Could you approach a brown dwarf

Brown dwarfs rotate at top speed

In our Milky Way alone, 100 billion brown dwarfs are said to exist: "failed" stars whose mass is insufficient for the nuclear fusion of hydrogen to ignite inside them. They therefore only glow weakly and are also more difficult to observe than real stars. Megan Tannock from the University of Western Ontario and her colleagues managed to observe three special specimens of these brown dwarfs. As they write in the "Astronomical Journal" and in advance on the arXiv, those specimens rotate at their equator at a speed of around 100 kilometers per second - the highest value recorded so far for brown dwarfs and close to the maximum that is considered possible for such protostars .

The three brown dwarfs only need between 1.08 and 1.23 hours for a complete revolution. This is about a third faster than previous measurements have shown. Tannock and Co discovered the trio when they were evaluating data from the Spitzer space telescope. They then compared these with the values ​​of two other telescopes. A comparison with the earth shows how extreme the speed of rotation is: At the equator, it rotates at a speed of almost 1,650 kilometers per hour, whereas the brown dwarfs rotate at 360,000 kilometers per hour.

This article is featured in Spectrum - The Week, 15/2021

The next fastest brown dwarf needs 1.4 hours for one revolution. And despite an intensive search, the group did not find any other specimens with a similar pace. Tannock therefore suspects that her team may have discovered the maximum possible rotation speed. Because with the rotation speed the centrifugal forces, which counteract the force of gravity, also increase. At some point it could tear the objects apart.

Another reason for a kind of speed limit is that the three observed brown dwarfs are of different hot, old and massive amounts. Yet they rotate at the same speed. So you may actually move on the edge of what is physically possible.

However, this contradicts model calculations according to which such large and heavy brown dwarfs could be 50 to 80 percent faster, the researchers write. Further studies have to show what slows the objects down or whether there are actually faster specimens in space. The high pressure inside the brown dwarfs may cause a braking effect: It ensures that hydrogen becomes a conductive metal, which in turn generates electromagnetic fields, which can then reduce the speed. But so far this is only a speculation.