Expansion Details

A new estimate of the local expansion rate, known as the Hubble constant (Ho), has brought to light an intriguing discrepancy. This reinforces the ongoing conundrum in the field of cosmology, where evidence for acceleration is ever-present.

For the calibration of relatively short distances the team observed Cepheid variables. These are pulsating stars which fade and brighten at rates that are proportional to their true brightness and this property allows astronomers to determine their distances. The researchers calibrated the distances to the Cepheids using a basic geometrical technique called parallax. With Hubble’s sharp-eyed Wide Field Camera 3 (WFC3), they extended the parallax measurements further than previously possible, across the Milky Way galaxy. To get accurate distances to nearby galaxies, the team then looked for galaxies containing both Cepheids and Type Ia supernovae. Type Ia supernovae always have the same intrinsic brightness and are also bright enough to be seen at relatively large distances. By comparing the observed brightness of both types of stars in those nearby galaxies, the team could then accurately measure the true brightness of the supernova. Using this calibrated rung on the distance ladder the accurate distance to additional 300 type Ia supernovae in far-flung galaxies was calculated. They compare those distance measurements with how the light from the supernovae is stretched to longer wavelengths by the expansion of space. Finally, they use these two values to calculate how fast the universe expands with time, called the Hubble constant.

Webb Space Telescope Detects Earlier Galaxies 

When astronomers got their first glimpses of galaxies in the early universe from NASA’s James Webb Space Telescope, they were expecting to find galactic pipsqueaks, but instead they found what appeared to be a bevy of Olympic bodybuilders. Some galaxies appeared to have grown so massive, so quickly, that simulations couldn’t account for them. Some researchers suggested this meant that something might be wrong with the theory that explains what the universe is made of and how it has evolved since the big bang, known as the standard model of cosmology.

According to a new study in the Astronomical Journal led by University of Texas at Austin graduate student Katherine Chworowsky, some of those early galaxies are in fact much less massive than they first appeared. Black holes in some of these galaxies make them appear much brighter and bigger than they really are.

“We are still seeing more galaxies than predicted, although none of them are so massive that they ‘break’ the universe,” Chworowsky said.

The evidence was provided by Webb’s Cosmic Evolution Early Release Science (CEERS) Survey, led by Steven Finkelstein, a professor of astronomy at UT Austin and study co-author.

CEERS Deep Field (NIRCam) Image

Although they’ve settled the main dilemma, a less thorny problem remains: There are still roughly twice as many massive galaxies in Webb’s data of the early universe than expected from the standard model. One possible reason might be that stars formed more quickly in the early universe than they do today.

“And so there is still that sense of intrigue,” Chworowsky said. “Not everything is fully understood. That’s what makes doing this kind of science fun, because it’d be a terribly boring field if one paper figured everything out, or there were no more questions to answer.”The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it.

The James Webb Space Telescope or JWST, offers humanity a powerful new tool to see deep into space. Launched in 2021, the successor to the Hubble Telescope has taken stunningly sharp images, revealed new aspects of faraway worlds, and collected unprecedented data, opening new windows on the universe.

More Recent Studies & Methods (Aug 2024) 

In a paper submitted to The Astrophysical Journal, currently available on the arXiv preprint server, University of Chicago cosmologist Wendy Freedman and her colleagues analyzed new data taken by NASA's powerful James Webb Space Telescope. They measured the distance to 10 nearby galaxies and measured a new value for the rate at which the universe is expanding at the present time.

Their measurement, 70 kilometers per second per megaparsec, overlaps the other major method for the Hubble constant.

Freedman and her colleagues used the telescope to make measurements of ten nearby galaxies that provide a foundation for the measurement of the universe's expansion rate.

To cross-check their results, they used three independent methods:

The first uses a type of star known as a Cepheid variable star, which varies predictably in its brightness over time.

The second method is known as the "Tip of the Red Giant Branch," and uses the fact that low-mass stars reach a fixed upper limit to their brightnesses.

The third, and newest, method employs a type of star called carbon stars, which have consistent colors and brightnesses in the near-infrared spectrum of light. The new analysis is the first to use all three methods simultaneously, within the same galaxies.

In each case, the values were within the margin of error for the value given by the cosmic microwave background method of 67.4 kilometers per second per megaparsec.

"Getting good agreement from three completely different types of stars, to us, is a strong indicator that we're on the right track," said Freedman.

"Future observations with JWST will be critical for confirming or refuting the Hubble tension and assessing the implications for cosmology," said study co-author Barry Madore of the Carnegie Institution for Science and visiting faculty at the University of Chicago.

Looking At Expansion in a Different Way

When we look at the universe, we are looking into the past, so it would be incorrect to discuss the expansion as happening NOW?

We need to change our viewpoint and the following graph provides another explanation of what we are seeing.

As highlighted earlier, our view of the universe is relative. For example, we think of it as relatively expanding but what if the universe started at its maximum size then started deflating it would it be denser but from our relative viewpoint our perception of time is also reduced so we do not notice any changes. Older 'space' virtual particles were created billions of years ago but are they renewed, if  so, can we  assume old 'space' remains the same or is the renewal process existing across time??