Astronomers struggle to understand the discrepancies when measuring the rate of expansion of the universe by various methods and are desperate for a creative idea to resolve the tension. A new method involving some of the oldest stars in the universe could do just the right thing.
Astronomers have several methods of measuring the current rate of expansion of the universe, known as the Hubble constant. A common method is to measure the brightness of distant supernovae. Another method is to examine the leftover light from the early universe, known as the cosmic microwave background. However, these two measurements do not agree.
“One of the most exciting questions in cosmology today is whether there is a new physics that is missing from our current understanding of the evolution of the universe. A recent discrepancy in the measurement of Hubble’s constant could indicate a new physical property of the universe or, more generally, undetected measurement uncertainties, ”said Wendy L. Freedman, professor of astronomy and astrophysics at John and Marion Sullivan University.
Step inside the JAGB (Asymptotic Giant Branch) stars of the J Region, which are a special type of red giants with a lot of carbon in their atmosphere.
How do JAGB stars help? They appear to have near-standard brightness, which means that we can compare the brightness we measured to the brightness we know they need to calculate the distance to them. By combining this measurement with the rate of recession of their host galaxies, we can estimate the rate of expansion of the universe independently of supernovae and the cosmic microwave background.
“We have empirically observed that these stars have a known intrinsic brightness from galaxy to galaxy,” said University of Chicago astrophysicist and PhD student Abigail Lee, lead author of a new study examining the use of JAGB stars to measure the rate of expansion has been.
As a bonus, JAGB stars are usually very bright, allowing astronomers to spot them in galaxies very far away.
This technique is still in its infancy and needs to be thoroughly reviewed and validated before it can help us resolve the modern tension in Hubble’s constant.
“Because this method is relatively new, the aim of this project was to see if it could compete with other distance indicators in terms of precision and accuracy,” said Lee.
Initially, the team aimed at the Wolf-Lundmark-Melotte galaxy, which is on the edge of our local galactic group. They compared the distance obtained with JAGB stars to other methods and found great agreement, suggesting that this method could be a crucial cross-check in future studies.
“We don’t really have the value of Hubble’s constant under control, so this is really important work to tackle one of the biggest problems in cosmology,” Lee said.
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