One of the biggest space puzzles today concerns the expanding universe.
During the first billion years of cosmic history, as the density of matter and radiation decreased, the expansion rate of the universe decreased and distant galaxies retreated from our own at a slower rate. But over the past 6 billion years or so, the retreat of distant galaxies has accelerated, and while the rate of expansion is still declining, it is not heading towards zero. Two different methods of measuring the expansion rate give conflicting values. The actual rate of expansion remains a matter of debate.
credit : NASA/STSci/AnfieldEach of the two main methods gives incompatible answers with low error.
NASA’s JWST has shown us the most distant galaxies in the universe ever discovered, exceeding the limits of previous observatories, including all ground-based telescopes on Earth and the Hubble telescope. Once enough observed and measured galaxies have been assigned 3D locations, JWST’s CEERS data can be used to construct a visualized cosmic flythrough. Measurement of dilatation is difficult because different methods give different results and are not compatible with each other.
credit With: Frank Summers (STScI), Greg Bacon (STScI), Joseph DePasquale (STScI), Leah Hastak (STScI), Joseph Olmsted (STScI), Alyssa Pagan (STScI). Scientific Contacts: Steve Finkelstein (UT Austin), Rebecca Larson (RIT), Micaela Bagley (UT Austin)By tracking the evolution of early relic signals, an expansion of 67 km/s/Mpc was measured.
If our telescopes allow it, we can arbitrarily look far back into the universe, and clusters of galaxies should reveal a particular distance scale, the acoustic scale. This scale should evolve over time in a specific way, just like the acoustic “peaks and valleys” of the Earth. The cosmic microwave background also reveals this scale. Evolution over time at this scale is an early relic revealing a low expansion rate of ~67 km/s/Mpc.
credit : EM Huff, SDSS-III Team, Antarctic Telescope Team. Graphics: Zosia RostomianStarting close and watching the recession grow with distance, we measured 73 km/s/Mpc.
Building the cosmic distance ladder involves heading from our solar system to stars, nearby galaxies, and distant galaxies. Each “step” comes with its own uncertainty, especially the steps to which the various “runs” of a ladder are connected. However, recent refinements of the distance ladder have demonstrated how robust their results are.
credit : NASA, ESA, A. Field (STScI), and A. Reese (JHU)This contradiction, or “Hubble tension,” is a modern cosmic conundrum.
The latest measured tension from the distance ladder (red) and early signal data from the CMB and BAO (blue) are shown in contrast. We believe that the initial signal method is correct and that the distance ladder is fundamentally flawed. There is a small error that biases the initial signal method and could be due to either the distance ladder being correct or both groups being correct and due to some new physics (shown at the top). The idea that there was an early form of dark energy is interesting, but it means that there was more dark energy in the early days, which (mostly) has since decayed.
credit : AG Riess, Nat Rev Phys, 2020Many speculate that an observation error on the “distance ladder” side may be the cause.
Back in 2001, various sources of error existed that could skew the optimal distance ladder measurements of the Hubble constant and the expansion of the universe to significantly higher or lower values. Thanks to the painstaking and careful work of many people, errors have been greatly reduced and are no longer possible. Although not shown here, the new JWST study reduced the Cepheid-related and periodic photometric errors even further than those shown here.
credit : AG Riess et al., ApJ, 2022We will start by observing the Cepheid variable stars in the Milky Way galaxy.
The variable star RS Papis, whose light echoes through interstellar clouds. There are various types of variable stars. One of them, the Cepheid variable star, can be measured both in our galaxy as well as in galaxies up to 50-60 million light-years away. This allows us to estimate the distances from our own galaxy to galaxies far in the universe. RR Lyra and AGB branch tip stars can be used in a similar manner.
credit : NASA, ESA, G. Bacon (STScI), Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration, and H. Bond (STScI and Penn State University)We accurately estimate their distance by measuring astronomical parallax.
As the Earth moves through space in its orbit around the Sun, the stars closest to the Earth will appear to move periodically relative to the more distant stars. Before the heliocentric model was established, we were looking for a baseline of about 12,000 kilometers overnight, the diameter of the Earth as it rotates, rather than a baseline “change” of about 300 million kilometers over about six months. was its axis. The distance to the star is so great that it wasn’t until the 1830s that the first parallax, whose baseline was her 300 million km, was detected. Today, we measured the parallax of over a billion stars on ESA’s Gaia mission.
credit : ESA/ATG Media LabThen measure the Cepheids of nearby well-measured galaxies.
