Tech UPTechnologyIs the Sun shrinking?

Is the Sun shrinking?


The universe keeps many mysteries and there are some secrets that we have managed to reveal and others that resist us. We know that the Sun, as a star, was created from a huge cloud of gas and dust, in a molecular cloud that contains enough material to give life to hundreds of millions of stars. In one of these stellar nurseries the Sun was born, which, once it accumulated enough matter in one area, the cloud began to heat up and finally created a protostar.

Young protostars gain weight by gathering matter from a dense disk of gas and dust swirling around them, thus feeding on the surrounding material and becoming hot and large enough to initiate the process of thermonuclear fusion.

Thanks to a recent study using the Atacama Large Millimeter/sub-millimeter Array (ALMA), astronomers observed the protostar IRS 63 or IRAS 16285-2355, a child star less than 500,000 years old located in the L1709 region of the molecular cloud Ophiuchus, which is located 470 light-years away from Earth in the constellation Ophiuchus. Their observations revealed several interesting structures:

The protostar is surrounded by a huge cloud of gas and dust that is larger than most stars of its age.

“Traditionally it was thought that a star undergoes most of its formation before the planets form, but our observations showed that they form simultaneously. The rings in the disk around IRS 63 are very young”, explained Dominique Segura-Cox. , astronomer at the Max Planck Institute for Extraterrestrial Physics “ We used to think that stars entered adulthood first and then were the mothers of the planets that came after , but now we see that protostars and protoplanets grow and evolve together since ancient times , like brothers”.

These observations also revealed implications for understanding the formation of our own solar system. “Even the mass of the protostar is a little less than that of our Sun. Studying such young planet-forming disks around protostars can give us important information about our own origins,” say the experts.

But what about the Sun? Does the fact that it loses mass tell us that it is ‘shrinking’?

We know that our star burns every second, as it produces nuclear energy, 4 million tons of hydrogen, so it loses mass: around 5 million tons of mass every second. And, as time passes, stars, like our Sun, accumulate more and more helium in their core; this increasing amount of melting ash causes the core to heat up and expand in volume.

However, if the rate of mass loss is continuous due to fusion and solar winds, shouldn’t it be the other way around?

The Sun has about 5 billion years left on the main sequence; then it will be twice as luminous and considerably larger than it is now . This time scale for usual mass loss is much longer than the expected lifetime of the Sun, so such mass loss will hardly affect the radius of the star.

During the main sequence stage (the one we’re in), the Sun’s radius stays pretty much the same. This is because the star is in balance between radiation pressure and gravitational pull. Every time a star starts to shrink, the reaction rate of the core increases and thus the radiation pressure increases. As a result, the star expands again until equilibrium is once again reached.

Once those 5 billion years are up, the Sun will become a red giant. In this case, the core of the star will shrink, but its outer layers will expand to the orbit of Mars, engulfing everything around it in the process . Including our planet if it is still there.


Referencia: Izidoro, A., Dasgupta, R., Raymond, S.N. et al. Planetesimal rings as the cause of the Solar System’s planetary architecture. Nat Astron 6, 357–366 (2022).

D.M. Segura-Cox et al. 2020. Four annular structures in a protostellar disk less than 500,000 years old. Nature 586, 228-231; doi: 10.1038/s41586-020-2779-6

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