At the heart of every white dwarf star, a dense stellar object that remains after a star burns its gas supply as it nears the end of its life cycle, is a quantum mystery: when white dwarfs add mass, they shrink in size until they become so small and tightly packed that they can’t stand falling into a neutron star.
This amazing relationship between the mass and size of a white dwarf, called the mass-radius ratio, was first theorized by Nobel Prize-winning physicist Subrahmanyan Chandrasekhar in the 1930s. Now a team of astrophysicists, Jones Hopkins, has developed a method for observing the phenomenon itself, using astronomical data collected from the Sloan Digital Sky Survey and a recent set of data released by the Gay Space Observatory. The combined datasets yielded more than 3,000 white dwarfs for the study team.
A report of their findings led by senior Vedant Chandra Hopkins is now in the press Astrophysical Journal and is available online at arXiv.
“The ratio of mass to radius is an impressive combination of quantum mechanics and gravity, but for us it’s counter-intuitive – we believe that as a subject gains mass, it should increase,” said Nadiya Zakamska, an associate professor of physics and astronomy who led the research students. . “The theory has been around for a long time, but it’s remarkable that the data set we use has unprecedented size and unprecedented accuracy. These measurement methods, which in some cases were developed years ago, suddenly work much better, and these old theories can finally be explored.”
The team obtained its results through a combination of measurements, including primarily the effect of gravitational redshift, which is to change the wavelengths of light from blue to red as light moves away from the object. This is a direct result of Einstein’s theory of general relativity.
“For me, the beauty of this work is that we all study these theories about how light affects gravity in school and textbooks, but now we actually see such a relationship in the stars themselves,” says Fifth-year graduate student Hsiang. -Chih Hwang, who proposed a study and first recognized the effect of gravitational redshift in the data.
The team also had to consider how the star’s motion through space could affect the perception of its gravitational redshift. Just as the siren of a fire engine changes pitch according to its motion relative to the person listening, the frequencies of light also change depending on the motion of the light emitting object relative to the observer. This is called the Doppler effect and is essentially a distraction “noise” that makes it difficult to measure the gravitational effect of redshift, says research fellow Xiao Cheng, a fourth-year graduate student.
To account for variations caused by the Doppler effect, the team classified white dwarfs in a sample set by the radius. They then averaged the redshifts of stars of similar size, effectively determining that no matter where the star itself is located or where it moves relative to the Earth, it can be expected to have its own gravitational redshift of a certain value. Think of it as taking the average measurement of all the resins of all fire engines moving in a certain area at a given time – you can hope that any fire engine, no matter in which direction it moves, will have its own step of this average. value value.
These properties of the gravitational redshift can be used to study the stars observed in future datasets. The researchers say that future and more accurate datasets will further refine their measurements, and that these data could help further analyze the chemical composition of the white dwarf.
They also say that their research represents exciting progress from theory to observable phenomena.
“As a star gets smaller as it becomes more massive, the effect of gravitational redshift also increases with mass,” says Zakamska. “And it’s a little easier to understand – it’s easier to get out of a less dense, larger object than to get out of a more massive, compact object. And that’s what we saw in the data.”
The team even finds captive audiences for their research at home – where they conducted their work amid a coronavirus pandemic.
“The way I gave it to my grandfather, you basically see Einstein’s quantum mechanics and general relativity combined to get that result,” says Chandra. “He was very excited when I said that.”
Astrophysicists confirm the basis of Einstein’s theory of relativity
Gravitational measurement of white dwarf shift switching with mass radius of communication, arXiv: 2007.14517 [astro-ph.SR] arxiv.org/abs/2007.14517
Provided by Johns Hopkins University
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