by You must be feeling like a brown dwarf. Not only has their failure to ignite like normal stars earned them an unfortunate nickname – failed stars – but new results from the Hubble Space Telescope have shown that they can’t even have a relationship with each other.
Brown dwarfs are celestial objects that form when massive clouds of gas and dust, known as molecular clouds, develop dense patches that fall off. Unlike your regular old star, however, a brown dwarf cannot collect enough material from the remnants of that cloud to accumulate enough mass to start fusing hydrogen with helium in its core. A brown dwarf combines several features, but the fusion of hydrogen to helium in particular is what defines a “main sequence” star – hence the moniker “failed star”.
Like many stars, brown dwarfs are often believed to be born in binary pairs. However, there is a large gap in the literature on this topic. Although about 75% of massive stars in the universe are known to have a companion star, and about 50% of solar-sized stars appear in such binary formations, the number of detected brown dwarf binaries is almost zero . Why would that be?
Well, Hubble’s observations may hold an answer. The older the brown dwarf, the less likely it is to have a mate. This suggests that the gravitationally bound pairs of brown dwarf binaries may be so weak that the two bodies drift apart over a few hundred million years. What would make them drift apart? Perhaps the gravitational pull of any other passing star is much stronger.
Related: The orbital body of a record-breaking ‘failed’ star is 2,000 degrees hotter than the sun
“Our survey confirms that widely separated companions are extremely rare among the lowest and coolest isolated brown matter, although binary brown dwarfs are seen at younger ages,” Clémence Fontanive, lead research author and scientist at the Institute Trottier’s research on. Exoplanets, said in a statement. “This suggests that such systems do not survive over time. When they are young, they are part of a molecular cloud, and then, as they age, the cloud disperses. As it happens that, things start to move around, and the stars go on. at each other.”
“Because brown dwarfs are so light,” Fontanive added, “the gravitational hold that binds pairs of wide binaries is very weak, and these binaries can easily be torn apart by the stars that avoid them.”
In a way (apologies in advance) but this makes brown dwarfs a bit like the cosmic equivalent of the distracted boy meme. You know the one.
Growing apart with age
Hubble allows astronomers to detect binaries with components that sit as close as 298 million miles (480 million kilometers) apart. This is equivalent to about three times the distance between the Earth and the sun, which is quite small in cosmic terms.
First the team selected a sample of brown dwarfs previously seen by NASA’s Wide-Field Infrared Survey Explorer (WISE). The researchers then narrowed this sample down until they found some of the coolest and lowest stars that failed in the relative vicinity of the solar system. Because brown dwarfs cannot sustain nuclear fusion in their hearts, they exhibit cool temperatures equivalent to a few hundred degrees hotter than Jupiter, which has a temperature of about minus 166 degrees Fahrenheit (minus 110 degrees Celsius). Such cool temperatures ensure that they can last for a long time.
To search for the coolest brown companions, the team was counting on these frigid failed stars to have condensed water in their atmospheres. Fontanive and colleagues used two different near-infrared filters to study this water material. One filter showed the cool brown dwarfs brightly, while the other covered specific wavelengths that made the failed stars appear very faint as a result of water absorption in their atmospheres.
Fontanive and colleagues conducted a similar study with Hubble several years ago, focusing on very young brown dwarfs. Some of these failed infant stars had binary companions, confirming that they were brown dwarfs. could exist in binaries, and that the mechanisms that birth stars can create low-mass binaries – even if these cases are vanishingly rare.
The scientists theorized that the lack of observed binary dwarfs indicated that they had difficulty staying gravitationally bound for long periods of time. This new Hubble discovery lends further support to this concept.
“Most stars have friends – whether that’s a binary companion or an exoplanet,” Beth Biller, a team member and scientist at the University of Edinburgh, said in the statement. “This survey actually shows that the same is not true for brown dwarfs. After a short period early in their lives, most brown dwarfs remain single for the rest of their very long lives.”
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Fontanive added that the motivation for this study was to determine how low the mass of a stellar object must be to maintain the trends seen in multi-star systems.
“Our Hubble survey provides direct evidence that these binaries we observe when they are young are unlikely to survive into old age, they are likely to be disrupted,” he said. “This is the best observational evidence to date that brown dwarf pairs disappear from each other over time. We could not have conducted this kind of survey and confirmed earlier models without Hubble’s sharp vision and sensitivity.”
The team’s research is published in the journal Monthly Notices of the Royal Astronomical Society.
