'The Accident' In The Galaxy: All About The Strange Cosmic Object Discovered By Sheer Luck

New study explains significance of the discovery of a very old brown dwarf, 'The Accident', near Milky Way, and how it suggests the possibility of similar dwarfs existing in our galactic neighbourhood

New Delhi: Last year, scientists had announced the discovery of a strange object that they had found by accident. The object is a 'brown dwarf', nicknamed 'The Accident'. The paper announcing the discovery was published in The Astrophysics journal last year.

Now, in a new study published in The Astrophysical Journal Letters, scientists have explained how The Accident came to be. It also suggests that there may be many more 'brown dwarfs' lurking in our galaxy than scientists previously thought, NASA stated in a press release. 

What Is A Brown Dwarf?

A brown dwarf is an object with a size between that of a giant planet like Jupiter and that of a small star. Their size is between 13 and 80 times that of Jupiter. Brown dwarfs don't shine like stars as they don't have enough mass to commence nuclear fusion, the process that causes stars to shine and burn. 

They cool off with age, causing changes in their brightness in different wavelengths. Infrared light, or wavelengths longer than visible light, are emitted by them.

How Was The Accident Discovered?

The brown dwarf was called The Accident as it was found by sheer luck. It stands out because it has no resemblance to the other brown dwarfs (over 2,000 of them) discovered so far in the Milky Way Galaxy.

NASA's Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE), launched in 2009 and managed by NASA's Jet Propulsion Laboratory, first spotted The Accident. Brown dwarfs are very faint, and it is only when they are relatively very close to our planet that they can be spotted.

To understand more about The Accident, scientists observed it with a ground-based telescope at the W.M. Keck Observatory in Hawaii. They used additional infrared wavelengths to observe it, but couldn't detect it as it appeared faint, proving their suggestion that it was very cold.

NASA's Hubble and Spitzer Space Telescopes were used to make precise distance measurements of The Accident, which was found to be 50 light years away from Earth. 

Citizen scientist Dan Caselden, who was using an online program built by him to find brown dwarfs in NEOWISE data, discovered The Accident. Attempts to remove stationary infrared objects like distant stars from the NEOWISE maps, and to highlight moving objects with characteristics resembling brown dwarfs, were made by Caselden's program. Caselden was observing a brown dwarf, when he accidentally noticed a different object, which was much fainter and was moving quickly across the screen. This later turned out to be The Accident, which hadn't been caught by the program earlier as it didn't match the profile of brown dwarfs as per the system.

What Is Unusual About The Accident?

Scientists were surprised by The Accident because unlike normal brown dwarfs, it was faint in some key wavelengths, suggesting cold temperatures there, but bright in other wavelengths, indicating higher temperatures.

Davy Kirkpatrick, lead author of the study and astrophysicist at Infrared Processing and Analysis Center (IPAC) at Caltech in California, was quoted in an NASA statement as saying: "This object defied all our expectations".

The study explains that The Accident might be 10 billion to 13 billion years old, which is at least double the median age of other known brown dwarfs. The Accident also moves very fast, at a speed of about half a million miles per hour (800,000 kph). This speed is much greater than the speeds of other brown dwarfs located at the same distance from the Earth as The Accident.

Why Does This Discovery Signify? 

The fact that The Accident is very old suggests that its chemical composition is quite different, and that it was formed when the Milky Way Galaxy was much younger, the study explains. The study also says that the reason why The Accident moves at speeds higher than other brown dwarfs is probably because the former had been lurking around our galaxy for a long time, and was being accelerated by other massive objects.

Most brown dwarfs with a temperature similar to that of The Accident contain Methane, which is composed of hydrogen and carbon. However, The Accident contains very less methane, as suggested by its light profile. Absorption of specific wavelengths of light by methane causes brown dwarfs to be dim. The Accident appearing bright in those wavelengths is indicative of low methane levels in it.

The light profile matches that of a very old brown dwarf that formed when the galaxy had little carbon, indicating the fact that The Accident was formed at a time when the galaxy was carbon poor; thereby resulting in low levels of methane.

The scientists explain that the discovery of The Accident points to the possible existence of many more ancient brown dwarfs moving in our galactic neighborhood. 

Federico Marocco, an astrophysicist at IPAC at Caltech, said that it was not surprising to spot an old brown dwarf. Rather, he said, it was astonishing to find one in our galactic neighborhood.

He added that old brown dwarfs were expected to be rare, and that the chance of finding one so close to our solar system could either be a lucky coincidence, or an indication towards the fact that they are common than what scientists thought.

Lead author Kirkpatrick was quoted as saying: "This 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.”