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Another way to measure the universe’s expansioncould be offered by ‘Singing’ red giant stars

The cosmic distance ladder might have another rung soon.

In about 5 billion years, the sun will become bereft of the fuel needed for nuclear fusion in its core. This will make inner core of the sun to collapse under the force of own gravity of the sun. At this juncture, the sun’s outer layers (where nuclear fusion is still on) will swell out, and it will enter a stage of stellar life termed the red giant phase.This red giant phase will signal annihilation for inner solar system planets, Earth included. Other stars in the cosmos will experience the very same fate as our sun, meaning any exoplanets revolving around those other stars will also face similar destruction.

But, astronomers might have now hit upon a technique that can be employed to use the destructive red giant phase of stars constructively.A team of researchers led by Richard I. Anderson (EPFL scientist) has proposed that the acoustic oscillations, or “singing,” of red giants at different ages can be utilized to more accurately measure cosmic distances. Just as music is believed to soothe the ferocious beast, this celestial melody could provide assistance in solving a savage cosmological problem called “Hubble tension.”

“We found that the acoustic oscillations of red giant stars tell us how to best measure cosmic distances using the Tip of the Red Giant Branch method,” Anderson stated.Anderson is ostensibly referring to the spot, or “branch,” that red giants occupy on a chart outlining stellar lives named the Hertzsprung-Russell diagram (HR diagram). The “Tip of the Red Giant Branch (TRGB)” is a crucial point where the cores of red giant stars have collapsed, becoming enough dense to ignite helium and reverse their brightening.

A brand new rung on the cosmic distance ladder

Astronomers have a range of ways to measure huge cosmological distances; such techniques are suitable for mapping progressively larger distances. These measurement methods combine together to form the metaphorical rungs of the “cosmic distance ladder,” more formally called as the “extragalactic distance scale.”

First rung, if you will, is built using stellar parallax — the change in apparent loci of distant stars as Earth changes position around the sun. This method can measure distances extending just beyond the solar system.

The highest rung on the ladder is studied by examining the redshifts of distant galaxies. This method can be used to measure distances billions of light-years across. Redshift occurs because, as substances race away from us due to the expansion of the cosmos, the light they discharge that takes billions of years to reach us has its wavelength stretched by this expansion.

The different measurement methods of the cosmic distance ladder disagree with each other on the value of the Hubble constant though. This problem is termed the “Hubble tension,” and experts think adding extra rungs to the cosmic distance ladder could help resolve it.

The TRGB can be employed as a distance measurement because of the mostly uniform light yield seen at this point in red giant evolution. This basically means red giants at different distances can have their brightnesses matched, thus offering a measurement of the distances between them. This makes red giants at the TRGB point of the HR diagram something that scientists call a “standard candle”.


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