The universe is vast, and seemingly limitless. Naturally, there’s bound to be a handful of cosmic oddities out there, waiting for astronomers to chance at glancing over them at their next data report. Astronomers have certainly noticed some of them before, like the “Unicorn” black hole that made news a few months back. Now, we’ve found another oddity: scientists call it “the Accident,” and it seemingly brought with itself more questions than answers. The findings for the cosmic oddity was published in the journal The Astrophysical Journal Letters.
A Refresher
Stars form from the gravitational compression of nebulae, massive gas clouds in the cosmos containing elements like hydrogen and helium. Once enough hydrogen and helium gas are compressed together from their own mutual gravitational attraction, the hydrogen in the gravitational center gets heated and compressed even further; in fact, they get so compressed that their atomic nuclei start to fuse together, initiating nuclear fusion of hydrogen into helium and starting a stellar engine that will keep going for billions of years. From that point onwards, the compressing gas cloud has turned into a star.
Of course, not every compressing gas cloud in the cosmos will churn out a star. There needs to be enough material in the nebula for gravitational attraction to be significant enough to initiate nuclear fusion; should the total gaseous mass be inefficient, stellar fusion cannot initiate. However, the gases remain gravitationally bound to each other, forming a giant spherical mass of gas called a brown dwarf.
“The Accident”
As brown dwarfs cannot generate starlight, they are pretty difficult to spot in the sky without specialized equipment. This is where infrared telescopes, like the National Aeronautics and Space Administration’s (NASA’s) Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE), come in. As infrared telescopes view the universe in wavelengths beyond the visible spectrum of electromagnetic radiation, we can use it to look for astronomical objects that would otherwise appear dark in the visible spectrum, like brown dwarfs. With the help of citizen scientists the world over, NEOWISE has helped in the identification of over 2,000 brown dwarfs. Despite this, they only found the brown dwarf WISEA J153429.75-104303.3—and only because it seems to possess qualities unlike the rest of its kind.
Dan Caselden, one of the citizen scientists for NEOWISE, noticed a fast-moving oddity in one of the surveys “by accident” as it zoomed past other objects of interest in the sky that were potential brown dwarfs. This was how the oddity was given its nickname “the Accident.”
Prompted by its odd behavior, astronomers point their telescopes at it for examination, employing even NASA’s Hubble and Spitzer space telescopes to gather data. As it turns out, its method of discovery wouldn’t be the last of its oddities
So, So Many Oddities
For one, its infrared wavelength signature made it appear to be both an old, and cold, brown dwarf and a warm and young one at the same time. “The Accident” was also found to be some 50 light-years from Earth, and was zooming through the Milky Way Galaxy at a blistering 800,000 kilometers per hour (500,000 miles per hour)—much faster than a typical brown dwarf. According to astronomers, this means “the Accident” is likely a very old brown dwarf, having its speed built up to such an extent after being jostled around by the gravity of much larger objects for billions of years.
An analysis of the wavelengths of infrared radiation produced by “the Accident” only make it even weirder: this brown dwarf, as it turns out, is low on methane gas (CH4). This may not seem like much, but as a reminder: carbon is formed in the universe through stellar fusion, and is spit out by the stars that form them once they die out. (Read more on how stars create the elements in the universe here, where a couple of astronomers illustrate the ordeal with a couple of colored markers.)
This, then, means that “the Accident” must have formed during a time when not much stars have died out around it—certainly not enough for the nebula that made it to contain much methane. “The Accident,” as it turns out, might be very old—close to 10 to 13 billion years old, in fact, during the time period when the Milky Way Galaxy was filled with gases like hydrogen and helium but not much carbon. This makes “the Accident” more than double the median age of all its fellow brown dwarfs.
Much Work To Be Done
According to Federico Marocco, co-author of the study and Caltech astrophysicist: “It’s not a surprise to find a brown dwarf this old, but it is a surprise to find one in our backyard. We expected that brown dwarfs this old exist, but we also expected them to be incredibly rare.”
Davy Kirkpatrick, another Caltech astrophysicist and lead author of the study, adds that the object “defied all our expectations,” continuing that “[t]his discovery is telling us that there’s more variety in brown dwarf compositions than we’ve seen so far. There are likely more weird ones out there, and we need to think about how to look for them.”
Looking for brown dwarfs like “the Accident” can be challenging, but the help given by Dan Caselden and other fellow citizen scientists are tremendous, and significantly hasten an otherwise painstakingly long process. Despite the challenges in front of the concerted effort, Marocco maintains that “the Accident’” might be more than just what its nickname implies. “The chance of finding one so close to the solar system could be a lucky coincidence—or it tells us that they’re more common than we thought.”
Bibliography
- Encyclopedia Britannica. (n.d.). Brown dwarf. Encyclopedia Britannica. Retrieved September 20, 2021, from https://www.britannica.com/science/brown-dwarf
- Encyclopedia Britannica. (n.d.). Star formation and evolution. Encyclopedia Britannica. Retrieved September 20, 2021, from https://www.britannica.com/science/star-astronomy/Star-formation-and-evolution
- Mathewson, S. (2021, September 2). Strange brown dwarf ‘The Accident’ hints at possible treasure trove of cosmic anomalies. Space.com. Retrieved September 20, 2021, from https://www.space.com/the-accident-brown-dwarf-discovery-citizen-scientist
- NASA/JPL-Caltech. (2021, August 31). An Accidental Discovery Hints at a Hidden Population of Cosmic Objects. NASA Jet Propulsion Laboratory. Retrieved September 20, 2021, from https://www.jpl.nasa.gov/news/an-accidental-discovery-hints-at-a-hidden-population-of-cosmic-objects
- Specktor, B. (2021, September 2). Mysterious object called ‘The Accident’ has been careening through the Milky Way for 10 billion years. Live Science. Retrieved September 20, 2021, from https://www.livescience.com/the-accident-old-cold-brown-dwarf-star.html
- Kirkpatrick, J. D., Marocco, F., Caselden, D., Meisner, A. M., Faherty, J. K., Schneider, A. C., Kuchner, M. J., Casewell, S. L., Gelino, C. R., Cushing, M. C., Eisenhardt, P. R., Wright, E. L., & Schurr, S. D. (2021). The enigmatic brown dwarf wisea j153429. 75-104303. (A. K. A. “The accident”)3. The Astrophysical Journal Letters, 915(1), L6. https://doi.org/10.3847/2041-8213/ac0437
