On September 9, 2017, a rocky, elongated body in the shape of a cosmic cigar visited our solar system from outside the Sun’s regions – the first recorded interstellar object to cross through our part of the galaxy.
We called it “Oumuamua”, which means “A messenger from afar who arrives first” in Hawaiian.
‘Oumuamua was like nothing that astronomers had previously observed, neither a comet nor an asteroid, but definitely not an alien probe, as some tried to claim. Perhaps the only way to explain this strange object, an even stranger story of origin, is that Oumuamua is made of hydrogen ice that was ejected from a massive cloud of molecules.
The new study was accepted for publication in The Astrophysical Journal Letters, and was published as a preprint at arXiv.org.
What makes Oumuamua so funny? ̵
However, it couldn’t be an asteroid either because it was accelerated by the sun. ‘Oumuamua hurled past the sun at a speed of 196,000 miles an hour – which is too fast to be explained by the sun’s gravity alone.
“Oumuamua is also very elongated and extends over 900 feet in its longest dimension.
The team behind the new study was looking for a strange cosmic story to explain an equally strange cosmic being.
“We have developed a theory that explains all the strange properties of Oumuamua,” said Gregory Laughlin, professor of astronomy at Yale University and lead author of the new study, in a statement.
The study suggests that ‘Oumuamua consists of a huge block of hydrogen water that has emerged from a massive cloud of molecules. These clouds act as giant star nurseries that span hundreds of light years and contain enough dense gas and dust to produce thousands of stars.
Hydrogen is the most common element in the universe. It makes up about 75% of all normal matter and promotes the formation of new stars. However, it is rarely observed in solid form.
In order for hydrogen to solidify, extremely cold temperatures would be required.
Molecular clouds are very cold with temperatures between -440 to -370 degrees Fahrenheit.
This is cold enough to freeze hydrogen and convert it to solids.
Therefore, the study suggests that hydrogen ice blocks such as’ Oumuamua could form in the icy nuclei of molecular clouds, and there could be many more of them.
“When ‘Oumuamua approached the sun and received its warmth, melting hydrogen would have quickly boiled off the icy surface, provided the observed acceleration, and brought’ Oumuamua into its strange, elongated shape – like a bar of soap in a thin band after many uses in the shower, “said Laughlin.
If this theory is correct, then Oumuamua is not only the first interstellar object observed by scientists, but also the first hydrogen iceberg that they hurled through space. Observing additional objects could help scientists unravel the mysteries of star and planet formation in the early universe.
“Your presence would be a close study of the conditions in the dark niches of star-forming clouds,” said Laughlin. “And provide a crucial new clue to understanding the earliest stages of the still mysterious processes that lead to the birth of stars and their associated planets.”
Abstract: `Oumuamua (I1 2017) was the first macroscopic body (approx. 100 m) to cross the inner solar system in an unbound hyperbolic orbit. Its light curve showed strong periodic variations and it showed no evidence of coma or emission from molecular outgassing. Astrometric measurements indicate that Oumuamua has experienced a non-gravitational acceleration on its outgoing trajectory, but energy balance arguments indicate that this acceleration is incompatible with a jet of water sublimation driven by the comets of the solar system. We show that all observed properties of Oumaumua can be explained if it contains a significant amount of molecular hydrogen (H2) ice. H2 sublimation at a rate proportional to the incident solar flux creates a surface-covering ray that reproduces the observed acceleration. Mass waste through sublimation leads to a monotonous increase in the body axis ratio, which explains the shape of Oumuamua. Tracing Oumuamua’s trajectory through the solar system enables its mass and aspect ratio to be calculated before it encounters the sun. We show that H2-rich bodies plausibly form in the coldest dense nuclei of giant molecular clouds, in which the number densities are on the order of n ~ 105 and the temperatures approach the T = 3K background. Exposure to galactic cosmic rays after formation implies an age of τ∼100 myr, which explains the kinematics of the incoming trajectory from Oumuamua.