision may be the cause the discrepancy; 2020, The discrepancy
is now past the 5-σ level, with standard candle methods (using
supernovae or gravitational lenses, independently) giving 73.8 ±
1.1 km/s/Mpc, and cmb 67.4 ± 0.5 km/s/Mpc.
* Remark: The values
below are estimated values of the current expansion rate; H
actually varies in time.
* 1990: H0 = 75 –
100 km/s/Mpc [@ Fukugita & Hogan Nat(90)sep];
Seems to require Λ ≠ 0, otherwise the universe is too young.
* 1991: H0 = 50 ± 17
km/s/Mpc [gravitational lensing, @ Rhee Nat(91)mar].
* 1996: W Freedman et al estimate 68–78
(from Cepheids, supernovae, the Tully-Fischer relation, etc), A Sandage et al 57.
* 1999:
H0 = 66 ± 6 km/s/Mpc (Cepheids),
72 ± 4 (type Ia supernovae), 65–80 (lensing), 71 ± 6 (combined).
* 2000: H0
= 74 ± 7 km/s/Mpc (Cepheids), H0 = 65 km/s/Mpc
(favored?), H0 = 72 ± 8 km/s/Mpc (var).
* 2001: H0
= 64 + 14 − 11 ± 14sys (std CDM) or 66 + 14 −11
± 15sys (Λ-cdm) km/s/Mpc (from SZ effect).
* 2002: H0
= 70 km/s/Mpc (cmb and 2dF galaxy redshift survey).
* 2003: H0
= 70 + 4 − 3 km/s/Mpc (WMAP, SDSS, and weak lensing).
* 2006: H0
= 71 km/s/Mpc accepted value; Distance to Triangulum galaxy by Bonanos et al,
and Cepheid distance to NGC 4258 give higher values.
* 2010: H0
= 66 − 4 + 6 km/s/Mpc from 18 galaxy lenses with time-delay measurements;
Another estimate is 73 ± 2 ± 4 km/s/Mpc.
* 2012: H0
= 79 – 17 + 23 km/s/Mpc (68%CL) using type IIn supernovae;
74.3 ± 2.1 km/s/Mpc, using Spitzer's measurements of Cepheid variables.
* 2013: H0
= 67.15 ± ... km/s/Mpc, from Planck mission data.
* 2014: H0
= 69.6 ± 0.7 km/s/Mpc (cmb, baryon acoustic oscillations and cosmic distance ladder);
68.11 ± 0.86 km/s/Mpc (acoustic oscillations).
* 2015: H0
= 67.8 ± 0.9 km/s/Mpc, from Planck mission cmb data.
* 2016: H0
= 73.03 ± 1.79 km/sec/Mpc in the local universe, from improved observations
of Cepheid variables and other uncertainty reductions.
* 2017: The discrepancy between
supernova and quasar data (73 and 72 km/s/Mpc) and cmb data (67 km/s/Mpc) persists [@ news sn(17)feb].
* 2019: The discrepancy between local ands global
measurements of H0 is not a statistical glitch [@ news
cosmos(19)apr]; Was it early dark energy?
* 2020: The ACT Collaboration reports
H0 = 67.9 ± 1.5 km/s/Mpc from cmb data,
consistent with Planck and with a real discrepancy
[@ sn(20)jul].
> Related topics: see
issues and effects [including global-local discrepancy].
References > s.a. geometry of the universe [distances];
history of relativistic gravity; redshift
[measurement]; relativistic cosmology.
@ General:
Ferrarese et al ASP-ap/99 [combined];
Freedman et al ApJ(01)ap/00 [HST],
AS(03) [high-precision cosmology];
Mason et al ApJL-ap/01 [Sunyaev-Zeldovich effect];
Chen et al PASP(03)ap [errors];
Tammann RMA(06)ap/05-conf [history];
Wang et al ApJ(06)ap;
Macri et al ApJ(06)ap [NGC 4258];
Jackson LRR(07)-a0709;
Gorecki et al a1001-MG12 [very-high-energy gamma rays];
Freedman & Madore ARAA(10)-a1004 [accuracy];
Riess et al ApJ(11);
Suyu et al a1202-rp [motivation for better measurements];
news jpl(12)oct [Spitzer];
Livio & Riess PT(13)oct;
Bennett et al ApJ(14)-a1406;
Klöckner et al a1501-conf [using the HI signal];
Pritychenko a1506 [recommended value];
Singh et al JCAP(16)-a1506 [random errors in the data set];
Jackson LRR(15) [rev];
Arciniega et al a2102
[parametric form for ω(z)].
@ In the local universe:
Ekholm et al A&AL-ap/01 [near the Local group];
Peñarrubia et al MNRAS(14)-a1405 [dynamical model];
Hess & Kitaura MNRAS(16)-a1412 [and cosmic flows];
Riess et al ApJ(16)-a1604 [2.4% determination];
Fernández-Arenas et al MNRAS(18)-a1710;
news cosmos(19)apr [1.9%].
@ In the intermediate universe: Moresco et al JCAP(12)-a1201 [0.15 < z < 1.1];
Verde et al a1403/PDU [0.1 < z < 1.2].
@ From Cepheids: Hendry et al MNRAS(01)ap/99-conf;
Abdel-Sabour et al RAJ(09)-a1409;
Casertano et al a1609/A&A;
Follin & Knox a1707 [insensitivity to Cepheid calibration].
@ From supernovae:
Richtler & Drenkhahn LNP-ap/99;
Blinnikov et al JETPL(12)-a1206 [type IIn];
Campbell et al MNRAS(16)-a1602 [and SN Ia host-galaxy properties];
L'Huillier & Shafieloo JCAP(17)-a1606 [and BOSS data, 68.49 ± 1.83 km/sec/Mpc];
Zhang et al MNRAS-a1706 [low-redshift type Ia supernovae];
Dhawan et al A&A(18)-a1707 [as near-infrared standard candles];
Coughlin et al a1908 [kilonovae as standard candles];
Amendola & Quartin MNRAS-a1912 [standard candle clustering].
@ From lensing: Bernstein & Fischer AJ(99)ap;
Schechter IAU-ap/00,
IAU(04)ap;
Saha et al ApJL(06)ap;
Paraficz & Hjorth ApJ(10)-a1002;
Barnacka et al ApJ(14)-a1408,
Bonvin et al MNRAS(17)-a1607 [time delays].
@ From large-structure: Lee JCAP(14)-a1307;
Wang et al ApJ(17)-a1706 [galaxy redshift surveys].
@ From gravitational waves: Del Pozzo PRD(11)-a1108;
Nissanke et al a1307/ApJ [merging compact binaries];
Di Valentino & Melchiorri PRD(18)-a1710;
LSC, Virgo et al Nat(17)nov [GW170817];
Alfaro & Gamonal GRG(20)-a1902 [and PTA];
news pt(19)mar [binary neutron star mergers];
LSC and Virgo a1908;
Nicolaou et al MNRAS-a1909 [impact of peculiar velocities];
Dietrich et al a2002 [constraints from multimessenger astronomy];
Calderón et al ApJL(21)-a2006 [binary neutron star mergers];
D'Orazio & Loeb a2009 [using pulsar timing arrays].
@ Other methods: Qin MPLA(99)ap/00;
Lew et al ap/05-wd [from proper motions of radio jets];
Cheng & Huang SCPMA(15)-a1409 [from baryon acoustic oscillations];
Onuchukwu & Ezeribe a1507 [from the relation between distance modulus and redshift];
news sn(21)apr [using fast radio bursts].
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