Figure 1: Type II supernova sample used for the Hubble constant measurement. The images show the host galaxies of the ten supernovae, with the explosion sites marked by red star symbols. The images are aligned with a redshift scale reflecting the relative distances of the supernovae from Earth. © MPA
Figure 2: Spectral fitting and the Hubble diagram for Type II supernovae. The top panels show two examples of spectral fits used to determine the supernova distances. By comparing observed spectra (black) with model predictions (colour), researchers can extract key physical properties and infer the intrinsic brightness, enabling a direct distance measurement. The bottom panel presents a Hubble diagram, where the measured luminosity distances of the supernovae are plotted against their redshifts. The data points represent individual spectral observations, meaning multiple measurements can exist for each supernova. The dashed black line represents the best-fit relationship between distance and redshift, and its slope is determined by the Hubble constant. The grey-shaded regions indicate the uncertainties for this fit (68% and 95% confidence intervals). The best-fit value for the Hubble constant and its 68% confidence interval are H₀ = 74.9 ± 1.9 km/s/Mpc. © MPA
Figure 3: Artist’s impression of the Hubble tension, showing the two different approaches to measuring the Hubble constant as two bridges that do not quite connect. The depicted early-Universe measurements yield an average value of 67.4 km/s/Mpc, the local measurements an average value of 73.0 km/s/Mpc. The new measurement from this study, based on Type II supernovae (orange), is completely independent of all other measurements and provides compelling support for the Hubble tension. The local route also includes results from various incarnations of the cosmic distance ladder, as well as other direct methods such as gravitational lensing and water masers. Image Credit: Original image by NOIRLab/NSF/AURA/J. da Silva, sourced from NOIRLab (CC BY 4.0), modified by S. Taubenberger.
The expansion rate of the Universe, quantified by the Hubble constant (H₀), remains one of the most debated quantities in cosmology. Measurements based on nearby objects yield a higher value than those inferred from observations of the early Universe—a discrepancy known as the "Hubble tension". Researchers at the Max Planck Institute for Astrophysics and their collaborators have now presented a new, independent determination of H₀ using Type II supernovae. By modeling the light from these exploding stars with advanced radiation transport techniques, they were able to directly measure distances without relying on the traditional distance ladder. The resulting H₀ value agrees with other local measurements and adds to the growing body of evidence for the Hubble tension, offering an important cross-check and a promising path toward resolving this cosmic puzzle.
One of the biggest puzzles in modern cosmology is the ongoing discrepancy in measurements of the Hubble constant (H₀) between local and early Universe probes, known as the “Hubble tension”. Since H₀ describes the current expansion rate of the Universe, it is a local quantity and can only be directly measured using nearby objects. In contrast, methods based on the early Universe, such as those using the cosmic microwave background (CMB), do not measure H₀ directly. Instead, they infer its value by assuming a cosmological model to extrapolate from the conditions 13 billion years ago to today. The fact that these two approaches yield conflicting values—with local distance-ladder measurements giving a higher H₀ than early-Universe methods—suggests that our standard cosmological model may be incomplete, potentially pointing to new physics.
Researchers at the Max Planck Institute for Astrophysics (MPA) and their collaborators have explored an independent way of measuring H₀ using Type II supernovae (SNe II). Unlike traditional approaches, this method does not rely on the cosmic distance ladder, making it a powerful cross-check against existing techniques. Their results provide a new, highly precise measurement of H₀ and further contribute to the debate over the expansion rate of the Universe.
Determining the Hubble constant requires accurate measurements of distances to astronomical objects at different redshifts. The most widely used technique, the cosmic distance ladder, relies on several interconnected steps: distances to nearby objects (such as Cepheid variable stars) are used to calibrate further reaching indicators such as Type Ia supernovae (SNe Ia), which then serve as standard candles to measure distances to faraway galaxies.
However, the reliance on multiple steps introduces possible systematic uncertainties, and different teams report slightly different results. A direct measurement based on known physics offers a valuable complementary approach, as it is affected by different systematics and does not depend on empirical calibrations. This is where Type II supernovae provide an exciting alternative.
Type II supernovae occur when massive, hydrogen-rich stars explode at the end of their lives. While their brightness varies depending on factors such as temperature, expansion velocity, and chemical composition, it can be accurately predicted using radiation transport models. This allows researchers to determine their intrinsic luminosity and use them as distance indicators, independent of empirical calibration methods.
A critical step in this process is identifying the best-fitting model for each observed supernova. Key physical properties leave distinct imprints on the supernova spectrum: temperature shapes the overall continuum, expansion velocity sets the width of spectral lines via Doppler broadening, and chemical composition determines the strength of specific absorption and emission features. By systematically comparing observed spectra to simulated spectra from radiative transfer models, researchers can find the model that most accurately describes the supernova’s physical conditions. With such a well-matched model the intrinsic brightness—and thus the distance—can be precisely determined.
To make this process efficient, the team used a spectral emulator, an advanced machine-learning tool trained on precomputed simulations. Instead of running time-intensive radiation transport calculations for every supernova, the emulator rapidly interpolates between models, allowing for fast and accurate spectral fitting.
The research team applied their spectral modeling approach to a sample of ten Type II supernovae at redshifts between 0.01 and 0.04, using publicly available data not specifically designed for distance measurements (Fig. 1). Despite the limitations of the dataset, their method yielded reliable distances. By constructing a Hubble diagram from these measurements (Fig. 2), they obtained an independent estimate of H₀: H₀ = 74.9 ± 1.9 km/s/Mpc
This value is consistent with most other local measurements, such as those from Cepheid-calibrated supernovae and supports the tension with early-Universe probes. The achieved precision is comparable to the most competitive techniques, demonstrating that Type II supernovae are a promising tool for cosmology (Fig. 3).
