Cosmic divorces: Failed stars “grow old” alone

Using data collected by the Hubble telescope, astronomers have identified a pattern associated with brown dwarfs. Pairs of such objects break up quite quickly, after which they spend the rest of their lives alone. 

What is a brown dwarf

Brown dwarfs are objects that occupy an intermediate position between giant planets and stars. Their masses range from 13 to 80 Jupiter masses. This is not enough for permanent thermonuclear fusion reactions based on hydrogen atoms to “start” in their depths.

Brown dwarf in the artist’s impression. Source: newscientist

At the same time, unlike giant planets, some reactions involving deuterium and lithium nuclei can still occur inside brown dwarfs. But, by astronomical standards, they last very short, after which the brown dwarfs gradually cool down. Because of this, they are sometimes also called “failed stars”.

Loneliness of brown dwarfs

An international team of researchers has drawn attention to a curious pattern associated with brown dwarfs. It lies in the fact that the older a brown dwarf is, the lower the probability that it has a dwarf companion. 

A lonely brown dwarf in the artist’s impression. Source: NASA, ESA, J. Olmsted (STScI)

Scientists came to this conclusion during the analysis of data collected by the Hubble telescope. It is able to find pairs of brown dwarfs separated by a distance of 480 million km. This is comparable to the distance between our Sun and the asteroid belt. But the astronomers who conducted the study did not find any such pair in the sample of brown dwarfs in the vicinity of the Sun. At the same time, Hubble had previously found pairs of newborn dwarfs that were just forming in molecular clouds.

According to the researchers, the revealed pattern is explained by the fact that pairs of brown dwarfs are very weakly bound by gravity. Therefore, under the influence of gravity by passing stars, their bonds break quite quickly — on average, it takes only a few hundred million years. After that, they are doomed to live alone.

Earlier, we talked about how astronomers managed to find clouds in the atmosphere of a nearby brown dwarf.

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