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In the last years a discrepancy between two methods to measure the Hubble constant appeared. Measurements based on redshift and the cosmic distance ladder produced results of about 73 km/(s*Mpc) while measurements based on the cosmic microwave background lead to results of about 68 km/(s*Mpc). While not completely outside the uncertainties the difference was still curious.
There are two additional independent measurements of the Hubble constant but so far they don't have the necessary precision to help: Gravitational waves from binary neutron star mergers (##70^{+12}_{-8}## from LIGO/Virgo based one one event) and multiply imaged quasars (##72.5 \pm 2.2## from H0LiCOW).
Luckily we have Gaia. More precise parallax measurements show distances could have been underestimated. A larger distance for the same redshift means a smaller Hubble constant, closer to the value from CMB measurements. Preprint:
GAIA Cepheid parallaxes and 'Local Hole' relieve H0 tension
There are two additional independent measurements of the Hubble constant but so far they don't have the necessary precision to help: Gravitational waves from binary neutron star mergers (##70^{+12}_{-8}## from LIGO/Virgo based one one event) and multiply imaged quasars (##72.5 \pm 2.2## from H0LiCOW).
Luckily we have Gaia. More precise parallax measurements show distances could have been underestimated. A larger distance for the same redshift means a smaller Hubble constant, closer to the value from CMB measurements. Preprint:
GAIA Cepheid parallaxes and 'Local Hole' relieve H0 tension