- 3126 - HUBBLE CONSTANT - how fast universe is expanding? One of the most exciting questions in cosmology today is whether there is new physics that is missing from our current understanding of how the universe is evolving. A current discrepancy in the measurement of the Hubble constant could be signaling a new physical property of the universe unrecognized measurement uncertainties.
---------- 3126 - HUBBLE CONSTANT - how fast universe is expanding?
- A new method of measuring distances to faraway galaxies Despite a century of measurements, astronomers can’t agree on the rate at which the universe is expanding. A technique that relies on measuring distances to a specific type of aging star in other galaxies, the J-region Asymptotic Giant Branch, or JAGB method.
-
- In 1920, Edwin Hubble first noticed the relationship between a galaxy’s distance and how fast it was moving away from us. This value, now known as the “Hubble constant“, is a key parameter in cosmological models.
-
- Hubble first measured this constant by comparing galactic distance and velocity measurements derived from a specific kind of star that pulses regularly. Measurements using direct methods like Hubble’s have improved greatly over the decades, but they don’t agree with methods that extrapolate from the Cosmic Microwave Background, light leftover from the very early universe.
-
- Stars in the J-region Asymptotic Giant Branch are a specific type of aging giants that contain a substantial amount of carbon in their atmospheres that is brought to the surface by convection currents, giving them a very distinct color and brightness that allows them to be identified in a set of stars within a galaxy.
-
- This makes them prime candidates for being what astronomers call “standard candles“. Because the apparent brightness of a star as observed depends on both its distance from the observer and its intrinsic brightness, knowing the intrinsic brightness of a star can allow astronomers to infer its distance.
-
- By using a single object as the target and applying four different independent measurement methods, the team could compare the accuracy and precision of the JAGB method to previously established methods.
-
- After analyzing the data four different ways, researchers determined that the JAGB method is not only an independent check on other distance measurement methods, but that it requires less observing time—a scarce commodity among a community of astronomers competing for time on a limited number of powerful telescopes.
-
- Because JAGB stars are brighter than stars used in other distance measurements, they can also be seen further away, which will allow for more distant calibrations than are possible with other methods. Additionally, JAGB stars are found in all types of galaxies, as opposed to the pulsating stars used by Hubble, which are found only in the more limited subset of spiral galaxies and often suffer from crowding and significant interference from dust.
-
- Type 1a supernovae are used to measure more distant galaxies, but they need to be calibrated by shorter range distance measurements using techniques like the JAGB method.
-
- The law also known as Hubble-Lamaitre law is the observation that galaxies are moving away from the Earth at speeds proportional to their distance. In other words, the farther they are the faster they are moving away from Earth. The velocity of the galaxies has been determined by their “redshift“, a shift of the light they emit toward the red end of the spectrum.
-
- Hubble’s law is considered the first observational basis for the expansion of the universe, and today it serves as one of the pieces of evidence most often cited in support of the Big Bang model.
-
- Hubble constant is most frequently quoted in (km/s)/Mpc, thus giving the speed in km/s of a galaxy 1 megaparsec (3.09×1019 km) away, and its value is about 70 (km/s)/Mpc. However, the SI unit of is simply s−1, and the SI unit for the reciprocal of is simply the second. The reciprocal of is known as the “Hubble time“.
The Hubble constant can also be interpreted as the relative rate of expansion. In this form = 7%/Gyr, meaning that at the current rate of expansion it takes a billion years for an unbound structure to grow by 7%.
-
- In February 2020, the Megamaser Cosmology Project published results that confirmed the distance ladder results and differed from the early-universe results at a statistical significance level of 95%. In July 2020, measurements of the cosmic background predict that the Universe should be expanding more slowly than is currently observed.
-
- Georges Lemaître, in a 1927 article, independently derived that the universe might be expanding, observed the proportionality between recessional velocity of, and distance to, distant bodies, and suggested an estimated value for the proportionality constant.
-
- This constant, when Edwin Hubble confirmed the existence of cosmic expansion and determined a more accurate value for it two years later, came to be known by his name as the Hubble constant. Hubble inferred the recession velocity of the objects from their redshifts, many of which were earlier measured and related to velocity by Vesto Slipher in 1917.
-
- Though the Hubble constant is roughly constant in the velocity-distance space at any given moment in time, the Hubble parameter , which the Hubble constant is the current value of, varies with time, so the term constant is sometimes thought of as somewhat of a misnomer.
-
- April 18, 2021 HUBBLE CONSTANT - of expansion? 3125
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ----
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
--------------------- --- Monday, April 19, 2021 ---------------------------
No comments:
Post a Comment