Enigmatic former brown dwarf spotted in the solar quarter | Astronomy
WISEA J153429.75-104303.3 (WISE 1534-1043 for short) – nicknamed “The Accident” by its discoverer, citizen scientist Dan Caselden – is a cold brown, very metal-poor dwarf located about 50 light years away in the constellation Libra.
As brown dwarfs age, they cool down and their brightness in different wavelengths of light changes. It is reminiscent of how some metals, when heated, change from bright white to dark red as they cool.
WISE 1534-1043 confused astronomers because it was weak in some key wavelengths, suggesting it was very cold (and old), but bright in others, indicating a higher temperature.
“This object defied all of our expectations,” said Dr Davy Kirkpatrick, astrophysicist at IPAC / Caltech.
In their new study, Dr Kirkpatrick and colleagues postulate that WISE 1534-1043 may be between 10 and 13 billion years old – at least double the median age of other known brown dwarfs.
This means that the brown dwarf would have formed when our Milky Way galaxy was much younger and had a different chemical makeup.
Astronomers observed WISE 1534-1043 in infrared wavelengths with a ground telescope at the WM Keck Observatory.
But the object appeared so weak in those wavelengths that they couldn’t detect it at all, apparently confirming their suggestion that it was very cold.
They also determined the object’s distance – about 50 light years from Earth – and realized that it was moving fast – about 800,000 km / h (500,000 mph).
It’s much faster than any other brown dwarf known to be this distance from Earth, which means it has probably been circling the Galaxy for a long time, encountering massive objects that speed it up with their gravity.
With a slew of evidence suggesting that WISE 1534-1043 is extremely old, researchers propose that its strange properties are not at all strange and that they may be a clue to its age.
When the Milky Way was formed about 13.6 billion years ago, it was almost entirely made up of hydrogen and helium. Other elements, like carbon, have formed inside stars; when the most massive stars exploded into supernovae, they scattered the elements throughout the Galaxy.
Methane, made up of hydrogen and carbon, is common in most brown dwarfs which have a temperature similar to WISE 1534-1043. But the object’s light profile suggests that it contains very little methane.
Like all molecules, methane absorbs specific wavelengths of light, so a methane-rich brown dwarf would be weak in those wavelengths. WISE 1534-1043, on the other hand, is bright at these wavelengths, which could indicate low levels of methane.
Thus, the light profile of WISE 1534-1043 could correspond to that of a very old brown dwarf that formed when the galaxy was still low in carbon; very little carbon in formation means very little methane in its atmosphere today.
“It’s no surprise to find such an old brown dwarf, but it’s a surprise to find one in our backyardSaid Dr Federico Marocco, astrophysicist at IPAC / Caltech.
“We expected such ancient brown dwarfs to exist, but we also expected them to be incredibly rare.”
“The luck of 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.”
The to study was published in the Letters from astrophysical journals.
J. Davy Kirkpatrick et al. 2021. The Enigmatic Brown Dwarf WIEA J153429.75-104303.3 (aka ‘The Accident’). ApJL 915, L6; doi: 10.3847 / 2041-8213 / ac0437