HUBBLE CONSTANT

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Context

• The Hubble tension, remains a perplexing problem in terms of our understanding of cosmology.
• However, a new study in Astronomy & Astrophysics could move scientists closer than ever to unraveling this longstanding cosmic mystery.

Background

Hubble Tension and Hubble Constant

• Astrophysicists have known about the expansion of the Universe for about 100 years. However, scientists disagree about the rate of the expansion, a problem known as the "Hubble tension." The problem results from a disagreement between two methods used to measure the Hubble constant.
• One of the major problems of cosmology has been to determine the value of the Hubble constant. The tension arises because the various methods applied to determine its value have yielded different values of what, in the end, must be a single number.
• The Hubble constant (or Hubble–Lemaître constant) is the name given to the present expansion rate of the Universe.
• The Hubble constant (H0) is named after the astrophysicist who, together with Georges Lemaitre, discovered the phenomenon in the late 1920s.
• It's measured in kilometers per second per megaparsec (km/s/Mpc), where 1 Mpc is around 3.26 million light years.
• The current best direct measurement of the Hubble constant is 73.8 km/sec/Mpc (give or take 2.4 km/sec/Mpc including, both random and systematic errors), corresponding to a 3% uncertainty.

Recent Study

• Researchers achieved the most accurate calibration of Cepheid stars -- a type of variable star whose luminosity fluctuates over a defined period. The cycling of luminosity these stars possess allows astronomers to gauge their distance from Earth. These variable stars were used to calculate the most accurate distance measurements known to date.

American astronomer Henrietta Leavitt showed that special stars called Cepheid variables, whose luminosity regularly rises and falls, had a tight correlation between the period of their variation and their intrinsic brightness. By knowing how bright a Cepheid truly is and how dim its light appeared when seen from Earth, Hubble was able to derive the Cepheid's distance. What Hubble found was remarkable. All of the galaxies in the universe appeared to be moving away from our planet. Furthermore, the farther a galaxy was, the faster it was receding. This observation, which Hubble made in 1929, became the basis for what's known as Hubble's law, which states that there is a relationship between the distance an object in the cosmos is from us and the speed at which it is receding. Now, heavenly entities are moving away at a rate that increases with distance. Hubble attempted to estimate the constant, coming up with a value of around 342,000 mph per million light-years or 501 kilometers per second per megaparsec (Mpc) in cosmologists' units.

Implications of the recent research

• The recent research allowed the recalibration of what is known as the Hubble constant. Hubble Constant entails the observation that galaxies are moving away from Earth at speeds that are proportional to their distance.
• The calibration further amplifies the Hubble tension.
• The study confirms the 73 km/s/Mpc expansion rate, but more importantly, it also provides the most precise, reliable calibrations of Cepheids as tools to measure distances to date.

HUBBLE TELESCOPE: https://www.iasgyan.in/daily-current-affairs/hubble-telescope-23

PRACTICE QUESTION Q. The Hubble Space Telescope’s legacy cannot be overstated as it represents an important technological innovation centuries in the making as the first orbiting, astronomical, true observatory. Shed light on the contributions of Hubble Telescope in understanding and unravelling the secrets of our Universe.

https://www.aninews.in/news/science/a-new-measurement-could-change-understanding-of-the-universe-study20230406232725/