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Red Giants Offer an Innovative Method for Calculating Cosmic Distances
Red Giants Offer a New Way to Measure Distance in the Universe
For nearly three decades now, it’s been clear that the expansion of the Universe is speeding up. Some unknown quantity, dramatically dubbed ‘dark energy’, is pushing the Universe apart. But the rate at which the Universe’s expansion is increasing – called the Hubble Constant – hasn’t yet been nailed down to a single number.
Not for lack of trying.
In fact, there are multiple ways of measuring it. The problem is that these methods don’t agree with each other. They each give different numbers, which is a confounding – and exciting – puzzle. It means there may be new physics to uncover, if we look carefully.
This mystery is known as the Hubble tension, and it’s only becoming more intractable as measurement techniques become more precise. So astronomers are on the hunt for new and better ways to measure the expansion of the Universe.
In a new paper this week, three Swiss scientists describe a method for significantly improving one measurement technique.
The method uses a specific subset of red giant stars: old stars that have burned away most of the hydrogen in their cores. As they age, red giants get larger, less dense, and dimmer. But at a certain point in their evolution, they switch from burning hydrogen to burning helium, a change that causes a dramatic uptick in brightness. Stars in this phase of their life are considered to have reached the ‘Tip-of-the-Red-Giant-Branch’, or TRGB.
When stars in the TRGB ignite helium, they achieve a known, reliably measured level of brightness: they become ‘standard candles’, making distance measurements between them more accurate.
But that brightness isn’t perfectly constant: there are oscillations – sound waves rippling through the layers of the star. Scientists knew about these acoustic oscillations from previous studies of stellar evolution, but they hadn’t yet been accounted for in attempts at resolving the Hubble tension.
That’s what this new paper sets out to do.
“Younger red giant stars near the TRGB are a little less bright than their older cousins,” says lead author Richard Anderson. “The acoustic oscillations that we observe as brightness fluctuations allow us to understand which type of star we’re dealing with: the older stars oscillate at lower frequency – just like a baritone sings with a deeper voice than a tenor!”
“Now that we can distinguish the ages of the red giants that make up the TRGB, we will be able to further improve the Hubble constant measurement based thereon,” says Anderson.
That’s good news, securing new confidence in our understanding of how the Universe expands. However, by itself, it isn’t likely to resolve the Hubble tension. The widest gap amongst different Hubble constant measurements is between recent Universe observations: type 1A supernovae, cepheid variables, kilonovae, and red giants; and early Universe observations: especially the cosmic microwave background.
That tension remains. Still, the more confident we can be about the accuracy of our measurements, the more sure we can be that there is something new about how the Universe works waiting to be discovered. Accounting for the TRGB oscillations is a concrete step in that direction.
Learn more:
“The baritone of Red Giants refines cosmic distance measurements.” EPFL.
Richard Anderson, Nolan Koblischke, and Laurent Eyer, “Small-amplitude Red Giants Elucidate the Nature of the Tip of the Red Giant Branch as a Standard Candle.” ApJL, March 7, 2024.
News
Kevin McCarthy, former House Speaker, seeks revenge
Ousted House Speaker Kevin McCarthy is out for vengeance. After being voted out as House speaker, McCarthy left office at the end of 2023. Now, he is traveling the country giving speeches, appearing on TV, and plotting revenge against those who orchestrated his downfall.
Eight Republican lawmakers joined with Democrats in toppling McCarthy, marking the first time a House leader has been voted out. Two of the Republicans who voted against him are retiring, while three others are facing strong primary challenges. McCarthy is working behind the scenes to ensure their defeat, using his political connections and resources to support their opponents.
McCarthy’s main nemesis in this battle for vengeance is Rep. Matt Gaetz, who was instrumental in McCarthy’s ouster. During a recent appearance at Georgetown University, McCarthy accused Gaetz of pushing him out of the speakership due to an ethics complaint involving a 17-year-old girl. Gaetz denied the allegations and called McCarthy a liar.
Despite the turmoil of his speakership lasting less than nine months, McCarthy feels liberated and focused on campaigns and elections, which have always been his forte. He remains close to lawmakers he recruited and maintains a vast donor network built over years as a top GOP strategist.
McCarthy’s top priority is to secure Republican control of the House in the upcoming elections. He is also focused on reelecting key members, such as Young Kim, Michelle Steel, and Lori Chavez-DeRemer, who have diversified the House GOP.
At a recent seminar on American democracy, McCarthy displayed both charm and self-deprecation. He broke with former President Trump by supporting aid for Ukraine and acknowledging Joe Biden’s victory in the 2020 election. However, McCarthy also dodged questions and made false equivalences, drawing criticism from his detractors.
Despite speculation about a second Trump administration, McCarthy has not shown interest in becoming an influence peddler. Instead, he prefers working in the campaign realm, where his skills and talents are best utilized. McCarthy’s focus is on electing viable Republican candidates and achieving payback against those who pushed him out of power.
In conclusion, Kevin McCarthy is on a mission for vengeance, using his political savvy and resources to take down his opponents and secure Republican victories. His determination and focus on campaigns and elections show that McCarthy is not one to back down easily, making him a force to be reckoned with in the world of politics.
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