Do astronomers know which star in the universe is the oldest and which star is the youngest? How do they know? Picture: The oldest known star, officially named HD 140283, but nicknamed Methusara, 190.1 light-years away from us. The British Schmidt Telescope photographed stars in

Does astronomers know which star in the universe is the oldest and which star is the youngest? How do they know?

Figure: The oldest known star, officially named HD 140283, but nicknamed Methusara, 190.1 light years away from us. The British Schmidt Telescope photographed stars in blue light for digital sky patrols. (Photo source: Digital Sky Survey (DSS), STScI/AURA, Palomar/Caltech and UKSTU/AAO)

Among the countless stars that flash in the vast space, some are old and have experienced the dawn of the universe, and some are still young, and even the most powerful telescopes on Earth cannot observe them. But is it possible to know which star is the youngest and which star is the oldest?

The youngest star in our universe is difficult to determine because stars are constantly born, but there are some candidates among the stars we know. By contrast, scientists have known for decades that the oldest star on record—properly nicknamed Methusara.

Stars were born in the depths of a huge cloud of dust and gases known as nebula. Some of the gas clusters in the nebula are pressed by so much matter that their own gravity forces them to collapse (because a larger mass means greater gravity), and the strong gravity at the center of the collapsed cloud creates gas—mainly hydrogen—to blend into what becomes the protostar. These stellar embryos begin to fuse hydrogen nuclei into helium, and emit radiation in the process. A star cannot be called a star before it radiates energy, which is why it becomes so bright. Some faint stars just shine in life.

Figure: New stars have been forming, but in 2022, astronomer Dong Ruobing and his colleagues captured an image of a young star embryo in the binary star system Canis Big Z. The perturbation from the cosmic invaders was captured by the Subaru Telescope, the Karl G. Jansky super-large array and the Atacama large millimeter/sub-millimeter array. (Picture source: ALMA (ESO/NAOJ/NRAO), S. Dagnello (NRAO/AUI/NSF), NAOJ)

Astronomer Dong Ruobing (open in new tag) Assistant professor in the Department of Physics and Astronomy of Victoria University, Canada has observed these new stars. He led a 2022 study in the journal Nature Astronomy, on a binary protostar system believed to be only about one million years old. Dong and his colleagues were able to provide a rough age for some of these stellar embryos. They often lose their temper, which is called accretion explosion.

When stars experience an accretion burst, they become hotter and brighter. The substance around them is heated. Ice in the protoplanetary disk may evaporate, and some chemical reactions in the disk may be triggered by the heat of the substance.

Because young stars are still accumulating matter, they will eject huge jets of gas or outflows from both ends. This means they are still adding mass. Because the outflow fades with age, the amount of gas released helps astronomers estimate the age of the stars. More gas means younger stars.

At the same time, the age estimate of the star HD 140283 named Massarah has sparked controversy. According to NASA , based on observations in 2000, its age was estimated to be 16 billion years early. This will make it older than the universe, which is about 13.8 billion years old. Astronomers immediately said that the star's age was calculated incorrectly. If not, this increases the possibility that the universe will appear billions of years earlier than previously thought.

To trace the roots, astronomers used the Hubble Space Telescope to redetermine Methusara's age in 2013 and based on its brightness and distance to the Earth (about 190 light-years). This would make it only earlier than the universe, despite errors in age estimates.

With the help of the theoretical study of stellar evolution, we measured the distance to determine the absolute luminosity, thus determining the age. Within the uncertainty range of measurement and theoretical , we found an age compatible with the age of the universe.

Methusala is an sub-superstar , which is brighter than most stars, but still not as bright as giants, which are so large that their size seems abnormal to their temperature and mass. The sub-giant is also more redder than the giant. Stars release energy by burning hydrogen at their core and converting it into helium through nuclear fusion 7. When massive stars start to deplete their hydrogen reserves, they enter the sub-major star stage. At this stage of life in a stellar, its brightness or luminosity becomes an excellent way to estimate its age. The darker sub-superstars are older.

Methusala is slightly reddish and has been slowly getting dark for billions of years, although its relative proximity to the earth means it won't appear too dark for us and can be seen with the right binoculars . By contrast, the sun has hardly lived. Our star is less than 5 billion years old and is expected to live another 5 billion years, by then it will cool and expand into the solar system, so that it will swallow orbiting planets including the Earth.