Pranam
Scientists Say They Solved the Problem of the Expansion of the Universe
How fast is our universe expanding? To answer this question,
scientists used two different methods and found two answers that are
slightly different from each other and that's the source of 'Hubble
tension.' Astrophysicists have been divided into two groups, one which
thinks this difference in the answers is significant and we need new
physics to explain it. Others attribute it to the difference in the
methods. A recent study now says that the difference may not be that
different at all.
Hubble constant is the rate at which the universe expands. Knowing
this number can help us understand how old our universe is and how it has
evolved. To determine this number, scientists used two approaches.
In one, they looked at the faint light left after the Big Bang.
Called the cosmic microwave (CMW) background, this light was measured in
space as well as on the ground using telescopes. The observations were fed
into the 'standard model' of the early universe and used to estimate the
Hubble constant today. The answer is 67.4 kilometers per second per
megaparsec (km/s/Mpc)
The second method is to look at stars in a nearby universe and measure
how fast they are moving away from us. In 2001, Wendy Freedman and her team
at the University of Chicago used the Hubble Space Telescope to look at
stars called Cepheids. They found the Hubble constant to be 72 km/s/Mpc.
Freedman and her team continued to look at Cepheids over the years
but in 2019 decided to cross-check their method by looking at stars called
'red giants'. These are very large and luminous stars that reach peak
brightness and then fade rapidly. By measuring the actual peak brightness,
scientists can measure distances to their host galaxies. But the
measurements need to be accurate. So, Freedman and her team used four
different measurement methods for different stars and galaxies and found
them to be accurate within one percent error. They then used red giants to
estimate the Hubble constant and found its value to be 69.8 km/s/Mpc, much
closer to the value derived by observing the cosmic microwave background.
Explaining the cause for differences in two values her team derived,
Freedman said, "The Cepheid stars have always been a little noisier and a
little more complicated to fully understand; they are young stars in the
active star-forming regions of galaxies, and that means there's potential
for things like dust or contamination from other stars to throw off your
measurements."
With the launch of the James Webb Space Telescope, Freedman is
confident that with higher resolution and sensitivity, the data will
improve in the near future.
"There is still some room for new physics, but even if there isn't, it
would show that the standard model we have is basically correct, which is
also a profound conclusion," Freedman added. The study will be published in
the Astrophysical Journal.
KR: The start of 4.8 Billion years is now at present estimated at 13.6
Billion years since the Big bang whereas Indian Vedic system had concluded
at 155.2 Trillion years and we are in the 28th chatur yugam. KR IRS 5721
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