A 1,400-light-year object that orbits a star is challenging our ideas of what the Universe can be.
It’s a brown dwarf, the curious category of objects that straddle the gap between planets and stars, but it’s on such a close orbit with its very hot host star that its temperature exceeds a blistering 8,000 Kelvin (7,727 degrees Celsius, or 13,940 Fahrenheit) – hot enough to snap apart the molecules in its atmosphere into their composite atoms.
It’s much hotter that the surface temperature on the Sun at 5,778 Kelvin. In fact, this brown dwarf is a temperature record-breaker – the hottest object of its kind we’ve ever found.
Even though brown dwarfs tend to be hotter than planets, they burn cooler than the coolest red dwarf stars – they absolutely can’t reach Sun-like temperatures on their own internal fusion engines.
The object WD0032-317B was named by an international team of astrophysicists led by Na’ama Halakoun of Israel’s Weizmann Institute of Science.
The team believes that the discovery can help us to understand what happens when gas giants like Jupiter orbit extremely hot and massive stars.
Massive amounts of ultraviolet radiation are directed at planets in close proximity to their stars. The heat can cause the planets’ atmospheres to evaporate.
But we don’t really know much about this extreme environment. It can be very difficult to separate the signals of an orbiting planet from those from a star.
One exoplanet is hot enough to cause thermal dissociation. This is KELT-9b orbiting a supergiant blue star that heats up the dayside of the exoplanet to temperatures above 4,600 Kelvin (4,327 degrees Celsius, or 7,820 degrees Fahrenheit).
That’s Hotter than many stars – red dwarfs, the most common stars in the galaxy, have a maximum surface temperature of Approximately 4,000 Kelvin.
However, brown dwarfs in binary star systems with white dwarfs may be a way to study extreme regimes. White dwarfs, on the other hand, are smaller and dimmer than blue supergiants such as KELT-9. This makes it easier to detect any superheated objects.
The following are some of the ways to get in touch with each other Brown dwarfThis is neither a planet nor a stellar object. It is about 13 times as massive as JupiterA planet-like object may have enough heat and pressure in its core for it to ignite deuterium fusion.
It’s an ‘heavy isotope’ of hydrogen. The temperature and the pressure needed for its fusion is much lower than what’s needed for the fusion process of the regular hydrogen found in stars’ cores.
Brown dwarfs are about the size of 80 Jupiter masses and can reach temperatures around Kelvin 2,500. They are cooler and dimmer, but they glow in infrared waves.
White dwarfs are the last stage of stars such as the Sun. The star, when it runs out of hydrogen, ejects the outer layers. The core, which is no longer supported by fusion’s outward pressure, collapses into a dense object about the size of Earth.
White dwarfs shine with residual heat, but the death process is very energetic – they’re extremely hot, with temperatures comparable to those of blue supergiants.
This leads us to WD0032-317 – a white dwarf with a low mass but incredibly hot temperatures. Around 40 percent of its mass is the Sun. It burns at temperatures of around 37,000 Kelvin.
Early in the 2000s, data collected using the Ultraviolet-Visual Echelle Spectrograph instrument (UVES) on the Very Large Telescope for the European Southern ObservatoryIt was suggested that WD0032-317 moved around and was being towed around by an orbiting, unseen companion. Near-infrared observations made late in the evening suggested that this companion was a Brown Dwarf.
Hallakou, her colleagues and UVES were able to make new observations on the star. They found the companion was a brown dwarf whose mass ranged between 75 and 85 kilograms. JupitersOn a breakneck rotation of only 2.3 hours.
Smoking star was the smoking gun that led to detection. Astronomers can detect hydrogen emissions from the brown dwarf, when the day side of the star is towards us.
Due to their close proximity, the brown dwarves and star are tidally entangled. That means one side – the day side – is perpetually facing the star, while the other remains in permanent night. The extreme temperatures were calculated by the team, and they are staggering.
“Depending on the white-dwarf core model used, the companion’s heated day-side temperature ranges between ≈7,250 and 9,800 Kelvin – as hot as an A-type star – with a night-side temperature of ≈1,300 − 3,000 Kelvin, or a temperature difference of ≈6,000 K – about four times as large as that of KELT-9b,” Write on your paper.
The night-side range of temperature covers T to M dwarfs. The ‘equilibrium’ black-body temperature of the irradiated companion (neglecting its intrinsic luminosity and albedo, and assuming it is in thermal equilibrium with the external irradiation) is about 5,100 Kelvin, hotter than any known giant planet, and ≈1,000 Kelvin hotter than KELT-9b, resulting in ≈ 5,600 times higher extreme-ultraviolet flux.”
No planet or brown dwarf has ever been hotter. This makes WD0032-317B a perfect candidate for studying the way extremely hot stars can vaporize their lower-mass partners. Researchers say that studying objects such as WD0032-317B can help us better understand outlier objects, like KELT-9b.
The research was published in Nature Astronomy.
A previous version of this article appeared in June 2023.