The top two panels show two nearby Cepheid-rich galaxies, NGC 4258 (left) and NGC 5584 (right), overlaid with the JWST field. The lower panel shows his JWST view, highlighting the separately identified Cepheid variables in each image.
credit : AG Riess et al., Submitted to ApJ/arXiv:2307.15806, 2023Finally, we will measure Type Ia supernovae within and outside these galaxies, linking these cosmic ‘steps’.
As of 2019, there were only 19 published galaxies with distances measured by Cepheid variables that have been observed to produce Type Ia supernovae. We currently measure distances from individual stars in galaxies hosting at least one type Ia supernova in 42 galaxies, 35 of which have excellent Hubble images. These 35 galaxies are shown here.
credit : AG Riess et al., ApJ, 2022Is it possible that the Cepheid error is biasing the measured expansion rate?
Using a cosmic distance ladder means piecing together different cosmic scales, and I’m always worried about the uncertainty of where the various “rungs” of the ladder are connected. As shown here, the ladder has been reduced to just three “steps” and the full measurements match each other nicely.
credit : AG Riess et al., ApJ, 2022by Measuring Cepheids in Nearby Galaxies JWST is investigating this possibility.
The nearby spiral galaxy, NGC 4258 (also known as Messier 106), is only about 20 million light-years away, but contains many known Cepheids similar to those found in the Milky Way. This is an important galaxy for calibrating the cosmic distance ladder.
credit : NASA, ESA, Hubble Legacy Team (STScI/AURA), and R. Gendler (for Hubble Legacy Team).Acknowledgments: J. Gabbanyobserve the galaxy NGC4258 JWST found no photometric bias for the Cepheid cluster.
This image shows several Cepheid variables with different periods in the nearby galaxy NGC 4258. This is an important galaxy for Cepheid and distance calibration. The bottom six rows show the same star measured at different wavelengths by both Hubble (grey label) and JWST (purple label). The superior resolution of JWST images validates previous results and significantly reduces previous Hubble errors while maintaining consistency with previous results.
credit : AG Riess et al., Submitted to ApJ/arXiv:2307.15806, 2023Instead, it confirmed and enhanced previous Hubble Space Telescope discoveries.
This composite image shows the barred spiral galaxy NGC 5584 and the bright supernova SN 2007af within it. Nearby galaxies with identifiable Cepheid variables and at least one type Ia supernova among them are of great importance for the cosmic distance ladder method to measure the expanding universe.
credit : ESOCepheid constellation NGC5584 also had Type Ia supernova (circa 2007) the bias is also not apparent.
This graph shows the relationship between the brightness magnitude (y-axis) and the period (x-axis) of Cepheid variable stars in the galaxies NGC 5584 (top) and NGC 4258 (bottom). New JWST data are shown in red and old Hubble data are shown in grey. Errors and uncertainties in this relationship in both galaxies are greatly reduced, mainly due to the better resolution of his JWST than the Hubble galaxy.
credit : AG Riess et al., Submitted to ApJ/arXiv:2307.15806, 2023of Relationship between period and brightness The primary calibrator for Cepheid stars, now more accurate than ever.
JWST has further reduced the uncertainties in their distances by enabling a deeper understanding of the nearby Garay NGC 4258 and NGC 5584 Cepheid variables. The points at the bottom of the graph show estimates of the distance to NGC 5584 from the inflation rate inferred from the distance ladder (left) and that expected from the early relic method (right). This disagreement is significant and compelling.
credit : AG Riess et al., Submitted to ApJ/arXiv:2307.15806, 2023With excellent resolution, JWST has reduced all uncertainties to the lowest values ever.
The standard candle (left) and standard ruler (right) are two different techniques that astronomers have used to measure the expansion of space at various times/distances in the past. Based on how quantities such as luminosity and angular size change with distance, we can infer the expansion history of the universe. Using the candle method is part of the distance ladder and yields 73 km/s/Mpc. The use of rulers was part of early signal methods and yields 67 km/s/Mpc. New JWST data deepens the mystery surrounding the expansion rate of the universe.
credit : NASA/JPL-CaltechMostly Mute Monday tells an astronomical story with images, visuals, and under 200 words.