Stellar Weight Loss Secrets

How do stars lose mass? For a star like the Sun, it shoots out a swath of charged particles into space and sheds mass at a rate of 4 million tons per second! Though even at this rate, the Sun only loses 1% of its total mass every 160 Billion years, so it’s not disappearing anytime soon.  For more massive stars, the process can become complex and strange.

The star VY Canis Majoris is a red hypergiant, one of the largest known stars in the Milky Way. Credit: ESO

The red hypergiant VY Canis Majoris, one of the largest known stars, is about 40 times as massive as the Sun, but humungous in scale.  If this star were to replace the Sun, it’s edge would extend to the orbit of Jupiter.  Goodbye inner solar system.

The photo above was taken with the SPHERE instrument on the ESO’s Very Large Telescope (VLT).  The adaptive optics system on this instrument is one of the most advanced in the world, and allows images to be taken of objects that are incredibly close to a distant star. In the image above, the intense radiation of VY Canis Majoris is illuminating the thick clouds of gas and dust that surround it.

Measuring the size of the dust grains in this image, they were found to be about 50 times larger than dust grains that circle a normal star.  Massive stars at the end of their lives, like VY Canis Majoris, expel huge amounts of gas and dust in the few hundred thousand years before they explode as a supernova.  This star is shedding 30 times the mass of the entire Earth every single year.

But the mystery of these giant stars has been how they push away dust before they explode.  Radiation pressure alone isn’t enough to push away normal grains of dust.  But now that much larger grains have been identified around VY Canis Majoris, the observations make sense.

“Massive stars live short lives,” says lead author of the paper, Peter Scicluna, of the Academia Sinica Institute for Astronomy and Astrophysics, Taiwan. “When they near their final days, they lose alot of mass. In the past, we could only theorise about how this happened. But now, with the new SPHERE data, we have found large grains of dust around this hypergiant. These are big enough to be pushed away by the star’s intense radiation pressure, which explains the star’s rapid mass loss.”

Dust grains of this size not only can be pushed away by massive stars, but they can survive the massive supernova explosions that the stars will inevitably undergo.  This means that the synthesized elements the star produces can survive to seed new stars in the far future.

And that’s a necessary step for future life.

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