Monstrous gas cloud on collision course with our galaxy will create 2 million suns

A massive cloud of hydrogen gas speeding towards the Milky Way at speeds topping 700,000 miles per hours could form up to two million new stars once it finally arrives, according to new research published in a recent edition of the Astrophysical Journal Letters.

While researchers first discovered the object known as the Smith Cloud in the 1960s, little was known about its chemical composition until Dr. Nicolas Lehner of the University of Notre Dame and his colleagues determined that it contained elements extremely similar to our sun.

What that means, The Independent explained, is that it originated in the outer edges of the Milky Way and was not a starless galaxy or a big body of gas that had originated in intergalactic space, as some researchers had speculated. Following its formation, it was somehow ejected into space roughly 70 million years ago, Dr. Lehner and his colleagues reported in their study.


This diagram shows the 100-million-year-long trajectory of the Smith Cloud as it arcs out of the plane of our Milky Way galaxy and then returns like a boomerang. Hubble Space Telescope measurements show that the cloud came out of a region near the edge of the galaxy’s disk of stars 70 million years ago. The cloud is now stretched into the shape of a comet by gravity and gas pressure. Following a ballistic path, the cloud will fall back into the disk and trigger new star formation 30 million years from now. (Credit: NASA/ESA/A. Feild (STScI))

Currently, the Smith Cloud is speeding back towards its galaxy of origin, and it is expected to crash into the Milky Way’s disk in approximately 30 million years, according to NASA. Once it returns, it is expected to be the catalyst for a “spectacular burst of star formation,” since it could provide enough gas to produce up to two million suns, they added.

Determining its origin by figuring out its chemical composition

Dr. Lehner and his fellow researchers used the Hubble space telescope to determine the amount of heavier elements the Smith Cloud contained relative to its hydrogen content. Using Hubble’s Cosmic Origins Spectrograph, they observed UV radiation from the cores of three active galaxies located billions of light years behind the cloud to estimate its chemical composition.

Specifically, they searched for absorption from the element sulfur, which can be used to figure out the amount of heavier elements that reside within a gas cloud. By doing so, they determined that the Smith Cloud was as rich in sulfur as the outer disk of the Milky Way, which means that it was polluted by stellar material, which would not be the case had it originated from outside the galaxy.

gas cloud

Hubble’s Cosmic Origins Spectrograph can measure how the light from distant background objects is affected as it passes through the cloud, yielding clues to the chemical composition of the cloud. Astronomers trace the cloud’s origin to the disk of our Milky Way. Combined ultraviolet and radio observations correlate to the cloud’s infall velocities, providing solid evidence that the spectral features link to the cloud’s dynamics. (Credit: NASA/ESA/A. Feild (STScI))

“The cloud is an example of how the galaxy is changing with time,” researcher Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland, said in a statement. “It’s telling us that the Milky Way is a bubbling, very active place where gas can be thrown out of one part of the disk and then return back down into another.”

“We have found several massive gas clouds in the Milky Way halo that may serve as future fuel for star formation in its disk, but, for most of them, their origins remain a mystery,” Dr. Lehner added. “The Smith Cloud is certainly one of the best examples that shows that recycled gas is an important mechanism in the evolution of galaxies.”

Now that they have determined the cloud’s origins, and have a good idea what will happen once it finally returns to the Milky Way, one mystery remains: how did the cloud come to arrive at its current location? What force or phenomenon forced it out of the Milky Way, and how did it stay intact? That, the researchers said, is a question that only additional research can answer.


This composite image shows the size and location of the Smith Cloud on the sky. The cloud appears in false-color, radio wavelengths as observed by the Green Bank Telescope in West Virginia. The visible-light image of the background star field shows the cloud’s location in the direction of the constellation Aquila. (Credit: Saxton/Lockman/NRAO/AUI/NSF/Mellinger)