Unexpected behavior of stellar winds

Unexpected behavior of stellar winds

The XMM-Newton Space Telescope detected unexpected changes in powerful gas streams from two massive stars. It turns out that the colliding stellar winds do not behave as expected.

Massive stars (several orders of magnitude larger than the Sun) are distinguished by active life. They are rapidly burning nuclear fuel and releasing a huge amount of material into their surrounding space.

As a result, fierce stellar winds are formed, carrying masses equivalent to that of the Earth. They move at a speed of millions of km / h, so when they collide, a huge amount of energy is released. Such events heat up the gas to a million degrees, causing it to glow brightly in X-rays.

Unexpected behavior of stellar winds

Evolution of the stellar wind

The headwinds usually change little, because there are no transformations in their stars and orbits. But some massive stars stand out for drama. It happened with HD 5980 - two giant stars, 60 times the solar mass. The distance between them is 100 million km (closer to the Earth-Sun distance).

In 1994, they noticed a large flash, resembling an eruption, which made Eta Carina the second brightest star for 18 years in the XIX century. In 2007, scientists from the University of Liege (Belgium) recorded a collision of winds from these stars using surveys at XMM-Newton and the Chandra X-ray Observatory. In 2016, they took another look at what was happening in XMM-Newton.

It was expected that the HD 5980 will fade gently, but it happened the other way around. It turned out that the star couple increased the brightness by 2.5 times, and the X-rays became even more energetic. Previously, this was not observed during a wind collision.

Unexpected behavior of stellar winds

Location HD 5980

Recently offered a theory that can explain the situation. When the stellar winds collide, a huge amount of X-rays is released. But if a hot substance emits too much light, then it is rapidly cooled and the X-rays "fade out".

This is exactly what they thought happened at the first observation 10 years ago. Most likely, by 2016 the impact weakened, reducing the instability, which made it possible to release more X-rays. Now this idea is tested in computer models.

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