This study serves as a proof of concept, showing that Type II supernovae can provide precise and reliable distance measurements in the Hubble flow. Future work will focus on increasing the sample size and improving the accuracy of the technique by using dedicated observations. To this end, the researchers have assembled the adH0cc dataset (https://adh0cc.github.io/), a collection of Type II supernova observations from the ESO Very Large Telescope, specifically designed for precise distance measurements. This dataset will serve as a key resource for refining the method. By providing an independent check on the local determination of H₀, Type II supernovae help astrophysicists tackle one of the most pressing questions in cosmology today: Is the Hubble tension real, and if so, what does it tell us about the fundamental nature of the Universe?
One of the biggest puzzles in modern cosmology is the ongoing discrepancy in measurements of the Hubble constant (H₀) between local and early Universe probes, known as the “Hubble tension”. Since H₀ describes the current expansion rate of the Universe, it is a local quantity and can only be directly measured using nearby objects. In contrast, methods based on the early Universe, such as those using the cosmic microwave background (CMB), do not measure H₀ directly. Instead, they infer its value by assuming a cosmological model to extrapolate from the conditions 13 billion years ago to today. The fact that these two approaches yield conflicting values—with local distance-ladder measurements giving a higher H₀ than early-Universe methods—suggests that our standard cosmological model may be incomplete, potentially pointing to new physics.
Researchers at the Max Planck Institute for Astrophysics (MPA) and their collaborators have explored an independent way of measuring H₀ using Type II supernovae (SNe II). Unlike traditional approaches, this method does not rely on the cosmic distance ladder, making it a powerful cross-check against existing techniques. Their results provide a new, highly precise measurement of H₀ and further contribute to the debate over the expansion rate of the Universe.
Determining the Hubble constant requires accurate measurements of distances to astronomical objects at different redshifts. The most widely used technique, the cosmic distance ladder, relies on several interconnected steps: distances to nearby objects (such as Cepheid variable stars) are used to calibrate further reaching indicators such as Type Ia supernovae (SNe Ia), which then serve as standard candles to measure distances to faraway galaxies.
However, the reliance on multiple steps introduces possible systematic uncertainties, and different teams report slightly different results. A direct measurement based on known physics offers a valuable complementary approach, as it is affected by different systematics and does not depend on empirical calibrations. This is where Type II supernovae provide an exciting alternative.
Type II supernovae occur when massive, hydrogen-rich stars explode at the end of their lives. While their brightness varies depending on factors such as temperature, expansion velocity, and chemical composition, it can be accurately predicted using radiation transport models. This allows researchers to determine their intrinsic luminosity and use them as distance indicators, independent of empirical calibration methods.
A critical step in this process is identifying the best-fitting model for each observed supernova. Key physical properties leave distinct imprints on the supernova spectrum: temperature shapes the overall continuum, expansion velocity sets the width of spectral lines via Doppler broadening, and chemical composition determines the strength of specific absorption and emission features. By systematically comparing observed spectra to simulated spectra from radiative transfer models, researchers can find the model that most accurately describes the supernova’s physical conditions. With such a well-matched model the intrinsic brightness—and thus the distance—can be precisely determined.
To make this process efficient, the team used a spectral emulator, an advanced machine-learning tool trained on precomputed simulations. Instead of running time-intensive radiation transport calculations for every supernova, the emulator rapidly interpolates between models, allowing for fast and accurate spectral fitting.
The research team applied their spectral modeling approach to a sample of ten Type II supernovae at redshifts between 0.01 and 0.04, using publicly available data not specifically designed for distance measurements (Fig. 1). Despite the limitations of the dataset, their method yielded reliable distances. By constructing a Hubble diagram from these measurements (Fig. 2), they obtained an independent estimate of H₀: H₀ = 74.9 ± 1.9 km/s/Mpc
This value is consistent with most other local measurements, such as those from Cepheid-calibrated supernovae and supports the tension with early-Universe probes. The achieved precision is comparable to the most competitive techniques, demonstrating that Type II supernovae are a promising tool for cosmology (Fig. 3).
This study serves as a proof of concept, showing that Type II supernovae can provide precise and reliable distance measurements in the Hubble flow. Future work will focus on increasing the sample size and improving the accuracy of the technique by using dedicated observations. To this end, the researchers have assembled the adH0cc dataset (https://adh0cc.github.io/), a collection of Type II supernova observations from the ESO Very Large Telescope, specifically designed for precise distance measurements. This dataset will serve as a key resource for refining the method. By providing an independent check on the local determination of H₀, Type II supernovae help astrophysicists tackle one of the most pressing questions in cosmology today: Is the Hubble tension real, and if so, what does it tell us about the fundamental nature of the Universe?
Authors:
Christian Vogl
Postdoc
2297
cvogl@mpa-garching.mpg.de
Stefan Taubenberger
2019
tauben@mpa-garching.mpg.de
Wolfgang Hillebrandt
Emeritus Director
Original publication
Vogl, Christian; Taubenberger, Stefan; et al.
No rungs attached: A distance-ladder free determination of the Hubble constant through type II supernova spectral modelling
submitted to A&A
Emeritus Director
Original publication
Vogl, Christian; Taubenberger, Stefan; et al.
No rungs attached: A distance-ladder free determination of the Hubble constant through type II supernova spectral modelling
submitted to A&A
