Massive gas jets seen streaming from early universe galaxy
Scientists study star formation in a young and rambunctious system. Ben Lewis reports.
Astronomers have spotted massive fast-moving jets of gas streaming from a galaxy in the very early universe, just one billion years after the Big Bang.
The outflows from the dusty star-forming galaxy SPT2318-55 are expected shut down its star-formation activity, at least until the gas falls back in a few billion years.
The findings, published in the journal Science, were made by Justin Spilker and colleagues from the University of Texas in the US.
Some galaxies, such as the Milky Way, have relatively slow rates of star formation, with about one new star igniting each year. However, other galaxies can birth hundreds or thousands in the same period. This furious pace, however, cannot be maintained indefinitely.
To avoid growing too big too quickly and burning out in a blaze of glory, some galaxies limit their potenially runaway star-birth by expelling vast quantities of gas. This can be caused by several forces, including radiation pressure, supernovae, or supermassive black holes pulling the matter away.
“Galaxies are complicated, messy beasts, and we think outflows and winds are critical pieces to how they form and evolve, regulating their ability to grow,” says Spilker.
These outflowing winds have been seen in nearby galaxies. However, their extent in earlier galaxies hasn’t been clear because they are notoriously difficult to observe. The spectral features can be very faint, and evidence of the outflow unreliable.
Using the Atacama Large Millimetre/submillimetre Array (ALMA), in northern Chile, and a magnifying effect from the gravitational lensing of an intervening galaxy, Spilker and the team were able to observe the gas streaming from SPT2319-55 over 12 billion light-years away, making it the most distant unambiguous outflow ever seen in the early universe.
As dust surrounding the newly formed stars heats up it begins emitting infrared light. When that light passes through the winds spewing from the galaxy, hydroxyl molecules contained in the stream absorb particular wavelengths which can then be observed by ALMA.
“From that we can also tell how fast the wind is moving, and get a rough idea of how much material is contained in the outflow,” says Spilker.
For each solar mass-equivalent of stars formed, somewhere between the same amount and double the material is removed by the wind, dramatically reducing the gas reservoir for future stars.
The massive outflows were estimated to be travelling up to 800 kilometres per second, and rather than just being confined to the centre of the galaxy, appear to cluster together in several clumps.
“Young galaxies are not the stately well-ordered spirals of mature galaxies like the Milky Way with stars (and hence winds) from a central region,” says Alan Duffy, an astronomer at Swinburne University in Australia who was not involved in the study.
“They are made of several blobs and each of those blobs are forming stars that launch these winds,”
The high velocity of the winds is surprising, he adds. “These winds were occurring at a time when the universe itself was smaller and denser, meaning they were pushing into much more gas around the galaxy. That would slow them down.”
Despite the huge volumes, the astronomers suggest that only 10% of the outflowing gas is travelling fast enough to eventually escape the galaxy. The rest of it will remain in the galaxy’s halo and ultimately fall back into SPT2319−55.
With the limiting effect of the outflow, star formation in SPT2319-55 is expected to be suppressed within the next 100 million years.
What that means in the long term is still unclear. It may result in a permanent quenching of star formation, or, given that a large quantity of gas will stay within the galaxy, see a future round of star making in the distant future.
“So far, we have only observed one galaxy at such a remarkable cosmic distance, but we’d like to know if winds like these are also present in other galaxies to see just how common they are,” concludes Spilker.
“If they occur in basically every galaxy, we know that molecular winds are both ubiquitous and also a really common way for galaxies to self-regulate their growth.”