Hubble constant (expansion rate of the universe) is still controversial. It is known as a key parameter to explain Big Bang theory, the expansion of the universe and relative motion of the galaxies, etc. Is the value of Hubble constant, driven from the velocity-distance relation, consistent with the discovery of accelerating universe and dark matter/dark energy phenomena?
It resembles to be linear:
Hubble constant --> accelerating expansion of universe --> Dark matter/ Dark energy phenomena??
1. The velocity of the galaxy is determined by measuring the redshift of spectral lines in the spectrum of the galaxy. For velocities much smaller than the speed of light, the regular linear Doppler formula is used.
2. The distance to a galaxy is determined by measuring the brightness of the stars in that galaxy whose absolute light output we can measure. Such stars can be used to estimate the distance to galaxies 300 million light years away. If a galaxy is too far away for us to distinguish individual stars, astronomers can use supernovae in the same manner, because the light output of supernovae at their peak brightness is a known fact. Supernovae can be used to measure the distance to galaxies as far as 10 billion light years away. this Brightness-distance relationship is also linear.
3. The velocity of the galaxies is not constant; “Dark energy” which is believed to be smooth and persistent, makes the universe accelerate; In fact, far galaxies move faster than near galaxies.
Ref: HubbleSite.org
Hubble constant is really an indicative of the involving phenomena of the universe. It was initially estimated ~ 500 km/s/Mpc (160 km/sec/million light years) in 1930's; But with the benefit of the Hubble Telescope, H is now estimated to be ~ 72 km/s/Mpc. Is this drastic difference due to the better accuracy of the measurement and higher resolution of the optical instruments? or it arises from the assumptions and theories?
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