Astronomers have taken another detailed look at a mysterious galaxy object known as “The Accident”. According to the analyzes, it would be an incredibly old brown dwarf, formed while the Universe was still poor in methane.
An unusual brown dwarf
It’s not quite a star, but it’s not quite a planet either. In reality, “The Accident” incorporates a class of objects stuck in between: that of the brown dwarfs. These “failed stars,” as they are called, can be up to eighty times the size of Jupiter. On the other hand, they are not sufficiently massive to maintain nuclear fusion in their nuclei. This is the reason why they do not shine like the real stars. Instead, brown dwarfs slowly cool and darken over millions or billions of years.
There are currently around 2,000 of these faintly luminous objects in the galaxy. Most were spotted by NASA’s Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE).
Spotted in the first place by an amateur astronomer, “The Accident” nevertheless quickly stood out from the others, hence its name. At the time of its discovery, the object indeed appeared faint in certain infrared wavelengths, suggesting that it was a very cold and ancient brown dwarf. On the flip side, it also appeared glowing in other wavelengths, indicating that it was a hot brunette young dwarf. This contradiction therefore naturally pushed astronomers to continue the analyzes.
To do this, the scientists relied on the Hubble and Spitzer space telescopes, as well as on the infrared telescope of the WM Keck observatory (Hawaii). These new data finally helped to tip the scales.
Artist illustration of a brown dwarf. Credit: NASA / JPL-Caltech
A very old object
Located about fifty light years from Earth, the brown dwarf spins at over 800,000 km / h across the galaxy. It’s much faster than a typical brown dwarf. For the authors, who publish their work in The Astrophysical Journal Letters, this measurement suggests that the speed of the object has been accelerated by many larger objects for billions of years. “The Accident” would therefore indeed be very old, and not very young.
The elements of its atmosphere also lean towards this hypothesis. Analysis of the wavelengths of infrared light indeed shows that the object is very poor in methane which, normally, is a common gas in brown dwarfs with similar temperatures. Since methane is made up of hydrogen and carbon, a virtual absence of this gas means that the object initially formed between ten to thirteen billion years ago. At the time, our galaxy was indeed bathed in hydrogen and helium, but still contained very little carbon.
All these analyzes therefore suggest that “The Accident” is an exceptionally old brown dwarf (more than twice as old as all known brown dwarfs).
“It’s no surprise to find such an old brown dwarf, but it’s a surprise to find one in our backyard,” said Federico Marocco, astrophysicist at Caltech. “Finding one so close to the Solar System could be a happy coincidence or it tells us that they are more common than we thought.”