The Webb Space Telescope measures the expansion rate of the universe

Combined observations from NASA’s NIRCam (Near Infrared Camera) and NASA’s WFC3 (Wide Field Camera 3) camera show spiral galaxy NGC 5584, 72 million light-years from Earth. Among the bright stars in NGC 5584 are pulsars called Cepheid variables and a Type Ia supernova, a special class of exploding stars. Astronomers use Cepheid variables and Type Ia supernovae as reliable distance markers to measure the expansion rate of the universe. Image source: NASA, ESA, CSA, and A. Riess (STScI)

Hubble tension refers to the difference between the observed and expected expansion rate of the universe. the James Webb Space Telescope Revises measurements he made previously Hubble Space Telescope. Despite the progress, questions remain about the rapid expansion of the universe and possible underlying cosmic phenomena.

The rate at which the universe is expanding, known as the Hubble constant, is one of the fundamental criteria for understanding the evolution and ultimate fate of the universe. However, there is a persistent difference called the “Hubble tension” that appears between the value of the constant measured by a wide range of independent distance indices and its value expected from the great explosion twilight.

NASAThe James Webb Space Telescope provides new capabilities to examine and refine some of the strongest observational evidence for this tension. Nobel laureate Adam Ries of Johns Hopkins University and the Space Telescope Science Institute presents his and his colleagues’ recent work using Webb observations to improve the accuracy of local measurements of the Hubble constant.

The cosmological measurement challenge

“Have you ever struggled to see a mark that was at the edge of your vision? What does it say? What does it mean? Even with the most powerful telescopes, the ‘marks’ that astronomers want to read seem so small that we struggle, too.”

“The sign that cosmologists want to read is the sign of the cosmic speed limit that tells us how fast the universe is expanding — a number called the Hubble constant. Our sign is written in the stars in distant galaxies. The brightness of some stars in those galaxies tells us how far away they are, and therefore how much time that light has traveled.” To reach us, the redshifts of galaxies tell us how much the universe expanded during that period, and thus the expansion an average.

This chart shows the combined power of NASA’s Hubble and Webb space telescopes in determining precise distances to a special class of variable stars used to calibrate the expansion rate of the universe. These Cepheid variable stars are seen in crowded star fields. Light pollution from surrounding stars may make measuring Cepheid’s brightness less accurate. Webb’s sharper infrared view allows the Cepheid target to be more clearly isolated from surrounding stars, as seen on the right side of the diagram. Webb’s data confirms the accuracy of 30 years of Hubble observations of Cepheids that were crucial in determining the bottom rung of the cosmic distance scale for measuring the expansion rate of the universe. On the left, NGC 5584 is shown in a composite image from Webb NIRCam (Near Infrared Camera) and Hubble’s Wide Field Camera 3. Image credit: NASA, ESA, A. Riess (STScI), W. Yuan (STScI)

“A particular class of stars, Cepheid variables, have given us the most accurate measurements of distance for more than a century because these stars are extraordinarily bright: they are giant stars, a hundred thousand times the luminosity of the Sun. Moreover, they pulsate (i.e. expand and contract in Magnitude) over a period of weeks indicating their relative brightness. The longer the period, the intrinsically brighter it is. It is the gold standard instrument for the purpose of measuring distances between galaxies a hundred million light-years or more away, and is a crucial step in determining the Hubble constant. Unfortunately , stars in galaxies are clustered together in a small area from our distant viewpoint, so we often lack the resolution to separate them from their line-of-sight neighbors.

Hubble’s contribution and Webb’s developments

“The main justification for building the Hubble Space Telescope was to solve this problem. Before Hubble’s 1990 launch and its subsequent Cepheid measurements, the expansion rate of the universe was so uncertain that astronomers were not sure whether the universe was expanding for 10 billion or 20 billion years. This is because A faster expansion rate will lead to a younger age of the universe, and a slower rate of expansion will lead to an older age of the universe. Hubble has better visible wavelength resolution than any ground-based telescope because it is located above the nebulous effects of Earth’s atmosphere. As a result, it can identify individual Cepheid variables in galaxies farther away More than a hundred million light-years away and measure the time interval over which its brightness changes.

