Astronomers discover ‘brown dwarf’ that’s hotter than our sun

A little-known oddity in the universe are “brown dwarfs” – astronomical objects that aren’t really stars or planets.

Brown dwarfs are called “failed stars” because they are heavier than planets, but unlike stars, they don’t have enough mass to support nuclear fusion in their cores.

Now researchers have found the hottest known brown dwarf yet, even hotter than our own sun and 1,400 light-years away.

Named WD0032-317B, the object reaches an impressive 8,000 Kelvin (7,727°C or 13,940°F) because it orbits so close to its star.

For comparison, the surface temperature of our sun is about 5,778 Kelvin (5,498°C or 9,930°F).

Brown dwarf WD0032-317B is also up to 88 times the mass of Jupiter – making it one of the most massive brown dwarfs known, as well as the hottest.

It revolves around the eponymous star WD0032-317, a white dwarf – the hot, dense remnants of a star that has burned off all of its fuel.

A new study on the finding, led by Naama Hallakoun at the Weizmann Institute of Science in Israel, is now available on the arXiv pre print server.

“We report observations revealing an extremely irradiated bright companion of the hot white dwarf WD 0032-317,” they say.

“With a mass of about 75 to 88 Jupiter masses, this near hydrogen burn limit object is potentially one of the most massive brown dwarfs known.”

Even some astronomers struggle to put their finger on mysterious brown dwarfs, described by NASA as the link between tiny stars and giant planets.

Brown dwarfs form just like stars, from the contraction of gas that collapses into a dense core under the force of its own gravity.

This is different from planets – which form from the accumulation of leftover debris from these stellar births.

However, unlike stars, brown dwarfs don’t have enough mass for their cores to burn nuclear fuel and emit starlight (hence the nickname “failed stars”).

Brown dwarfs have masses between the most massive gas giant planets and the least massive stars — about 13 to 80 times that of Jupiter

Brown dwarfs are too big to be planets, but they are described as “planet-like” because they have complex planet-like outer atmospheres, including clouds and molecules such as H2O.

Brown dwarfs orbit one star or travel in isolation, believed to have been ejected from their galaxy early in their formation.

This particular brown dwarf – WD0032-317B – takes only 2.3 hours to complete one orbit around its star because it is so close to it, which is why it is so hot – 8,000 Kelvin.

The star, WD0032-317, is even hotter; although it has only 40 percent of the mass of our sun, it has a temperature of about 37,000 Kelvin.

The star was first observed in the early 2000s by a team studying data from the European Southern Observatory’s Very Large Telescope.

At the time, the researchers had noticed something tugging at the star, suggesting it had a companion star, as seen in some solar systems.

However, Hallakoun and colleagues have now discovered that it is a brown dwarf, not a companion star, by obtaining more information about its mass and orbital period and irradiance from telescopic data.

It is also tidally, meaning that the same side always faces the star (‘the day side’), while it is colder ‘night side’ is forever turned to space (“night side”).

Its mass is about 75 to 88 Jupiters and it orbits its star rapidly, with a period of just 2.3 hours (image from the team’s newspaper)

On one side of the brown dwarf are hot temperatures of about 7,250 to 9,800 Kelvin and on the other side are cooler temperatures of about 1,300 to 3,000 Kelvin.

Temperatures on the hot side are about 5,100 Kelvin hotter than any other known giant planet.

That makes WD0032-317B the hottest known brown dwarf and hotter than any known planet.

Planets orbiting near hot stars experience intense extreme ultraviolet radiation, potentially leading to atmospheric evaporation and loss of molecules, known as “thermal dissociation.”

Only one known ultra-hot giant planet, KELT-9b, receives enough ultraviolet radiation for molecular dissociation, with a daytime temperature of about 4,600 Kelvin — nowhere near the daytime temperature of this brown dwarf.

Overall, the researchers suggest that WD0032-317B and its star could provide information about how hot stars cause companion objects to vaporize.

BROWN DWARF: AT LEAST 13 TIMES BIGGER THAN JUPITER BUT NOT BIG ENOUGH TO START FUSION

Brown dwarfs are thought to be the missing link between planets and stars, with masses between 13 and 80 times that of Jupiter.

But their centers are not hot or dense enough to generate energy through nuclear fusion, from hydrogen to helium, as main-sequence stars do.

Brown dwarf stars are larger than Jupiter but smaller than low-mass stars capable of fusing hydrogen into helium and sustaining the fusion over time

While they can’t handle traditional fusion, unlike a giant plant, they can fuse a heavy isotope of hydrogen called deuterium into helium.

It is thought that a galaxy the size of the Milky Way could have as many as 100 billion brown dwarf stars, many of which roam interstellar space.

Self-luminous objects, such as stars, are given a letter category based on their surface temperature – with 0 the brightest and hottest, going through B, A, F, G, K and on to, M the coolest of the main sequence stars.

Astronomers also added L, T, and Y for Red Dwarf and Brown Dwarf stars, as well as a range of other classifications for unusual star types.

Over the course of their lifetime, a brown dwarf star will go through M, L, T, and Y because they don’t go through a stable merger, so they cool down over time.

To the naked eye, they appear in different colors depending on the stage they are at in their evolution.

The warmest may appear orange or red and the coolest magenta, and may have layers like Jupiter or a uniform appearance.