three brown dwarfs with extreme spin speeds

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Sometimes called “failed stars”, brown dwarfs can spin at over 360,000 kilometers per hour, but that could be a limit that these objects could not cross… at the risk of self-destructing.

Brown dwarfs are objects that are too massive to be considered planets, but too little massive to fit into the rank of stars. They are in fact incapable of triggering thermonuclear fusion reactions. This is why brown dwarfs do not glow.

It is therefore an intermediate object class. However, if we hear less about brown dwarfs than about stars or planets, make no mistake: these worlds number in the billions in our galaxy. It is therefore important to consider them.

A team of astronomers relying on data from the Spitzer space telescope (now retired) has also announced that they have identified three new brown dwarfs having one thing in common: an extreme speed of rotation.

The fastest brown dwarfs known so far completed one rotation every 1.4 hours, while others spin in almost ten hours. These three dwarfs, which are roughly the same diameter as Jupiter, but are between forty and seventy times more massive, turn on themselves about once an hour.

Based on their size, the largest of these three new objects is estimated to turn at more than one hundred kilometers per second (360,000 kilometers per hour).

Brown dwarfs (in the middle of the image) are more massive than the planets, but not as massive as the stars. Credit: NASA / JPL-Caltech

A limit not to cross?

Like stars or planets, brown dwarfs spin faster and faster as they cool and contract. What surprises the scientists here is that these three objects have almost the same speed of rotation.

However, these brown dwarfs did not form together. They are not at the same stage of their development either. For authors, who publish their work in The astronomical journal, these almost identical speeds are not a coincidence. These three objects, they think, would have reaches their speed limit. Beyond that, they would tear apart in space, carried away by the centripetal force.

We know in fact that in other rotating cosmic objects, such as stars, natural braking mechanisms at work make it possible to prevent this destruction. It is not yet known if similar mechanisms exist in brown dwarfs, but the authors believe so.

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