“However, we must also observe Cepheid stars in the near-infrared part of the spectrum to see the light that passes unscathed through the intervening dust. (The dust absorbs and scatters blue optical light, making distant objects appear faint and tricking us into thinking they are farther away than they are.) Unfortunately, Hubble’s view of red light is not as sharp as blue light, so the Cepheid starlight we see there is mixed with other stars in its field of view. We can calculate the average amount of mixing, Statistically, in the same way that a doctor calculates your weight by subtracting the average weight of clothing from the scale reading, but doing so adds confusion to the measurements. Some people’s clothes are heavier than others.

“However, sharp infrared vision is one of the superpowers of the James Webb Space Telescope. With its large mirror and sensitive optics, it can easily separate Cepheid light from nearby stars with little mixing. In Webb’s first year of operations with our observer program In 1685, we collected observations of Cepheids found by Hubble in two steps along what is known as the cosmic distance ladder. The first step involves observing Cepheids in a galaxy with a known geometric distance that allows us to calibrate the true luminosity of Cepheids. For our program, this galaxy is NGC 4258. The second step is to observe the Cepheids in the host galaxies of recent Type Ia supernovae. Combining the first two steps transfers knowledge of the distance to the supernovae to calibrate their true brightness. The third step is to observe those distant supernovae where the expansion of the universe is evident and can be measured by Comparing distances inferred from the brightnesses and redshifts of supernova host galaxies.This sequence of steps is known as the distance ladder.

“We have recently obtained the first Webb measurements from Steps 1 and 2 allowing us to complete the distance ladder and compare them to previous measurements using Hubble (see figure). Webb’s measurements have significantly reduced noise in Cepheid measurements due to the observatory’s accuracy at near-infrared wavelengths. This kind of improvement is what astronomers dream of! We observed more than 320 cepheid stars during the first two steps. We confirmed that previous measurements by the Hubble Space Telescope were accurate, albeit noisier. We also observed four supernova hosts using Webb, We saw a similar result for the entire sample.

Compare the relationships between Cepheid period and luminosity used to measure distances. The red dots are from NASA’s Webb, and the gray dots are from NASA’s Hubble. The top panel is dedicated to NGC 5584, the host of the type Ia supernova, with an inset showing image stamps of the same Cepheid seen by each telescope. The bottom panel is for NGC 4258, a galaxy with a known geometric distance, with the inset showing the difference in distance coefficients between NGC 5584 and NGC 4258 as measured using each telescope. The two telescopes are in excellent agreement. Image credit: NASA, ESA, A. Riess (STScI), and G. Anand(STScI)

The ongoing mystery of Hubble tension

“What the results have not yet explained is why the universe is expanding so rapidly! We can pridect The expansion rate of the universe by observing its nascent image Cosmic microwave background, then we use our best model of how it grows over time to tell us how fast the universe should be expanding today. The fact that the current measure of the expansion rate is dramatically exceeding expectations is a decade-long problem called “Hubble jitter.” The most exciting possibility is that stress is evidence of something we miss in our understanding of the universe.

“This could indicate the presence of exotic dark energy, exotic dark matter, a revision of our understanding of gravity, or the existence of a unique particle or field. The most simple explanation is that multiple measurement errors conspire in the same direction (the astronomers ruled out one error using independent steps), That’s why it’s so important to repeat the measurements more precisely. With Webb’s confirmation of Hubble’s measurements, Webb’s measurements provide the strongest evidence yet that systematic errors in Hubble’s Cepheid photometry do not play a significant role in Hubble’s current jitter. As a result, the most likely Interest is on the table and the tense mystery deepens.

This post highlights data from A paper Which has been accepted before Astrophysical Journal.

Reference: “No More Crowding: Accuracy of the Hubble Constant Tested by High-Resolution Observations of Cepheid Objects with the James Webb Space Telescope” by Adam J. Rees, Gagandeep S. Anand, Wenlong Yuan, Stefano Casertano, Andrew Dolphin, Lucas M. Macri, Louise Proval, Dan Skolnick, Marshall Perrin, and Richard I. Anderson, accepted, Astrophysical Journal.
arXiv:2307.15806

Author: Adam Ries is the Bloomberg Distinguished Professor at Johns Hopkins University, the Thomas G. Barber Professor of Space Studies in the JHU Krieger School of Arts and Sciences, a distinguished astronomer at the Space Telescope Science Institute, and the recipient of the 2011 Nobel Prize in Physics.